MMUSIC Working Group                                      H. Schulzrinne
Internet-Draft                                       Columbia University
Obsoletes: 2326 (if approved)                                     A. Rao
Intended status: Standards Track                                   Cisco
Expires: April 30, September 13, 2012                                  R. Lanphier

                                                           M. Westerlund
                                                             Ericsson AB
                                                    M. Stiemerling (Ed.)
                                                                     NEC
                                                        October 28, 2011
                                                          March 12, 2012

                Real Time Streaming Protocol 2.0 (RTSP)
                    draft-ietf-mmusic-rfc2326bis-28
                    draft-ietf-mmusic-rfc2326bis-29

Abstract

   This memorandum defines RTSP version 2.0 which obsoletes RTSP version
   1.0 which is defined in RFC 2326.

   The Real Time Streaming Protocol, or RTSP, is an application-level
   protocol for setup and control of the delivery of data with real-time
   properties.  RTSP provides an extensible framework to enable
   controlled, on-demand delivery of real-time data, such as audio and
   video.  Sources of data can include both live data feeds and stored
   clips.  This protocol is intended to control multiple data delivery
   sessions, provide a means for choosing delivery channels such as UDP,
   multicast UDP and TCP, and provide a means for choosing delivery
   mechanisms based upon RTP (RFC 3550).

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 30, September 13, 2012.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  11
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  13
     2.1.   Presentation Description . . . . . . . . . . . . . . . .  13
     2.2.   Session Establishment  . . . . . . . . . . . . . . . . .  14
     2.3.   Media Delivery Control . . . . . . . . . . . . . . . . .  15
     2.4.   Session Parameter Manipulations  . . . . . . . . . . . .  17
     2.5.   Media Delivery . . . . . . . . . . . . . . . . . . . . .  17
       2.5.1.   Media Delivery Manipulations . . . . . . . . . . . .  18
     2.6.   Session Maintenance and Termination  . . . . . . . . . .  20
     2.7.   Extending RTSP . . . . . . . . . . . . . . . . . . . . .  21
   3.  Document Conventions  . . . . . . . . . . . . . . . . . . . .  23
     3.1.   Notational Conventions . . . . . . . . . . . . . . . . .  23
     3.2.   Terminology  . . . . . . . . . . . . . . . . . . . . . .  23
   4.  Protocol Parameters . . . . . . . . . . . . . . . . . . . . .  27
     4.1.   RTSP Version . . . . . . . . . . . . . . . . . . . . . .  27
     4.2.   RTSP IRI and URI . . . . . . . . . . . . . . . . . . . .  27
     4.3.   Session Identifiers  . . . . . . . . . . . . . . . . . .  29
     4.4.   SMPTE Relative Timestamps  . . . . . . . . . . . . . . .  29
     4.5.   Normal Play Time . . . . . . . . . . . . . . . . . . . .  30
     4.6.   Absolute Time  . . . . . . . . . . . . . . . . . . . . .  31
     4.7.   Feature-Tags . . . . . . . . . . . . . . . . . . . . . .  31
     4.8.   Message Body Tags  . . . . . . . . . . . . . . . . . . .  31
     4.9.   Media Properties . . . . . . . . . . . . . . . . . . . .  32
       4.9.1.   Random Access and Seeking  . . . . . . . . . . . . .  33
       4.9.2.   Retention  . . . . . . . . . . . . . . . . . . . . .  33
       4.9.3.   Content Modifications  . . . . . . . . . . . . . . .  34
       4.9.4.   Supported Scale Factors  . . . . . . . . . . . . . .  34
       4.9.5.   Mapping to the Attributes  . . . . . . . . . . . . .  34
   5.  RTSP Message  . . . . . . . . . . . . . . . . . . . . . . . .  35
     5.1.   Message Types  . . . . . . . . . . . . . . . . . . . . .  35
     5.2.   Message Headers  . . . . . . . . . . . . . . . . . . . .  35
     5.3.   Message Body . . . . . . . . . . . . . . . . . . . . . .  36
     5.4.   Message Length . . . . . . . . . . . . . . . . . . . . .  36
   6.  General Header Fields . . . . . . . . . . . . . . . . . . . .  38
   7.  Request . . . . . . . . . . . . . . . . . . . . . . . . . . .  39
     7.1.   Request Line . . . . . . . . . . . . . . . . . . . . . .  39
     7.2.   Request Header Fields  . . . . . . . . . . . . . . . . .  41
   8.  Response  . . . . . . . . . . . . . . . . . . . . . . . . . .  43
     8.1.   Status-Line  . . . . . . . . . . . . . . . . . . . . . .  43
       8.1.1.   Status Code and Reason Phrase  . . . . . . . . . . .  43
     8.2.   Response Headers . . . . . . . . . . . . . . . . . . . .  46
   9.  Message Body  . . . . . . . . . . . . . . . . . . . . . . . .  48
     9.1.   Message-Body Header Fields . . . . . . . . . . . . . . .  48
     9.2.   Message Body . . . . . . . . . . . . . . . . . . . . . .  49
   10. Connections . . . . . . . . . . . . . . . . . . . . . . . . .  50
     10.1.  Reliability and Acknowledgements . . . . . . . . . . . .  50
     10.2.  Using Connections  . . . . . . . . . . . . . . . . . . .  51
     10.3.  Closing Connections  . . . . . . . . . . . . . . . . . .  53
     10.4.  Timing Out Connections and RTSP Messages . . . . . . . .  54
     10.5.  Showing Liveness . . . . . . . . . . . . . . . . . . . .  55
     10.6.  Use of IPv6  . . . . . . . . . . . . . . . . . . . . . .  56
     10.7.  Overload Control . . . . . . . . . . . . . . . . . . . .  56
   11. Capability Handling . . . . . . . . . . . . . . . . . . . . .  58
   12. Pipelining Support  . . . . . . . . . . . . . . . . . . . . .  60
   13. Method Definitions  . . . . . . . . . . . . . . . . . . . . .  61
     13.1.  OPTIONS  . . . . . . . . . . . . . . . . . . . . . . . .  62
     13.2.  DESCRIBE . . . . . . . . . . . . . . . . . . . . . . . .  63
     13.3.  SETUP  . . . . . . . . . . . . . . . . . . . . . . . . .  65
       13.3.1.  Changing Transport Parameters  . . . . . . . . . . .  68
     13.4.  PLAY . . . . . . . . . . . . . . . . . . . . . . . . . .  69
       13.4.1.  General Usage  . . . . . . . . . . . . . . . . . . .  69
       13.4.2.  Aggregated Sessions  . . . . . . . . . . . . . . . .  74
       13.4.3.  Updating current PLAY Requests . . . . . . . . . . .  75
       13.4.4.  Playing On-Demand Media  . . . . . . . . . . . . . .  77
       13.4.5.  Playing Dynamic On-Demand Media  . . . . . . . . . .  78
       13.4.6.  Playing Live Media . . . . . . . . . . . . . . . . .  78
       13.4.7.  Playing Live with Recording  . . . . . . . . . . . .  79
       13.4.8.  Playing Live with Time-Shift . . . . . . . . . . . .  79
     13.5.  PLAY_NOTIFY  . . . . . . . . . . . . . . . . . . . . . .  80
       13.5.1.  End-of-Stream  . . . . . . . . . . . . . . . . . . .  81
       13.5.2.  Media-Properties-Update  . . . . . . . . . . . . . .  82
       13.5.3.  Scale-Change . . . . . . . . . . . . . . . . . . . .  83
     13.6.  PAUSE  . . . . . . . . . . . . . . . . . . . . . . . . .  84
     13.7.  TEARDOWN . . . . . . . . . . . . . . . . . . . . . . . .  87
       13.7.1.  Client to Server . . . . . . . . . . . . . . . . . .  87
       13.7.2.  Server to Client . . . . . . . . . . . . . . . . . .  88
     13.8.  GET_PARAMETER  . . . . . . . . . . . . . . . . . . . . .  89
     13.9.  SET_PARAMETER  . . . . . . . . . . . . . . . . . . . . .  91
     13.10. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . .  92
   14. Embedded (Interleaved) Binary Data  . . . . . . . . . . . . .  95
   15. Proxies . . . . . . . . . . . . . . . . . . . . . . . . . . .  97
     15.1.  Proxies and Protocol Extensions  . . . . . . . . . . . .  98
     15.2.  Multiplexing and Demultiplexing of Messages  . . . . . .  99
   16. Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
     16.1.  Validation Model . . . . . . . . . . . . . . . . . . . . 100
       16.1.1.  Last-Modified Dates  . . . . . . . . . . . . . . . . 102
       16.1.2.  Message Body Tag Cache Validators  . . . . . . . . . 102
       16.1.3.  Weak and Strong Validators . . . . . . . . . . . . . 102
       16.1.4.  Rules for When to Use Message Body Tags and
                Last-Modified Dates  . . . . . . . . . . . . . . . . 104
       16.1.5.  Non-validating Conditionals  . . . . . . . . . . . . 106
     16.2.  Invalidation After Updates or Deletions  . . . . . . . . 106
   17. Status Code Definitions . . . . . . . . . . . . . . . . . . .  97
     15.1. 108
     17.1.  Success 1xx  . . . . . . . . . . . . . . . . . . . . . .  97
       15.1.1. 108
       17.1.1.  100 Continue . . . . . . . . . . . . . . . . . . . .  97
     15.2. 108
     17.2.  Success 2xx  . . . . . . . . . . . . . . . . . . . . . .  97
       15.2.1. 108
       17.2.1.  200 OK . . . . . . . . . . . . . . . . . . . . . . .  97
     15.3. 108
     17.3.  Redirection 3xx  . . . . . . . . . . . . . . . . . . . .  97
       15.3.1. 108
       17.3.1.  301 Moved Permanently  . . . . . . . . . . . . . . .  98
       15.3.2. 109
       17.3.2.  302 Found  . . . . . . . . . . . . . . . . . . . . .  98
       15.3.3. 109
       17.3.3.  303 See Other  . . . . . . . . . . . . . . . . . . .  98
       15.3.4. 109
       17.3.4.  304 Not Modified . . . . . . . . . . . . . . . . . .  98
       15.3.5. 109
       17.3.5.  305 Use Proxy  . . . . . . . . . . . . . . . . . . .  99
     15.4. 110
     17.4.  Client Error 4xx . . . . . . . . . . . . . . . . . . . .  99
       15.4.1. 110
       17.4.1.  400 Bad Request  . . . . . . . . . . . . . . . . . .  99
       15.4.2. 110
       17.4.2.  401 Unauthorized . . . . . . . . . . . . . . . . . .  99
       15.4.3. 110
       17.4.3.  402 Payment Required . . . . . . . . . . . . . . . . 100
       15.4.4. 111
       17.4.4.  403 Forbidden  . . . . . . . . . . . . . . . . . . . 100
       15.4.5. 111
       17.4.5.  404 Not Found  . . . . . . . . . . . . . . . . . . . 100
       15.4.6. 111
       17.4.6.  405 Method Not Allowed . . . . . . . . . . . . . . . 100
       15.4.7. 111
       17.4.7.  406 Not Acceptable . . . . . . . . . . . . . . . . . 100
       15.4.8. 111
       17.4.8.  407 Proxy Authentication Required  . . . . . . . . . 101
       15.4.9. 112
       17.4.9.  408 Request Timeout  . . . . . . . . . . . . . . . . 101
       15.4.10. 112
       17.4.10. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 101
       15.4.11. 112
       17.4.11. 411 Length Required  . . . . . . . . . . . . . . . . 101
       15.4.12. 112
       17.4.12. 412 Precondition Failed  . . . . . . . . . . . . . . 102
       15.4.13. 113
       17.4.13. 413 Request Message Body Too Large . . . . . . . . . 102
       15.4.14. 113
       17.4.14. 414 Request-URI Too Long . . . . . . . . . . . . . . 102
       15.4.15. 113
       17.4.15. 415 Unsupported Media Type . . . . . . . . . . . . . 102
       15.4.16. 113
       17.4.16. 451 Parameter Not Understood . . . . . . . . . . . . 102
       15.4.17. 113
       17.4.17. 452 reserved . . . . . . . . . . . . . . . . . . . . 102
       15.4.18. 114
       17.4.18. 453 Not Enough Bandwidth . . . . . . . . . . . . . . 103
       15.4.19. 114
       17.4.19. 454 Session Not Found  . . . . . . . . . . . . . . . 103
       15.4.20. 114
       17.4.20. 455 Method Not Valid in This State . . . . . . . . . 103
       15.4.21. 114
       17.4.21. 456 Header Field Not Valid for Resource  . . . . . . 103
       15.4.22. 114
       17.4.22. 457 Invalid Range  . . . . . . . . . . . . . . . . . 103
       15.4.23. 114
       17.4.23. 458 Parameter Is Read-Only . . . . . . . . . . . . . 103
       15.4.24. 114
       17.4.24. 459 Aggregate Operation Not Allowed  . . . . . . . . 103
       15.4.25. 114
       17.4.25. 460 Only Aggregate Operation Allowed . . . . . . . . 103
       15.4.26. 115
       17.4.26. 461 Unsupported Transport  . . . . . . . . . . . . . 104
       15.4.27. 115
       17.4.27. 462 Destination Unreachable  . . . . . . . . . . . . 104
       15.4.28. 115
       17.4.28. 463 Destination Prohibited . . . . . . . . . . . . . 104
       15.4.29. 115
       17.4.29. 464 Data Transport Not Ready Yet . . . . . . . . . . 104
       15.4.30. 115
       17.4.30. 465 Notification Reason Unknown  . . . . . . . . . . 104
       15.4.31. 115
       17.4.31. 466 Key Management Error . . . . . . . . . . . . . . 104
       15.4.32. 116
       17.4.32. 470 Connection Authorization Required  . . . . . . . 105
       15.4.33. 116
       17.4.33. 471 Connection Credentials not accepted  . . . . . . 105
       15.4.34. 116
       17.4.34. 472 Failure to establish secure connection . . . . . 105
     15.5. 116
     17.5.  Server Error 5xx . . . . . . . . . . . . . . . . . . . . 105
       15.5.1. 116
       17.5.1.  500 Internal Server Error  . . . . . . . . . . . . . 105
       15.5.2. 116
       17.5.2.  501 Not Implemented  . . . . . . . . . . . . . . . . 105
       15.5.3. 116
       17.5.3.  502 Bad Gateway  . . . . . . . . . . . . . . . . . . 105
       15.5.4. 117
       17.5.4.  503 Service Unavailable  . . . . . . . . . . . . . . 106
       15.5.5. 117
       17.5.5.  504 Gateway Timeout  . . . . . . . . . . . . . . . . 106
       15.5.6. 117
       17.5.6.  505 RTSP Version Not Supported . . . . . . . . . . . 106
       15.5.7. 117
       17.5.7.  551 Option not supported . . . . . . . . . . . . . . 106
   16. 117
   18. Header Field Definitions  . . . . . . . . . . . . . . . . . . 107
     16.1. 118
     18.1.  Accept . . . . . . . . . . . . . . . . . . . . . . . . . 117
     16.2. 128
     18.2.  Accept-Credentials . . . . . . . . . . . . . . . . . . . 117
     16.3. 128
     18.3.  Accept-Encoding  . . . . . . . . . . . . . . . . . . . . 118
     16.4. 129
     18.4.  Accept-Language  . . . . . . . . . . . . . . . . . . . . 119
     16.5. 130
     18.5.  Accept-Ranges  . . . . . . . . . . . . . . . . . . . . . 120
     16.6. 131
     18.6.  Allow  . . . . . . . . . . . . . . . . . . . . . . . . . 120
     16.7. 131
     18.7.  Authorization  . . . . . . . . . . . . . . . . . . . . . 120
     16.8. 131
     18.8.  Bandwidth  . . . . . . . . . . . . . . . . . . . . . . . 121
     16.9. 132
     18.9.  Blocksize  . . . . . . . . . . . . . . . . . . . . . . . 122
     16.10. 133
     18.10. Cache-Control  . . . . . . . . . . . . . . . . . . . . . 122
     16.11. 133
     18.11. Connection . . . . . . . . . . . . . . . . . . . . . . . 125
     16.12. 136
     18.12. Connection-Credentials . . . . . . . . . . . . . . . . . 125
     16.13. 136
     18.13. Content-Base . . . . . . . . . . . . . . . . . . . . . . 126
     16.14. 137
     18.14. Content-Encoding . . . . . . . . . . . . . . . . . . . . 126
     16.15. 137
     18.15. Content-Language . . . . . . . . . . . . . . . . . . . . 127
     16.16. 138
     18.16. Content-Length . . . . . . . . . . . . . . . . . . . . . 128
     16.17. 139
     18.17. Content-Location . . . . . . . . . . . . . . . . . . . . 128
     16.18. 139
     18.18. Content-Type . . . . . . . . . . . . . . . . . . . . . . 129
     16.19. 140
     18.19. CSeq . . . . . . . . . . . . . . . . . . . . . . . . . . 129
     16.20. 140
     18.20. Date . . . . . . . . . . . . . . . . . . . . . . . . . . 130
     16.21. 141
     18.21. Expires  . . . . . . . . . . . . . . . . . . . . . . . . 131
     16.22. 142
     18.22. From . . . . . . . . . . . . . . . . . . . . . . . . . . 131
     16.23. 143
     18.23. If-Match . . . . . . . . . . . . . . . . . . . . . . . . 132
     16.24. 143
     18.24. If-Modified-Since  . . . . . . . . . . . . . . . . . . . 132
     16.25. 144
     18.25. If-None-Match  . . . . . . . . . . . . . . . . . . . . . 133
     16.26. 144
     18.26. Last-Modified  . . . . . . . . . . . . . . . . . . . . . 134
     16.27. 145
     18.27. Location . . . . . . . . . . . . . . . . . . . . . . . . 134
     16.28. 145
     18.28. Media-Properties . . . . . . . . . . . . . . . . . . . . 134
     16.29. 146
     18.29. Media-Range  . . . . . . . . . . . . . . . . . . . . . . 136
     16.30. 148
     18.30. MTag . . . . . . . . . . . . . . . . . . . . . . . . . . 137
     16.31. 148
     18.31. Notify-Reason  . . . . . . . . . . . . . . . . . . . . . 137
     16.32. 149
     18.32. Pipelined-Requests . . . . . . . . . . . . . . . . . . . 137
     16.33. 149
     18.33. Proxy-Authenticate . . . . . . . . . . . . . . . . . . . 139
     16.34. 150
     18.34. Proxy-Authorization  . . . . . . . . . . . . . . . . . . 139
     16.35. 150
     18.35. Proxy-Require  . . . . . . . . . . . . . . . . . . . . . 139
     16.36. 151
     18.36. Proxy-Supported  . . . . . . . . . . . . . . . . . . . . 140
     16.37. 151
     18.37. Public . . . . . . . . . . . . . . . . . . . . . . . . . 141
     16.38. 152
     18.38. Range  . . . . . . . . . . . . . . . . . . . . . . . . . 141
     16.39. 153
     18.39. Referrer . . . . . . . . . . . . . . . . . . . . . . . . 143
     16.40. 154
     18.40. Request-Status . . . . . . . . . . . . . . . . . . . . . 144
     16.41. 155
     18.41. Require  . . . . . . . . . . . . . . . . . . . . . . . . 144
     16.42. 155
     18.42. Retry-After  . . . . . . . . . . . . . . . . . . . . . . 145
     16.43. 156
     18.43. RTP-Info . . . . . . . . . . . . . . . . . . . . . . . . 145
     16.44. 157
     18.44. Scale  . . . . . . . . . . . . . . . . . . . . . . . . . 148
     16.45. 159
     18.45. Seek-Style . . . . . . . . . . . . . . . . . . . . . . . 149
     16.46. 160
     18.46. Server . . . . . . . . . . . . . . . . . . . . . . . . . 150
     16.47. 162
     18.47. Session  . . . . . . . . . . . . . . . . . . . . . . . . 151
     16.48. 162
     18.48. Speed  . . . . . . . . . . . . . . . . . . . . . . . . . 152
     16.49. 163
     18.49. Supported  . . . . . . . . . . . . . . . . . . . . . . . 153
     16.50. 164
     18.50. Terminate-Reason . . . . . . . . . . . . . . . . . . . . 153
     16.51. 165
     18.51. Timestamp  . . . . . . . . . . . . . . . . . . . . . . . 154
     16.52. 165
     18.52. Transport  . . . . . . . . . . . . . . . . . . . . . . . 154
     16.53. 166
     18.53. Unsupported  . . . . . . . . . . . . . . . . . . . . . . 161
     16.54. 173
     18.54. User-Agent . . . . . . . . . . . . . . . . . . . . . . . 161
     16.55. Vary 173
     18.55. Via  . . . . . . . . . . . . . . . . . . . . . . . . . . 162
     16.56. Via 173
     18.56. WWW-Authenticate . . . . . . . . . . . . . . . . . . . . 174
   19. Security Framework  . . . . . . 162
     16.57. WWW-Authenticate . . . . . . . . . . . . . . . 175
     19.1.  RTSP and HTTP Authentication . . . . . 163
   17. Proxies . . . . . . . . . 175
     19.2.  RTSP over TLS  . . . . . . . . . . . . . . . . . . 164
     17.1.  Proxies and Protocol Extensions . . . 175
     19.3.  Security and Proxies . . . . . . . . . 165
     17.2.  Multiplexing and Demultiplexing of Messages . . . . . . 166
   18. Caching . . . 176
       19.3.1.  Accept-Credentials . . . . . . . . . . . . . . . . . 177
       19.3.2.  User approved TLS procedure  . . . . . . . 167
     18.1.  Validation Model . . . . . 178
   20. Syntax  . . . . . . . . . . . . . . . 167
       18.1.1.  Last-Modified Dates . . . . . . . . . . . . 181
     20.1.  Base Syntax  . . . . 169
       18.1.2.  Message Body Tag Cache Validators . . . . . . . . . 169
       18.1.3.  Weak and Strong Validators . . . . . . . . . 181
     20.2.  RTSP Protocol Definition . . . . 169
       18.1.4.  Rules for When to Use Message Body Tags and
                Last-Modified Dates . . . . . . . . . . . . 183
       20.2.1.  Generic Protocol elements  . . . . 171
       18.1.5.  Non-validating Conditionals . . . . . . . . . 183
       20.2.2.  Message Syntax . . . 173
     18.2.  Invalidation After Updates or Deletions . . . . . . . . 173
   19. Security Framework . . . . . . . . 186
       20.2.3.  Header Syntax  . . . . . . . . . . . . . 175
     19.1.  RTSP and HTTP Authentication . . . . . . 190
     20.3.  SDP extension Syntax . . . . . . . . 175
     19.2.  RTSP over TLS . . . . . . . . . . 199
   21. Security Considerations . . . . . . . . . . . 175
     19.3.  Security and Proxies . . . . . . . . . . . . . . . . . . 176
       19.3.1.  Accept-Credentials . . . . . . . . . . . . . . . . . 177
       19.3.2.  User approved TLS procedure  . . . . . . . . . . . . 178
   20. Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
     20.1.  Base Syntax  . . . . . . . . . . . . . . . . . . . . . . 181
     20.2.  RTSP Protocol Definition . . . . . . . . . . . . . . . . 183
       20.2.1.  Generic 200
     21.1.  Signaling Protocol elements  . . . . . . . . . . . . . 183
       20.2.2.  Message Syntax . . . . . . . Threats . . . . . . . . . . . . 186
       20.2.3.  Header Syntax  . . . . . . . . . . . . . . 200
     21.2.  Media Stream Delivery Threats  . . . . . 190
     20.3.  SDP extension Syntax . . . . . . . . 203
       21.2.1.  Remote denial of Service Attack  . . . . . . . . . . 199
   21. 204
       21.2.2.  RTP Security Considerations . . . . . . . . . . . . . . . . analysis  . . . 200
     21.1.  Remote denial of Service Attack . . . . . . . . . . . . 202 205
   22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 204 207
     22.1.  Feature-tags . . . . . . . . . . . . . . . . . . . . . . 204 207
       22.1.1.  Description  . . . . . . . . . . . . . . . . . . . . 205 208
       22.1.2.  Registering New Feature-tags with IANA . . . . . . . 205 208
       22.1.3.  Registered entries . . . . . . . . . . . . . . . . . 205 208
     22.2.  RTSP Methods . . . . . . . . . . . . . . . . . . . . . . 206 209
       22.2.1.  Description  . . . . . . . . . . . . . . . . . . . . 206 209
       22.2.2.  Registering New Methods with IANA  . . . . . . . . . 206 209
       22.2.3.  Registered Entries . . . . . . . . . . . . . . . . . 206 209
     22.3.  RTSP Status Codes  . . . . . . . . . . . . . . . . . . . 207 210
       22.3.1.  Description  . . . . . . . . . . . . . . . . . . . . 207 210
       22.3.2.  Registering New Status Codes with IANA . . . . . . . 207 210
       22.3.3.  Registered Entries . . . . . . . . . . . . . . . . . 207 210
     22.4.  RTSP Headers . . . . . . . . . . . . . . . . . . . . . . 207 210
       22.4.1.  Description  . . . . . . . . . . . . . . . . . . . . 207 210
       22.4.2.  Registering New Headers with IANA  . . . . . . . . . 208 211
       22.4.3.  Registered entries . . . . . . . . . . . . . . . . . 208 211

     22.5.  Accept-Credentials . . . . . . . . . . . . . . . . . . . 209 212
       22.5.1.  Accept-Credentials policies  . . . . . . . . . . . . 209 212
       22.5.2.  Accept-Credentials hash algorithms . . . . . . . . . 209 213
     22.6.  Cache-Control Cache Directive Extensions . . . . . . . . 210 213
     22.7.  Media Properties . . . . . . . . . . . . . . . . . . . . 211 214
       22.7.1.  Description  . . . . . . . . . . . . . . . . . . . . 211 214
       22.7.2.  Registration Rules . . . . . . . . . . . . . . . . . 211 215
       22.7.3.  Registered Values  . . . . . . . . . . . . . . . . . 211 215
     22.8.  Notify-Reason header . . . . . . . . . . . . . . . . . . 211 215
       22.8.1.  Description  . . . . . . . . . . . . . . . . . . . . 211 215
       22.8.2.  Registration Rules . . . . . . . . . . . . . . . . . 212 215
       22.8.3.  Registered Values  . . . . . . . . . . . . . . . . . 212 216
     22.9.  Range header formats . . . . . . . . . . . . . . . . . . 212 216
       22.9.1.  Description  . . . . . . . . . . . . . . . . . . . . 212 216
       22.9.2.  Registration Rules . . . . . . . . . . . . . . . . . 212 216
       22.9.3.  Registered Values  . . . . . . . . . . . . . . . . . 213 216
     22.10. Terminate-Reason Header  . . . . . . . . . . . . . . . . 213 217
       22.10.1. Redirect Reasons . . . . . . . . . . . . . . . . . . 213 217
       22.10.2. Terminate-Reason Header Parameters . . . . . . . . . 213 217
     22.11. RTP-Info header parameters . . . . . . . . . . . . . . . 214 217
       22.11.1. Description  . . . . . . . . . . . . . . . . . . . . 214 217
       22.11.2. Registration Rules . . . . . . . . . . . . . . . . . 214 218
       22.11.3. Registered Values  . . . . . . . . . . . . . . . . . 214 218
     22.12. Seek-Style Policies  . . . . . . . . . . . . . . . . . . 215 218
       22.12.1. Description  . . . . . . . . . . . . . . . . . . . . 215 218
       22.12.2. Registration Rules . . . . . . . . . . . . . . . . . 215 218
       22.12.3. Registered Values  . . . . . . . . . . . . . . . . . 215 219
     22.13. Transport Header Registries  . . . . . . . . . . . . . . 215 219
       22.13.1. Transport Protocol Specification . . . . . . . . . . 216 219
       22.13.2. Transport modes  . . . . . . . . . . . . . . . . . . 217 221
       22.13.3. Transport Parameters . . . . . . . . . . . . . . . . 217 221
     22.14. URI Schemes  . . . . . . . . . . . . . . . . . . . . . . 218 222
       22.14.1. The rtsp URI Scheme  . . . . . . . . . . . . . . . . 218 222
       22.14.2. The rtsps URI Scheme . . . . . . . . . . . . . . . . 219 223
       22.14.3. The rtspu URI Scheme . . . . . . . . . . . . . . . . 220 224
     22.15. SDP attributes . . . . . . . . . . . . . . . . . . . . . 221 224
     22.16. Media Type Registration for text/parameters  . . . . . . 222 225
   23. References  . . . . . . . . . . . . . . . . . . . . . . . . . 224 227
     23.1.  Normative References . . . . . . . . . . . . . . . . . . 224 227
     23.2.  Informative References . . . . . . . . . . . . . . . . . 226 229
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . . 229 232
     A.1.   Media on Demand (Unicast)  . . . . . . . . . . . . . . . 229 232
     A.2.   Media on Demand using Pipelining . . . . . . . . . . . . 233 236
     A.3.   Media on Demand (Unicast)  . . . . . . . . . . . . . . . 235 238
     A.4.   Single Stream Container Files  . . . . . . . . . . . . . 239 242
     A.5.   Live Media Presentation Using Multicast  . . . . . . . . 241 244
     A.6.   Capability Negotiation . . . . . . . . . . . . . . . . . 242 245
   Appendix B.  RTSP Protocol State Machine  . . . . . . . . . . . . 244 247
     B.1.   States . . . . . . . . . . . . . . . . . . . . . . . . . 244 247
     B.2.   State variables  . . . . . . . . . . . . . . . . . . . . 244 247
     B.3.   Abbreviations  . . . . . . . . . . . . . . . . . . . . . 244 247
     B.4.   State Tables . . . . . . . . . . . . . . . . . . . . . . 245 248
   Appendix C.  Media Transport Alternatives . . . . . . . . . . . . 251 254
     C.1.   RTP  . . . . . . . . . . . . . . . . . . . . . . . . . . 251 254
       C.1.1.   AVP  . . . . . . . . . . . . . . . . . . . . . . . . 251 254
       C.1.2.   AVP/UDP  . . . . . . . . . . . . . . . . . . . . . . 251 254
       C.1.3.   AVPF/UDP . . . . . . . . . . . . . . . . . . . . . . 252 255
       C.1.4.   SAVP/UDP . . . . . . . . . . . . . . . . . . . . . . 253 256
       C.1.5.   SAVPF/UDP  . . . . . . . . . . . . . . . . . . . . . 255 258
       C.1.6.   RTCP usage with RTSP . . . . . . . . . . . . . . . . 255 258
     C.2.   RTP over TCP . . . . . . . . . . . . . . . . . . . . . . 257 260
       C.2.1.   Interleaved RTP over TCP . . . . . . . . . . . . . . 257 260
       C.2.2.   RTP over independent TCP . . . . . . . . . . . . . . 257 260
     C.3.   Handling Media Clock Time Jumps in the RTP Media Layer . 261 264
     C.4.   Handling RTP Timestamps after PAUSE  . . . . . . . . . . 265 268
     C.5.   RTSP / RTP Integration . . . . . . . . . . . . . . . . . 267 270
     C.6.   Scaling with RTP . . . . . . . . . . . . . . . . . . . . 267 270
     C.7.   Maintaining NPT synchronization with RTP timestamps  . . 267 270
     C.8.   Continuous Audio . . . . . . . . . . . . . . . . . . . . 267 270
     C.9.   Multiple Sources in an RTP Session . . . . . . . . . . . 267 270
     C.10.  Usage of SSRCs and the RTCP BYE Message During an
            RTSP Session . . . . . . . . . . . . . . . . . . . . . . 267 270
     C.11.  Future Additions . . . . . . . . . . . . . . . . . . . . 268 271
   Appendix D.  Use of SDP for RTSP Session Descriptions . . . . . . 269 272
     D.1.   Definitions  . . . . . . . . . . . . . . . . . . . . . . 269 272
       D.1.1.   Control URI  . . . . . . . . . . . . . . . . . . . . 269 272
       D.1.2.   Media Streams  . . . . . . . . . . . . . . . . . . . 270 273
       D.1.3.   Payload Type(s)  . . . . . . . . . . . . . . . . . . 271 274
       D.1.4.   Format-Specific Parameters . . . . . . . . . . . . . 271 274
       D.1.5.   Directionality of media stream . . . . . . . . . . . 271 274
       D.1.6.   Range of Presentation  . . . . . . . . . . . . . . . 272 275
       D.1.7.   Time of Availability . . . . . . . . . . . . . . . . 273 276
       D.1.8.   Connection Information . . . . . . . . . . . . . . . 273 276
       D.1.9.   Message Body Tag . . . . . . . . . . . . . . . . . . 273 277
     D.2.   Aggregate Control Not Available  . . . . . . . . . . . . 274 277
     D.3.   Aggregate Control Available  . . . . . . . . . . . . . . 275 278
     D.4.   Grouping of Media Lines in SDP . . . . . . . . . . . . . 276 279
     D.5.   RTSP external SDP delivery . . . . . . . . . . . . . . . 276 279
   Appendix E.  RTSP Use Cases . . . . . . . . . . . . . . . . . . . 277 280
     E.1.   On-demand Playback of Stored Content . . . . . . . . . . 277 280
     E.2.   Unicast Distribution of Live Content . . . . . . . . . . 278 281
     E.3.   On-demand Playback using Multicast . . . . . . . . . . . 279 282
     E.4.   Inviting an RTSP server into a conference  . . . . . . . 279 282
     E.5.   Live Content using Multicast . . . . . . . . . . . . . . 280 283
   Appendix F.  Text format for Parameters . . . . . . . . . . . . . 282 285
   Appendix G.  Requirements for Unreliable Transport of RTSP  . . . 283 286
   Appendix H.  Backwards Compatibility Considerations . . . . . . . 285 288
     H.1.   Play Request in Play State . . . . . . . . . . . . . . . 285 288
     H.2.   Using Persistent Connections . . . . . . . . . . . . . . 285 288
   Appendix I.  Changes  . . . . . . . . . . . . . . . . . . . . . . 286 289
     I.1.   Brief Overview . . . . . . . . . . . . . . . . . . . . . 286 289
     I.2.   Detailed List of Changes . . . . . . . . . . . . . . . . 287 290
   Appendix J.  Acknowledgements . . . . . . . . . . . . . . . . . . 294 297
     J.1.   Contributors . . . . . . . . . . . . . . . . . . . . . . 294 297
   Appendix K.  RFC Editor Consideration . . . . . . . . . . . . . . 296 299
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 297 300

1.  Introduction

   This memo defines version 2.0 of the Real Time Streaming Protocol
   (RTSP 2.0).  RTSP 2.0 is an application-level protocol for setup and
   control over the delivery of data with real-time properties,
   typically streaming media.  Streaming media is, for instance, video
   on demand or audio live streaming.  Put simply, RTSP acts as a
   "network remote control" for multimedia servers, similar to the
   remote control for a DVD player.

   The protocol operates between RTSP 2.0 clients and servers, but also
   supports the usage of proxies placed between clients and servers.
   Clients can request information about streaming media from servers by
   asking for a description of the media or use media description
   provided externally.  The media delivery protocol is used to
   establish the media streams described by the media description.
   Clients can then request to play out the media, pause it, or stop it
   completely, as known from DVD players remote control or media
   players.  The requested media can consist of multiple audio and video
   streams that are delivered as a time-synchronized streams from
   servers to clients.

   RTSP 2.0 is a replacement of RTSP 1.0 [RFC2326] and obsoletes that
   specification.  This protocol is based on RTSP 1.0 but is not
   backwards compatible other than in the basic version negotiation
   mechanism.  The changes are documented in Appendix I.  There are many

   reasons why RTSP 2.0 can't be backwards compatible with RTSP 1.0 but
   some of the main ones are:

   o  Most headers that needed to be extensible did not define the
      allowed syntax, preventing safe deployment of extensions;

   o  The changed behavior of the PLAY method when received in Play
      state;

   o  Changed behavior of the extensibility model and its mechanism;

   o  The change of syntax for some headers.

   In summary, there are so many small details that changing version
   became necessary to enable clarification and consistent behavior.

   This document is structured as follows.  It begins with an overview
   of the protocol operations and its functions in an informal way.
   Then a set of definitions of used terms and document conventions is
   introduced.  It is followed by the actual RTSP 2.0 core protocol
   specification.  The appendixes describe and define some
   functionalities that are not part of the core RTSP specification, but
   which are still important to enable some usages.  Among them, the RTP
   usage is defined in Appendix C and the SDP usage with RTSP is defined
   in Appendix D, which are two mandatory appendixes.  While others
   include a number of informational parts discussing the changes, use
   cases, different considerations or motivations.

2.  Protocol Overview

   This section provides an informative overview of the different
   mechanisms in the RTSP 2.0 protocol, to give the reader a high level
   understanding before getting into all the different details.  In case
   of conflict with this description and the later sections, the later
   sections take precedence.  For more information about considered use
   cases for RTSP see Appendix E.

   RTSP 2.0 is a bi-directional request and response protocol that first
   establishes a context including content resources (the media) and
   then controls the delivery of these content resources from the
   provider to the consumer.  RTSP has three fundamental parts: Session
   Establishment, Media Delivery Control, and an extensibility model
   described below.  The protocol is based on some assumptions about
   existing functionality to provide a complete solution for client
   controlled real-time media delivery.

   RTSP uses text-based messages, requests and responses, that may
   contain a binary message body.  An RTSP request starts with a method
   line that identifies the method, the protocol and version and the
   resource to act on.  Following the method line are a number of RTSP
   headers.  This part is ended by two consecutive carriage return line
   feed (CRLF) character pairs.  The message body if present follows the
   two CRLF and the body's length is described by a message header.
   RTSP responses are similar, but start with a response line with the
   protocol and version, followed by a status code and a reason phrase.
   RTSP messages are sent over a reliable transport protocol between the
   client and server.  RTSP 2.0 requires clients and servers to
   implement TCP, and TLS over TCP, as mandatory transports for RTSP
   messages.

2.1.  Presentation Description

   RTSP exists to provide access to multi-media presentations and
   content, but tries to be agnostic about the media type or the actual
   media delivery protocol that is used.  To enable a client to
   implement a complete system, an RTSP-external mechanism for
   describing the presentation and the delivery protocol(s) is used.
   RTSP assumes that this description is either delivered completely out
   of bands or as a data object in the response to a client's request
   using the DESCRIBE method (Section 13.2).

   Parameters that commonly have to be included in the Presentation
   Description are the following:

   o  Number of media streams;
   o  The resource identifier for each media stream/resource that is to
      be controlled by RTSP;

   o  The protocol that each media stream is to be delivered over;

   o  Transport protocol parameters that are not negotiated or vary with
      each client;

   o  Media encoding information enabling a client to correctly decode
      the media upon reception;

   o  An aggregate control resource identifier.

   RTSP uses its own URI schemes ("rtsp" and "rtsps") to reference media
   resources and aggregates under common control.

   This specification describes in Appendix D how one uses SDP [RFC4566]
   for Presentation Description

2.2.  Session Establishment

   The RTSP client can request the establishment of an RTSP session
   after having used the presentation description to determine which
   media streams are available, and also which media delivery protocol
   is used and their particular resource identifiers.  The RTSP session
   is a common context between the client and the server that consists
   of one or more media resources that are to be under common media
   delivery control.

   The client creates an RTSP session by sending a request using the
   SETUP method (Section 13.3) to the server.  In the SETUP request the
   client also includes all the transport parameters necessary to enable
   the media delivery protocol to function in the "Transport" header
   (Section 16.52). 18.52).  This includes parameters that are pre-established
   by the presentation description but necessary for any middlebox to
   correctly handle the media delivery protocols.  The Transport header
   in a request may contain multiple alternatives for media delivery in
   a prioritized list, which the server can select from.  These
   alternatives are typically based on information in the presentation
   description.

   The server determines if the media resource is available upon
   receiving a SETUP request and if any of the transport parameter
   specifications are acceptable.  If that is successful, an RTSP
   session context is created and the relevant parameters and state is
   stored.  An identifier is created for the RTSP session and included
   in the response in the Session header (Section 16.47). 18.47).  The SETUP
   response includes a Transport header that specifies which of the
   alternatives has been selected and relevant parameters.

   A SETUP request that references an existing RTSP session but
   identifies a new media resource is a request to add that media
   resource under common control with the already present media
   resources in an aggregated session.  A client can expect this to work
   for all media resources under RTSP control within a multi-media
   content.  However, aggregating resources from different content are
   likely to be refused by the server.  The RTSP session as aggregate is
   referenced by the aggregate control URI, even if the RTSP session
   only contains a single media.

   To avoid an extra round trip in the session establishment of
   aggregated RTSP sessions, RTSP 2.0 supports pipelined requests; i.e.,
   the client can send multiple requests back-to-back without waiting
   first for the completion of any of them.  The client uses client-
   selected identifier in the Pipelined-Requests header to instruct the
   server to bind multiple requests together as if they included the
   session identifier.

   The SETUP response also provides additional information about the
   established sessions in a couple of different headers.  The Media-
   Properties header includes a number of properties that apply for the
   aggregate that is valuable when doing media delivery control and
   configuring user interface.  The Accept-Ranges header informs the
   client about which range formats that the server supports with these
   media resources.  The Media-Range header inform the client about the
   time range of the media currently available.

2.3.  Media Delivery Control

   After having established an RTSP session, the client can start
   controlling the media delivery.  The basic operations are Start by
   using the PLAY method (Section 13.4) and Halt by using the PAUSE
   method (Section 13.6).  PLAY also allows for choosing the starting
   media position from which the server should deliver the media.  The
   positioning is done by using the Range header (Section 16.38) 18.38) that
   supports several different time formats: Normal Play Time (NPT)
   (Section 4.5), SMPTE Timestamps (Section 4.4) and absolute time
   (Section 4.6).  The Range header does further allow the client to
   specify a position where delivery should end, thus allowing a
   specific interval to be delivered.

   The support for positioning/searching within a content depends on the
   content's media properties.  Content exists in a number of different
   types, such as: on-demand, live, and live with simultaneous
   recording.  Even within these categories there are differences in how
   the content is generated and distributed, which affect how it can be
   accessed for playback.  The properties applicable for the RTSP
   session are provided by the server in the SETUP response using the
   Media-Properties header (Section 16.28). 18.28).  These are expressed using
   one or several independent attributes.  A first attribute is Random
   Access, which expresses if positioning can be done, and with what
   granularity.  Another aspect is whether the content will change
   during the lifetime of the session.  While on-demand content will
   provided in full from the beginning, a live stream being recorded
   results in the length of the accessible content growing as the
   session goes on.  There also exist content that is dynamically built
   by another protocol than RTSP and thus also changes in steps during
   the session, but maybe not continuously.  Furthermore, when content
   is recorded, there are cases where not the complete content is
   maintained, but, for example, only the last hour.  All these
   properties result in the need for mechanisms that will be discussed
   below.

   When the client accesses on-demand content that allows random access,
   the client can issue the PLAY request for any point in the content
   between the start and the end.  The server will deliver media from
   the closest random access point prior to the requested point and
   indicate that in its PLAY response.  If the client issues a PAUSE,
   the delivery will be halted and the point at which the server stopped
   will be reported back in the response.  The client can later resume
   by sending a PLAY request without a range header.  When the server is
   about to complete the PLAY request by delivering the end of the
   content or the requested range, the server will send a PLAY_NOTIFY
   request indicating this.

   When playing live content with no extra functions, such as recording,
   the client will receive the live media from the server after having
   sent a PLAY request.  Seeking in such content is not possible as the
   server does not store it, but only forwards it from the source of the
   session.  Thus delivery continues until the client sends a PAUSE
   request, tears down the session, or the content ends.

   For live sessions that are being recorded the client will need to
   keep track of how the recording progresses.  Upon session
   establishment the client will learn the current duration of the
   recording from the Media-Range header.  As the recording is ongoing
   the content grows in direct relation to the passed time.  Therefore,
   each server's response to a PLAY request will contain the current
   Media-Range header.  The server should also regularly send every 5
   minutes the current media range in a PLAY_NOTIFY request.  If the
   live transmission ends, the server must send a PLAY_NOTIFY request
   with the updated Media-Properties indicating that the content stopped
   being a recorded live session and instead became on-demand content;
   the request also contains the final media range.  While the live
   delivery continues the client can request to play the current live
   point by using the NPT timescale symbol "now", or it can request a
   specific point in the available content by an explicit range request
   for that point.  If the requested point is outside of the available
   interval the server will adjust the position to the closest available
   point, i.e., either at the beginning or the end.

   A special case of recording is that where the recording is not
   retained longer than a specific time period, thus as the live
   delivery continues the client can access any media within a moving
   window that covers, for example, "now" to "now" minus 1 hour.  A
   client that pauses on a specific point within the content may not be
   able to retrieve the content anymore.  If the client waits too long
   before resuming the pause point, the content may no longer be
   available.  In this case the pause point will be adjusted to the end
   of the available media.

2.4.  Session Parameter Manipulations

   A session may have additional state or functionality that effects how
   the server or client treats the session, content, how it functions,
   or feedback on how well the session works.  Such extensions are not
   defined in this specification, but may be done in various extensions.
   RTSP has two methods for retrieving and setting parameter values on
   either the client or the server: GET_PARAMETER (Section 13.8) and
   SET_PARAMETER (Section 13.9).  These methods carry the parameters in
   a message body of the appropriate format.  One can also use headers
   to query state with the GET_PARAMETER method.  As an example, clients
   needing to know the current media-range for a time-progressing
   session can use the GET_PARAMETER method and include the media-range.
   Furthermore, synchronization information can be requested by using a
   combination of RTP-Info and Range.

   RTSP 2.0 does not have a strong mechanism for providing negotiation
   of which headers, or parameters and their formats, that can be used.
   However, responses will indicate request headers or parameters that
   are not supported.  A priori determination of what features are
   available needs to be done through out-of-band mechanisms, like the
   session description, or through the usage of feature tags
   (Section 4.7).

2.5.  Media Delivery

   The delivery of media to the RTSP client is done with a protocol
   outside of RTSP and this protocol is determined during the session
   establishment.  This document specifies how media is delivered with
   RTP [RFC3550] over UDP, UDP [RFC0768], TCP [RFC0793] or the RTSP control
   connection.  Additional protocols may be specified in the future
   based on demand.

   The usage of RTP as media delivery protocol requires some additional
   information to function well.  The PLAY response contains information
   to enable reliable and timely delivery of how a client should
   synchronize different sources in the different RTP sessions.  It also
   provides a mapping between RTP timestamps and the content time scale.
   When the server wants to notify the client about the completion of
   the media delivery, it sends a PLAY_NOTIFY request to the client.
   The PLAY_NOTIFY request includes information about the stream end,
   including the last RTP sequence number for each stream, thus enabling
   the client to empty the buffer smoothly.

2.5.1.  Media Delivery Manipulations

   The basic playback functionality of RTSP enables delivery of a range
   of requested content to the client at the pace intended by the
   content's creator.  However, RTSP can also manipulate the delivery to
   the client in two ways.

   Scale:  The ratio of media content time delivered per unit playback
      time.

   Speed:  The ratio of playback time delivered per unit of wallclock
      time.

   Both affect the media delivery per time unit.  However, they
   manipulate two independent time scales and the effects are possible
   to combine.

   Scale is used for fast forward or slow motion control as it changes
   the amount of content timescale that should be played back per time
   unit.  Scale > 1.0, means fast forward, e.g.  Scale=2.0 results in
   that 2 seconds of content is played back every second of playback.
   Scale = 1.0 is the default value that is used if no Scale is
   specified, i.e., playback at the content's original rate.  Scale
   values between 0 and 1.0 is providing for slow motion.  Scale can be
   negative to allow for reverse playback in either regular pace (Scale
   = -1.0) or fast backwards (Scale < -1.0) or slow motion backwards
   (-1.0 < Scale < 0).  Scale = 0 is equal to pause and is not allowed.

   In most cases the realization of scale means server side manipulation
   of the media to ensure that the client can actually play it back.
   These media manipulation and when they are needed are highly media-
   type dependent.  Let's consider an example with two common media
   types audio and video.

   It is very difficult to modify the playback rate of audio.  A maximum
   of 10-30% is possible by changing the pitch-rate of speech.  Music
   goes out of tune if one tries to manipulate the playback rate by
   resampling it.  This is a well known problem and audio is commonly
   muted or played back in short segments with skips to keep up with the
   current playback point.

   For video it is possible to manipulate the frame rate, although the
   rendering capabilities are often limited to certain frame rates.
   Also the allowed bitrates in decoding, the structure used in the
   encoding and the dependency between frames and other capabilities of
   the rendering device limits the possible manipulations.  Therefore,
   the basic fast forward capabilities often are implemented by
   selecting certain subsets of frames.

   Due to the media restrictions, the possible scale values are commonly
   restricted to the set of realizable scale ratios.  To enable the
   clients to select from the possible scale values, RTSP can signal the
   supported Scale ratios for the content.  To support aggregated or
   dynamic content, where this may change during the ongoing session and
   dependent on the location within the content, a mechanism for
   updating the media properties and the currently used scale factor
   exist.

   Speed affects how much of the playback timeline is delivered in a
   given wallclock period.  The default is Speed = 1 which means to
   deliver at the same rate the media is consumed.  Speed > 1 means that
   the receiver will get content faster than it regularly would consume
   it.  Speed < 1 means that delivery is slower than the regular media
   rate.  Speed values of 0 or lower have no meaning and are not
   allowed.  This mechanism enables two general functionalities.  One is
   client side scale operations, i.e. the client receives all the frames
   and makes the adjustment to the playback locally.  The second is
   delivery control for buffering of media.  By specifying a speed over
   1.0 the client can build up the amount of playback time it has
   present in its buffers to a level that is sufficient for its needs.

   A naive implementation of Speed would only affect the transmission
   schedule of the media and has a clear impact on the needed bandwidth.
   This would result in the data rate being proportional to the speed
   factor.  Speed = 1.5, i.e., 50% faster than normal delivery, would
   result in a 50% increase in the data transport rate.  If that can be
   supported or not depends solely on the underlying network path.
   Scale may also have some impact on the required bandwidth due to the
   manipulation of the content in the new playback schedule.  An example
   is fast forward where only the independently decodable intra frames
   are included in the media stream.  This usage of solely intra frames
   increases the data rate significantly compared to a normal sequence
   with the same number of frames, where most frames are encoded using
   prediction.

   This potential increase of the data rate needs to be handled by the
   media sender.  The client has requested that the media will be
   delivered in a specific way, which should be honored.  However, the
   media sender cannot ignore if the network path between the sender and
   the receiver can't handle the resulting media stream.  In that case
   the media stream needs to be adapted to fit the available resources
   of the path.  This can result in a reduced media quality.

   The need for bitrate adaptation becomes especially problematic in
   connection with the Speed semantics.  If the goal is to fill up the
   buffer, the client may not want to do that at the cost of reduced
   quality.  If the client wants to make local playout changes then it
   may actually require that the requested speed be honored.  To resolve
   this issue, Speed uses a range so that both cases can be supported.
   The server is requested to use the highest possible speed value
   within the range which is compatible with the available bandwidth.
   As long as the server can maintain a speed value within the range it
   shall not change the media quality, but instead modify the actual
   delivery rate in response to available bandwidth and reflect this in
   the Speed value in the response.  However, if this is not possible,
   the server should instead modify the media quality to respect the
   lowest speed value and the available bandwidth.

   This functionality enables the local scaling implementation to use a
   tight range, or even a range where the lower bound equals the upper
   bound, to identify that it requires the server to deliver the
   requested amount of media time per delivery time independent of how
   much it needs to adapt the media quality to fit within the available
   path bandwidth.  For buffer filling, it is suitable to use a range
   with a reasonable span and with a lower bound at the nominal media
   rate 1.0, such as 1.0 - 2.5.  If the client wants to reduce the
   buffer, it can specify an upper bound that is below 1.0 to force the
   server to deliver slower than the nominal media rate.

2.6.  Session Maintenance and Termination

   The session context that has been established is kept alive by having
   the client show liveness.  This is done in two main ways:

   o  Media transport protocol keep-alive.  RTCP may be used when using
      RTP.

   o  Any RTSP request referencing the session context.

   Section 10.5 discusses the methods for showing liveness in more
   depth.  If the client fails to show liveness for more than the
   established session timeout value (normally 60 seconds), the server
   may terminate the context.  Other values may be selected by the
   server through the inclusion of the timeout parameter in the session
   header.

   The session context is normally terminated by the client sending a
   TEARDOWN request to the server referencing the aggregated control
   URI.  An individual media resource can be removed from a session
   context by a TEARDOWN request referencing that particular media
   resource.  If all media resources are removed from a session context,
   the session context is terminated.

   A client may keep the session alive indefinitely if allowed by the
   server; however, it is recommended to release the session context
   when an extended period of time without media delivery activity has
   passed.  The client can re-establish the session context if required
   later.  What constitutes an extended period of time is dependent on
   the server and its usage.  It is recommended that the client
   terminates the session before 10*times the session timeout value has
   passed.  A server may terminate the session after one session timeout
   period without any client activity beyond keep-alive.  When a server
   terminates the session context, it does that by sending a TEARDOWN
   request indicating the reason.

   A server can also request that the client tear down the session and
   re-establish it at an alternative server, as may be needed for
   maintenance.  This is done by using the REDIRECT method.  The
   Terminate-Reason header is used to indicate when and why.  The
   Location header indicates where it should connect if there is an
   alternative server available.  When the deadline expires, the server
   simply stops providing the service.  To achieve a clean closure, the
   client needs to initiate session termination prior to the deadline.
   In case the server has no other server to redirect to, and wants to
   close the session for maintenance, it shall use the TEARDOWN method
   with a Terminate-Reason header.

2.7.  Extending RTSP

   RTSP is quite a versatile protocol which supports extensions in many
   different directions.  Even this core specification contains several
   blocks of functionality that are optional to implement.  The use case
   and need for the protocol deployment should determine what parts are
   implemented.  Allowing for extensions makes it possible for RTSP to
   reach out to additional use cases.  However, extensions will affect
   the interoperability of the protocol and therefore it is important
   that they can be added in a structured way.

   The client can learn the capability of a server by using the OPTIONS
   method (Section 13.1) and the Supported header (Section 16.49). 18.49).  It
   can also try and possibly fail using new methods, or require that
   particular features are supported using the Require or Proxy-Require
   header.

   The RTSP protocol in itself can be extended in three ways, listed
   here in order of the magnitude of changes supported:

   o  Existing methods can be extended with new parameters, for example,
      headers, as long as these parameters can be safely ignored by the
      recipient.  If the client needs negative acknowledgment when a
      method extension is not supported, a tag corresponding to the
      extension may be added in the field of the Require or Proxy-
      Require headers (see Section 16.35). 18.35).

   o  New methods can be added.  If the recipient of the message does
      not understand the request, it must respond with error code 501
      (Not Implemented) so that the sender can avoid using this method
      again.  A client may also use the OPTIONS method to inquire about
      methods supported by the server.  The server must list the methods
      it supports using the Public response header.

   o  A new version of the protocol can be defined, allowing almost all
      aspects (except the position of the protocol version number) to
      change.  A new version of the protocol must be registered through
      an IETF standard track document.

   The basic capability discovery mechanism can be used to both discover
   support for a certain feature and to ensure that a feature is
   available when performing a request.  For a detailed explanation of
   this see Section 11.

   New media delivery protocols may be added and negotiated at session
   establishment, in addition to extensions to the core protocol.
   Certain types of protocol manipulations can be done through parameter
   formats using SET_PARAMETER and GET_PARAMETER.

3.  Document Conventions

3.1.  Notational Conventions

   Since a few of the definitions are identical to HTTP/1.1, this
   specification only points to the section where they are defined
   rather than copying it.  For brevity, [HX.Y] is to be taken to refer
   to Section X.Y of the current HTTP/1.1 specification ([RFC2616]).

   All the mechanisms specified in this document are described in both
   prose and the Augmented Backus-Naur form (ABNF) described in detail
   in [RFC5234].

   Indented and smaller-type paragraphs are used to provide informative
   background and motivation.  This is intended to give readers who were
   not involved with the formulation of the specification an
   understanding of why things are the way they are in RTSP.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   The word, "unspecified" is used to indicate functionality or features
   that are not defined in this specification.  Such functionality
   cannot be used in a standardized manner without further definition in
   an extension specification to RTSP.

3.2.  Terminology

   Aggregate control:  The concept of controlling multiple streams using
      a single timeline, generally maintained by the server.  A client,
      for example, uses aggregate control when it issues a single play
      or pause message to simultaneously control both the audio and
      video in a movie.  A session which is under aggregate control is
      referred to as an aggregated session.

   Aggregate control URI:  The URI used in an RTSP request to refer to
      and control an aggregated session.  It normally, but not always,
      corresponds to the presentation URI specified in the session
      description.  See Section 13.3 for more information.

   Client:  The client requests media service from the media server.

   Connection:  A transport layer virtual circuit established between
      two programs for the purpose of communication.

   Container file:  A file which may contain multiple media streams
      which often constitutes a presentation when played together.  The
      concept of a container file is not embedded in the protocol.
      However, RTSP servers may offer aggregate control on the media
      streams within these files.

   Continuous media:  Data where there is a timing relationship between
      source and sink; that is, the sink needs to reproduce the timing
      relationship that existed at the source.  The most common examples
      of continuous media are audio and motion video.  Continuous media
      can be real-time (interactive or conversational), where there is a
      "tight" timing relationship between source and sink, or streaming
      where the relationship is less strict.

   Feature-tag:  A tag representing a certain set of functionality, i.e.
      a feature.

   IRI:  Internationalized Resource Identifier, is the same as an URI,
      with the exception that it allows characters from the whole
      Universal Character Set (Unicode/ISO 10646), rather than the US-
      ASCII only.  See [RFC3987] for more information.

   Live:  Normally used to describe a presentation or session with media
      coming from an ongoing event.  This generally results in the
      session having an unbound or only loosely defined duration, and
      sometimes no seek operations are possible.

   Media initialization:  Datatype/codec specific initialization.  This
      includes such things as clock rates, color tables, etc.  Any
      transport-independent information which is required by a client
      for playback of a media stream occurs in the media initialization
      phase of stream setup.

   Media parameter:  Parameter specific to a media type that may be
      changed before or during stream delivery.

   Media server:  The server providing media delivery services for one
      or more media streams.  Different media streams within a
      presentation may originate from different media servers.  A media
      server may reside on the same host or on a different host from
      which the presentation is invoked.

   (Media) stream:  A single media instance, e.g., an audio stream or a
      video stream as well as a single whiteboard or shared application
      group.  When using RTP, a stream consists of all RTP and RTCP
      packets created by a source within an RTP session.

   Message:  The basic unit of RTSP communication, consisting of a
      structured sequence of octets matching the syntax defined in
      Section 20 and transmitted over a connection or a connectionless
      transport.  A message is either a Request or a Response.

   Message Body:  The information transferred as the payload of a
      message (Request and response).  A message body consists of meta-
      information in the form of message-body headers and content in the
      form of a message-body, as described in Section 9.

   Non-Aggregated Control:  Control of a single media stream.

   Presentation:  A set of one or more streams presented to the client
      as a complete media feed and described by a presentation
      description as defined below.  Presentations with more than one
      media stream are often handled in RTSP under aggregate control.

   Presentation description:  A presentation description contains
      information about one or more media streams within a presentation,
      such as the set of encodings, network addresses and information
      about the content.  Other IETF protocols such as SDP ([RFC4566])
      use the term "session" for a presentation.  The presentation
      description may take several different formats, including but not
      limited to the session description protocol format, SDP.

   Response:  An RTSP response to a Request.  One type of RTSP message.
      If an HTTP response is meant, it is indicated explicitly.

   Request:  An RTSP request.  One type of RTSP message.  If an HTTP
      request is meant, it is indicated explicitly.

   Request-URI:  The URI used in a request to indicate the resource on
      which the request is to be performed.

   RTSP agent:  Refers to either an RTSP client, an RTSP server, or an
      RTSP proxy.  In this specification, there are many capabilities
      that are common to these three entities such as the capability to
      send requests or receive responses.  This term will be used when
      describing functionality that is applicable to all three of these
      entities.

   RTSP session:  A stateful abstraction upon which the main control
      methods of RTSP operate.  An RTSP session is a common context; it
      is created and maintained on client's request and can be destroyed
      by either the client or server.  It is established by an RTSP
      server upon the completion of a successful SETUP request (when a
      200 OK response is sent) and is labeled with a session identifier
      at that time.  The session exists until timed out by the server or
      explicitly removed by a TEARDOWN request.  An RTSP session is a
      stateful entity; an RTSP server maintains an explicit session
      state machine (see Appendix B) where most state transitions are
      triggered by client requests.  The existence of a session implies
      the existence of state about the session's media streams and their
      respective transport mechanisms.  A given session can have one or
      more media streams associated with it.  An RTSP server uses the
      session to aggregate control over multiple media streams.

   Origin Server:  The server on which a given resource resides.

   Transport initialization:  The negotiation of transport information
      (e.g., port numbers, transport protocols) between the client and
      the server.

   URI:  Universal Resource Identifier, see [RFC3986].  The URIs used in
      RTSP are generally URLs as they give a location for the resource.
      As URLs are a subset of URIs, they will be referred to as URIs to
      cover also the cases when an RTSP URI would not be an URL.

   URL:  Universal Resource Locator, is an URI which identifies the
      resource through its primary access mechanism, rather than
      identifying the resource by name or by some other attribute(s) of
      that resource.

4.  Protocol Parameters

4.1.  RTSP Version

   This specification defines version 2.0 of RTSP.

   RTSP uses a "<major>.<minor>" numbering scheme to indicate versions
   of the protocol.  The protocol versioning policy is intended to allow
   the sender to indicate the format of a message and its capacity for
   understanding further RTSP communication, rather than the features
   obtained via that communication.  No change is made to the version
   number for the addition of message components which do not affect
   communication behavior or which only add to extensible field values.

   The <minor> number is incremented when the changes made to the
   protocol add features which do not change the general message parsing
   algorithm, but which may add to the message semantics and imply
   additional capabilities of the sender.  The <major> number is
   incremented when the format of a message within the protocol is
   changed.  The version of an RTSP message is indicated by an RTSP-
   Version field in the first line of the message.  Note that the major
   and minor numbers MUST be treated as separate integers and that each
   MAY be incremented higher than a single digit.  Thus, RTSP/2.4 is a
   lower version than RTSP/2.13, which in turn is lower than RTSP/12.3.
   Leading zeros MUST be ignored by recipients and MUST NOT be sent.

4.2.  RTSP IRI and URI

   RTSP 2.0 defines and registers three URI schemes "rtsp", "rtsps" and
   "rtspu".  The usage of the last, "rtspu", is unspecified in RTSP 2.0,
   and is defined here to register and reserve the URI scheme that is
   defined in RTSP 1.0.  The "rtspu" scheme indicates unspecified
   transport of the RTSP messages over unreliable transport (UDP in RTSP
   1.0).  An RTSP server MUST response with an error code indicating the
   "rtspu" scheme is not implemented (501) to a request that carries a
   "rtspu" URI scheme.  The details of the syntax of "rtsp" and "rtsps"
   URIs has been changed from RTSP 1.0.

   This specification also defines the format of the RTSP IRI [RFC3987]
   that can be used as RTSP resource identifiers and locators, in web
   pages, user interfaces, on paper, etc.  However, the RTSP request
   message format only allows usage of the absolute URI format.  The
   RTSP IRI format MUST use the rules and transformation for IRIs to
   URIs, as defined in [RFC3987].  This way RTSP 2.0 URIs for request
   can be produced from an RTSP IRI.

   The RTSP IRI and URI are both syntax restricted compared to the
   generic syntax defined in [RFC3986] and [RFC3987]:

   o  An absolute URI requires the authority part; i.e., a host identity
      must be provided.

   o  Parameters in the path element are prefixed with the reserved
      separator ";".

   The RTSP URI and IRI are case sensitive, with the exception of those
   parts that [RFC3986] and [RFC3987] defines as case-insensitive; for
   example, the scheme and host part.

   The fragment identifier is used as defined in sections 3.5 and 4.3 of
   [RFC3986], i.e. the fragment is to be stripped from the IRI by the
   requester and not included in the request URI.  The user agent needs
   to interpret the value of the fragment based on the media type the
   request relates to; i.e., the media type indicated in Content-Type
   header in the response to DESCRIBE.

   The syntax of any URI query string is unspecified and responder
   (usually the server) specific.  The query is, from the requester's
   perspective, an opaque string and needs to be handled as such.
   Please note that relative URI with queries are difficult to handle
   due to the RFC 3986 relative URI handling rules.  Any change of the
   path element using a relative URI results in the stripping of the
   query, which means the relative part needs to contain the query.

   The URI scheme "rtsp" requires that commands are issued via a
   reliable protocol (within the Internet, TCP), while the scheme
   "rtsps" identifies a reliable transport using secure transport (TLS
   [RFC5246], see (Section 19).

   For the scheme "rtsp", if no port number is provided in the authority
   part of the URI port number 554 MUST be used.  For the scheme
   "rtsps", the TCP port 322 is registered and MUST be assumed.

   A presentation or a stream is identified by a textual media
   identifier, using the character set and escape conventions of URIs
   [RFC3986].  URIs may refer to a stream or an aggregate of streams;
   i.e., a presentation.  Accordingly, requests described in
   (Section 13) can apply to either the whole presentation or an
   individual stream within the presentation.  Note that some request
   methods can only be applied to streams, not presentations, and vice
   versa.

   For example, the RTSP URI:

      rtsp://media.example.com:554/twister/audiotrack

   may identify the audio stream within the presentation "twister",
   which can be controlled via RTSP requests issued over a TCP
   connection to port 554 of host media.example.com.

   Also, the RTSP URI:

      rtsp://media.example.com:554/twister

   identifies the presentation "twister", which may be composed of audio
   and video streams, but could also be something else like a random
   media redirector.

      This does not imply a standard way to reference streams in URIs.
      The presentation description defines the hierarchical
      relationships in the presentation and the URIs for the individual
      streams.  A presentation description may name a stream "a.mov" and
      the whole presentation "b.mov".

   The path components of the RTSP URI are opaque to the client and do
   not imply any particular file system structure for the server.

      This decoupling also allows presentation descriptions to be used
      with non-RTSP media control protocols simply by replacing the
      scheme in the URI.

4.3.  Session Identifiers

   Session identifiers are strings of length 8-128 characters.  A
   session identifier MUST be chosen cryptographically random (see
   [RFC4086]).  It is RECOMMENDED that it contains 128 bits of entropy,
   i.e. approximately 22 characters from a high quality generator (see
   Section 21).  However, note that the session identifier does not
   provide any security against session hijacking unless it is kept
   confidential by the client, server and trusted proxies.

4.4.  SMPTE Relative Timestamps

   A SMPTE relative timestamp expresses time relative to the start of
   the clip.  Relative timestamps are expressed as SMPTE time codes for
   frame-level access accuracy.  The time code has the format

      hours:minutes:seconds:frames.subframes,

   with the origin at the start of the clip.  The default SMPTE format
   is "SMPTE 30 drop" format, with frame rate is 29.97 frames per
   second.  Other SMPTE codes MAY be supported (such as "SMPTE 25")
   through the use of "smpte-type".  For SMPTE 30, the "frames" field in
   the time value can assume the values 0 through 29.  The difference
   between 30 and 29.97 frames per second is handled by dropping the
   first two frame indices (values 00 and 01) of every minute, except
   every tenth minute.  If the frame and the subframe values are zero,
   they may be omitted.  Subframes are measured in one-hundredth of a
   frame.

   Examples:

     smpte=10:12:33:20-
     smpte=10:07:33-
     smpte=10:07:00-10:07:33:05.01
     smpte-25=10:07:00-10:07:33:05.01

4.5.  Normal Play Time

   Normal play time (NPT) indicates the stream absolute position
   relative to the beginning of the presentation, not to be confused
   with the Network Time Protocol (NTP) [RFC5905].  The timestamp
   consists of two parts: the mandatory first part may be expressed in
   either seconds or hours, minutes, and seconds.  The optional second
   part consists of a decimal point and decimal figures and indicates
   fractions of a second.

   The beginning of a presentation corresponds to 0.0 seconds.  Negative
   values are not defined.

   The special constant "now" is defined as the current instant of a
   live event.  It MAY only be used for live events, and MUST NOT be
   used for on-demand (i.e., non-live) content.

   NPT is defined as in DSM-CC [ISO.13818-6.1995]: "Intuitively, NPT is
   the clock the viewer associates with a program.  It is often
   digitally displayed on a VCR.  NPT advances normally when in normal
   play mode (scale = 1), advances at a faster rate when in fast scan
   forward (high positive scale ratio), decrements when in scan reverse
   (negative scale ratio) and is fixed in pause mode.  NPT is
   (logically) equivalent to SMPTE time codes."

   Examples:

     npt=123.45-125
     npt=12:05:35.3-
     npt=now-
      The syntax conforms to ISO 8601 [ISO.8601.2000].  The npt-sec
      notation is optimized for automatic generation, the npt-hhmmss
      notation for consumption by human readers.  The "now" constant
      allows clients to request to receive the live feed rather than the
      stored or time-delayed version.  This is needed since neither
      absolute time nor zero time are appropriate for this case.

4.6.  Absolute Time

   Absolute time is expressed as ISO 8601 [ISO.8601.2000] timestamps,
   using UTC (GMT).  Fractions of a second may be indicated.

   Example for November 8, 1996 at 14h 37 min and 20 and a quarter
   seconds UTC:

     19961108T143720.25Z

4.7.  Feature-Tags

   Feature-tags are unique identifiers used to designate features in
   RTSP.  These tags are used in Require (Section 16.41), 18.41), Proxy-Require
   (Section 16.35), 18.35), Proxy-Supported (Section 16.36), 18.36), Supported
   (Section 16.49) 18.49) and Unsupported (Section 16.53) 18.53) header fields.

   A feature-tag definition MUST indicate which combination of clients,
   servers or proxies it applies to.

   The creator of a new RTSP feature-tag should either prefix the
   feature-tag with a reverse domain name (e.g.,
   "com.example.mynewfeature" is an apt name for a feature whose
   inventor can be reached at "example.com"), or register the new
   feature-tag with the Internet Assigned Numbers Authority (IANA) (see
   IANA Section 22).

   The usage of feature-tags is further described in Section 11 that
   deals with capability handling.

4.8.  Message Body Tags

   Message body tags are opaque strings that are used to compare two
   message bodies from the same resource, for example in caches or to
   optimize setup after a redirect.  Message body tags can be carried in
   the MTag header (see Section 16.30) 18.30) or in SDP (see Appendix D.1.9).
   MTag is similar to ETag in HTTP/1.1.

   A message body tag MUST be unique across all versions of all message
   bodies associated with a particular resource.  A given message body
   tag value MAY be used for message bodies obtained by requests on
   different URIs.  The use of the same message body tag value in
   conjunction with message bodies obtained by requests on different
   URIs does not imply the equivalence of those message bodies

   Message body tags are used in RTSP to make some methods conditional.
   The methods are made conditional through the inclusion of headers;
   see "If-Match" (Section 16.23) 18.23) and "If-None-Match" (Section 16.25). 18.25).
   Note that RTSP message body tags apply to the complete presentation;
   i.e., both the presentation description and the individual media
   streams.  Thus message body tags can be used to verify at setup time
   after a redirect that the same session description applies to the
   media at the new location using the If-Match header.

4.9.  Media Properties

   When an RTSP server handles media, it is important to consider the
   different properties a media instance for delivery and playback can
   have.  This specification considers the below listed media properties
   in its protocol operations.  They are derived from the differences
   between a number of supported usages.

   On-demand:  Media that has a fixed (given) duration that doesn't
      change during the life time of the RTSP session and is known at
      the time of the creation of the session.  It is expected that the
      content of the media will not change, even if the representation,
      i.e encoding, quality, etc, may change.  Generally one can seek,
      i.e. request any range, within the media.

   Dynamic On-demand:  This is a variation of the on-demand case where
      external methods are used to manipulate the actual content of the
      media setup for the RTSP session.  The main example is a content
      defined by a playlist.

   Live:  Live media represents a progressing content stream (such as
      broadcast TV) where the duration may or may not be known.  It is
      not seekable, only the content presently being delivered can be
      accessed.

   Live with Recording:  A Live stream that is combined with a server-
      side capability to store and retain the content of the live
      session, and allow for random access delivery within the part of
      the already recorded content.  The actual behavior of the media
      stream is very much dependent on the retention policy for the
      media stream; either the server will be able to capture the
      complete media stream, or it will have a limitation in how much
      will be retained.  The media range will dynamically change as the
      session progress.  For servers with a limited amount of storage
      available for recording, there will typically be a sliding window
      that moves forwards while new data is made available and older
      data is discarded.

   To cover the above usages, the following media properties with
   appropriate values are specified:

4.9.1.  Random Access and Seeking

   Random Access is the ability to specify and get media delivered from
   any point inside the content, an operation called seeking.  This
   possibility is signaled using the Seek-Style header (see
   Section 16.45) 18.45) which can take the following different values:

   Random Access:  The media is seekable to any out of a large number of
      points within the media.  Due to media encoding limitations, a
      particular point may not be reachable, but seeking to a point
      close by is enabled.  A floating point number of seconds may be
      provided to express the worst case distance between random access
      points.

   Conditional Random Access:  Based on the above Random Access but
      intended to handle a case where the distance in the media between
      random access points is large, and where small seek forward using
      Random Access would move the client further away than the current
      point.

   Return To Start:  Seeking is only possible to the beginning of the
      content.

   No seeking:  Seeking is not possible at all.

4.9.2.  Retention

   Media may have different retention policies in place that affect the
   operation on media.  The following different media retention policies
   are envisioned and taken into consideration where applicable:

   Unlimited:  The media will not be removed as long as the RTSP session
      is in existence.

   Time Limited:  The media will not be removed before given wallclock
      time.  After that time it may or may not be available any more.

   Duration limited:  Each individual unit of the media will be retained
      for the specified duration.

4.9.3.  Content Modifications

   There is also the question of how the content may change during time
   for a given media resource:

   Immutable:  The content of the media will not change, even if the
      representation, i.e., encoding, quality, etc., may change.

   Dynamic:  Between explicit updates the media content will not change,
      but the content may change due to external methods or triggers,
      such as playlists.

   Time Progressing:  As times progresses new content will become
      available.  If the content also is retained it will become longer
      as everything between the start point and the point currently
      being made available can be accessed.  If the media server uses a
      sliding window policy for retention, the start point will also
      change as time progresses.

4.9.4.  Supported Scale Factors

   Content often supports only a limited set or range of scales when
   delivering the media..  To enable the client to know what values or
   ranges of scale operations that the whole content or the current
   position supports, a media properties attribute for this is defined
   which contains a list with the values and/or ranges that are
   supported.  The attribute is named "Scales".  It may be updated at
   any point in the content due to content consisting of spliced pieces
   or content being dynamically updated by out-of-band mechanisms.

4.9.5.  Mapping to the Attributes

   This section shows examples of how one would map the above usages to
   the properties and their values.

   On-demand:  Random Access: Random Access=5s, Content Modifications:
      Immutable, Retention: unlimited or time limited.

   Dynamic On-demand:  Random Access: Random Access=3s, Content
      Modifications: Dynamic, Retention: unlimited or time limited.

   Live:  Random Access: No seeking, Content Modifications: Time
      Progressing, Retention: Duration limited=0.0s

   Live with Recording:  Random Access: Random Access=3s, Content
      Modifications: Time Progressing, Retention: Duration limited=2H

5.  RTSP Message

   RTSP is a text-based protocol and uses the ISO 10646 character set in
   UTF-8 encoding RFC 3629 [RFC3629].  Lines MUST be terminated by CRLF.

      Text-based protocols make it easier to add optional parameters in
      a self-describing manner.  Since the number of parameters and the
      frequency of commands is low, processing efficiency is not a
      concern.  Text-based protocols, if done carefully, also allow easy
      implementation of research prototypes in scripting languages such
      as TCL, Visual Basic and Perl.

   The ISO 10646 character set avoids tricky character set switching,
   but is invisible to the application as long as US-ASCII is being
   used.  This is also the encoding used for RTCP [RFC3550].

   Requests contain methods, the object the method is operating upon and
   parameters to further describe the method.  Methods are idempotent
   unless otherwise noted.  Methods are also designed to require little
   or no state maintenance at the media server.

5.1.  Message Types

   RTSP messages consist of requests from client to server, or server to
   client, and responses in the reverse direction.  Request (Section 7)
   and Response (Section 8) messages use a format based on the generic
   message format of RFC 2822 [RFC2822] for transferring bodies (the
   payload of the message).  Both types of messages consist of a start-
   line, zero or more header fields (also known as "headers"), an empty
   line (i.e., a line with nothing preceding the CRLF) indicating the
   end of the header, and possibly the data of the message body.
   generic-message = start-line
                   *(message-header CRLF)
                     CRLF
                   [ message-body-data ]
   start-line = Request-Line | Status-Line

   In the interest of robustness, agents MUST ignore any empty line(s)
   received where a Request-Line or Response-Line is expected.  In other
   words, if the agent is reading the protocol stream at the beginning
   of a message and receives a CRLF first, it MUST ignore the CRLF.

5.2.  Message Headers

   RTSP header fields (see Section 16) 18) include general-header, request-
   header, response-header, and message-body header fields.

   The order in which header fields with differing field names are
   received is not significant.  However, it is "good practice" to send
   general-header fields first, followed by request-header or response-
   header fields, and ending with the Message-body header fields.

   Multiple message-header fields with the same field-name MAY be
   present in a message if and only if the entire field-value for that
   header field is defined as a comma-separated list.  It MUST be
   possible to combine the multiple header fields into one "field-name:
   field-value" pair, without changing the semantics of the message, by
   appending each subsequent field-value to the first, each separated by
   a comma.  The order in which header fields with the same field-name
   are received is therefore significant to the interpretation of the
   combined field value, and thus a proxy MUST NOT change the order of
   these field values when a message is forwarded.

   Unknown message headers MUST be ignored (skipping over the header to
   the next protocol element, and not causing an error) by a RTSP server
   or client.  An RTSP Proxy MUST forward unknown message headers.
   Message headers defined outside of this specification that are
   required to be interpreted by the RTSP agent will need to use feature
   tags (Section 4.7) and include them in the appropriate Require
   (Section 16.41) 18.41) or Proxy-Require (Section 16.35) 18.35) header.

5.3.  Message Body

   The message body (if any) of an RTSP message is used to carry further
   information for a particular resource associated with the request or
   response.  An example of a message body is the Session Description
   Protocol (SDP).

   The presence of a message body in either a request or a response MUST
   be signaled by the inclusion of a Content-Length header (see
   Section 16.16). 18.16).  A message body MUST NOT be included in a request or
   response if the specification of the particular method (see Method
   Definitions (Section 13)) does not allow sending a message body.

5.4.  Message Length

   When a message body is included in a message, the length of that body
   is determined by one of the following (in order of precedence):

   1.  Any response message which MUST NOT include a message body (such
       as the 1xx, 204, and 304 responses) is always terminated by the
       first empty line after the header fields, regardless of the
       message-header fields present in the message.  (Note: An empty
       line is a line with nothing preceding the CRLF.)

   2.  If a Content-Length header(Section 16.16) 18.16) is present, its value
       in bytes represents the length of the message-body.  If this
       header field is not present, a value of zero is assumed.

   Unlike an HTTP message, an RTSP message MUST contain a Content-Length
   header whenever it contains a message body.  Note that RTSP does not
   support the HTTP/1.1 "chunked" transfer coding (see [H3.6.1]).

      Given the moderate length of presentation descriptions returned,
      the server should always be able to determine its length, even if
      it is generated dynamically, making the chunked transfer encoding
      unnecessary.

6.  General Header Fields

   General headers are headers that may be used in both requests and
   responses.  The general headers are listed in Table 1:

                +--------------------+--------------------+
                | Header Name        | Defined in Section |
                +--------------------+--------------------+
                | Accept-Ranges      | Section 16.5 18.5       |
                |                    |                    |
                | Cache-Control      | Section 16.10 18.10      |
                |                    |                    |
                | Connection         | Section 16.11 18.11      |
                |                    |                    |
                | CSeq               | Section 16.19 18.19      |
                |                    |                    |
                | Date               | Section 16.20 18.20      |
                |                    |                    |
                | Media-Properties   | Section 16.28 18.28      |
                |                    |                    |
                | Media-Range        | Section 16.29 18.29      |
                |                    |                    |
                | Pipelined-Requests | Section 16.32 18.32      |
                |                    |                    |
                | Proxy-Supported    | Section 16.36 18.36      |
                |                    |                    |
                | RTP-Info           | Section 16.43 18.43      |
                |                    |                    |
                | Seek-Style         | Section 16.45 18.45      |
                |                    |                    |
                | Supported          | Section 16.49 18.49      |
                |                    |                    |
                | Timestamp          | Section 16.51 18.51      |
                |                    |                    |
                | Via                | Section 16.56 18.55      |
                +--------------------+--------------------+

                 Table 1: The general headers used in RTSP

7.  Request

   A request message uses the format outlined below regardless of the
   direction of a request, client to server or server to client:

   o  Request line, containing the method to be applied to the resource,
      the identifier of the resource, and the protocol version in use;

   o  Zero or more Header lines, that can be of the following types:
      general headers (Section 6), request headers (Section 7.2), or
      message body headers (Section 9.1);

   o  One empty line (CRLF) to indicate the end of the header section;

   o  Optionally a message-body, consisting of one or more lines.  The
      length of the message body in bytes is indicated by the Content-
      Length message header.

7.1.  Request Line

   The request line provides the key information about the request: what
   method, on what resources and using which RTSP version.  The methods
   that are defined by this specification are listed in Table 2.

                  +---------------+--------------------+
                  | Method        | Defined in Section |
                  +---------------+--------------------+
                  | DESCRIBE      | Section 13.2       |
                  |               |                    |
                  | GET_PARAMETER | Section 13.8       |
                  |               |                    |
                  | OPTIONS       | Section 13.1       |
                  |               |                    |
                  | PAUSE         | Section 13.6       |
                  |               |                    |
                  | PLAY          | Section 13.4       |
                  |               |                    |
                  | PLAY_NOTIFY   | Section 13.5       |
                  |               |                    |
                  | REDIRECT      | Section 13.10      |
                  |               |                    |
                  | SETUP         | Section 13.3       |
                  |               |                    |
                  | SET_PARAMETER | Section 13.9       |
                  |               |                    |
                  | TEARDOWN      | Section 13.7       |
                  +---------------+--------------------+

                         Table 2: The RTSP Methods

   The syntax of the RTSP request line is the following:

      <Method> SP <Request-URI> SP <RTSP-Version> CRLF

   Note: This syntax cannot be freely changed in future versions of
   RTSP.  This line needs to remain parsable by older RTSP
   implementations since it indicates the RTSP version of the message.

   In contrast to HTTP/1.1 [RFC2616], RTSP requests identify the
   resource through an absolute RTSP URI (including scheme, host, and
   port) (see Section 4.2) rather than just the absolute path.

      HTTP/1.1 requires servers to understand the absolute URI, but
      clients are supposed to use the Host request header.  This is
      purely needed for backward-compatibility with HTTP/1.0 servers, a
      consideration that does not apply to RTSP.

   An asterisk "*" can be used instead of an absolute URI in the
   Request-URI part to indicate that the request does not apply to a
   particular resource, but to the server or proxy itself, and is only
   allowed when the request method does not necessarily apply to a
   resource.

   For example:

      OPTIONS * RTSP/2.0

   An OPTIONS in this form will determine the capabilities of the server
   or the proxy that first receives the request.  If the capability of
   the specific server needs to be determined, without regard to the
   capability of an intervening proxy, the server should be addressed
   explicitly with an absolute URI that contains the server's address.

   For example:

      OPTIONS rtsp://example.com RTSP/2.0

7.2.  Request Header Fields

   The RTSP headers in Table 3 can be included in a request, as request
   headers, to modify the specifics of the request.  Some of these
   headers may also be used in the response to a request, as response
   headers, to modify the specifics of a response (Section 8.2).

                +--------------------+--------------------+
                | Header             | Defined in Section |
                +--------------------+--------------------+
                | Accept             | Section 16.1 18.1       |
                |                    |                    |
                | Accept-Credentials | Section 16.2 18.2       |
                |                    |                    |
                | Accept-Encoding    | Section 16.3 18.3       |
                |                    |                    |
                | Accept-Language    | Section 16.4 18.4       |
                |                    |                    |
                | Authorization      | Section 16.7 18.7       |
                |                    |                    |
                | Bandwidth          | Section 16.8 18.8       |
                |                    |                    |
                | Blocksize          | Section 16.9 18.9       |
                |                    |                    |
                | From               | Section 16.22 18.22      |
                |                    |                    |
                | If-Match           | Section 16.23 18.23      |
                |                    |                    |
                | If-Modified-Since  | Section 16.24 18.24      |
                |                    |                    |
                | If-None-Match      | Section 16.25 18.25      |
                |                    |                    |
                | Notify-Reason      | Section 16.31 18.31      |
                |                    |                    |
                | Proxy-Require      | Section 16.35 18.35      |
                |                    |                    |
                | Range              | Section 16.38 18.38      |
                |                    |                    |
                | Referrer           | Section 16.39 18.39      |
                |                    |                    |
                | Request-Status     | Section 16.40 18.40      |
                |                    |                    |
                | Require            | Section 16.41 18.41      |
                |                    |                    |
                | Scale              | Section 16.44 18.44      |
                |                    |                    |
                | Session            | Section 16.47 18.47      |
                |                    |                    |
                | Speed              | Section 16.48 18.48      |
                |                    |                    |
                | Supported          | Section 16.49 18.49      |
                |                    |                    |
                | Terminate-Reason   | Section 16.50 18.50      |
                |                    |                    |
                | Transport          | Section 16.52 18.52      |
                |                    |                    |
                | User-Agent         | Section 16.54 18.54      |
                +--------------------+--------------------+

                     Table 3: The RTSP request headers

   Detailed header definition are provided in Section 16. 18

   New request headers may be defined.  If the receiver of the request
   is required to understand the request header, the request MUST
   include a corresponding feature tag in a Require or Proxy-Require
   header to ensure the processing of the header.

8.  Response

   After receiving and interpreting a request message, the recipient
   responds with an RTSP response message.  Normally, there is only one,
   final, response.  Only responses using the response code class 1xx,
   are allowed to send one or more 1xx response messages prior to the
   final response message.

   The valid response codes and the methods they can be used with are
   listed in Table 4.

8.1.  Status-Line

   The first line of a Response message is the Status-Line, consisting
   of the protocol version followed by a numeric status code and the
   textual phrase associated with the status code, with each element
   separated by SP characters.  No CR or LF is allowed except in the
   final CRLF sequence.

   <RTSP-Version> SP <Status-Code> SP <Reason-Phrase> CRLF

8.1.1.  Status Code and Reason Phrase

   The Status-Code element is a 3-digit integer result code of the
   attempt to understand and satisfy the request.  These codes are fully
   defined in Section 15. 17.  The Reason-Phrase is intended to give a short
   textual description of the Status-Code.  The Status-Code is intended
   for use by automata and the Reason-Phrase is intended for the human
   user.  The client is not required to examine or display the Reason-
   Phrase.

   The first digit of the Status-Code defines the class of response.
   The last two digits do not have any categorization role.  There are 5
   values for the first digit:

   1xx:  Informational - Request received, continuing process

   2xx:  Success - The action was successfully received, understood, and
         accepted

   3rr:  Redirection - Further action needs to be taken in order to
         complete the request

   4xx:  Client Error - The request contains bad syntax or cannot be
         fulfilled

   5xx:  Server Error - The server failed to fulfill an apparently valid
         request

   The individual values of the numeric status codes defined for
   RTSP/2.0, and an example set of corresponding Reason-Phrases, are
   presented in Table 4.  The reason phrases listed here are only
   recommended; they may be replaced by local equivalents without
   affecting the protocol.  Note that RTSP adopts most HTTP/1.1
   [RFC2616] status codes and adds RTSP-specific status codes starting
   at x50 to avoid conflicts with future HTTP status codes that are
   desirable to import into RTSP.

   RTSP status codes are extensible.  RTSP applications are not required
   to understand the meaning of all registered status codes, though such
   understanding is obviously desirable.  However, applications MUST
   understand the class of any status code, as indicated by the first
   digit, and treat any unrecognized response as being equivalent to the
   x00 status code of that class, with the exception that an
   unrecognized response MUST NOT be cached.  For example, if an
   unrecognized status code of 431 is received by the client, it can
   safely assume that there was something wrong with its request and
   treat the response as if it had received a 400 status code.  In such
   cases, user agents SHOULD present to the user the message body
   returned with the response, since that message body is likely to
   include human-readable information which will explain the unusual
   status.

   +------+---------------------------------+--------------------------+
   | Code | Reason                          | Method                   |
   +------+---------------------------------+--------------------------+
   | 100  | Continue                        | all                      |
   |      |                                 |                          |
   |      |                                 |                          |
   | 200  | OK                              | all                      |
   |      |                                 |                          |
   |      |                                 |                          |
   | 301  | Moved Permanently               | all                      |
   |      |                                 |                          |
   | 302  | Found                           | all                      |
   |      |                                 |                          |
   | 303  | reserved                        | n/a                      |
   |      |                                 |                          |
   | 304  | Not Modified                    | all                      |
   |      |                                 |                          |
   | 305  | Use Proxy                       | all                      |
   |      |                                 |                          |
   |      |                                 |                          |
   | 400  | Bad Request                     | all                      |
   | 401  | Unauthorized                    | all                      |
   |      |                                 |                          |
   | 402  | Payment Required                | all                      |
   |      |                                 |                          |
   | 403  | Forbidden                       | all                      |
   |      |                                 |                          |
   | 404  | Not Found                       | all                      |
   |      |                                 |                          |
   | 405  | Method Not Allowed              | all                      |
   |      |                                 |                          |
   | 406  | Not Acceptable                  | all                      |
   |      |                                 |                          |
   | 407  | Proxy Authentication Required   | all                      |
   |      |                                 |                          |
   | 408  | Request Timeout                 | all                      |
   |      |                                 |                          |
   | 410  | Gone                            | all                      |
   |      |                                 |                          |
   | 411  | Length Required                 | all                      |
   |      |                                 |                          |
   | 412  | Precondition Failed             | DESCRIBE, SETUP          |
   |      |                                 |                          |
   | 413  | Request Message Body Too Large  | all                      |
   |      |                                 |                          |
   | 414  | Request-URI Too Long            | all                      |
   |      |                                 |                          |
   | 415  | Unsupported Media Type          | all                      |
   |      |                                 |                          |
   | 451  | Parameter Not Understood        | SET_PARAMETER,           |
   |      |                                 | GET_PARAMETER            |
   |      |                                 |                          |
   | 452  | reserved                        | n/a                      |
   |      |                                 |                          |
   | 453  | Not Enough Bandwidth            | SETUP                    |
   |      |                                 |                          |
   | 454  | Session Not Found               | all                      |
   |      |                                 |                          |
   | 455  | Method Not Valid In This State  | all                      |
   |      |                                 |                          |
   | 456  | Header Field Not Valid          | all                      |
   |      |                                 |                          |
   | 457  | Invalid Range                   | PLAY, PAUSE              |
   |      |                                 |                          |
   | 458  | Parameter Is Read-Only          | SET_PARAMETER            |
   |      |                                 |                          |
   | 459  | Aggregate Operation Not Allowed | all                      |
   |      |                                 |                          |
   | 460  | Only Aggregate Operation        | all                      |
   |      | Allowed                         |                          |
   |      |                                 |                          |
   | 461  | Unsupported Transport           | all                      |
   |      |                                 |                          |
   | 462  | Destination Unreachable         | all                      |
   |      |                                 |                          |
   | 463  | Destination Prohibited          | SETUP                    |
   |      |                                 |                          |
   | 464  | Data Transport Not Ready Yet    | PLAY                     |
   |      |                                 |                          |
   | 465  | Notification Reason Unknown     | PLAY_NOTIFY              |
   |      |                                 |                          |
   | 466  | Key Management Error            | all                      |
   |      |                                 |                          |
   | 470  | Connection Authorization        | all                      |
   |      | Required                        |                          |
   |      |                                 |                          |
   | 471  | Connection Credentials not      | all                      |
   |      | accepted                        |                          |
   |      |                                 |                          |
   | 472  | Failure to establish secure     | all                      |
   |      | connection                      |                          |
   |      |                                 |                          |
   |      |                                 |                          |
   | 500  | Internal Server Error           | all                      |
   |      |                                 |                          |
   | 501  | Not Implemented                 | all                      |
   |      |                                 |                          |
   | 502  | Bad Gateway                     | all                      |
   |      |                                 |                          |
   | 503  | Service Unavailable             | all                      |
   |      |                                 |                          |
   | 504  | Gateway Timeout                 | all                      |
   |      |                                 |                          |
   | 505  | RTSP Version Not Supported      | all                      |
   |      |                                 |                          |
   | 551  | Option Not Support              | all                      |
   +------+---------------------------------+--------------------------+

          Table 4: Status codes and their usage with RTSP methods

8.2.  Response Headers

   The response-header allows the request recipient to pass additional
   information about the response which cannot be placed in the Status-
   Line.  This header gives information about the server and about
   further access to the resource identified by the Request-URI.  All
   headers currently classified as response headers are listed in
   Table 5.

              +------------------------+--------------------+
              | Header                 | Defined in Section |
              +------------------------+--------------------+
              | Connection-Credentials | Section 16.12 18.12      |
              |                        |                    |
              | Location               | Section 16.27 18.27      |
              |                        |                    |
              | MTag                   | Section 16.30 18.30      |
              |                        |                    |
              | Proxy-Authenticate     | Section 16.33 18.33      |
              |                        |                    |
              | Public                 | Section 16.37 18.37      |
              |                        |                    |
              | Range                  | Section 16.38 18.38      |
              |                        |                    |
              | Retry-After            | Section 16.42 18.42      |
              |                        |                    |
              | Scale                  | Section 16.44 18.44      |
              |                        |                    |
              | Session                | Section 16.47 18.47      |
              |                        |                    |
              | Server                 | Section 16.46 18.46      |
              |                        |                    |
              | Speed                  | Section 16.48 18.48      |
              |                        |                    |
              | Transport              | Section 16.52 18.52      |
              |                        |                    |
              | Unsupported            | Section 16.53      |
              |                        |                    |
              | Vary                   | Section 16.55 18.53      |
              |                        |                    |
              | WWW-Authenticate       | Section 16.57 18.56      |
              +------------------------+--------------------+

                    Table 5: The RTSP response headers

   Response-header names can be extended reliably only in combination
   with a change in the protocol version.  However, the usage of
   feature-tags in the request allows the responding party to learn the
   capability of the receiver of the response.  A new or experimental
   header MAY be given the semantics of response-header if all parties
   in the communication recognize them to be response-header.
   Unrecognized headers in responses are treated as message-headers and
   hence MUST be ignored.

9.  Message Body

   Request and Response messages MAY transfer a message body, if not
   otherwise restricted by the request method or response status code.
   The message body consists of the content data itself (see also
   Section 5.2.

   The SET_PARAMETER and GET_PARAMETER request and response, and
   DESCRIBE response MAY have a message body.  All 4xx and 5xx responses
   MAY also have a message body.

   In this section, both sender and recipient refer to either the client
   or the server, depending on who sends and who receives the message
   body.

9.1.  Message-Body Header Fields

   Message-body header fields define meta-information about the content
   data in the message body.  The message-body header fields are listed
   in Table 6.

                 +------------------+--------------------+
                 | Header           | Defined in Section |
                 +------------------+--------------------+
                 | Allow            | Section 16.6 18.6       |
                 |                  |                    |
                 | Content-Base     | Section 16.13 18.13      |
                 |                  |                    |
                 | Content-Encoding | Section 16.14 18.14      |
                 |                  |                    |
                 | Content-Language | Section 16.15 18.15      |
                 |                  |                    |
                 | Content-Length   | Section 16.16 18.16      |
                 |                  |                    |
                 | Content-Location | Section 16.17 18.17      |
                 |                  |                    |
                 | Content-Type     | Section 16.18 18.18      |
                 |                  |                    |
                 | Expires          | Section 16.21 18.21      |
                 |                  |                    |
                 | Last-Modified    | Section 16.26 18.26      |
                 +------------------+--------------------+

                  Table 6: The RTSP message-body headers

   The extension-header mechanism allows additional message-body header
   fields to be defined without changing the protocol, but these fields
   cannot be assumed to be recognizable by the recipient.  Unrecognized
   header fields MUST be ignored by the recipient and forwarded by
   proxies.

9.2.  Message Body

   An RTSP message with a message body MUST include the Content-Type and
   Content-Length headers.  When a message body is included with a
   message, the data type of that content data is determined via the
   header fields Content-Type and Content-Encoding.

   Content-Type specifies the media type of the underlying data.
   Content-Encoding may be used to indicate any additional content
   codings applied to the data, usually for the purpose of data
   compression, that are a property of the requested resource.  There is
   no default encoding.

   The Content-Length of a message is the length of the content,
   measured in bytes.

10.  Connections

   RTSP requests can be transmitted using the two different connection
   scenarios listed below:

   o  persistent - a transport connection is used for several request/
      response transactions;

   o  transient - a transport connection is used for a single request/
      response transaction.

   RFC 2326 attempted to specify an optional mechanism for transmitting
   RTSP messages in connectionless mode over a transport protocol such
   as UDP.  However, it was not specified in sufficient detail to allow
   for interoperable implementations.  In an attempt to reduce
   complexity and scope, and due to lack of interest, RTSP 2.0 does not
   attempt to define a mechanism for supporting RTSP over UDP or other
   connectionless transport protocols.  A side-effect of this is that
   RTSP requests MUST NOT be sent to multicast groups since no
   connection can be established with a specific receiver in multicast
   environments.

   Certain RTSP headers, such as the CSeq header (Section 16.19), 18.19), which
   may appear to be relevant only to connectionless transport scenarios
   are still retained and MUST be implemented according to the
   specification.  In the case of CSeq, it is quite useful for matching
   responses to requests if the requests are pipelined (see Section 12).
   It is also useful in proxies for keeping track of the different
   requests when aggregating several client requests on a single TCP
   connection.

10.1.  Reliability and Acknowledgements

   Since RTSP messages are transmitted using reliable transport
   protocols, they MUST NOT be retransmitted at the RTSP protocol level.
   Instead, the implementation must rely on the underlying transport to
   provide reliability.  The RTSP implementation may use any indication
   of reception acknowledgment of the message from the underlying
   transport protocols to optimize the RTSP behavior.

      If both the underlying reliable transport such as TCP and the RTSP
      application retransmit requests, each packet loss or message loss
      may result in two retransmissions.  The receiver typically cannot
      take advantage of the application-layer retransmission since the
      transport stack will not deliver the application-layer
      retransmission before the first attempt has reached the receiver.
      If the packet loss is caused by congestion, multiple
      retransmissions at different layers will exacerbate the
      congestion.

   Lack of acknowledgment of an RTSP request should be handled within
   the constraints of the connection timeout considerations described
   below (Section 10.4).

10.2.  Using Connections

   A TCP transport can be used for both persistent connections (for
   several message exchanges) and transient connections (for a single
   message exchange).  Implementations of this specification MUST
   support RTSP over TCP.  The scheme of the RTSP URI (Section 4.2)
   indicates the default port that the server will listen on if the port
   is not explicitly given.

   A server MUST handle both persistent and transient connections.

      Transient connections facilitate mechanisms for fault tolerance.
      They also allow for application layer mobility.  A server and
      client pair that support transient connections can survive the
      loss of a TCP connection; e.g., due to a NAT timeout.  When the
      client has discovered that the TCP connection has been lost, it
      can set up a new one when there is need to communicate again.

   A persistent connection is RECOMMENDED to be used for all
   transactions between the server and client, including messages for
   multiple RTSP sessions.  However, a persistent connection MAY be
   closed after a few message exchanges.  For example, a client may use
   a persistent connection for the initial SETUP and PLAY message
   exchanges in a session and then close the connection.  Later, when
   the client wishes to send a new request, such as a PAUSE for the
   session, a new connection would be opened.  This connection may
   either be transient or persistent.

   An RTSP agent SHOULD NOT have more than one connection to the server
   at any given point.  If a client or proxy handles multiple RTSP
   sessions on the same server, it SHOULD use only one connection for
   managing those sessions.

      This saves connection resources on the server.  It also reduces
      complexity by enabling the server to maintain less state about its
      sessions and connections.

   RTSP allows a server to send requests to a client.  However, this can
   be supported only if a client establishes a persistent connection
   with the server.  In cases where a persistent connection does not
   exist between a server and its client, due to the lack of a signaling
   channel the server may be forced to silently discard RTSP messages,
   and may even drop an RTSP session without notifying the client.  An
   example of such a case is when the server desires to send a REDIRECT
   request for an RTSP session to the client but is not able to do so
   because it cannot reach the client.  A server that attempts to send a
   request to a client that has no connection currently to the server
   SHOULD discard the request directly, but it MAY queue it for later
   delivery.  However, if the server queues the request it SHOULD when
   adding additional requests to the queue ensure to remove older
   requests that are now redundant.

      Without a persistent connection between the client and the server,
      the media server has no reliable way of reaching the client.
      Because the likely failure of server to client established
      connections the server will not even attempt establishing any
      connection.

   The sending of client and server requests can be asynchronous events.
   To avoid deadlock situations both client and server MUST be able to
   send and receive requests simultaneously.  As an RTSP response may be
   queued up for transmission, reception or processing behind the peer
   RTSP agent's own requests, all RTSP agents are required to have a
   certain capability of handling outstanding messages.  A potential
   issue is that outstanding requests may timeout despite them being
   processed by the peer due to the response is caught in the queue
   behind a number of request that the RTSP agent is processing but that
   take some time to complete.  To avoid this problem an RTSP agent is
   recommended to buffer incoming messages locally so that any response
   messages can be processed immediately upon reception.  If responses
   are separated from requests and directly forwarded for processing,
   not only can the result be used immediately, the state associated
   with that outstanding request can also be released.  However,
   buffering a number of requests on the receiving RTSP agent consumes
   resources and enables a resource exhaustion attack on the agent.
   Therefore this buffer should be limited so that an unreasonable
   number of requests or total message size is not allowed to consume
   the receiving agent's resources.  In most APIs, having the receiving
   agent stop reading from the TCP socket will result in TCP's window
   being clamped.  Thus forcing the buffering onto the sending agent
   when the load is larger than expected.  However, as both RTSP message
   sizes and frequency may be changed in the future by protocol
   extensions, an agent should be careful against taking harsher
   measurements against a potential attack.  When under attack an RTSP
   agent can close TCP connections and release state associated with
   that TCP connection.

   To provide some guidance on what is reasonable the following
   guidelines are given.  It is RECOMMENDED that:

   o  an RTSP agent should not have more than 10 outstanding requests
      per RTSP session;

   o  an RTSP agent should not have more than 10 outstanding requests
      that are not related to an RTSP session or that are requesting to
      create an RTSP session.

   In light of the above, it is RECOMMENDED that clients use persistent
   connections whenever possible.  A client that supports persistent
   connections MAY "pipeline" its requests (see Section 12).

10.3.  Closing Connections

   The client MAY close a connection at any point when no outstanding
   request/response transactions exist for any RTSP session being
   managed through the connection.  The server, however, SHOULD NOT
   close a connection until all RTSP sessions being managed through the
   connection have been timed out (Section 16.47). 18.47).  A server SHOULD NOT
   close a connection immediately after responding to a session-level
   TEARDOWN request for the last RTSP session being controlled through
   the connection.  Instead, it should wait for a reasonable amount of
   time for the client to receive the TEARDOWN response, take
   appropriate action, and initiate the connection closing.  The server
   SHOULD wait at least 10 seconds after sending the TEARDOWN response
   before closing the connection.

      This is to ensure that the client has time to issue a SETUP for a
      new session on the existing connection after having torn the last
      one down. 10 seconds should give the client ample opportunity to
      get its message to the server.

   A server SHOULD NOT close the connection directly as a result of
   responding to a request with an error code.

      Certain error responses such as "460 Only Aggregate Operation
      Allowed" (Section 15.4.25) 17.4.25) are used for negotiating capabilities
      of a server with respect to content or other factors.  In such
      cases, it is inefficient for the server to close a connection on
      an error response.  Also, such behavior would prevent
      implementation of advanced/special types of requests or result in
      extra overhead for the client when testing for new features.  On
      the flip side, keeping connections open after sending an error
      response poses a Denial of Service security risk (Section 21).

   The server MAY close a connection if it receives an incomplete
   message and if the message is not completed within a reasonable
   amount of time.  It is RECOMMENDED that the server waits at least 10
   seconds for the completion of a message or for the next part of the
   message to arrive (which is an indication that the transport and the
   client are still alive).  Servers believing they are under attack or
   otherwise starved for resources during that event MAY consider using
   a shorter timeout.

   If a server closes a connection while the client is attempting to
   send a new request, the client will have to close its current
   connection, establish a new connection and send its request over the
   new connection.

   An RTSP message SHOULD NOT be terminated by closing the connection.
   Such a message MAY be considered to be incomplete by the receiver and
   discarded.  An RTSP message is properly terminated as defined in
   Section 5.

10.4.  Timing Out Connections and RTSP Messages

   Receivers of a request (responder) SHOULD respond to requests in a
   timely manner even when a reliable transport such as TCP is used.
   Similarly, the sender of a request (requester) SHOULD wait for a
   sufficient time for a response before concluding that the responder
   will not be acting upon its request.

   A responder SHOULD respond to all requests within 5 seconds.  If the
   responder recognizes that processing of a request will take longer
   than 5 seconds, it SHOULD send a 100 (Continue) response as soon as
   possible.  It SHOULD continue sending a 100 response every 5 seconds
   thereafter until it is ready to send the final response to the
   requester.  After sending a 100 response, the receiver MUST send a
   final response indicating the success or failure of the request.

   A requester SHOULD wait at least 10 seconds for a response before
   concluding that the responder will not be responding to its request.
   After receiving a 100 response, the requester SHOULD continue waiting
   for further responses.  If more than 10 seconds elapses without
   receiving any response, the requester MAY assume that the responder
   is unresponsive and abort the connection.

   A requester SHOULD wait longer than 10 seconds for a response if it
   is experiencing significant transport delays on its connection to the
   responder.  The requester is capable of determining the RTT of the
   request/response cycle using the Timestamp header (Section 16.51) 18.51) in
   any RTSP request.

      10 seconds was chosen for the following reasons.  It gives TCP
      time to perform a couple of retransmissions, even if operating on
      default values.  It is short enough that users may not abandon the
      process themselves.  However, it should be noted that 10 seconds
      can be aggressive on certain type of networks.  The 5 seconds
      value for 1xx messages is half the timeout giving a reasonable
      change of successful delivery before timeout happens on the
      requester side.

10.5.  Showing Liveness

   The mechanisms for showing liveness of the client is, any RTSP
   request with a Session header, if RTP & RTCP is used an RTCP message,
   or through any other used media protocol capable of indicating
   liveness of the RTSP client.  It is RECOMMENDED that a client does
   not wait to the last second of the timeout before trying to send a
   liveness message.  The RTSP message may be lost or when using
   reliable protocols, such as TCP, the message may take some time to
   arrive safely at the receiver.  To show liveness between RTSP request
   issued to accomplish other things, the following mechanisms can be
   used, in descending order of preference:

   RTCP: If RTP is used for media transport RTCP SHOULD be used.  If
         RTCP is used to report transport statistics, it MUST also work
         as keep alive.  The server can determine the client by network
         address and port together with the fact that the client is
         reporting on the servers SSRC(s).  A downside of using RTCP is
         that it only gives statistical guarantees to reach the server.
         However, the probability of a false client timeout is so low
         that it can be ignored in most cases.  For example, assume a
         session with 60 seconds timeout and enough bitrate assigned to
         RTCP messages to send a message from client to server on
         average every 5 seconds.  That client has, for a network with 5
         % packet loss, the probability to fail showing liveness sign in
         that session within the timeout interval of 2.4*E-16.  Sessions
         with shorter timeouts, or much higher packet loss, or small
         RTCP bandwidths SHOULD also use any of the mechanisms below.

   SET_PARAMETER:  When using SET_PARAMETER for keep alive, no body
         SHOULD be included.  This method is the RECOMMENDED RTSP method
         to use for a request intended only to perform keep-alive.

   GET_PARAMETER:  When using GET_PARAMETER for keep alive, no body
         SHOULD be included.

   OPTIONS:  This method is also usable, but it causes the server to
         perform more unnecessary processing and results in bigger
         responses than necessary for the task.  The reason is that the
         server needs to determine the capabilities associated with the
         media resource to correctly populate the Public and Allow
         headers.

   The timeout parameter MAY be included in a SETUP response, and MUST
   NOT be included in requests.  The server uses it to indicate to the
   client how long the server is prepared to wait between RTSP commands
   or other signs of life before closing the session due to lack of
   activity (see Appendix B).  The timeout is measured in seconds, with
   a default of 60 seconds.  The length of the session timeout MUST NOT
   be changed in an established session.

10.6.  Use of IPv6

   Explicit IPv6 [RFC2460] support was not present in RTSP 1.0 (RFC
   2326).  RTSP 2.0 has been updated for explicit IPv6 support.
   Implementations of RTSP 2.0 MUST understand literal IPv6 addresses in
   URIs and headers.

10.7.  Overload Control

   Overload in RTSP can occur when servers and proxies have insufficient
   resources to complete the processing of a request.  An improper
   handling of such an overload situation at proxies and servers can
   impact the operation of the RTSP deployment, and probably worsen the
   situation.  RTSP defines the 503 (Service Unavailable) response
   (Section 15.5.4) 17.5.4) to let servers and proxies notify requesting proxies
   and RTSP clients about an overload situation.  In conjunction with
   the Retry-After header (Section 16.42) 18.42) the server or proxy can
   indicate the time after the requesting entity can send another
   request to the proxy or server.

   Simply implementing and using the 503 (Service Unavailable) is not
   sufficient for properly handling overload situations.  For instance,
   a simplistic approach would be to send the 503 response with a Retry-
   After header set to a fixed value.  However, this can cause the
   situation where multiple RTSP clients again send requests to a proxy
   or server at roughly the same time which may again cause an overload
   situation, or if the "old" overload situation is not yet solved,
   i.e., the length indicated in the Retry-After header was too short.

   An RTSP server or proxy in an overload situation must select the
   value of the Retry-After header carefully and in dependency of its
   current load situation.  It is RECOMMENDED to increase the length
   proportional with the current load of the server, i.e., an increasing
   workload should result in an increased length of the indicated
   unavailability.  It is RECOMMENDED to not send the same value in the
   Retry-After header to all requesting proxies and clients, but to add
   a variation to the mean value of the Retry-After header.

   Another issue are load balancing RTSP proxies, i.e., where an RTSP
   proxy is used to select amongst a set of RTSP servers to handle the
   requests, or when multiple server addresses are available for a given
   server name.  The proxy or client may receive a 503 (Service
   Unavailable) from one of its RTSP servers or a TCP timeout (if the
   server is even unable to handled the request message).  The proxy or
   client simply retries the other addresses, but may also receive a 503
   (Service Unavailable) response or TCP timeouts from those addresses.
   In such a situation, where none of the RTSP servers/addresses can
   handle the request, the RTSP agent has to wait before it can send any
   new requests to the RTSP server.  Any additional request to a
   specific address MUST be delayed according to the Retry-After headers
   received.  For addresses where no response was received or TCP
   timeout occurred, an initial wait timer SHOULD be set to 5 seconds.
   That timer MUST be doubled for each additional failure to connect or
   receive response.  It is RECOMMENDED to not set the same value in the
   timer, but to add a variation to the mean value.

11.  Capability Handling

   This section describes the available capability handling mechanism
   which allows RTSP to be extended.  Extensions to this version of the
   protocol are basically done in two ways.  First, new headers can be
   added.  Secondly, new methods can be added.  The capability handling
   mechanism is designed to handle both cases.

   When a method is added, the involved parties can use the OPTIONS
   method to discover whether it is supported.  This is done by issuing
   an OPTIONS request to the other party.  Depending on the URI it will
   either apply in regards to a certain media resource, the whole server
   in general, or simply the next hop.  The OPTIONS response MUST
   contain a Public header which declares all methods supported for the
   indicated resource.

   It is not necessary to use OPTIONS to discover support of a method,
   as the client could simply try the method.  If the receiver of the
   request does not support the method it will respond with an error
   code indicating the method is either not implemented (501) or does
   not apply for the resource (405).  The choice between the two
   discovery methods depends on the requirements of the service.

   Feature-Tags are defined to handle functionality additions that are
   not new methods.  Each feature-tag represents a certain block of
   functionality.  The amount of functionality that a feature-tag
   represents can vary significantly.  A feature-tag can for example
   represent the functionality a single RTSP header provides.  Another
   feature-tag can represent much more functionality, such as the
   "play.basic" feature-tag which represents the minimal media delivery
   for playback implementation.

   Feature-tags are used to determine whether the client, server or
   proxy supports the functionality that is necessary to achieve the
   desired service.  To determine support of a feature-tag, several
   different headers can be used, each explained below:

   Supported:  This header is used to determine the complete set of
         functionality that both client and server have.  The intended
         usage is to determine before one needs to use a functionality
         that it is supported.  It can be used in any method, but
         OPTIONS is the most suitable one as it at the same time
         determines all methods that are implemented.  When sending a
         request the requester declares all its capabilities by
         including all supported feature-tags.  This results in the
         receiver learns the requester's feature support.  The receiver
         then includes its set of features in the response.

   Proxy-Supported:  This header is used similarly to the Supported
         header, but instead of giving the supported functionality of
         the client or server it provides both the requester and the
         responder a view of what functionality the proxy chain between
         the two supports.  Proxies are required to add this header
         whenever the Supported header is present, but proxies may also
         add it independently of the requester.

   Require:  This header can be included in any request where the end-
         point, i.e. the client or server, is required to understand the
         feature to correctly perform the request.  This can, for
         example, be a SETUP request where the server is required to
         understand a certain parameter to be able to set up the media
         delivery correctly.  Ignoring this parameter would not have the
         desired effect and is not acceptable.  Therefore the end-point
         receiving a request containing a Require MUST negatively
         acknowledge any feature that it does not understand and not
         perform the request.  The response in cases where features are
         not supported are 551 (Option Not Supported).  Also the
         features that are not supported are given in the Unsupported
         header in the response.

   Proxy-Require:  This header has the same purpose and workings as
         Require except that it only applies to proxies and not the end-
         point.  Features that need to be supported by both proxies and
         end-points need to be included in both the Require and Proxy-
         Require header.

   Unsupported:  This header is used in a 551 error response, to
         indicate which features were not supported.  Such a response is
         only the result of the usage of the Require and/or Proxy-
         Require header where one or more feature where not supported.
         This information allows the requester to make the best of
         situations as it knows which features are not supported.

12.  Pipelining Support

   Pipelining is a general method to improve performance of request
   response protocols by allowing the requesting agent to have more than
   one request outstanding and send them over the same persistent
   connection.  For RTSP, where the relative order of requests will
   matter, it is important to maintain the order of the requests.
   Because of this, the responding agent MUST process the incoming
   requests in their sending order.  The sending order can be determined
   by the CSeq header and its sequence number.  For TCP the delivery
   order will be the same as the sending order.  The processing of the
   request MUST also have been finished before processing the next
   request from the same agent.  The responses MUST be sent in the order
   the requests were processed.

   RTSP 2.0 has extended support for pipelining compared to RTSP 1.0.
   The major improvement is to allow all requests to setup and initiate
   media delivery to be pipelined after each other.  This is
   accomplished by the utilization of the Pipelined-Requests header (see
   Section 16.32). 18.32).  This header allows a client to request that two or
   more requests are processed in the same RTSP session context which
   the first request creates.  In other words, a client can request that
   two or more media streams are set-up and then played without needing
   to wait for a single response.  This speeds up the initial startup
   time for an RTSP session with at least one RTT.

   If a pipelined request builds on the successful completion of one or
   more prior requests the requester must verify that all requests were
   executed as expected.  A common example will be two SETUP requests
   and a PLAY request.  In case one of the SETUP fails unexpectedly, the
   PLAY request can still be successfully executed.  However, the
   resulting presentation will not be as expected by the requesting
   client, as only a single media instead of two will be played.  In
   this case the client can send a PAUSE request, correct the failing
   SETUP request and then request it to be played.

13.  Method Definitions

   The method indicates what is to be performed on the resource
   identified by the Request-URI.  The method name is case-sensitive.
   New methods may be defined in the future.  Method names MUST NOT
   start with a $ character (decimal 36) and MUST be a token as defined
   by the ABNF [RFC5234] in the syntax chapter Section 20.  The methods
   are summarized in Table 7.

    +---------------+-----------+--------+-------------+-------------+
    | method        | direction | object | Server req. | Client req. |
    +---------------+-----------+--------+-------------+-------------+
    | DESCRIBE      | C -> S    | P,S    | recommended | recommended |
    |               |           |        |             |             |
    | GET_PARAMETER | C -> S    | P,S    | optional    | optional    |
    |               |           |        |             |             |
    |               | S -> C    | P,S    | optional    | optional    |
    |               |           |        |             |             |
    | OPTIONS       | C -> S    | P,S    | required    | required    |
    |               |           |        |             |             |
    |               | S -> C    | P,S    | optional    | optional    |
    |               |           |        |             |             |
    | PAUSE         | C -> S    | P,S    | required    | required    |
    |               |           |        |             |             |
    | PLAY          | C -> S    | P,S    | required    | required    |
    |               |           |        |             |             |
    | PLAY_NOTIFY   | S -> C    | P,S    | required    | required    |
    |               |           |        |             |             |
    | REDIRECT      | S -> C    | P,S    | optional    | required    |
    |               |           |        |             |             |
    | SETUP         | C -> S    | S      | required    | required    |
    |               |           |        |             |             |
    | SET_PARAMETER | C -> S    | P,S    | required    | optional    |
    |               |           |        |             |             |
    |               | S -> C    | P,S    | optional    | optional    |
    |               |           |        |             |             |
    | TEARDOWN      | C -> S    | P,S    | required    | required    |
    |               |           |        |             |             |
    |               | S -> C    | P      | required    | required    |
    +---------------+-----------+--------+-------------+-------------+

   Table 7: Overview of RTSP methods, their direction, and what objects
               (P: presentation, S: stream) they operate on.

      Note on Table 7: GET_PARAMETER is optional.  For example, a fully
      functional server can be built to deliver media without any
      parameters.  SET_PARAMETER is required, however, due to its usage
      for keep-alive.  PAUSE is now required because it is the only way
      of leaving the Play state without terminating the whole session.

   If an RTSP agent does not support a particular method, it MUST return
   501 (Not Implemented) and the requesting RTSP agent, in turn, SHOULD
   NOT try this method again for the given agent / resource combination.
   An RTSP proxy whose main function is to log or audit and not modify
   transport or media handling in any way MAY forward RTSP messages with
   unknown methods.  Note that the proxy still needs to perform the
   minimal required processing, like adding the Via header.

13.1.  OPTIONS

   The semantics of the RTSP OPTIONS method is similar to that of the
   HTTP OPTIONS method described in [H9.2].  In RTSP however, OPTIONS is
   bi-directional, in that a client can request it to a server and vice
   versa.  A client MUST implement the capability to send an OPTIONS
   request and a server or a proxy MUST implement the capability to
   respond to an OPTIONS request.  The client, server or proxy MAY also
   implement the converse of their required capability, but still retain
   the prior mentioned about what is a "MUST implement".

   An OPTIONS request may be issued at any time.  Such a request does
   not modify the session state.  However, it may prolong the session
   lifespan (see below).  The URI in an OPTIONS request determines the
   scope of the request and the corresponding response.  If the Request-
   URI refers to a specific media resource on a given host, the scope is
   limited to the set of methods supported for that media resource by
   the indicated RTSP agent.  A Request-URI with only the host address
   limits the scope to the specified RTSP agent's general capabilities
   without regard to any specific media.  If the Request-URI is an
   asterisk ("*"), the scope is limited to the general capabilities of
   the next hop (i.e. the RTSP agent in direct communication with the
   request sender).

   Regardless of scope of the request, the Public header MUST always be
   included in the OPTIONS response listing the methods that are
   supported by the responding RTSP agent.  In addition, if the scope of
   the request is limited to a media resource, the Allow header MUST be
   included in the response to enumerate the set of methods that are
   allowed for that resource unless the set of methods completely
   matches the set in the Public header.  If the given resource is not
   available, the RTSP agent SHOULD return an appropriate response code
   such as 3rr or 4xx.  The Supported header MAY be included in the
   request to query the set of features that are supported by the
   responding RTSP agent.

   The OPTIONS method can be used to keep an RTSP session alive.
   However, this is not the preferred way of session keep-alive
   signaling, see Section 16.47. 18.47.  An OPTIONS request intended for
   keeping alive an RTSP session MUST include the Session header with
   the associated session ID.  Such a request SHOULD also use the media
   or the aggregated control URI as the Request-URI.

   Example:

     C->S:  OPTIONS rtsp://server.example.com RTSP/2.0
            CSeq: 1
            User-Agent: PhonyClient/1.2
            Proxy-Require: gzipped-messages
            Supported: play.basic

     S->C:  RTSP/2.0 200 OK
            CSeq: 1
            Public: DESCRIBE, SETUP, TEARDOWN, PLAY, PAUSE, OPTIONS
            Supported: play.basic, setup.rtp.rtcp.mux, play.scale
            Server: PhonyServer/1.1

   Note that some of the feature-tags in Supported and Proxy-Require are
   fictional features.

13.2.  DESCRIBE

   The DESCRIBE method is used to retrieve the description of a
   presentation or media object from a server.  The Request-URI of the
   DESCRIBE request identifies the media resource of interest.  The
   client MAY include the Accept header in the request to list the
   description formats that it understands.  The server MUST respond
   with a description of the requested resource and return the
   description in the message body of the response, if the DESCRIBE
   method request can be successfully fulfilled.  The DESCRIBE reply-
   response pair constitutes the media initialization phase of RTSP.

   The DESCRIBE response SHOULD contain all media initialization
   information for the resource(s) that it describes.  Servers SHOULD
   NOT use the DESCRIBE response as a means of media indirection by
   having the description point at another server; instead, using the
   3rr responses is RECOMMENDED.

      By forcing a DESCRIBE response to contain all media initialization
      information for the set of streams that it describes, and
      discouraging the use of DESCRIBE for media indirection, any
      looping problems can be avoided that might have resulted from
      other approaches.

   Example:

     C->S: DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/2.0
           CSeq: 312
           User-Agent: PhonyClient/1.2
           Accept: application/sdp, application/example

     S->C: RTSP/2.0 200 OK
           CSeq: 312
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Server: PhonyServer/1.1
           Content-Base: rtsp://server.example.com/fizzle/foo/
           Content-Type: application/sdp
           Content-Length: 358

           v=0
           o=mhandley 2890844526 2890842807 IN IP4 192.0.2.46
           s=SDP Seminar
           i=A Seminar on the session description protocol
           u=http://www.example.com/lectures/sdp.ps
           e=seminar@example.com (Seminar Management)
           c=IN IP4 0.0.0.0
           a=control:*
           t=2873397496 2873404696
           m=audio 3456 RTP/AVP 0
           a=control:audio
           m=video 2232 RTP/AVP 31
           a=control:video

   Media initialization is a requirement for any RTSP-based system, but
   the RTSP specification does not dictate that this is required to be
   done via the DESCRIBE method.  There are three ways that an RTSP
   client may receive initialization information:

   o  via an RTSP DESCRIBE request

   o  via some other protocol (HTTP, email attachment, etc.)

   o  via some form of user interface

   If a client obtains a valid description from an alternate source, the
   client MAY use this description for initialization purposes without
   issuing a DESCRIBE request for the same media.  The client should use
   any MTag to either validate the presentation description or make the
   session establishment conditional on being valid.

   It is RECOMMENDED that minimal servers support the DESCRIBE method,
   and highly recommended that minimal clients support the ability to
   act as "helper applications" that accept a media initialization file
   from a user interface, and/or other means that are appropriate to the
   operating environment of the clients.

13.3.  SETUP

   Note: The states described in this section and the following are
   described in detail in Appendix B.

   The SETUP request for an URI specifies the transport mechanism to be
   used for the streamed media.  The SETUP method may be used in two
   different cases; Create an RTSP session and change the transport
   parameters of already set up media stream.  SETUP can be used in all
   three states; Init, and Ready, for both purposes and in PLAY to
   change the transport parameters.  There is also a third possible
   usage for the SETUP method which is not specified in this memo:
   adding a media to a session.  Using SETUP to add media to an existing
   session, when the session is in Play state, is unspecified.

   The Transport header, see Section 16.52, 18.52, specifies the media
   transport parameters acceptable to the client for data transmission;
   the response will contain the transport parameters selected by the
   server.  This allows the client to enumerate in descending order of
   preference the transport mechanisms and parameters acceptable to it,
   while the server can select the most appropriate.  It is expected
   that the session description format used will enable the client to
   select a limited number of possible configurations that are offered
   to the server to choose from.  All transport related parameters SHALL
   be included in the Transport header; the use of other headers for
   this purpose is NOT RECOMMENDED due to middleboxes, such as firewalls
   or NATs.

   For the benefit of any intervening firewalls, a client MUST indicate
   the known transport parameters, even if it has no influence over
   these parameters, for example, where the server advertises a fixed
   multicast address as destination.

      Since SETUP includes all transport initialization information,
      firewalls and other intermediate network devices (which need this
      information) are spared the more arduous task of parsing the
      DESCRIBE response, which has been reserved for media
      initialization.

   The client MUST include the Accept-Ranges header in the request
   indicating all supported unit formats in the Range header.  This
   allows the server to know which formats it may use in future session
   related responses, such as a PLAY response without any range in the
   request.  If the client does not support a time format necessary for
   the presentation the server MUST respond using 456 (Header Field Not
   Valid for Resource) and include the Accept-Ranges header with the
   range unit formats supported for the resource.

   In a SETUP response the server MUST include the Accept-Ranges header
   (see Section 16.5) 18.5) to indicate which time formats are acceptable to
   use for this media resource.

   The SETUP response 200 OK MUST include the Media-Properties header
   (see Section 16.28 18.28 ).  The combination of the parameters of the
   Media-Properties header indicates the nature of the content present
   in the session (see also Section 4.9).  For example, a live stream
   with time shifting is indicated by

   o  Random Access set to Random-Access,

   o  Content Modifications set to Time Progressing,

   o  Retention set to Time-Duration (with specific recording window
      time value).

   The SETUP response 200 OK MUST include the Media-Range header (see
   Section 16.29) 18.29) if the media is Time-Progressing.

   A basic example for SETUP:

     C->S: SETUP rtsp://example.com/foo/bar/baz.rm RTSP/2.0
           CSeq: 302
           Transport: RTP/AVP;unicast;dest_addr=":4588"/":4589",
                      RTP/AVP/TCP;unicast;interleaved=0-1
           Accept-Ranges: NPT, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 302
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Server: PhonyServer/1.1
           Session: 47112344;timeout=60
           Transport: RTP/AVP;unicast;dest_addr="192.0.2.53:4588"/
                      "192.0.2.53:4589"; src_addr="198.51.100.241:6256"/
                      "198.51.100.241:6257"; ssrc=2A3F93ED
           Accept-Ranges: NPT
           Media-Properties: Random-Access=3.2, Time-Progressing,
                             Time-Duration=3600.0
           Media-Range: npt=0-2893.23

   In the above example the client wants to create an RTSP session
   containing the media resource "rtsp://example.com/foo/bar/baz.rm".
   The transport parameters acceptable to the client are either RTP/AVP/
   UDP (UDP per default) to be received on client port 4588 and 4589 at
   the address the RTSP setup connection comes from or RTP/AVP
   interleaved on the RTSP control channel.  The server selects the RTP/
   AVP/UDP transport and adds the address and ports it will send and
   receive RTP and RTCP from, and the RTP SSRC that will be used by the
   server.

   The server MUST generate a session identifier in response to a
   successful SETUP request, unless a SETUP request to a server includes
   a session identifier or a Pipelined-Requests header referencing an
   existing session context, in which case the server MUST bundle this
   setup request into the existing session (aggregated session) or
   return error 459 (Aggregate Operation Not Allowed) (see
   Section 15.4.24). 17.4.24).  An Aggregate control URI MUST be used to control
   an aggregated session.  This URI MUST be different from the stream
   control URIs of the individual media streams included in the
   aggregate (see Section 13.4.2 for aggregated sessions and for the
   particular URIs see Appendix D.1.1).  The Aggregate control URI is to
   be specified by the session description if the server supports
   aggregated control and aggregated control is desired for the session.
   However, even if aggregated control is offered the client MAY chose
   to not set up the session in aggregated control.  If an Aggregate
   control URI is not specified in the session description, it is
   normally an indication that non-aggregated control should be used.
   The SETUP of media streams in an aggregate which has not been given
   an aggregated control URI is unspecified.

      While the session ID sometimes carries enough information for
      aggregate control of a session, the Aggregate control URI is still
      important for some methods such as SET_PARAMETER where the control
      URI enables the resource in question to be easily identified.  The
      Aggregate control URI is also useful for proxies, enabling them to
      route the request to the appropriate server, and for logging,
      where it is useful to note the actual resource that a request was
      operating on.

   A session will exist until it is either removed by a TEARDOWN request
   or is timed-out by the server.  The server MAY remove a session that
   has not demonstrated liveness signs from the client(s) within a
   certain timeout period.  The default timeout value is 60 seconds; the
   server MAY set this to a different value and indicate so in the
   timeout field of the Session header in the SETUP response.  For
   further discussion see Section 16.47. 18.47.  Signs of liveness for an RTSP
   session are:

   o  Any RTSP request from a client which includes a Session header
      with that session's ID.

   o  If RTP is used as a transport for the underlying media streams, an
      RTCP sender or receiver report from the client(s) for any of the
      media streams in that RTSP session.  RTCP Sender Reports may for
      example be received in sessions where the server is invited into a
      conference session and is valid for keep-alive.

   If a SETUP request on a session fails for any reason, the session
   state, as well as transport and other parameters for associated
   streams MUST remain unchanged from their values as if the SETUP
   request had never been received by the server.

13.3.1.  Changing Transport Parameters

   A client MAY issue a SETUP request for a stream that is already set
   up or playing in the session to change transport parameters, which a
   server MAY allow.  If it does not allow changing of parameters, it
   MUST respond with error 455 (Method Not Valid In This State).  The
   reasons to support changing transport parameters include allowing
   application layer mobility and flexibility to utilize the best
   available transport as it becomes available.  If a client receives a
   455 when trying to change transport parameters while the server is in
   Play state, it MAY try to put the server in ready state using PAUSE,
   before issuing the SETUP request again.  If that also fails the
   changing of transport parameters will require that the client
   performs a TEARDOWN of the affected media and then to set it up
   again.  For an aggregated session avoiding tearing down all the media
   at the same time will avoid the creation of a new session.

   All transport parameters MAY be changed.  However, the primary usage
   expected is to either change the transport protocol completely, like
   switching from Interleaved TCP mode to UDP or vice versa, or to
   change the delivery address.

   In a SETUP response for a request to change the transport parameters
   while in Play state, the server MUST include the Range to indicate at
   what point the new transport parameters will be used.  Further, if
   RTP is used for delivery, the server MUST also include the RTP-Info
   header to indicate at what timestamp and RTP sequence number the
   change will take place.  If both RTP-Info and Range are included in
   the response the "rtp_time" parameter and start point in the Range
   header MUST be for the corresponding time, i.e. be used in the same
   way as for PLAY to ensure the correct synchronization information is
   available.

   If the transport parameters change while in Play state results in a
   change of synchronization related information, for example changing
   RTP SSRC, the server MUST provide in the SETUP response the necessary
   synchronization information.  However, the server is RECOMMENDED to
   avoid changing the synchronization information if possible.

13.4.  PLAY

   This section describes the usage of the PLAY method in general, for
   aggregated sessions, and in different usage scenarios.

13.4.1.  General Usage

   The PLAY method tells the server to start sending data via the
   mechanism specified in SETUP and which part of the media should be
   played out.  PLAY requests are valid when the session is in Ready or
   Play states.  A PLAY request MUST include a Session header to
   indicate which session the request applies to.

   Upon receipt of the PLAY request, the server MUST position the normal
   play time to the beginning of the range specified in the received
   Range header and deliver stream data until the end of the range if
   given, until a new PLAY request is received, or until the end of the
   media is reached.  If no Range header is present in the PLAY request
   the server SHALL play from current pause point until the end of
   media.  The pause point defaults at session start to the beginning of
   the media.  For media that is time-progressing and has no retention,
   the pause point will always be set equal to NPT "now", i.e., the
   current delivery point.  The pause point may also be set to a
   particular point in the media by the PAUSE method, see Section 13.6.
   The pause point for media that is currently playing is equal to the
   current media position.  For time-progressing media with time-limited
   retention, if the pause point represents a position that is older
   than what is retained by the server, the pause point will be moved to
   the oldest retained.

   What range values are valid depends on the type of content.  For
   content that isn't time progressing the range value is valid if the
   given range is part of any media within the aggregate.  In other
   words the valid media range for the aggregate is the union of all of
   the media components in the aggregate.  If a given range value points
   outside of the media, the response MUST be the 457 (Invalid Range)
   error code and include the Media-Range header (Section 16.29) 18.29) with
   the valid range for the media.  Except for time progressing content
   where the client requests a start point prior to what is retained,
   the start point is adjusted to the oldest retained content.  For a
   start point that is beyond the media front edge, i.e. beyond the
   current value for "now", the server SHALL adjust the start value to
   the current front edge.  The Range header's stop point value may
   point beyond the current media edge.  In that case, the server SHALL
   deliver media from the requested (and possibly adjusted) start point
   until the provided stop point, or the end of the media is reached
   prior to the specified stop point.  Please note that if one simply
   wants to play from a particular start point until the end of media
   using a Range header with an implicit stop point is RECOMMENDED.

   If a client requests to start playing at the end of media, either
   explicitly with a Range header or implicitly with a pause point that
   is at the end of media, a 457 (Invalid Range) error MUST be sent and
   include the Media-Range header (Section 16.29). 18.29).  It is specified
   below that the Range header also must be included in the response and
   that it will carry the pause point in the media, in the case of the
   session being in Ready State.  Note that this also applies if the
   pause point or requested start point is at the beginning of the media
   and a Scale header (Section 16.44) 18.44) is included with a negative value
   (playing backwards).

   For media with random access properties a client may express its
   preference on which policy for start point selection the server shall
   use.  This is done by including the Seek-Style header (Section 16.45) 18.45)
   in the PLAY request.  The Seek-Style applied will effect the content
   of the Range header as it will be adjusted to indicate from what
   point the media actually is delivered.

   A client desiring to play the media from the beginning MUST send a
   PLAY request with a Range header pointing at the beginning, e.g.
   npt=0-.  If a PLAY request is received without a Range header and
   media delivery has stopped at the end, the server SHOULD respond with
   a 457 "Invalid Range" error response.  In that response, the current
   pause point MUST be included in a Range header.

   All range specifiers in this specification allow for ranges with an
   implicit start point (e.g. "npt=-30").  When used in a PLAY request,
   the server treats this as a request to start or resume delivery from
   the current pause point, ending at the end time specified in the
   Range header.  If the pause point is located later than the given end
   value, a 457 (Invalid Range) response MUST be given.

   The example below will play seconds 10 through 25.  It also requests
   the server to deliver media from the first Random Access Point prior
   to the indicated start point.

     C->S: PLAY rtsp://audio.example.com/audio RTSP/2.0
           CSeq: 835
           Session: 12345678
           Range: npt=10-25
           Seek-Style: RAP
           User-Agent: PhonyClient/1.2

   Servers MUST include a "Range" header in any PLAY response, even if
   no Range header was present in the request.  The response MUST use
   the same format as the request's range header contained.  If no Range
   header was in the request, the format used in any previous PLAY
   request within the session SHOULD be used.  If no format has been
   indicated in a previous request the server MAY use any time format
   supported by the media and indicated in the Accept-Ranges header in
   the SETUP request.  It is RECOMMENDED that NPT is used if supported
   by the media.

   For any error response to a PLAY request, the server's response
   depends on the current session state.  If the session is in Ready
   state, the current pause-point is returned using Range header with
   the pause point as the explicit start-point and an implicit stop-
   point.  For time-progressing content where the pause-point moves with
   real-time due to limited retention, the current pause point is
   returned.  For sessions in Play state, the current playout point and
   the remaining parts of the range request is returned.  For any media
   with retention longer than 0 seconds the currently valid Media-Range
   header SHALL also be included in the response.

   A PLAY response MAY include a header carrying synchronization
   information.  As the information necessary is dependent on the media
   transport format, further rules specifying the header and its usage
   are needed.  For RTP the RTP-Info header is specified, see
   Section 16.43, 18.43, and used in the following example.

   Here is a simple example for a single audio stream where the client
   requests the media starting from 3.52 seconds and to the end.  The
   server sends a 200 OK response with the actual play time which is 10
   ms prior (3.51) and the RTP-Info header that contains the necessary
   parameters for the RTP stack.

   C->S: PLAY rtsp://example.com/audio RTSP/2.0
         CSeq: 836
         Session: 12345678
         Range: npt=3.52-
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 836
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Server: PhonyServer/1.0
         Range: npt=3.51-324.39
         Seek-Style: First-Prior
         RTP-Info:url="rtsp://example.com/audio"
            ssrc=0D12F123:seq=14783;rtptime=2345962545

   S->C: RTP Packet TS=2345962545 => NPT=3.51
         Media duration=0.16 seconds

   The server replies with the actual start point that will be
   delivered.  This may differ from the requested range if alignment of
   the requested range to valid frame boundaries is required for the
   media source.  Note that some media streams in an aggregate may need
   to be delivered from even earlier points.  Also, some media formats
   have a very long duration per individual data unit, therefore it
   might be necessary for the client to parse the data unit, and select
   where to start.  The server SHALL also indicate which policy it uses
   for selecting the actual start point by including a Seek-Style
   header.

   In the following example the client receives the first media packet
   that stretches all the way up and past the requested playtime.  Thus,
   it is the client's decision whether to render to the user the time
   between 3.52 and 7.05, or to skip it.  In most cases it is probably
   most suitable not to render that time period.

   C->S: PLAY rtsp://example.com/audio RTSP/2.0
         CSeq: 836
         Session: 12345678
         Range: npt=7.05-
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 836
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Server: PhonyServer/1.0
         Range: npt=3.52-
         Seek-Style: First-Prior
         RTP-Info:url="rtsp://example.com/audio"
            ssrc=0D12F123:seq=14783;rtptime=2345962545

   S->C: RTP Packet TS=2345962545 => NPT=3.52
         Duration=4.15 seconds

   After playing the desired range, the presentation does NOT change to
   the Ready state, media delivery simply stops.  A PAUSE request MUST
   be issued to make the stream enter the Ready state.  A PLAY request
   while the stream is still in the Play state is legal, and can be
   issued without an intervening PAUSE request.  Such a request MUST
   replace the current PLAY action with the new one requested, i.e.
   being handled the same as the request was received in Ready state.
   In the case the range in Range header has an implicit start time
   (-endtime), the server MUST continue to play from where it currently
   was until the specified end point.  This is useful to change end at
   another point than in the previous request.

   The following example plays the whole presentation starting at SMPTE
   time code 0:10:20 until the end of the clip.  Note: The RTP-Info
   headers has been broken into several lines, where following lines
   start with whitespace as allowed by the syntax.

   C->S: PLAY rtsp://audio.example.com/twister.en RTSP/2.0
         CSeq: 833
         Session: 12345678
         Range: smpte=0:10:20-
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 833
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Session: 12345678
         Server: PhonyServer/1.0
         Range: smpte=0:10:22-0:15:45
         Seek-Style: Next
         RTP-Info:url="rtsp://example.com/twister.en"
            ssrc=0D12F123:seq=14783;rtptime=2345962545

   For playing back a recording of a live presentation, it may be
   desirable to use clock units:

   C->S: PLAY rtsp://audio.example.com/meeting.en RTSP/2.0
         CSeq: 835
         Session: 12345678
         Range: clock=19961108T142300Z-19961108T143520Z
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 835
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Session: 12345678
         Server: PhonyServer/1.0
         Range: clock=19961108T142300Z-19961108T143520Z
         Seek-Style: Next
         RTP-Info:url="rtsp://example.com/meeting.en"
            ssrc=0D12F123:seq=53745;rtptime=484589019

13.4.2.  Aggregated Sessions

   PLAY requests can operate on sessions controlling a single media and
   on aggregated sessions controlling multiple media.

   In an aggregated session the PLAY request MUST contain an aggregated
   control URI.  A server MUST respond with error 460 (Only Aggregate
   Operation Allowed) if the client PLAY Request-URI is for a single
   media.  The media in an aggregate MUST be played in sync.  If a
   client wants individual control of the media, it needs to use
   separate RTSP sessions for each media.

   For aggregated sessions where the initial SETUP request (creating a
   session) is followed by one or more additional SETUP requests, a PLAY
   request MAY be pipelined after those additional SETUP requests
   without awaiting their responses.  This procedure can reduce the
   delay from start of session establishment until media play-out has
   started with one round trip time.  However, a client needs to be
   aware that using this procedure will result in the playout of the
   server state established at the time of processing the PLAY, i.e.,
   after the processing of all the requests prior to the PLAY request in
   the pipeline.  This state may not be the intended one due to failure
   of any of the prior requests.  A client can easily determine this
   based on the responses from those requests.  In case of failure, the
   client can halt the media playout using PAUSE and try to establish
   the intended state again before issuing another PLAY request.

13.4.3.  Updating current PLAY Requests

   Clients can issue PLAY requests while the stream is in Play state and
   thus updating their request.

   The important difference compared to a PLAY request in Ready state is
   the handling of the current play point and how the Range header in
   request is constructed.  The session is actively playing media and
   the play point will be moving, making the exact time a request will
   take action hard to predict.  Depending on how the PLAY header
   appears two different cases exist: total replacement or continuation.
   A total replacement is signaled by having the first range
   specification have an explicit start value, e.g. npt=45- or
   npt=45-60, in which case the server stops playout at the current
   playout point and then starts delivering media according to the Range
   header.  This is equivalent to having the client first send a PAUSE
   and then a new PLAY request that isn't based on the pause point.  In
   the case of continuation the first range specifier has an implicit
   start point and an explicit stop value (Z), e.g. npt=-60, which
   indicate that it MUST convert the range specifier being played prior
   to this PLAY request (X to Y) into (X to Z) and continue as this was
   the request originally played.  If the current delivery point is
   beyond the stop point, the server SHALL immediately pause delivery.
   As the request has been completed successfully it shall be responded
   with 200 OK.  A PLAY_NOTIFY with end-of-stream is also sent to
   indicate the actual stop point.  The pause point is set to the
   requested stop point.

   Following is an example of this behavior: The server has received
   requests to play ranges 10 to 15.  If the new PLAY request arrives at
   the server 4 seconds after the previous one, it will take effect
   while the server still plays the first range (10-15).  The server
   changes the current play to continue to 25 seconds, i.e. the
   equivalent single request would be PLAY with range: npt=10-25.

     C->S: PLAY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 834
           Session: 12345678
           Range: npt=10-15
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 834
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Session: 12345678
           Server: PhonyServer/1.0
           Range: npt=10-15
           Seek-Style: Next
           RTP-Info:url="rtsp://example.com/fizzle/audiotrack"
                   ssrc=0D12F123:seq=5712;rtptime=934207921,
                   url="rtsp://example.com/fizzle/videotrack"
                   ssrc=789DAF12:seq=57654;rtptime=2792482193
           Session: 12345678

     C->S: PLAY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 835
           Session: 12345678
           Range: npt=-25
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 835
           Date: Thu, 23 Jan 1997 15:35:09 GMT
           Session: 12345678
           Server: PhonyServer/1.0
           Range: npt=14-25
           Seek-Style: Next
           RTP-Info:url="rtsp://example.com/fizzle/audiotrack"
                   ssrc=0D12F123:seq=5712;rtptime=934239921,
                   url="rtsp://example.com/fizzle/videotrack"
                   ssrc=789DAF12:seq=57654;rtptime=2792842193

   A common use of a PLAY request while in Play state is changing the
   scale of the media, i.e., entering or leaving from fast forward or
   fast rewind.  The client can issue an updating PLAY request that is
   either a continuation or a complete replacement, as discussed above
   this section.  We give an example of a client that is requesting a
   fast forward (scale=2) without giving a stop point and then change
   from fast forward to regular playout (scale = 1).  In the second PLAY
   request the time is set explicitly to be where ever the server
   currently plays out (npt=now-) and the server responds with the
   actual playback point where the new scale actually takes effect
   (npt=2:17:27.144-).

     C->S: PLAY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 2034
           Session: 12345678
           Range: npt=now-
           Scale: 2.0
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 2034
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Session: 12345678
           Server: PhonyServer/1.0
           Range: npt=2:17:21.394-
           Seek-Style: Next
           RTP-Info:url="rtsp://example.com/fizzle/audiotrack"
                   ssrc=0D12F123:seq=5712;rtptime=934207921,
                   url="rtsp://example.com/fizzle/videotrack"
                   ssrc=789DAF12:seq=57654;rtptime=2792482193

   [playing in fast forward and now returning to scale = 1]

     C->S: PLAY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 2035
           Session: 12345678
           Range: npt=now-
           Scale: 1.0
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 2035
           Date: Thu, 23 Jan 1997 15:35:09 GMT
           Session: 12345678
           Server: PhonyServer/1.0
           Range: npt=2:17:27.144-
           Seek-Style: Next
           RTP-Info:url="rtsp://example.com/fizzle/audiotrack"
                   ssrc=0D12F123:seq=5712;rtptime=934239921,
                   url="rtsp://example.com/fizzle/videotrack"
                   ssrc=789DAF12:seq=57654;rtptime=2792842193

13.4.4.  Playing On-Demand Media

   On-demand media is indicated by the content of the Media-Properties
   header in the SETUP response by (see also Section 16.28): 18.28):

   o  Random-Access property is set to Random Access;
   o  Content Modifications set to Immutable;

   o  Retention set to Unlimited or Time-Limited.

   Playing on-demand media follows the general usage as described in
   Section 13.4.1.

13.4.5.  Playing Dynamic On-Demand Media

   Dynamic on-demand media is indicated by the content of the Media-
   Properties header in the SETUP response by (see also Section 16.28): 18.28):

   o  RandomAccess set to Random-Access;

   o  Content Modifications set to Dynamic;

   o  Retention set to Unlimited or Time-Limited.

   Playing on-demand media follows the general usage as described in
   Section 13.4.1 as long as the media has not been changed.

   There are two ways for the client to be informed about changes of
   media resources in Play state.  The client will receive a PLAY_NOTIFY
   request with Notify-Reason header set to media-properties-update (see
   Section 13.5.2.  The client can use the value of the Media-Range to
   decide further actions, if the Media-Range header is present in the
   PLAY_NOTIFY request.  The second way is that the client issues a
   GET_PARAMETER request without a body but including a Media-Range
   header.  The 200 OK response MUST include the current Media-Range
   header (see Section 16.29). 18.29).

13.4.6.  Playing Live Media

   Live media is indicated by the content of the Media-Properties header
   in the SETUP response by (see also Section 16.28): 18.28):

   o  Random-Access set to No-Seeking;

   o  Content Modifications set to Time-Progressing;

   o  Retention with Time-Duration set to 0.0.

   For live media, the SETUP response 200 OK MUST include the Media-
   Range header (see Section 16.29). 18.29).

   A client MAY send PLAY requests without the Range header.  If the
   request includes the Range header it MUST use a symbolic value
   representing "now".  For NPT that range specification is "npt=now-".

   The server MUST include the Range header in the response and it MUST
   indicate an explicit time value and not a symbolic value.  In other
   words, "npt=now-" is not valid to be used in the response.  Instead
   the time since session start is recommended expressed as an open
   interval, e.g. "npt=96.23-".  An absolute time value (clock) for the
   corresponding time MAY be given, i.e. "clock=20030213T143205Z-".  The
   UTC clock format can only be used if client has shown support for it
   using the Accept-Ranges header.

13.4.7.  Playing Live with Recording

   Certain media servers may offer recording services of live sessions
   to their clients.  This recording would normally be from the
   beginning of the media session.  Clients can randomly access the
   media between now and the beginning of the media session.  This live
   media with recording is indicated by the content of the Media-
   Properties header in the SETUP response by (see also Section 16.28): 18.28):

   o  Random-Access set to Random-Access;

   o  Content Modifications set to Time-Progressing;

   o  Retention set to Time-limited or Unlimited

   The SETUP response 200 OK MUST include the Media-Range header (see
   Section 16.29) 18.29) for this type of media.  For live media with
   recording, the Range header indicates the current delivery point in
   the media and the Media-Range header indicates the currently
   available media window around the current time.  This window can
   cover recorded content in the past (seen from current time in the
   media) or recorded content in the future (seen from current time in
   the media).  The server adjusts the delivery point to the requested
   border of the window, if the client requests a delivery point that is
   located outside the recording windows, e.g., if requested to far in
   the past, the server selects the oldest range in the recording.  The
   considerations in Section 13.5.3 apply, if a client requests delivery
   with Scale (Section 16.44) 18.44) values other than 1.0 (Normal playback
   rate) while delivering live media with recording.

13.4.8.  Playing Live with Time-Shift

   Certain media servers may offer time-shift services to their clients.
   This time shift records a fixed interval in the past, i.e., a sliding
   window recording mechanism, but not past this interval.  Clients can
   randomly access the media between now and the interval.  This live
   media with recording is indicated by the content of the Media-
   Properties header in the SETUP response by (see also Section 16.28): 18.28):

   o  Random-Access set to Random-Access;

   o  Content Modifications set to Time-Progressing;

   o  Retention set to Time-Duration and a value indicating the
      recording interval (>0).

   The SETUP response 200 OK MUST include the Media-Range header (see
   Section 16.29) 18.29) for this type of media.  For live media with recording
   the Range header indicates the current time in the media and the
   Media Range indicates a window around the current time.  This window
   can cover recorded content in the past (seen from current time in the
   media) or recorded content in the future (seen from current time in
   the media).  The server adjusts the play point to the requested
   border of the window, if the client requests a play point that is
   located outside the recording windows, e.g., if requested too far in
   the past, the server selects the oldest range in the recording.  The
   considerations in Section 13.5.3 apply, if a client requests delivery
   using a Scale (Section 16.44) 18.44) value other than 1.0 (Normal playback
   rate) while delivering live media with time-shift.

13.5.  PLAY_NOTIFY

   The PLAY_NOTIFY method is issued by a server to inform a client about
   an asynchronous event for a session in Play state.  The Session
   header MUST be presented in a PLAY_NOTIFY request and indicates the
   scope of the request.  Sending of PLAY_NOTIFY requests requires a
   persistent connection between server and client, otherwise there is
   no way for the server to send this request method to the client.

   PLAY_NOTIFY requests have an end-to-end (i.e. server to client)
   scope, as they carry the Session header, and apply only to the given
   session.  The client SHOULD immediately return a response to the
   server.

   PLAY_NOTIFY requests MAY be used with a message body, depending on
   the value of the Notify-Reason header.  It is described in the
   particular section for each Notify-Reason if a message body is used.
   However, currently there is no Notify-Reason that allows using a
   message body.  In this case, there is a need to obey some limitations
   when adding new Notify-Reasons that intend to use a message body: the
   server can send any type of message body, but it is not ensured that
   the client can understand the received message body.  This is related
   to DESCRIBE (see Section 13.2 ), but in this particular case the
   client can state its acceptable message bodies by using the Accept
   header.  In the case of PLAY_NOTIFY, the server does not know which
   message bodies are understood by the client.

   The Notify-Reason header (see Section 16.31) 18.31) specifies the reason why
   the server sends the PLAY_NOTIFY request.  This is extensible and new
   reasons MAY be added in the future (see Section 22.8).  In case the
   client does not understand the reason for the notification it MUST
   respond with an 465 (Notification Reason Unknown) (Section 15.4.30) 17.4.30)
   error code.  Servers can send PLAY_NOTIFY with these types:

   o  end-of-stream (see Section 13.5.1);

   o  media-properties-update (see Section 13.5.2);

   o  scale-change (see Section 13.5.3).

13.5.1.  End-of-Stream

   A PLAY_NOTIFY request with Notify-Reason header set to end-of-stream
   indicates the completion or near completion of the PLAY request and
   the ending delivery of the media stream(s).  The request MUST NOT be
   issued unless the server is in the Play state.  The end of the media
   stream delivery notification may be used to indicate either a
   successful completion of the PLAY request currently being served, or
   to indicate some error resulting in failure to complete the request.
   The Request-Status header (Section 16.40) 18.40) MUST be included to
   indicate which request the notification is for and its completion
   status.  The message response status codes (Section 8.1.1) are used
   to indicate how the PLAY request concluded.  The sender of a
   PLAY_NOTIFY can issue an updated PLAY_NOTIFY, in the case of a
   PLAY_NOTIFY sent with wrong information.  For instance, a PLAY_NOTIFY
   was issued before reaching the end-of-stream, but some error occurred
   resulting in that the previously sent PLAY_NOTIFY contained a wrong
   time when the stream will end.  In this case a new PLAY_NOTIFY MUST
   be sent including the correct status for the completion and all
   additional information.

   PLAY_NOTIFY requests with Notify-Reason header set to end-of-stream
   MUST include a Range header and the Scale header if the scale value
   is not 1.  The Range header indicates the point in the stream or
   streams where delivery is ending with the timescale that was used by
   the server in the PLAY response for the request being fulfilled.  The
   server MUST NOT use the "now" constant in the Range header; it MUST
   use the actual numeric end position in the proper timescale.  When
   end-of-stream notifications are issued prior to having sent the last
   media packets, this is evident as the end time in the Range header is
   beyond the current time in the media being received by the client,
   e.g., npt=-15, if npt is currently at 14.2 seconds.  The Scale header
   is to be included so that it is evident if the media time scale is
   moving backwards and/or have a non-default pace.  The end-of-stream
   notification does not prevent the client from sending a new PLAY
   request.

   If RTP is used as media transport, a RTP-Info header MUST be
   included, and the RTP-Info header MUST indicate the last sequence
   number in the seq parameter.

   A PLAY_NOTIFY request with Notify-Reason header set to end-of-stream
   MUST NOT carry a message body.

   This example request notifies the client about a future end-of-stream
   event:
     S->C: PLAY_NOTIFY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 854
           Notify-Reason: end-of-stream
           Request-Status: cseq=853 status=200 reason="OK"
           Range: npt=-145
           RTP-Info:url="rtsp://example.com/audio"
              ssrc=0D12F123:seq=14783;rtptime=2345962545
           Session: uZ3ci0K+Ld-M
           Date: Mon, 08 Mar 2010 13:37:16 GMT

     C->S: RTSP/2.0 200 OK
           CSeq: 854
           User-Agent: PhonyClient/1.2
           Session: uZ3ci0K+Ld-M

13.5.2.  Media-Properties-Update

   A PLAY_NOTIFY request with Notify-Reason header set to media-
   properties-update indicates an update of the media properties for the
   given session (see Section 16.28) 18.28) and/or the available media range
   that can be played as indicated by Media-Range (Section 16.29). 18.29).
   PLAY_NOTIFY requests with Notify-Reason header set to media-
   properties-update MUST include a Media-Properties and Date header and
   SHOULD include a Media-Range header.

   This notification MUST be sent for media that are time-progressing
   every time an event happens that changes the basis for making
   estimates on how the media range progress.  In addition it is
   RECOMMENDED that the server sends these notifications every 5 minutes
   for time-progressing content to ensure the long-term stability of the
   client estimation and allowing for clock skew detection by the
   client.  Requests for the just mentioned reasons MUST include Media-
   Range header to provide current Media duration and the Range header
   to indicate the current playing point and any remaining parts of the
   requested range.

      The recommendation for sending updates every 5 minutes is due to
      any clock skew issues.  In 5 minutes the clock skew should not
      become too significant as this is not used for media playback and
      synchronization, only for determining which content is available
      to the user.

   A PLAY_NOTIFY request with Notify-Reason header set to media-
   properties-update MUST NOT carry a message body.
     S->C: PLAY_NOTIFY rtsp://example.com/fizzle/foo RTSP/2.0
           Date: Tue, 14 Apr 2008 15:48:06 GMT
           CSeq: 854
           Notify-Reason: media-properties-update
           Session: uZ3ci0K+Ld-M
           Media-Properties: Time-Progressing,
                 Time-Limited=20080415T153919.36Z, Random-Access=5.0
           Media-Range: npt=0-1:37:21.394
           Range: npt=1:15:49.873-

     C->S: RTSP/2.0 200 OK
           CSeq: 854
           User-Agent: PhonyClient/1.2
           Session: uZ3ci0K+Ld-M

13.5.3.  Scale-Change

   The server may be forced to change the rate, when a client request
   delivery using a Scale (Section 16.44) 18.44) value other than 1.0 (normal
   playback rate).  For time progressing media with some retention, i.e.
   the server stores already sent content, a client requesting to play
   with Scale values larger than 1 may catch up with the front end of
   the media.  The server will then be unable to continue to provide
   content at Scale larger than 1 as content is only made available by
   the server at Scale=1.  Another case is when Scale < 1 and the media
   retention is time-duration limited.  In this case the delivery point
   can reach the oldest media unit available, and further playback at
   this scale becomes impossible as there will be no media available.
   To avoid having the client lose any media, the scale will need to be
   adjusted to the same rate at which the media is removed from the
   storage buffer, commonly Scale = 1.0.

   Another case is when the content itself consists of spliced pieces or
   is dynamically updated.  In these cases the server may be required to
   change from one supported scale value (different than Scale=1.0) to
   another.  In this case the server will pick the closest value and
   inform the client of what it has picked.  In these cases the media
   properties will also be sent updating the supported Scale values.
   This enables a client to adjust the used Scale value.

   To minimize impact on playback in any of the above cases the server
   MUST modify the playback properties and set Scale to a supportable
   value and continue delivery of the media.  When doing this
   modification it MUST send a PLAY_NOTIFY message with the Notify-
   Reason header set to "scale-change".  The request MUST contain a
   Range header with the media time where the change took effect, a
   Scale header with the new value in use, Session header with the ID
   for the session it applies to and a Date header with the server
   wallclock time of the change.  For time progressing content also the
   Media-Range and the Media-Properties at this point in time MUST be
   included.  The Media-Properties header MUST be included if the scale
   change was due to the content changing what scale values that is
   supported.

   For media streams being delivered using RTP also a RTP-Info header
   MUST be included.  It MUST contain the rtptime parameter with a value
   corresponding to the point of change in that media and optionally
   also the sequence number.

   A PLAY_NOTIFY request with Notify-Reason header set to "Scale-Change"
   MUST NOT carry a message body.

     S->C: PLAY_NOTIFY rtsp://example.com/fizzle/foo RTSP/2.0
           Date: Tue, 14 Apr 2008 15:48:06 GMT
           CSeq: 854
           Notify-Reason: scale-change
           Session: uZ3ci0K+Ld-M
           Media-Properties: Time-Progressing,
                 Time-Limited=20080415T153919.36Z, Random-Access=5.0
           Media-Range: npt=0-1:37:21.394
           Range: npt=1:37:21.394-
           Scale: 1
           RTP-Info: url="rtsp://example.com/fizzle/foo/audio"
               ssrc=0D12F123:rtptime=2345962545

     C->S: RTSP/2.0 200 OK
           CSeq: 854
           User-Agent: PhonyClient/1.2
           Session: uZ3ci0K+Ld-M

13.6.  PAUSE

   The PAUSE request causes the stream delivery to immediately be
   interrupted (halted).  A PAUSE request MUST be done either with the
   aggregated control URI for aggregated sessions, resulting in all
   media being halted, or the media URI for non-aggregated sessions.
   Any attempt to do muting of a single media with a PAUSE request in an
   aggregated session MUST be responded to with error 460 (Only
   Aggregate Operation Allowed).  After resuming playback,
   synchronization of the tracks MUST be maintained.  Any server
   resources are kept, though servers MAY close the session and free
   resources after being paused for the duration specified with the
   timeout parameter of the Session header in the SETUP message.

   Example:

     C->S: PAUSE rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 834
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 834
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Range: npt=45.76-75.00

   The PAUSE request causes stream delivery to be interrupted
   immediately on receipt of the message and the pause point is set to
   the current point in the presentation.  That pause point in the media
   stream needs to be maintained.  A subsequent PLAY request without
   Range header resume from the pause point and plays until media end.

   The pause point after any PAUSE request MUST be returned to the
   client by adding a Range header with what remains unplayed of the
   PLAY request's range.  For media with random access properties, if
   one desires to resume playing a ranged request, one simply includes
   the Range header from the PAUSE response and includes the Seek-Style
   header with the Next policy in the PLAY request.  For media that is
   time-progressing and has retention duration=0 the follow-up PLAY
   request to start media delivery again, will need to use "npt=now-"
   and not the answer given in the response to PAUSE.

     C->S: PLAY rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 834
           Session: 12345678
           Range: npt=10-30
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 834
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Server: PhonyServer/1.0
           Range: npt=10-30
           Seek-Style: First-Prior
           RTP-Info:url="rtsp://example.com/fizzle/audiotrack"
                   ssrc=0D12F123:seq=5712;rtptime=934207921,
                   url="rtsp://example.com/fizzle/videotrack"
                   ssrc=4FAD8726:seq=57654;rtptime=2792482193
           Session: 12345678

   After 11 seconds, i.e. at 21 seconds into the presentation:
     C->S: PAUSE rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 835
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 835
           Date: 23 Jan 1997 15:35:17 GMT
           Server: PhonyServer/1.0
           Range: npt=21-30
           Session: 12345678

   If a client issues a PAUSE request and the server acknowledges and
   enters the Ready state, the proper server response, if the player
   issues another PAUSE, is still 200 OK.  The 200 OK response MUST
   include the Range header with the current pause point.  See examples
   below:

     C->S: PAUSE rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 834
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 834
           Session: 12345678
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Range: npt=45.76-98.36

     C->S: PAUSE rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 835
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 835
           Session: 12345678
           Date: 23 Jan 1997 15:35:07 GMT
           Range: npt=45.76-98.36

13.7.  TEARDOWN

13.7.1.  Client to Server

   The TEARDOWN client to server request stops the stream delivery for
   the given URI, freeing the resources associated with it.  A TEARDOWN
   request MAY be performed on either an aggregated or a media control
   URI.  However, some restrictions apply depending on the current
   state.  The TEARDOWN request MUST contain a Session header indicating
   what session the request applies to.

   A TEARDOWN using the aggregated control URI or the media URI in a
   session under non-aggregated control (single media session) MAY be
   done in any state (Ready and Play).  A successful request MUST result
   in that media delivery being immediately halted and the session state
   being destroyed.  This MUST be indicated through the lack of a
   Session header in the response.

   A TEARDOWN using a media URI in an aggregated session MAY only be
   done in Ready state.  Such a request only removes the indicated media
   stream and associated resources from the session.  This may result in
   that a session returns to non-aggregated control, due to that it only
   contains a single media after the requests completion.  A session
   that will exist after the processing of the TEARDOWN request MUST in
   the response to that TEARDOWN request contain a Session header.  Thus
   the presence of the Session header indicates to the receiver of the
   response if the session is still existing or has been removed.

   Example:

     C->S: TEARDOWN rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 892
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 892
           Server: PhonyServer/1.0

13.7.2.  Server to Client

   The server can send TEARDOWN requests in the server to client
   direction to indicate that the server has been forced to terminate
   the ongoing session.  This may happen for several reasons, such as
   server maintenance without available backup, or that the session has
   been inactive for extended periods of time.  The reason is provided
   in the Terminate-Reason header (Section 16.50). 18.50).

   When a RTSP client has maintained a RTSP session that otherwise is
   inactive for an extended period of time the server may reclaim the
   resources.  That is done by issuing a TEARDOWN request with the
   Terminate-Reason set to "Session-Timeout".  This MAY be done when the
   client has been inactive in the RTSP session for more than one
   Session Timeout period (Section 16.47). 18.47).  However, the server is
   RECOMMENDED to not perform this operation until an extended period of
   inactivity has passed.  The time period is considered extended when
   it is 10 times the Session Timeout period.  Consideration of the
   application of the server and its content should be performed when
   configuring what is considered as extended period of time.

   In case the server needs to stop providing service to the established
   sessions and there is no server to point at in a REDIRECT request,
   then TEARDOWN SHALL be used to terminate the session.  This method
   can also be used when non-recoverable internal errors have happened
   and the server has no other option then to terminate the sessions.

   The TEARDOWN request MUST be done only on the session aggregate
   control URI (i.e., it is not allowed to terminate individual media
   streams, if it is a session aggregate) and MUST include the following
   headers; Session and Terminate-Reason headers.  The request only
   applies to the session identified in the Session header.  The server
   may include a message to the client's user with the "user-msg"
   parameter.

   The TEARDOWN request may alternatively be done on the wild card URI *
   and without any session header.  The scope of such a request is
   limited to the next-hop (i.e. the RTSP agent in direct communication
   with the server) and applies, as well, to the control connection
   between the next-hop RTSP agent and the server.  This request
   indicates that all sessions and pending requests being managed via
   the control connection are terminated.  Any intervening proxies
   SHOULD do all of the following in the order listed:

   1.  respond to the TEARDOWN request

   2.  disconnect the control channel from the requesting server

   3.  pass the TEARDOWN request to each applicable client (typically
       those clients with an active session or an unanswered request)

      Note: The proxy is responsible for accepting TEARDOWN responses
      from its clients; these responses MUST NOT be passed on to either
      the original server or the target server in the redirect.

13.8.  GET_PARAMETER

   The GET_PARAMETER request retrieves the value of any specified
   parameter or parameters for a presentation or stream specified in the
   URI.  If the Session header is present in a request, the value of a
   parameter MUST be retrieved in the specified session context.  There
   are two ways of specifying the parameters to be retrieved.  The first
   is by including headers which have been defined such that you can use
   them for this purpose.  Headers for this purpose should allow empty,
   or stripped value parts to avoid having to specify bogus data when
   indicating the desire to retrieve a value.  The successful completion
   of the request should also be evident from any filled out values in
   the response.  The Media-Range header (Section 16.29) 18.29) is one such
   header.  The other way is to specify a message body that lists the
   parameter(s) that are desired to be retrieved.  The Content-Type
   header (Section 16.18) 18.18) is used to specify which format the message
   body has.

   The headers that MAY be used for retrieving their current value using
   GET_PARAMETER are:

   o  Accept-Ranges

   o  Media-Range

   o  Media-Properties
   o  Range

   o  RTP-Info

   The method MAY also be used without a message body or any header that
   request parameters for keep-alive purpose.  The keep-alive timer has
   been updated for any request that is successful, i.e., a 200 OK
   response is received.  Any non-required header present in such a
   request may or may not have been processed.  Normally the presence of
   filled out values in the header will be indication that the header
   has been processed.  However, for cases when this is difficult to
   determine, it is recommended to use a feature-tag and the Require
   header.  Due to this reason it is usually easier if any parameters to
   be retrieved are sent in the body, rather than using any header.

   Parameters specified within the body of the message must all be
   understood by the request receiving agent.  If one or more parameters
   are not understood a 451 (Parameter Not Understood) MUST be sent
   including a body listing these parameters that weren't understood.
   If all parameters are understood their values are filled in and
   returned in the response message body.

   Example:

     S->C: GET_PARAMETER rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 431
           User-Agent: PhonyClient/1.2
           Session: 12345678
           Content-Length: 26
           Content-Type: text/parameters

           packets_received
           jitter

     C->S: RTSP/2.0 200 OK
           CSeq: 431
           Session: 12345678
           Server: PhonyServer/1.1
           Date: Mon, 08 Mar 2010 13:43:23 GMT
           Content-Length: 38
           Content-Type: text/parameters

           packets_received: 10
           jitter: 0.3838

13.9.  SET_PARAMETER

   This method requests to set the value of a parameter or a set of
   parameters for a presentation or stream specified by the URI.  The
   method MAY also be used without a message body.  It is the
   RECOMMENDED method to be used in a request sent for the sole purpose
   of updating the keep-alive timer.  If this request is successful,
   i.e. a 200 OK response is received, then the keep-alive timer has
   been updated.  Any non-required header present in such a request may
   or may not have been processed.  To allow a client to determine if
   any such header has been processed, it is necessary to use a feature
   tag and the Require header.  Due to this reason it is RECOMMENDED
   that any parameters are sent in the body, rather than using any
   header.

   A request is RECOMMENDED to only contain a single parameter to allow
   the client to determine why a particular request failed.  If the
   request contains several parameters, the server MUST only act on the
   request if all of the parameters can be set successfully.  A server
   MUST allow a parameter to be set repeatedly to the same value, but it
   MAY disallow changing parameter values.  If the receiver of the
   request does not understand or cannot locate a parameter, error 451
   (Parameter Not Understood) MUST be used.  In the case a parameter is
   not allowed to change, the error code is 458 (Parameter Is Read-
   Only).  The response body MUST contain only the parameters that have
   errors.  Otherwise no body MUST be returned.

   Note: transport parameters for the media stream MUST only be set with
   the SETUP command.

      Restricting setting transport parameters to SETUP is for the
      benefit of firewalls.

      The parameters are split in a fine-grained fashion so that there
      can be more meaningful error indications.  However, it may make
      sense to allow the setting of several parameters if an atomic
      setting is desirable.  Imagine device control where the client
      does not want the camera to pan unless it can also tilt to the
      right angle at the same time.

   Example:

     C->S: SET_PARAMETER rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 421
           User-Agent: PhonyClient/1.2
           Session: iixT43KLc
           Date: Mon, 08 Mar 2010 14:45:04 GMT
           Content-length: 20
           Content-type: text/parameters

           barparam: barstuff

     S->C: RTSP/2.0 451 Parameter Not Understood
           CSeq: 421
           Session: iixT43KLc
           Server: PhonyServer/1.0
           Date: Mon, 08 Mar 2010 14:44:56 GMT
           Content-length: 20
           Content-type: text/parameters

           barparam: barstuff

13.10.  REDIRECT

   The REDIRECT method is issued by a server to inform a client that the
   service provided will be terminated and where a corresponding service
   can be provided instead.  This may happen for different reasons.  One
   is that the server is being administered such that it must stop
   providing service.  Thus the client is required to connect to another
   server location to access the resource indicated by the Request-URI.

   The REDIRECT request SHALL contain a Terminate-Reason header
   (Section 16.50) 18.50) to inform the client of the reason for the request.
   Additional parameters related to the reason may also be included.
   The intention here is to allow a server administrator to do a
   controlled shutdown of the RTSP server.  That requires sufficient
   time to inform all entities having associated state with the server
   and for them to perform a controlled migration from this server to a
   fall back server.

   A REDIRECT request with a Session header has end-to-end (i.e. server
   to client) scope and applies only to the given session.  Any
   intervening proxies SHOULD NOT disconnect the control channel while
   there are other remaining end-to-end sessions.  The REQUIRED Location
   header MUST contain a complete absolute URI pointing to the resource
   to which the client SHOULD reconnect.  Specifically, the Location
   MUST NOT contain just the host and port.  A client may receive a
   REDIRECT request with a Session header, if and only if, an end-to-end
   session has been established.

   A client may receive a REDIRECT request without a Session header at
   any time when it has communication or a connection established with a
   server.  The scope of such a request is limited to the next-hop (i.e.
   the RTSP agent in direct communication with the server) and applies
   to all sessions controlled, as well as the control connection between
   the next-hop RTSP agent and the server.  A REDIRECT request without a
   Session header indicates that all sessions and pending requests being
   managed via the control connection MUST be redirected.  The REQUIRED
   Location header, if included in such a request, SHOULD contain an
   absolute URI with only the host address and the OPTIONAL port number
   of the server to which the RTSP agent SHOULD reconnect.  Any
   intervening proxies SHOULD do all of the following in the order
   listed:

   1.  respond to the REDIRECT request

   2.  disconnect the control channel from the requesting server

   3.  connect to the server at the given host address

   4.  pass the REDIRECT request to each applicable client (typically
       those clients with an active session or an unanswered request)

      Note: The proxy is responsible for accepting REDIRECT responses
      from its clients; these responses MUST NOT be passed on to either
      the original server or the redirected server.

   When the server lacks any alternative server and needs to terminate a
   session or all sessions the TEARDOWN request SHALL be used instead.

   When no Terminate-Reason "time" parameter are included in a REDIRECT
   request, the client SHALL perform the redirection immediately and
   return a response to the server.  The server shall consider the
   session as terminated and can free any associated state after it
   receives the successful (2xx) response.  The server MAY close the
   signaling connection upon receiving the response and the client
   SHOULD close the signaling connection after sending the 2xx response.
   The exception to this is when the client has several sessions on the
   server being managed by the given signaling connection.  In this
   case, the client SHOULD close the connection when it has received and
   responded to REDIRECT requests for all the sessions managed by the
   signaling connection.

   The Terminate-Reason header "time" parameter MAY be used to indicate
   the wallclock time by when the redirection MUST have taken place.  To
   allow a client to determine that redirect time without being time
   synchronized with the server, the server MUST include a Date header
   in the request.  The client should have before the redirection time-
   line terminated the session and closed the control connection.  The
   server MAY simple cease to provide service when the deadline time has
   been reached, or it may issue TEARDOWN requests to the remaining
   sessions.

   If the REDIRECT request times out following the rules in Section 10.4
   the server MAY terminate the session or transport connection that
   would be redirected by the request.  This is a safeguard against
   misbehaving clients that refuse to respond to a REDIRECT request.
   That should not provide any benefit.

   After a REDIRECT request has been processed, a client that wants to
   continue to send or receive media for the resource identified by the
   Request-URI will have to establish a new session with the designated
   host.  If the URI given in the Location header is a valid resource
   URI, a client SHOULD issue a DESCRIBE request for the URI.

      Note: The media resource indicated by the Location header can be
      identical, slightly different or totally different.  This is the
      reason why a new DESCRIBE request SHOULD be issued.

   If the Location header contains only a host address, the client MAY
   assume that the media on the new server is identical to the media on
   the old server, i.e. all media configuration information from the old
   session is still valid except for the host address.  However, the
   usage of conditional SETUP using MTag identifiers are RECOMMENDED to
   verify the assumption.

   This example request redirects traffic for this session to the new
   server at the given absolute time:

     S->C: REDIRECT rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 732
           Location: rtsp://s2.example.com:8001
           Terminate-Reason: Server-Admin ;time=19960213T143205Z
           Session: uZ3ci0K+Ld-M
           Date: Thu, 13 Feb 1996 14:30:43 GMT

     C->S: RTSP/2.0 200 OK
           CSeq: 732
           User-Agent: PhonyClient/1.2
           Session: uZ3ci0K+Ld-M

14.  Embedded (Interleaved) Binary Data

   In order to fulfill certain requirements on the network side, e.g. in
   conjunction with network address translators that block RTP traffic
   over UDP, it may be necessary to interleave RTSP messages and media
   stream data.  This interleaving should generally be avoided unless
   necessary since it complicates client and server operation and
   imposes additional overhead.  Also, head of line blocking may cause
   problems.  Interleaved binary data SHOULD only be used if RTSP is
   carried over TCP.  Interleaved data is not allowed inside RTSP
   messages.

   Stream data such as RTP packets is encapsulated by an ASCII dollar
   sign (36 decimal), followed by a one-byte channel identifier,
   followed by the length of the encapsulated binary data as a binary,
   two-byte integer in network byte order.  The stream data follows
   immediately afterwards, without a CRLF, but including the upper-layer
   protocol headers.  Each $ block MUST contain exactly one upper-layer
   protocol data unit, e.g., one RTP packet.
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | "$" = 36      | Channel ID    | Length in bytes               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      : Length number of bytes of binary data                         :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The channel identifier is defined in the Transport header with the
   interleaved parameter (Section 16.52). 18.52).

   When the transport choice is RTP, RTCP messages are also interleaved
   by the server over the TCP connection.  The usage of RTCP messages is
   indicated by including an interval containing a second channel in the
   interleaved parameter of the Transport header, see Section 16.52. 18.52.  If
   RTCP is used, packets MUST be sent on the first available channel
   higher than the RTP channel.  The channels are bi-directional, using
   the same ChannelD in both directions, and therefore RTCP traffic are
   sent on the second channel in both directions.

      RTCP is sometimes needed for synchronization when two or more
      streams are interleaved in such a fashion.  Also, this provides a
      convenient way to tunnel RTP/RTCP packets through the TCP control
      connection when required by the network configuration and transfer
      them onto UDP when possible.

     C->S: SETUP rtsp://example.com/bar.file RTSP/2.0
           CSeq: 2
           Transport: RTP/AVP/TCP;unicast;interleaved=0-1
           Accept-Ranges: NPT, SMPTE, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 2
           Date: Thu, 05 Jun 1997 18:57:18 GMT
           Transport: RTP/AVP/TCP;unicast;interleaved=5-6
           Session: 12345678
           Accept-Ranges: NPT
           Media-Properties: Random-Access=0.2, Immutable, Unlimited

     C->S: PLAY rtsp://example.com/bar.file RTSP/2.0
           CSeq: 3
           Session: 12345678
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 3
           Session: 12345678
           Date: Thu, 05 Jun 1997 18:57:19 GMT
           RTP-Info: url="rtsp://example.com/bar.file"
             ssrc=0D12F123:seq=232433;rtptime=972948234
           Range: npt=0-56.8
           Seek-Style: RAP

     S->C: $005{2 byte length}{"length" bytes data, w/RTP header}
     S->C: $005{2 byte length}{"length" bytes data, w/RTP header}
     S->C: $006{2 byte length}{"length" bytes  RTCP packet}

15.  Status Code Definitions

   Where applicable, HTTP status [H10] codes  Proxies

   RTSP Proxies are reused.  Status codes RTSP agents that have the same meaning are not repeated here.  See Table 4 located in
   Section 8.1 for between a listing of which status codes may be returned by
   which requests.  All error messages, 4xx client and 5xx MAY return
   a body
   containing further information about the error.

15.1.  Success 1xx

15.1.1.  100 Continue

   The client SHOULD continue with its request.  This interim response
   is used to inform server.  A proxy can take on both the role as a client that and as
   server depending on what it tries to accomplish.  Proxies are also
   introduced for several different reasons and the initial part below listed are
   often combined.

   In general there are two categories of RTSP proxies, transparent (of
   which the request has
   been received and has client is not yet been rejected by aware) and the non-transparent proxies (of
   which the server.  The client SHOULD continue by sending is aware).  Transparent proxies are not visible to
   the remainder client in terms of that the request or, if
   the request has already been completed, ignore this response.  The
   server MUST send transport layer connection, e.g., TCP
   for RTSP, as there is only a final response after the request has been
   completed.

15.2.  Success 2xx

   This class of status code indicates that single transport connection which is
   terminated at the client's request was
   successfully received, understood, RTSP client and accepted.

15.2.1.  200 OK

   The request has succeeded.  The information returned with the
   response is dependent on the method used in RTSP server.  In the request.

15.3.  Redirection 3xx

   The notation "3rr" indicates response codes from 300 to 399 inclusive
   which case of
   non-transparent proxies, there are meant for redirection.  The response code 304 is excluded two transport layer connections,
   one from this set, as it is not used for redirection.

   Within RTSP, redirection may be used for load balancing or
   redirecting stream requests the RTSP client to the RTSP proxy and a server topologically closer to second from the
   client.  Mechanisms RTSP
   proxy to determine topological proximity are beyond the
   scope RTSP server.

   There are these types of this specification.

   A 3rr code MAY be used to respond to any request.  It RTSP proxies:

   Caching Proxy:  This type of proxy is RECOMMENDED
   that they are used if necessary before a session is established,
   i.e., in response to DESCRIBE or SETUP.  However, in cases where a
   server is not able to send a REDIRECT request to reduce the client, workload on
         servers and connections.  By caching the
   server MAY need to resort to using 3rr responses to inform description and media
         streams, i.e., the presentation, the proxy can serve a client
         with an established session about content, but without requesting it from the need for redirecting server once it
         has been cached and has not become stale.  See the
   session.  If a 3rr response caching
         Section 16.  This type of proxy is received for a request also expected to understand
         RTSP end-point functionality, i.e., functionality identified in relation
         the Require header in addition to what Proxy-Require demands.

   Translator Proxy:  This type of proxy is used to ensure that an established session, the RTSP
         client SHOULD send a TEARDOWN request for
   the session, gets access to servers and MAY reestablish the session content on an external
         network or using the resource
   indicated content encodings not supported by the Location.

   If client.
         The proxy performs the Location header necessary translation of addresses,
         protocols or encodings.  This type of proxy is used expected to also
         understand RTSP end-point functionality, i.e. functionality
         identified in a response it MUST contain an
   absolute URI pointing out the media resource the client is redirected
   to, the URI MUST NOT only contain the host name.

15.3.1.  301 Moved Permanently

   The requested resource Require header in addition to what Proxy-
         Require demands.

   Access Proxy:  This type of proxy is moved permanently and resides now at the
   URI given by the location header.  The user client SHOULD redirect
   automatically used to ensure that an RTSP
         clients get access to servers on an external network.  Thus
         this proxy is placed on the given URI.  This response MUST NOT contain border between two domains, e.g. a
   message-body.  The Location header MUST be included in the response.

15.3.2.  302 Found

   The requested resource resides temporarily at the URI given by
         private address space and the
   Location header. public Internet.  The Location header MUST be included in proxy
         performs the
   response. necessary translation, usually addresses.  This response is intended to be used for many types
         type of
   temporary redirects; e.g., load balancing.  It proxy is RECOMMENDED that
   the server set the reason phrase required to something more meaningful than
   "Found" in these cases.  The user client SHOULD redirect
   automatically to the given URI.  This response MUST NOT contain a
   message-body.

   This example shows a client being redirected media to itself or a different server:

     C->S: SETUP rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 2
           Transport: RTP/AVP/TCP;unicast;interleaved=0-1
           Accept-Ranges: NPT, SMPTE, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 302 Try Other Server
           CSeq: 2
           Location: rtsp://s2.example.com:8001/fizzle/foo

15.3.3.  303 See Other

   This status code MUST NOT be used in RTSP 2.0.  However, it was
   allowed to use in RTSP 1.0 (RFC 2326).

15.3.4.  304 Not Modified

   If
         controlled gateway that performs the client has performed a conditional DESCRIBE or SETUP (see
   Section 16.24) and translation before the requested resource has not been modified,
         media can reach the
   server SHOULD send a 304 response. client.

   Security Proxy:  This response MUST NOT contain type of proxy is used to help facilitate
         security functions around RTSP.  For example when having a
   message-body.

   The response MUST include
         firewalled network, the following header fields:

   o  Date

   o  MTag and/or Content-Location, if security proxy request that the header(s) would have been
      sent
         necessary pinholes in a 200 response to the same request.

   o  Expires, Cache-Control, and/or Vary, if the field-value might
      differ from that sent firewall are opened when a client in any previous response for the same
      variant.

   This response is independent for
         the DESCRIBE and SETUP requests.
   That is, a 304 response protected network wants to DESCRIBE does NOT imply that access media streams on the resource
   content is unchanged (only
         external side.  This proxy can also limit the session description) and a 304
   response clients access to SETUP does NOT imply that
         certain types of content.  This proxy can perform its function
         without redirecting the resource description is
   unchanged.  The MTag and If-Match headers may be used to link media between the
   DESCRIBE server and SETUP client.
         However, in deployments with private address spaces this manner.

15.3.5.  305 Use Proxy

   The requested resource MUST be accessed through the proxy given by
   the Location field.  The Location field gives the URI of the proxy.
   The recipient
         is expected likely to repeat this single request via the
   proxy. 305 responses MUST only be generated by origin servers.

15.4.  Client Error 4xx

15.4.1.  400 Bad Request

   The request could not be understood by the server due to malformed
   syntax.  The client SHOULD NOT repeat combined with the request without
   modifications.  If access proxy.  Anyway, the request does not have a CSeq header, the
   server MUST NOT include a CSeq in
         functionality of this proxy is usually closely tied into
         understanding all aspects of the response.

15.4.2.  401 Unauthorized

   The request requires user authentication.  The response MUST include
   a WWW-Authenticate header (Section 16.57) field containing media transport.

   Auditing Proxy:  RTSP proxies can also provide network owners with a
   challenge applicable to
         logging and audit point for RTSP sessions, e.g. for
         corporations that track their employees usage of the requested resource.  The client MAY
   repeat network.
         This type of proxy can perform its function without inserting
         itself or any other node in the request media transport.  This proxy
         type can also accept unknown methods as it doesn't interfere
         with a suitable Authorization header field.  If the request already included Authorization credentials, then clients' requests.

   All types of proxies can be used also when using secured
   communication with TLS as RTSP 2.0 allows the 401
   response indicates client to approve
   certificate chains used for connection establishment from a proxy,
   see Section 19.3.2.  However, that authorization has been refused trust model may not be suitable
   for all types of deployment.  In those
   credentials.  If the 401 response contains the same challenge as the
   prior response, and cases, the user agent has already attempted
   authentication at least once, then secured sessions do
   by-pass of the user proxies.

   Access proxies SHOULD NOT be presented the
   message body that was given used in the response, since equipment like NATs and
   firewalls that message body
   might include relevant diagnostic information.  HTTP access
   authentication aren't expected to be regularly maintained, like home
   or small office equipment.  In these cases it is explained better to use the
   NAT traversal procedures defined for RTSP 2.0
   [I-D.ietf-mmusic-rtsp-nat].  The reason for these recommendations is
   that any extensions of RTSP resulting in [RFC2617].

15.4.3.  402 Payment Required new media transport
   protocols or profiles, new parameters, etc. may fail in a proxy that
   isn't maintained.  This code is reserved for would impede RTSP's future use.

15.4.4.  403 Forbidden development and
   usage.

15.1.  Proxies and Protocol Extensions

   The server understood the request, but is refusing existence of proxies must always be considered when developing
   new RTSP extensions.  Most types of proxies will need to fulfill it.
   Authorization implement
   any new method to operate correctly in the presence of that
   extension.  New headers can be introduced and will not help be blocked by
   older proxies.  However, it is important to consider if this header
   and its function is required to be understood by the request SHOULD NOT proxy or can be repeated.
   forwarded.  If the server wishes header needs to make public why be understood, a feature-tag
   representing the request has not been
   fulfilled, it SHOULD describe functionality MUST be included in the reason Proxy-Require
   header.  Below are guidelines for analysis if the refusal header needs to be
   understood.  The transport header and its parameters also shows that
   headers that are extensible and require correct interpretation in the
   message body.  If the server does
   proxy also require handling rules.

   Whether a proxy needs to understand a header is not wish easy to make this information
   available
   determine, as they serve a broad variety of functions.  When
   evaluating if a header needs to the client, the status code 404 (Not Found) can be used
   instead.

15.4.5.  404 Not Found

   The server has not found anything matching the Request-URI.  No
   indication is given of whether understood, one can divide the condition is temporary or
   permanent.
   functionality into three main categories:

   Media modifying:  The 410 (Gone) status code SHOULD be used if caching and translator proxies are modifying
      the actual media and therefore needs to understand also request
      directed to the server
   knows, through some internally configurable mechanism, that an old
   resource is permanently unavailable and has no forwarding address.
   This status code affects how the media is commonly used when rendered.
      Thus, this type of proxy needs to also understand the server does not wish side
      functionality.

   Transport modifying:  The access and the security proxy both need to
   reveal exactly why
      understand how the request has been refused, or when no other
   response transport is applicable.

15.4.6.  405 Method Not Allowed

   The method specified in performed, either for opening
      pinholes or to translate the request outer headers, e.g.  IP and UDP.

   Non-modifying:  The audit proxy is special in that it does not allowed for modify
      the resource
   identified by messages in other ways than to insert the Request-URI.  The response MUST include an Allow
   header containing a list of valid methods Via header.  That
      makes it possible for the requested resource.
   This status code is also this type to be used forward RTSP messages that
      contain different types of unknown methods, headers or header
      parameters.

   Based on the above classification, one should evaluate if a request attempts to use a
   method not indicated during SETUP.

15.4.7.  406 Not Acceptable

   The resource identified by the request is only capable new
   functionality requires the Transport modifying type of generating
   response message bodies which proxies to
   understand it or not.

15.2.  Multiplexing and Demultiplexing of Messages

   RTSP proxies may have content characteristics not
   acceptable according to multiplex multiple RTSP sessions from their
   clients towards RTSP servers.  This requires that RTSP requests from
   multiple clients are multiplexed onto a common connection for
   requests outgoing to an RTSP server and on the Accept headers sent in way back the request.

   The responses
   are demultiplexed from the server to per client responses.  On the
   protocol level this requires that request and response SHOULD include a message body containing messages are
   handled in both ways, requiring that there is a list mechanism to
   correlate what request/response pair exchanged between proxy and
   server is mapped to what client (or client request).

   This multiplexing of
   available message body characteristics requests and location(s) from which the
   user or user agent can choose the one most appropriate.  The message
   body format demultiplexing of responses is specified done
   by using the media type given CSeq header field (see Section 18.19).  The proxy has to
   rewrite the CSeq in requests to the Content-Type
   header field.  Depending upon server and responses from the format
   server and remember what CSeq is mapped to what client.

16.  Caching

   In HTTP, request-response pairs are cached.  RTSP differs
   significantly in that respect.  Responses are not cacheable, with the capabilities
   exception of the
   user agent, selection of presentation description returned by DESCRIBE.
   (Since the most appropriate choice MAY be performed
   automatically.  However, this specification does responses for anything but DESCRIBE and GET_PARAMETER do
   not define return any
   standard data, caching is not really an issue for these
   requests.)  However, it is desirable for such automatic selection.

   If the response could be unacceptable, a user agent SHOULD
   temporarily stop receipt of more data and query the user for a
   decision on further actions.

15.4.8.  407 Proxy Authentication Required

   This code is similar to 401 (Unauthorized) (Section 15.4.2), but
   indicates that the client must first authenticate itself continuous media data,
   typically delivered out-of-band with respect to RTSP, to be cached,
   as well as the
   proxy.  The proxy MUST return session description.

   On receiving a Proxy-Authenticate header field
   (Section 16.33) containing SETUP or PLAY request, a challenge applicable to the proxy for ascertains whether it
   has an up-to-date copy of the requested resource.

15.4.9.  408 Request Timeout

   The client did not produce continuous media content and its
   description.  It can determine whether the copy is up-to-date by
   issuing a request within SETUP or DESCRIBE request, respectively, and comparing the time
   Last-Modified header with that of the server
   was prepared to wait.  The client MAY repeat cached copy.  If the request without
   modifications at any later time.

15.4.10.  410 Gone

   The requested resource copy is no longer available at
   not up-to-date, it modifies the server SETUP transport parameters as
   appropriate and forwards the
   forwarding address is not known.  This condition is expected request to be
   considered permanent.  If the server does not know, or has no
   facility to determine, whether origin server.
   Subsequent control commands such as PLAY or not the condition is permanent, PAUSE then pass the
   status code 404 (Not Found) SHOULD be used instead.  This response is
   cacheable unless indicated otherwise. proxy
   unmodified.  The 410 response is primarily intended proxy delivers the continuous media data to assist the task
   client, while possibly making a local copy for later reuse.  The
   exact allowed behavior of
   repository maintenance the cache is given by notifying the recipient that cache-response
   directives described in Section 18.10.  A cache MUST answer any
   DESCRIBE requests if it is currently serving the resource stream to the
   requester, as it is intentionally unavailable and possible that low-level details of the server owners desire that
   remote links to stream
   description may have changed on the origin-server.

   Note that resource be removed.  Such an event RTSP cache, is common
   for limited-time, promotional services and for resources belonging of the "cut-through" variety.  Rather
   than retrieving the whole resource from the origin server, the cache
   simply copies the streaming data as it passes by on its way to
   individuals no longer working at the server's site.  It is
   client.  Thus, it does not
   necessary introduce additional latency.

   To the client, an RTSP proxy cache appears like a regular media
   server, to mark all permanently unavailable resources the media origin server like a client.  Just as "gone" or an HTTP
   cache has to keep store the mark content type, content language, and so on for any length of time -- that is left
   the objects it caches, a media cache has to store the
   discretion of presentation
   description.  Typically, a cache eliminates all transport-references
   (e.g., multicast information) from the owner presentation description,
   since these are independent of the server.

15.4.11.  411 Length Required

   The server refuses data delivery from the cache to accept
   the request without a defined Content-
   Length.  The client MAY repeat client.  Information on the request if it adds a valid
   Content-Length header field containing encodings remains the length of same.  If the message-body
   in
   cache is able to translate the request message.

15.4.12.  412 Precondition Failed

   The precondition given in one or more of the request-header fields
   evaluated to false when cached media data, it was tested on the server.  This response
   code allows would create a
   new presentation description with all the client encoding possibilities it
   can offer.

16.1.   Validation Model

   When a cache has a stale entry that it would like to place preconditions on the current resource
   meta information (header field data) and thus prevent the requested
   method from being applied use as a
   response to a resource other than client's request, it first has to check with the one intended.

15.4.13.  413 Request Message Body Too Large

   The origin
   server is refusing to process (or possibly an intermediate cache with a request because the request
   message body fresh response) to
   see if its cached entry is larger than still usable.  We call this "validating"
   the server is willing or able cache entry.  Since we do not want to process.
   The server MAY close the connection have to prevent the client from
   continuing pay the request.

   If overhead of
   retransmitting the condition is temporary, full response if the server SHOULD include a Retry-
   After header field to indicate that it cached entry is temporary good, and after what
   time the client MAY try again.

15.4.14.  414 Request-URI Too Long

   The server is refusing we
   do not want to service pay the request because overhead of an extra round trip if the Request-URI cached
   entry is longer than invalid, the RTSP protocol supports the use of conditional
   methods.

   The key protocol features for supporting conditional methods are
   those concerned with "cache validators."  When an origin server is willing
   generates a full response, it attaches some sort of validator to interpret.  This rare
   condition it,
   which is only likely to occur when a client has used a request kept with long query information, when the cache entry.  When a client has descended into (user agent or
   proxy cache) makes a URI
   "black hole" of redirection (e.g., conditional request for a redirected URI prefix that
   points to resource for which it
   has a suffix of itself), or when cache entry, it includes the server is under attack by
   a client attempting to exploit security holes present associated validator in some servers
   using fixed-length buffers for reading or manipulating the Request-
   URI.

15.4.15.  415 Unsupported Media Type
   request.

   The server is refusing to service then checks that validator against the request because current validator
   for the requested resource, and, if they match (see Section 16.1.3),
   it responds with a special status code (usually, 304 (Not Modified))
   and no message
   body of the request is in body.  Otherwise, it returns a format not supported by the requested
   resource for full response
   (including message body).  Thus, we avoid transmitting the requested method.

15.4.16.  451 Parameter Not Understood

   The recipient of full
   response if the request validator matches, and we avoid an extra round trip
   if it does not support one or more parameters
   contained in the request.  When returning this error message the
   sender SHOULD return match.

   In RTSP, a message body containing conditional request looks exactly the offending
   parameter(s).

15.4.17.  452 reserved

   This error code was removed from RFC 2326 [RFC2326] same as it is
   obsolete.  This error code MUST NOT be used anymore.

15.4.18.  453 Not Enough Bandwidth

   The a normal
   request was refused because there was insufficient bandwidth.
   This may, for example, be the result of a resource reservation
   failure.

15.4.19.  454 Session Not Found

   The RTSP session identifier in the Session header is missing,
   invalid, or has timed out.

15.4.20.  455 Method Not Valid in This State

   The client or server cannot process this request in its current
   state.  The response MUST contain an Allow header to make error
   recovery possible.

15.4.21.  456 Header Field Not Valid for Resource

   The server could not act on same resource, except that it carries a required request header.  For example,
   if PLAY contains the Range special
   header field but the stream does not allow
   seeking.  This error message may also be used for specifying when the
   time format in Range is impossible for (which includes the resource.  In validator) that case
   the Accept-Ranges header MUST be returned to inform implicitly turns the client of
   which format(s) that are allowed.

15.4.22.  457 Invalid Range
   method (usually DESCRIBE or SETUP) into a conditional.

   The Range value given is out of bounds, e.g., beyond the end protocol includes both positive and negative senses of the
   presentation.

15.4.23.  458 Parameter Is Read-Only

   The parameter cache-
   validating conditions.  That is, it is possible to be set by SET_PARAMETER can be read but not
   modified.  When returning this error message the sender SHOULD return request either
   that a message body containing the offending parameter(s).

15.4.24.  459 Aggregate Operation Not Allowed

   The requested method be performed if and only if a validator matches or if
   and only if no validators match.

      Note: a response that lacks a validator may not still be applied on the URI in question since cached, and
      served from cache until it expires, unless this is an aggregate (presentation) URI.  The method may be applied on explicitly
      prohibited by a media URI.

15.4.25.  460 Only Aggregate Operation Allowed

   The requested method may cache-control directive (see Section 18.10).
      However, a cache cannot do a conditional retrieval if it does not be applied on
      have a validator for the URI in question since resource, which means it is will not an aggregate control (presentation) URI.  The method may be
   applied
      refreshable after it expires.

   Media streams that are being adapted based on the aggregate control URI.

15.4.26.  461 Unsupported Transport

   The Transport field did not contain a supported transport
   specification.

15.4.27.  462 Destination Unreachable

   The data transmission channel could capacity
   between the server and the cache makes caching more difficult.  A
   server needs to consider how it views caching of media streams that
   it adapts and potentially instruct any caches to not cache such
   streams.

16.1.1.  Last-Modified Dates

   The Last-Modified header (Section 18.26) value is often used as a
   cache validator.  In simple terms, a cache entry is considered to be established because
   valid if the
   client address could content has not be reached.  This error will most likely be been modified since the result of Last-Modified
   value.

16.1.2.  Message Body Tag Cache Validators

   The MTag response-header field value, a client attempt to place message body tag, provides
   for an invalid dest_addr
   parameter "opaque" cache validator.  This might allow more reliable
   validation in situations where it is inconvenient to store
   modification dates, where the Transport field.

15.4.28.  463 Destination Prohibited

   The data transmission channel was one-second resolution of RTSP-date
   values is not established because sufficient, or where the origin server
   prohibited access wishes to avoid
   certain paradoxes that might arise from the client address.  This error is most likely
   the result use of a client attempt to redirect media traffic to another
   destination with a dest_addr parameter modification
   dates.

   Message body tags are described in the Transport header.

15.4.29.  464 Data Transport Not Ready Yet

   The data transmission channel Section 4.8

16.1.3.  Weak and Strong Validators

   Since both origin servers and caches will compare two validators to
   decide if they represent the media destination is not yet
   ready for carrying data.  However, the responding agent still expects same or different entities, one normally
   would expect that if the data transmission channel will be established at some point
   in time.  Note, however, that this may result message body (i.e., the presentation
   description) or any associated message body headers changes in a permanent failure
   like 462 "Destination Unreachable".

   An example when any
   way, then the associated validator would change as well.  If this error may occur is in the case a client sends a
   PLAY request to
   true, then we call this validator a server prior to ensuring that "strong validator."  We call
   message body (i.e., the TCP connections
   negotiated presentation description) or any associated
   message body headers an entity for carrying media data was successfully established (In
   violation of this specification).  The a better understanding.

   However, there might be cases when a server would use this error
   code prefers to indicate that change the requested action could
   validator only on semantically significant changes, and not be performed due
   to the failure when
   insignificant aspects of completing the connection establishment.

15.4.30.  465 Notification Reason Unknown

   This indicates entity change.  A validator that does
   not always change when the client has received resource changes is a PLAY_NOTIFY
   (Section 13.5) with "weak validator."

   Message body tags are normally "strong validators," but the protocol
   provides a Notify-Reason header (Section 16.31) unknown mechanism to
   the client.

15.4.31.  466 Key Management Error

   This indicates that there has been an error in tag a Key Management
   function used in conjunction with message body tag as "weak."  One can
   think of a request.  For example usage strong validator as one that changes whenever the bits of
   MIKEY according to Appendix C.1.4.1 may result in this error.

15.4.32.  470 Connection Authorization Required

   The secured connection attempt needs user or client authorization
   before proceeding.  The next hops certificate is included in this
   response in
   an entity changes, while a weak value changes whenever the Accept-Credentials header.

15.4.33.  471 Connection Credentials not accepted

   When performing meaning of
   an entity changes.  Alternatively, one can think of a secure connection over multiple connections, strong
   validator as part of an
   intermediary has refused to connect to the next hop and carry out the
   request due to unacceptable credentials identifier for the used policy.

15.4.34.  472 Failure to establish secure connection

   A proxy fails to establish a secure connection to the next hop RTSP
   agent.  This is primarily caused by specific entity, while a fatal failure at the TLS
   handshake, for example due to server not accepting any cipher suites.

15.5.  Server Error 5xx

   Response status codes beginning with the digit "5" indicate cases in
   which the server is aware that it has erred or
   weak validator is incapable part of
   performing the request The server SHOULD include a message body
   containing an explanation identifier for a set of semantically
   equivalent entities.

      Note: One example of the error situation, and whether it is a
   temporary or permanent condition.  User agents SHOULD display any
   included message body to the user.  These response codes are
   applicable to any request method.

15.5.1.  500 Internal Server Error

   The server encountered strong validator is an unexpected condition which prevented integer that is
      incremented in stable storage every time an entity is changed.

      An entity's modification time, if represented with one-second
      resolution, could be a weak validator, since it
   from fulfilling the request.

15.5.2.  501 Not Implemented

   The server does not support the functionality required to fulfill the
   request.  This is possible that
      the appropriate response when the server does not
   recognize the request method and resource might be modified twice during a single second.

      Support for weak validators is not capable of supporting it optional.  However, weak validators
      allow for
   any resource.

15.5.3.  502 Bad Gateway

   The server, while acting as more efficient caching of equivalent objects.

   A "use" of a gateway or proxy, received an invalid
   response from the upstream server it accessed in attempting to
   fulfill the request.

15.5.4.  503 Service Unavailable

   The server validator is currently unable to handle the either when a client generates a request due to
   and includes the validator in a
   temporary overloading validating header field, or maintenance of the server.  The implication
   is when a
   server compares two validators.

   Strong validators are usable in any context.  Weak validators are
   only usable in contexts that this do not depend on exact equality of an
   entity.  For example, either kind is usable for a temporary condition which will be alleviated after
   some delay.  If known, the length conditional
   DESCRIBE of the delay MAY be indicated in a
   Retry-After header.  If no Retry-After full entity.  However, only a strong validator is given, the client SHOULD
   handle the response as it would
   usable for a 500 response.  The sub-range retrieval, since otherwise the client might
   end up with an internally inconsistent entity.

   Clients MAY issue DESCRIBE requests with either weak validators or
   strong validators.  Clients MUST
   honor the length, if given NOT use weak validators in the Retry-After header.

         Note: The existence other
   forms of the 503 status code does not imply requests.

   The only function that
         a server must use it when becoming overloaded.  Some servers
         may wish to simply refuse the connection.

15.5.5.  504 Gateway Timeout

   The server, while acting as a proxy, did not receive a timely
   response from RTSP protocol defines on validators is
   comparison.  There are two validator comparison functions, depending
   on whether the upstream server specified by comparison context allows the URI use of weak validators
   or some other
   auxiliary server (e.g., DNS) it needed to access not:

   o  The strong comparison function: in attempting order to
   complete the request.

15.5.6.  505 RTSP Version Not Supported be considered equal,
      both validators MUST be identical in every way, and both MUST NOT
      be weak.

   o  The server does not support, or refuses weak comparison function: in order to support, the RTSP protocol
   version that was used be considered equal,
      both validators MUST be identical in every way, but either or both
      of them MAY be tagged as "weak" without affecting the request message.  The server result.

   A message body tag is
   indicating that strong unless it is unable or unwilling to complete the request
   using the same major version explicitly tagged as weak.

   A Last-Modified time, when used as the client other than with this error
   message.  The response SHOULD contain a message body describing why validator in a request, is
   implicitly weak unless it is possible to deduce that version it is not supported and what other protocols are supported strong,
   using the following rules:

   o  The validator is being compared by an origin server to the actual
      current validator for the entity and,

   o  That origin server reliably knows that server.

15.5.7.  551 Option the associated entity did
      not supported

   A feature-tag given in change more than once during the Require or second covered by the Proxy-Require fields was
   not supported.
      presented validator.

   OR

   o  The Unsupported header MUST validator is about to be returned stating used by a client in an If-Modified-
      Since, because the
   feature client has a cache entry for which there is no support.

16.  Header Field Definitions

       +---------------+----------------+--------+---------+------+
       | method        | direction      | object | acronym | Body |
       +---------------+----------------+--------+---------+------+
       | DESCRIBE      | C -> S         | P,S    | DES     | r    |
       |               |                |        |         |      |
       | GET_PARAMETER | C -> S, S -> C | P,S    | GPR     | R,r  |
       |               |                |        |         |      |
       | OPTIONS       | C -> S, S -> C | P,S    | OPT     |      |
       |               |                |        |         |      |
       | PAUSE         | C -> S         | P,S    | PSE     |      |
       |               |                |        |         |      |
       | PLAY          | C -> S         | P,S    | PLY     |      |
       |               |                |        |         |      |
       | PLAY_NOTIFY   | S -> C         | P,S    | PNY     | R    |
       |               |                |        |         |      |
       | REDIRECT      | S -> C         | P,S    | RDR     |      |
       |               |                |        |         |      |
       | SETUP         | C -> S         | S      | STP     |      |
       |               |                |        |         |      |
       | SET_PARAMETER | C -> S, S -> C | P,S    | SPR     | R,r  |
       |               |                |        |         |      |
       | TEARDOWN      | C -> S         | P,S    | TRD     |      |
       |               |                |        |         |      |
       |               | S -> C         | P      | TRD     |      |
       +---------------+----------------+--------+---------+------+

   Table 8: Overview of RTSP methods, their direction, the associated
      entity, and what objects
   (P: presentation, S: stream) they operate on. Body notes if

   o  That cache entry includes a method Date value, which gives the time when
      the origin server sent the original response, and

   o  The presented Last-Modified time is allowed at least 60 seconds before the
      Date value.

   OR

   o  The validator is being compared by an intermediate cache to carry body and the
      validator stored in which direction, R = Request,
   r=response. Note: It is allowed its cache entry for all error messages 4xx the entity, and 5xx to
                                have

   o  That cache entry includes a body Date value, which gives the time when
      the origin server sent the original response, and

   o  The general syntax for header fields presented Last-Modified time is covered in Section 5.2.  This
   section lists at least 60 seconds before the full set of header fields along with notes
      Date value.

   This method relies on
   meaning, and usage.  The syntax definition for header fields are
   present in Section 20.2.3.  Throughout this section, we use [HX.Y] to
   informational refer to Section X.Y of the current HTTP/1.1
   specification RFC 2616 [RFC2616].  Examples fact that if two different responses were
   sent by the origin server during the same second, but both had the
   same Last-Modified time, then at least one of each header field are
   given.

   Information about header fields in relation those responses would
   have a Date value equal to methods and proxy
   processing is summarized in Table 9, Table 10, Table 11, and
   Table 12. its Last-Modified time.  The "where" column describes the request and response types in which arbitrary 60-
   second limit guards against the header field can be used.  Values in this column are:

   R:    header field may only appear in requests;

   r:    header field may only appear in responses;

   2xx, 4xx, etc.:  A numerical value or range indicates response codes
         with which possibility that the header field can be used;

   c:    header field is copied Date and Last-
   Modified values are generated from different clocks, or at somewhat
   different times during the request to preparation of the response.  An empty entry in the "where" column indicates
   implementation MAY use a value larger than 60 seconds, if it is
   believed that the header field
   may be present in both requests and responses.

   The "proxy" column describes the operations 60 seconds is too short.

   If a proxy may client wishes to perform a sub-range retrieval on a
   header field.  An empty proxy column indicates that the proxy MUST
   NOT do any changes to that header, all allowed operations are
   explicitly stated:

   a:    A proxy can add or concatenate the header field if not present.

   m:    A proxy can modify an existing header field value.

   d:    A proxy can delete value for
   which it has only a header field value.

   r:    A proxy needs to be able to read the header field, Last-Modified time and thus no opaque validator, it
   MAY do this header field cannot be encrypted.

   The rest of the columns relate to only if the presence of a header field Last-Modified time is strong in a
   method.  The method names when abbreviated, are according to Table 8:

   c:    Conditional; requirements on the header field depend on the
         context sense
   described here.

16.1.4.  Rules for When to Use Message Body Tags and Last-Modified Dates

   We adopt a set of the message.

   m:    The header field is mandatory.

   m*:   The header field SHOULD be sent, but clients/servers need rules and recommendations for origin servers,
   clients, and caches regarding when various validator types ought to
   be
         prepared to receive messages without that header field.

   o:    The header field used, and for what purposes.

   RTSP origin servers:

   o  SHOULD send a message body tag validator unless it is optional.

   *:    The header field MUST be present not feasible
      to generate one.

   o  MAY send a weak message body tag instead of a strong message body
      tag, if performance considerations support the use of weak message
      body tags, or if it is not
         empty.  See Section 16.16, Section 16.18 and Section 5.3 for
         details.

   -:    The header field is not applicable.

   "Optional" means that unfeasible to send a Client/Server MAY include the header field in strong message body
      tag.

   o  SHOULD send a request or response.  The Client/Server behavior when receiving
   such headers varies, for some it may ignore the header field, in
   other cases Last-Modified value if it is a request feasible to process the header.  This is regulated
   by send one,
      unless the method and header descriptions.  Example risk of headers a breakdown in semantic transparency that
   require processing are the Require and Proxy-Require header fields
   discussed could
      result from using this date in Section 16.41 and Section 16.35.  A "mandatory" an If-Modified-Since header
   field MUST be present in would
      lead to serious problems.

   In other words, the preferred behavior for an RTSP origin server is
   to send both a request, strong message body tag and MUST a Last-Modified value.

   In order to be understood by the
   Client/Server receiving legal, a strong message body tag MUST change whenever
   the request. associated entity value changes in any way.  A mandatory response header
   field weak message body
   tag SHOULD change whenever the associated entity changes in a
   semantically significant way.

      Note: in order to provide semantically transparent caching, an
      origin server MUST avoid reusing a specific strong message body
      tag value for two different entities, or reusing a specific weak
      message body tag value for two semantically different entities.
      Cache entries might persist for arbitrarily long periods,
      regardless of expiration times, so it might be present inappropriate to
      expect that a cache will never again attempt to validate an entry
      using a validator that it obtained at some point in the response, and past.

   RTSP clients:

   o  If a message body tag has been provided by the header field origin server, MUST be
   understood
      use that message body tag in any cache-conditional request (using
      If-Match or If-None-Match).

   o  If only a Last-Modified value has been provided by the Client/Server processing the response.  "Not
   applicable" means origin
      server, SHOULD use that the header field MUST NOT be present value in a
   request. non-subrange cache-conditional
      requests (using If-Modified-Since).

   o  If one is placed in both a request by mistake, it MUST be
   ignored message body tag and a Last-Modified value have been
      provided by the Client/Server origin server, SHOULD use both validators in
      cache-conditional requests.

   An RTSP origin server, upon receiving the request.  Similarly, a
   header field labeled "not applicable" for a response means conditional request that the
   Client/Server
   includes both a Last-Modified date (e.g., in an If-Modified-Since
   header) and one or more message body tags (e.g., in an If-Match, If-
   None-Match, or If-Range header field) as cache validators, MUST NOT place
   return a response status of 304 (Not Modified) unless doing so is
   consistent with all of the conditional header field fields in the response, request.

      Note: The general principle behind these rules is that RTSP
      servers and
   the Client/Server MUST ignore the header field clients should transmit as much non-redundant
      information as is available in the response.

   An their responses and requests.  RTSP agent MUST ignore extension headers that are not understood.
      systems receiving this information will make the most conservative
      assumptions about the validators they receive.

16.1.5.  Non-validating Conditionals

   The From and Location header fields contain an URI.  If principle behind message body tags is that only the URI
   contains service
   author knows the semantics of a comma, or semicolon, resource well enough to select an
   appropriate cache validation mechanism, and the URI MUST be enclosed in double
   quotes (").  Any URI parameters specification of any
   validator comparison function more complex than byte-equality would
   open up a can of worms.  Thus, comparisons of any other headers are contained within
   never used for purposes of validating a cache entry.

16.2.  Invalidation After Updates or Deletions

   The effect of certain methods performed on a resource at the origin
   server might cause one or more existing cache entries to become non-
   transparently invalid.  That is, although they might continue to be
   "fresh," they do not accurately reflect what the origin server would
   return for a new request on that resource.

   There is no way for the RTSP protocol to guarantee that all such
   cache entries are marked invalid.  For example, the request that
   caused the change at the origin server might not have gone through
   the proxy where a cache entry is stored.  However, several rules help
   reduce the likelihood of erroneous behavior.

   In this section, the phrase "invalidate an entity" means that the
   cache will either remove all instances of that entity from its
   storage, or will mark these quotes.
   If as "invalid" and in need of a mandatory
   revalidation before they can be returned in response to a subsequent
   request.

   Some RTSP methods MUST cause a cache to invalidate an entity.  This
   is either the entity referred to by the Request-URI, or by the
   Location or Content-Location headers (if present).  These methods
   are:

   o  DESCRIBE
   o  SETUP

   In order to prevent denial of service attacks, an invalidation based
   on the URI in a Location or Content-Location header MUST only be
   performed if the host part is not enclosed the same as in double quote, the Request-URI.

   A cache that passes through requests for methods it does not
   understand SHOULD invalidate any semicolon-delimited
   parameters entities referred to by the Request-
   URI.

17.  Status Code Definitions

   Where applicable, HTTP status [H10] codes are reused.  Status codes
   that have the same meaning are header-parameters, not URI parameters.

   +------------------+-------+-----+----+-----+-----+-----+-----+-----+
   | Header           | Where | Pro | DE | OPT | STP | PLY | PSE | TRD |
   |                  |       | xy  | S  |     |     |     |     |     |
   +------------------+-------+-----+----+-----+-----+-----+-----+-----+
   | Accept           | R     |     | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Credentia | R     | rm  | o  | o   | o   | o   | o   | o   |
   | ls               |       |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Encoding  | R     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Language  | R     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | R     | r   | -  | -   | m   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | r     | r   | -  | -   | m   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | 456   | r   | -  | -   | -   | m   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Allow            | r     | am  | c  | c   | c   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Allow            | 405   | am  | m  | m   | m   | m   | m   | m   |
   |                  |       |     |    |     |     |     |     |     |
   | Authorization    | R     |     | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | Bandwidth        | R     |     | o  | o   | o   | o   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Blocksize        | R     |     | o  | -   | o   | o   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Cache-Control    |       | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Connection       |       | ad  | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | Connection-Crede | 470,4 | ar  | o  | o   | o   | o   | o   | o   |
   | ntials           | 07    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Base     | r     |     | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Base     | 4xx,5 |     | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | R     | r   | -  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | R     | r   | -  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Length   | r     | r   | *  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Length   | 4xx,5 | r   | *  | *   | *   | *   | *   | *   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Location | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Location | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Type     | r     | r   | *  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Type     | 4xx,5 | ar  | *  | *   | *   | *   | *   | *   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | CSeq             | Rc    | rm  | m  | m   | m   | m   | m   | m   |
   |                  |       |     |    |     |     |     |     |     |
   | Date             |       | am  | o/ | o/* | o/* | o/* | o/* | o/* |
   |                  |       |     | *  |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Expires          | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | From             | R     | r   | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | If-Match         | R     | r   | -  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | If-Modified-Sinc | R     | r   | o  | -   | o   | -   | -   | -   |
   | e                |       |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | If-None-Match    | R     | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Last-Modified    | r     | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Location         | 3rr   |     | o  | o   | o   | o   | o   | o   |
   +------------------+-------+-----+----+-----+-----+-----+-----+-----+

     Table 9: Overview of RTSP header fields (A-L) related to methods
           DESCRIBE, OPTIONS, SETUP, PLAY, PAUSE, and TEARDOWN.

   +----------------+-------+------+-----+-----+-----+-----+-----+-----+
   | Header         | Where | Prox | DES | OPT | STP | PLY | PSE | TRD |
   |                |       | y    |     |     |     |     |     |     |
   +----------------+-------+------+-----+-----+-----+-----+-----+-----+
   | Media-         |       |      | -   | -   | m   | m   | m   | -   |
   | Properties     |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Media-Range    |       |      | -   | -   | m   | m   | m   | -   |
   |                |       |      |     |     |     |     |     |     |
   | MTag           | r     | r    | o   | -   | o   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Pipelined-Requ |       | amdr | -   | o   | o   | o   | o   | o   |
   | ests           |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | 407   | amr  | m   | m   | m   | m   | m   | m   |
   | Authenticate   |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | R     | rd   | o   | o   | o   | o   | o   | o   |
   | Authorization  |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy- Require | R     | ar   | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Proxy- Require | r     | r    | c   | c   | c   | c   | c   | c   |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | R     | amr  | c   | c   | c   | c   | c   | c   |
   | Supported      |       |      |     |     |     |     |     |     |
   | Proxy-         | r     |      | c   | c   | c   | c   | c   | c   |
   | Supported      |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Public         | r     | amr  | -   | m   | -   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Public         | 501   | amr  | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Range          | R     |      | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Range          | r     |      | -   | -   | c   | m   | m   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Referrer       | R     |      | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Request-       | R     |      | -   | -   | -   | -   | -   | -   |
   | Status         |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Require        | R     |      | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Retry-After    | 3rr,5 |      | o   | o   | o   | o   | o   | -   |
   |                | 03    |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Retry-After    | 413   |      | o   | -   | -   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | RTP-Info       | r     |      | -   | -   | c   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Scale          | R     | r    | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Scale          | r     | amr  | -   | -   | -   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Seek-Style     | R     |      | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Seek-Style     | r     |      | -   | -   | -   | m   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Server         | R     | r    | -   | o   | -   | -   | -   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Server         | r     | r    | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Session        | R     | r    | -   | o   | o   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Session        | r     | r    | -   | c   | m   | m   | m   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Speed          | R     | admr | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Speed          | r     | admr | -   | -   | -   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Supported      | R     | amr  | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Supported      | r     | amr  | c   | c   | c   | c   | c   | c   |
   | Terminate-Reas | R     | r    | -   | -   | -   | -   | -   | -   |
   | on             |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Timestamp      | R     | admr | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Timestamp      | c     | admr | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Transport      |       | mr   | -   | -   | m   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Unsupported    | r     |      | c   | c   | c   | c   | c   | c   |
   |                |       |      |     |     |     |     |     |     |
   | User-Agent     | R     |      | m*  | m*  | m*  | m*  | m*  | m*  |
   |                |       |      |     |     |     |     |     |     |
   | Vary           | r     |      | c   | c   | c   | c   | c   | c   |
   |                |       |      |     |     |     |     |     |     |
   | Via            | R     | amr  | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Via            | c     | dr   | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | WWW-           | 401   |      | m   | m   | m   | m   | m   | m   |
   | Authenticate   |       |      |     |     |     |     |     |     |
   +----------------+-------+------+-----+-----+-----+-----+-----+-----+

     Table 10: Overview of RTSP header fields (M-W) related to methods
           DESCRIBE, OPTIONS, SETUP, PLAY, PAUSE, and TEARDOWN.

   +------------------------+---------+-------+-----+-----+-----+-----+
   | Header                 | Where   | Proxy | GPR | SPR | RDR | PNY |
   +------------------------+---------+-------+-----+-----+-----+-----+
   | Accept                 | R       | arm   | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Credentials     | R       | rm    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Encoding        | TBD     | TBD   | TBD | TBD | TBD | TBD |
   |                        |         |       |     |     |     |     |
   | Accept-Language        | TBD     | TBD   | TBD | TBD | TBD | TBD |
   |                        |         |       |     |     |     |     |
   | Accept-Ranges          |         | rm    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Allow                  | 405     | amr   | m   | m   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Authorization          | R       |       | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Bandwidth              | R       |       | -   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Blocksize              | R       |       | -   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Cache-Control          |         | r     | o   | o   | -   | -   |
   | Connection             |         |       | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Connection-Credentials | 470,407 | ar    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | R       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | r       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | 4xx,5xx |       | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | R       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | r       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | 4xx,5xx | r     | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | R       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | r       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | 4xx,5xx | r     | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | R       | r     | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | r       | r     | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | 4xx,5xx | r     | *   | *   | *   | *   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | R       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | r       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | 4xx,5xx |       | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | R       |       | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | r       |       | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | 4xx,5xx |       | *   | *   | *   | *   |
   |                        |         |       |     |     |     |     |
   | CSeq                   | R,c     | mr    | m   | m   | m   | m   |
   |                        |         |       |     |     |     |     |
   | Date                   | R       | a     | o   | o   | m   | o   |
   |                        |         |       |     |     |     |     |
   | Date                   | r       | am    | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Expires                | TBD     | TBD   | TBD | TBD | TBD | TBD |
   |                        |         |       |     |     |     |     |
   | From                   | R       | r     | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | If-Match               | TBD     | TBD   | TBD | TBD | TBD | TBD |
   |                        |         |       |     |     |     |     |
   | If-Modified-Since      | R       | am    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | If-None-Match          | R       | am    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Last-Modified          | R       | r     | -   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Last-Modified          | r       | r     | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Location               | 3rr     |       | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Location               | R       |       | -   | -   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Media-Properties       | R       | amr   | o   | -   | -   | c   |
   |                        |         |       |     |     |     |     |
   | Media-Properties       | r       | mr    | c   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Media-Range            | R       |       | o   | -   | -   | c   |
   |                        |         |       |     |     |     |     |
   | Media-Range            | r       |       | c   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | MTag                   | TBD     | TBD   | TBD | TBD | TBD | TBD |
   |                        |         |       |     |     |     |     |
   | Notify-Reason          | R       |       | -   | -   | -   | m   |
   |                        |         |       |     |     |     |     |
   | Pipelined-Requests     | R       | amdr  | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Authenticate     | 407     | amr   | m   | m   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Authorization    | R       | rd    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Require          | R       | ar    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Require          | r       | r     | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Supported        | R       | amr   | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Supported        | r       |       | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Public                 | 501     | admr  | m   | m   | m   | -   |
   +------------------------+---------+-------+-----+-----+-----+-----+

     Table 11: Overview of RTSP header fields (A-P) related to methods
         GET_PARAMETER, SET_PARAMETER, REDIRECT, and PLAY_NOTIFY.

      +------------------+---------+-------+-----+-----+-----+-----+
      | Header           | Where   | Proxy | GPR | SPR | RDR | PNY |
      +------------------+---------+-------+-----+-----+-----+-----+
      | Range            | R       |       | o   | -   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Referrer         | R       |       | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Request-Status   | R       |       | -   | -   | -   | c   |
      |                  |         |       |     |     |     |     |
      | Require          | R       | r     | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Retry-After      | 3rr,503 |       | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Retry-After      | 413     |       | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | RTP-Info         | R       | r     | o   | -   | -   | C   |
      |                  |         |       |     |     |     |     |
      | RTP-Info         | r       | r     | c   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Scale            |         |       | -   | -   | -   | c   |
      |                  |         |       |     |     |     |     |
      | Seek-Style       |         |       | -   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Server           | R       | r     | o   | o   | o   | o   |
      |                  |         |       |     |     |     |     |
      | Server           | r       | r     | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Session          | R       | r     | o   | o   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Session          | r       | r     | c   | c   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Speed            |         |       | -   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Supported        | R       | adrm  | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Supported        | r       | adrm  | c   | c   | c   | -   |
      |                  |         |       |     |     |     |     |
      | Terminate-Reason | R       | r     | -   | -   | m   | -   |
      |                  |         |       |     |     |     |     |
      | Timestamp        | R       | adrm  | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Timestamp        | c       | adrm  | m   | m   | m   | -   |
      |                  |         |       |     |     |     |     |
      | Transport        | TBD     | TBD   | TBD | TBD | TBD | TBD |
      |                  |         |       |     |     |     |     |
      | Unsupported      | r       | arm   | c   | c   | c   | -   |
      |                  |         |       |     |     |     |     |
      | User-Agent       | R       | r     | m*  | m*  | -   | -   |
      | User-Agent       | r       | r     | m*  | m*  | m*  | m*  |
      |                  |         |       |     |     |     |     |
      | Vary             | r       |       | c   | c   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Via              | R       | amr   | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Via              | c       | dr    | m   | m   | m   | -   |
      |                  |         |       |     |     |     |     |
      | WWW-Authenticate | 401     |       | m   | m   | m   | -   |
      +------------------+---------+-------+-----+-----+-----+-----+ repeated here.  See Table 12: Overview 4 in
   Section 8.1 for a listing of which status codes may be returned by
   which requests.  All error messages, 4xx and 5xx MAY return a body
   containing further information about the error.

17.1.  Success 1xx

17.1.1.  100 Continue

   The client SHOULD continue with its request.  This interim response
   is used to inform the client that the initial part of the request has
   been received and has not yet been rejected by the server.  The
   client SHOULD continue by sending the remainder of the request or, if
   the request has already been completed, ignore this response.  The
   server MUST send a final response after the request has been
   completed.

17.2.  Success 2xx

   This class of status code indicates that the client's request was
   successfully received, understood, and accepted.

17.2.1.  200 OK

   The request has succeeded.  The information returned with the
   response is dependent on the method used in the request.

17.3.  Redirection 3xx

   The notation "3rr" indicates response codes from 300 to 399 inclusive
   which are meant for redirection.  The response code 304 is excluded
   from this set, as it is not used for redirection.

   Within RTSP, redirection may be used for load balancing or
   redirecting stream requests to a server topologically closer to the
   client.  Mechanisms to determine topological proximity are beyond the
   scope of this specification.

   A 3rr code MAY be used to respond to any request.  It is RECOMMENDED
   that they are used if necessary before a session is established,
   i.e., in response to DESCRIBE or SETUP.  However, in cases where a
   server is not able to send a REDIRECT request to the client, the
   server MAY need to resort to using 3rr responses to inform a client
   with an established session about the need for redirecting the
   session.  If a 3rr response is received for a request in relation to
   an established session, the client SHOULD send a TEARDOWN request for
   the session, and MAY reestablish the session using the resource
   indicated by the Location.

   If the Location header is used in a response it MUST contain an
   absolute URI pointing out the media resource the client is redirected
   to, the URI MUST NOT only contain the host name.

17.3.1.  301 Moved Permanently

   The requested resource is moved permanently and resides now at the
   URI given by the location header.  The user client SHOULD redirect
   automatically to the given URI.  This response MUST NOT contain a
   message-body.  The Location header MUST be included in the response.

17.3.2.  302 Found

   The requested resource resides temporarily at the URI given by the
   Location header.  The Location header MUST be included in the
   response.  This response is intended to be used for many types of
   temporary redirects; e.g., load balancing.  It is RECOMMENDED that
   the server set the reason phrase to something more meaningful than
   "Found" in these cases.  The user client SHOULD redirect
   automatically to the given URI.  This response MUST NOT contain a
   message-body.

   This example shows a client being redirected to a different server:

     C->S: SETUP rtsp://example.com/fizzle/foo RTSP/2.0
           CSeq: 2
           Transport: RTP/AVP/TCP;unicast;interleaved=0-1
           Accept-Ranges: NPT, SMPTE, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 302 Try Other Server
           CSeq: 2
           Location: rtsp://s2.example.com:8001/fizzle/foo

17.3.3.  303 See Other

   This status code MUST NOT be used in RTSP 2.0.  However, it was
   allowed to use in RTSP 1.0 (RFC 2326).

17.3.4.  304 Not Modified

   If the client has performed a conditional DESCRIBE or SETUP (see
   Section 18.24) and the requested resource has not been modified, the
   server SHOULD send a 304 response.  This response MUST NOT contain a
   message-body.

   The response MUST include the following header fields (R-W) related fields:

   o  Date

   o  MTag and/or Content-Location, if the header(s) would have been
      sent in a 200 response to methods
         GET_PARAMETER, SET_PARAMETER,  REDIRECT, the same request.

   o  Expires and PLAY_NOTIFY.

16.1.  Accept Cache-Control if the field-value might differ from
      that sent in any previous response for the same variant.

   This response is independent for the DESCRIBE and SETUP requests.
   That is, a 304 response to DESCRIBE does NOT imply that the resource
   content is unchanged (only the session description) and a 304
   response to SETUP does NOT imply that the resource description is
   unchanged.  The Accept request-header MTag and If-Match headers may be used to link the
   DESCRIBE and SETUP in this manner.

17.3.5.  305 Use Proxy

   The requested resource MUST be accessed through the proxy given by
   the Location field.  The Location field can gives the URI of the proxy.
   The recipient is expected to repeat this single request via the
   proxy. 305 responses MUST only be generated by origin servers.

17.4.  Client Error 4xx

17.4.1.  400 Bad Request

   The request could not be used to specify certain
   presentation description and parameter media types [RFC4288] which
   are acceptable for understood by the response server due to DESCRIBE and GET_PARAMETER
   requests.

   See Section 20.2.3 for the malformed
   syntax.

   Example of use:
     Accept: application/example ;q=1.0, application/sdp

16.2.  Accept-Credentials  The Accept-Credentials header is a client SHOULD NOT repeat the request header used to indicate to
   any trusted intermediary how to handle further secured connections to
   proxies or servers.  See Section 19 for without
   modifications.  If the usage of this header.  It request does not have a CSeq header, the
   server MUST NOT be included include a CSeq in server the response.

17.4.2.  401 Unauthorized

   The request requires user authentication.  The response MUST include
   a WWW-Authenticate header (Section 18.56) field containing a
   challenge applicable to the requested resource.  The client requests.

   In a request MAY
   repeat the request with a suitable Authorization header MUST contain field.  If
   the method (User, Proxy, or Any) request already included Authorization credentials, then the 401
   response indicates that authorization has been refused for approving credentials selected by those
   credentials.  If the requester. 401 response contains the same challenge as the
   prior response, and the user agent has already attempted
   authentication at least once, then the user SHOULD be presented the
   message body that was given in the response, since that message body
   might include relevant diagnostic information.  HTTP access
   authentication is explained in [RFC2617].

17.4.3.  402 Payment Required

   This code is reserved for future use.

17.4.4.  403 Forbidden

   The method MUST server understood the request, but is refusing to fulfill it.
   Authorization will not help and the request SHOULD NOT be changed by any proxy, unless it is "Proxy" when a proxy MAY
   change repeated.
   If the server wishes to make public why the request has not been
   fulfilled, it SHOULD describe the reason for the refusal in the
   message body.  If the server does not wish to "user" make this information
   available to take the role of user approving each further
   hop.  If client, the method status code 404 (Not Found) can be used
   instead.

17.4.5.  404 Not Found

   The server has not found anything matching the Request-URI.  No
   indication is "User" given of whether the header contains zero condition is temporary or more of
   credentials
   permanent.  The 410 (Gone) status code SHOULD be used if the server
   knows, through some internally configurable mechanism, that an old
   resource is permanently unavailable and has no forwarding address.
   This status code is commonly used when the client accepts. server does not wish to
   reveal exactly why the request has been refused, or when no other
   response is applicable.

17.4.6.  405 Method Not Allowed

   The header may contain zero
   credentials method specified in the first RTSP request to is not allowed for the resource
   identified by the Request-URI.  The response MUST include an Allow
   header containing a RTSP server when using list of valid methods for the
   "User" method. requested resource.
   This as status code is also to be used if a request attempts to use a
   method not indicated during SETUP.

17.4.7.  406 Not Acceptable

   The resource identified by the client has request is only capable of generating
   response message bodies which have content characteristics not yet received any
   credentials
   acceptable according to accept.  Each credential MUST consist the Accept headers sent in the request.

   The response SHOULD include a message body containing a list of one URI
   identifying
   available message body characteristics and location(s) from which the proxy
   user or server, user agent can choose the hash algorithm identifier, and one most appropriate.  The message
   body format is specified by the hash over that agent's DER encoded certificate [RFC5280] media type given in
   Base64 [RFC4648].  All RTSP clients the Content-Type
   header field.  Depending upon the format and proxies MUST implement the
   SHA-256[FIPS-pub-180-2] algorithm for computation capabilities of the hash
   user agent, selection of the
   DER encoded certificate.  The SHA-256 algorithm is identified by the
   token "sha-256".

   The intention with allowing most appropriate choice MAY be performed
   automatically.  However, this specification does not define any
   standard for other hash algorithms is to enable such automatic selection.

   If the future retirement response could be unacceptable, a user agent SHOULD
   temporarily stop receipt of algorithms that are not implemented
   somewhere else than here.  Thus more data and query the definition of future algorithms user for this purpose a
   decision on further actions.

17.4.8.  407 Proxy Authentication Required

   This code is intended to be extremely limited.  A feature tag
   can be used similar to ensure 401 (Unauthorized) (Section 17.4.2), but
   indicates that support for the replacement algorithm
   exist.

   Example:
   Accept-Credentials:User
     "rtsps://proxy2.example.com/";sha-256;exaIl9VMbQMOFGClx5rXnPJKVNI=,
     "rtsps://server.example.com/";sha-256;lurbjj5khhB0NhIuOXtt4bBRH1M=

16.3.  Accept-Encoding client must first authenticate itself with the
   proxy.  The Accept-Encoding request-header proxy MUST return a Proxy-Authenticate header field is similar
   (Section 18.33) containing a challenge applicable to Accept, but
   restricts the content-codings (see Section 16.14),i.e. transformation
   codings of proxy for
   the message body, such as gzip compression, requested resource.

17.4.9.  408 Request Timeout

   The client did not produce a request within the time that are
   acceptable in the response.

   A server tests whether a content-coding is acceptable, according
   was prepared to
   an Accept-Encoding field, using these rules:

   1.  If wait.  The client MAY repeat the content-coding request without
   modifications at any later time.

17.4.10.  410 Gone

   The requested resource is one of no longer available at the content-codings listed in server and the
       Accept-Encoding field, then it is acceptable, unless it
   forwarding address is
       accompanied by a qvalue of 0.  (As defined in [H3.9], a qvalue of
       0 means "not acceptable.")

   2.  The special "*" symbol in an Accept-Encoding field matches any
       available content-coding not explicitly listed in the header
       field.

   3. known.  This condition is expected to be
   considered permanent.  If multiple content-codings are acceptable, then the acceptable
       content-coding with server does not know, or has no
   facility to determine, whether or not the highest non-zero qvalue condition is preferred.

   4.  The "identity" content-coding permanent, the
   status code 404 (Not Found) SHOULD be used instead.  This response is always acceptable, i.e. no
       transformation at all,
   cacheable unless specifically refused because the
       Accept-Encoding field includes "identity;q=0", or because indicated otherwise.

   The 410 response is primarily intended to assist the
       field includes "*;q=0" and does not explicitly include task of
   repository maintenance by notifying the
       "identity" content-coding.  If recipient that the Accept-Encoding field-value resource
   is
       empty, then only intentionally unavailable and that the "identity" encoding is acceptable.

   If server owners desire that
   remote links to that resource be removed.  Such an Accept-Encoding field event is present in a request, common
   for limited-time, promotional services and if for resources belonging to
   individuals no longer working at the
   server cannot send a response which server's site.  It is not
   necessary to mark all permanently unavailable resources as "gone" or
   to keep the mark for any length of time -- that is acceptable according left to the
   Accept-Encoding header, then
   discretion of the owner of the server.

17.4.11.  411 Length Required

   The server SHOULD send an error response
   with refuses to accept the 406 (Not Acceptable) status code.

   If no Accept-Encoding field is present in request without a request, the server defined Content-
   Length.  The client MAY
   assume that repeat the client will accept any content coding.  In this case, request if "identity" is one of the available content-codings, then the
   server SHOULD use the "identity" content-coding, unless it has
   additional information that adds a different content-coding is meaningful
   to valid
   Content-Length header field containing the client.

16.4.  Accept-Language length of the message-body
   in the request message.

17.4.12.  412 Precondition Failed

   The Accept-Language precondition given in one or more of the 'if-' request-header field is similar
   fields evaluated to Accept, but
   restricts false when it was tested on the set of natural languages that are preferred as a
   response to server.  See
   these sections for the request.  Note that 'if-' headers: If-Match Section 18.23, If-
   Modified-Since Section 18.24, and If-None-Match Section 18.25.  This
   response code allows the language specified applies client to place preconditions on the presentation description current
   resource meta information (header field data) and any reason phrases, but not thus prevent the
   media content.

   A language tag identifies a natural language spoken, written, or
   otherwise conveyed by human beings for communication of information
   requested method from being applied to a resource other human beings.  Computer languages are explicitly excluded. than the one
   intended.

17.4.13.  413 Request Message Body Too Large

   The syntax and registry of RTSP 2.0 language tags server is refusing to process a request because the same as that
   defined by [RFC5646].

   Each language-range MAY be given an associated quality value which
   represents an estimate of the user's preference for request
   message body is larger than the languages
   specified by that range. server is willing or able to process.
   The quality value defaults server MAY close the connection to "q=1".  For
   example:

      Accept-Language: da, en-gb;q=0.8, en;q=0.7

   would mean: "I prefer Danish, but will accept British English and
   other types of English."  A language-range matches a language-tag if
   it exactly equals prevent the full tag, or if it exactly equals a prefix of client from
   continuing the tag, i.e., request.

   If the primary-tag in condition is temporary, the ABNF, such server SHOULD include a Retry-
   After header field to indicate that the character
   following primary-tag it is "-". temporary and after what
   time the client MAY try again.

17.4.14.  414 Request-URI Too Long

   The special range "*", if present in server is refusing to service the Accept-Language field, matches every tag not matched by any other
   range present in request because the Accept-Language field.

      Note: Request-URI
   is longer than the server is willing to interpret.  This use rare
   condition is only likely to occur when a client has used a request
   with long query information, when the client has descended into a URI
   "black hole" of redirection (e.g., a redirected URI prefix matching rule does not imply that
      language tags are assigned
   points to languages in such a way that it suffix of itself), or when the server is
      always true that if a user understands a language with under attack by
   a certain
      tag, then this user will also understand all languages with tags client attempting to exploit security holes present in some servers
   using fixed-length buffers for which this tag is a prefix.  The prefix rule simply allows reading or manipulating the
      use of prefix tags if this Request-
   URI.

17.4.15.  415 Unsupported Media Type

   The server is refusing to service the case.

   In request because the process message
   body of selecting a language, each language-tag is assigned
   a qualification factor, i.e., if a language being supported by the
   client request is actually in a format not supported by the server and what "preference"
   level requested
   resource for the language achieves. requested method.

17.4.16.  451 Parameter Not Understood

   The quality value (q-value) recipient of the
   longest language-range request does not support one or more parameters
   contained in the field that matches request.  When returning this error message the language-tag is
   assigned as
   sender SHOULD return a message body containing the qualification factor offending
   parameter(s).

17.4.17.  452 reserved

   This error code was removed from RFC 2326 [RFC2326] as it is
   obsolete.  This error code MUST NOT be used anymore.

17.4.18.  453 Not Enough Bandwidth

   The request was refused because there was insufficient bandwidth.
   This may, for example, be the result of a particalr language-tag.
   If no language-range resource reservation
   failure.

17.4.19.  454 Session Not Found

   The RTSP session identifier in the field matches the tag, the language
   qualification factor assigned is 0.  If no Accept-Language Session header is
   present missing,
   invalid, or has timed out.

17.4.20.  455 Method Not Valid in the request, the server SHOULD assume that all languages
   are equally acceptable.  If an Accept-Language header is present,
   then all languages which are assigned a qualification factor greater
   than 0 are acceptable.

16.5.  Accept-Ranges This State

   The Accept-Ranges general-header field allows indication of the
   format supported client or server cannot process this request in the Range header. its current
   state.  The client response MUST include the contain an Allow header in SETUP requests to indicate which formats it support to
   receive in PLAY and PAUSE responses, and REDIRECT requests. make error
   recovery possible.

17.4.21.  456 Header Field Not Valid for Resource

   The server MUST include could not act on a required request header.  For example,
   if PLAY contains the Range header in SETUP and 456 field but the stream does not allow
   seeking.  This error responses to
   indicate message may also be used for specifying when the formats supported
   time format in Range is impossible for the resource indicated by resource.  In that case
   the
   request URI.  The Accept-Ranges header MAY be included in GET_PARAMETER request and
   response pairs.  The GET_PARAMETER request MUST contain a Session
   header be returned to identify the session context inform the request is related to.
   The requester and responder will indicate their capabilities
   regarding client of
   which format(s) that are allowed.

17.4.22.  457 Invalid Range formats respectively.

      Accept-Ranges: NPT, SMPTE

   The syntax Range value given is defined in Section 20.2.3.

16.6.  Allow

   The Allow message-header field lists the methods supported by out of bounds, e.g., beyond the
   resource identified by end of the Request-URI.
   presentation.

17.4.23.  458 Parameter Is Read-Only

   The purpose of this field is parameter to strictly inform be set by SET_PARAMETER can be read but not
   modified.  When returning this error message the recipient of valid methods associated with sender SHOULD return
   a message body containing the
   resource.  An Allow header field MUST offending parameter(s).

17.4.24.  459 Aggregate Operation Not Allowed

   The requested method may not be applied on the URI in question since
   it is an aggregate (presentation) URI.  The method may be present in applied on
   a 405 (Method Not
   Allowed) response. media URI.

17.4.25.  460 Only Aggregate Operation Allowed

   The Allow header MUST also requested method may not be present applied on the URI in all
   OPTIONS responses where question since
   it is not an aggregate control (presentation) URI.  The method may be
   applied on the content of aggregate control URI.

17.4.26.  461 Unsupported Transport

   The Transport field did not contain a supported transport
   specification.

17.4.27.  462 Destination Unreachable

   The data transmission channel could not be established because the header will
   client address could not include
   exactly be reached.  This error will most likely be
   the same methods as listed result of a client attempt to place an invalid dest_addr
   parameter in the Public header. Transport field.

17.4.28.  463 Destination Prohibited

   The Allow MUST also be included in SETUP and DESCRIBE responses, if data transmission channel was not established because the methods allowed for server
   prohibited access to the resource client address.  This error is different than most likely
   the complete
   set of methods defined in this memo.

   Example result of use:
      Allow: SETUP, PLAY, SET_PARAMETER, DESCRIBE

16.7.  Authorization

   An RTSP a client that wishes attempt to authenticate itself redirect media traffic to another
   destination with a server using
   authentication mechanism from HTTP [RFC2617] , usually, but not
   necessarily, after receiving a 401 response, does so by including an
   Authorization request-header field with dest_addr parameter in the request. Transport header.

17.4.29.  464 Data Transport Not Ready Yet

   The
   Authorization field value consists of credentials containing data transmission channel to the
   authentication information of media destination is not yet
   ready for carrying data.  However, the user responding agent for still expects
   that the realm of data transmission channel will be established at some point
   in time.  Note, however, that this may result in a permanent failure
   like 462 "Destination Unreachable".

   An example when this error may occur is in the
   resource being requested.

   If case a client sends a
   PLAY request is authenticated and to a realm specified, server prior to ensuring that the same
   credentials SHOULD be valid TCP connections
   negotiated for all other requests within carrying media data was successfully established (In
   violation of this realm
   (assuming specification).  The server would use this error
   code to indicate that the authentication scheme itself does requested action could not require
   otherwise, such as credentials that vary according be performed due
   to a challenge
   value or using synchronized clocks).

   When a shared cache (see Section 18) receives a request containing an
   Authorization field, it MUST NOT return the corresponding response as
   a reply to any other request, unless one failure of completing the following specific
   exceptions holds:

   1.  If the response includes the "max-age" cache-control directive,
       the cache MAY use connection establishment.

17.4.30.  465 Notification Reason Unknown

   This indicates that response in replying to the client has received a subsequent
       request.  But (if PLAY_NOTIFY
   (Section 13.5) with a Notify-Reason header (Section 18.31) unknown to
   the specified maximum age client.

17.4.31.  466 Key Management Error

   This indicates that there has passed) been an error in a proxy
       cache MUST first revalidate it Key Management
   function used in conjunction with a request.  For example usage of
   MIKEY [RFC3830] according to Appendix C.1.4.1 may result in this
   error.

17.4.32.  470 Connection Authorization Required

   The secured connection attempt needs user or client authorization
   before proceeding.  The next hops certificate is included in this
   response in the origin server, using Accept-Credentials header.

17.4.33.  471 Connection Credentials not accepted

   When performing a secure connection over multiple connections, an
   intermediary has refused to connect to the
       request-headers from next hop and carry out the new
   request due to allow unacceptable credentials for the origin server used policy.

17.4.34.  472 Failure to establish secure connection

   A proxy fails to establish a secure connection to authenticate the new request.  (This next hop RTSP
   agent.  This is primarily caused by a fatal failure at the defined behavior TLS
   handshake, for max-age.)  If example due to server not accepting any cipher suites.

17.5.  Server Error 5xx

   Response status codes beginning with the response includes "max-age=0", digit "5" indicate cases in
   which the proxy
       MUST always revalidate server is aware that it before re-using it.

   2.  If the response includes has erred or is incapable of
   performing the "must-revalidate" cache-control
       directive, request The server SHOULD include a message body
   containing an explanation of the cache MAY use that response in replying to error situation, and whether it is a
       subsequent request.  But if
   temporary or permanent condition.  User agents SHOULD display any
   included message body to the user.  These response is stale, all caches
       MUST first revalidate codes are
   applicable to any request method.

17.5.1.  500 Internal Server Error

   The server encountered an unexpected condition which prevented it with the origin server, using the
       request-headers
   from fulfilling the new request to allow the origin request.

17.5.2.  501 Not Implemented

   The server does not support the functionality required to authenticate fulfill the new
   request.

   3.  If  This is the appropriate response includes when the "public" cache-control directive, server does not
   recognize the request method and is not capable of supporting it
       MAY be returned in reply to for
   any subsequent request.

16.8.  Bandwidth resource.

17.5.3.  502 Bad Gateway

   The Bandwidth request-header field describes the estimated bandwidth
   available to the client, expressed server, while acting as a positive integer and measured
   in kilobits per second.  The bandwidth available to the client may
   change during gateway or proxy, received an RTSP session, e.g., due to mobility, congestion,
   etc.

   Clients may not be able to accurately determine invalid
   response from the available
   bandwidth, for example due upstream server it accessed in attempting to that first hop is not a bottleneck.
   For example most local area networks (LAN) will not be a bottleneck
   if
   fulfill the request.

17.5.4.  503 Service Unavailable

   The server is not in the same LAN.  Thus link speeds of WLAN or
   Ethernet networks are normally not a basis for estimating currently unable to handle the
   available bandwidth.  Cellular devices or other devices directly
   connected request due to a modem
   temporary overloading or connection enabling device may more
   accurately estimate the bottleneck bandwidth and what is reasonable
   share maintenance of it for RTSP controlled media.  The client will also need to
   take into account other traffic sharing the bottleneck.  For example
   by only assigning a certain fraction to RTSP and its media streams.
   It server.  The implication
   is RECOMMENDED that only clients that has accurate and explicit
   information about bandwidth bottlenecks uses this header.

   This header is not a substitute for proper congestion control.  Only a method providing an initial estimate and coarsely determine if the
   selected content can temporary condition which will be delivered at all.

   Example:
     Bandwidth: 62360

16.9.  Blocksize

   The Blocksize request-header field alleviated after
   some delay.  If known, the length of the delay MAY be indicated in a
   Retry-After header.  If no Retry-After is sent from given, the client to the
   media server asking SHOULD
   handle the server response as it would for a particular media packet size.
   This packet size 500 response.  The client MUST
   honor the length, if given in the Retry-After header.

         Note: The existence of the 503 status code does not include lower-layer headers such as IP,
   UDP, or RTP.  The imply that
         a server is free to must use a blocksize which is lower
   than it when becoming overloaded.  Some servers
         may wish to simply refuse the one requested. connection.

17.5.5.  504 Gateway Timeout

   The server MAY truncate this packet size to server, while acting as a proxy, did not receive a timely
   response from the closest multiple of upstream server specified by the minimum, media-specific block size, URI or
   override some other
   auxiliary server (e.g., DNS) it with needed to access in attempting to
   complete the media-specific size if necessary. request.

17.5.6.  505 RTSP Version Not Supported

   The block
   size MUST be a positive decimal number, measured server does not support, or refuses to support, the RTSP protocol
   version that was used in octets. the request message.  The server only returns an error (4xx) if the value is syntactically
   invalid.

16.10.  Cache-Control

   The Cache-Control general-header field
   indicating that it is used unable or unwilling to specify directives complete the request
   using the same major version as the client other than with this error
   message.  The response SHOULD contain a message body describing why
   that MUST be obeyed version is not supported and what other protocols are supported
   by all caching mechanisms along that server.

17.5.7.  551 Option not supported

   A feature-tag given in the request/
   response chain.

   Cache directives Require or the Proxy-Require fields was
   not supported.  The Unsupported header MUST be passed through by a proxy or gateway
   application, regardless returned stating the
   feature for which there is no support.

18.  Header Field Definitions

       +---------------+----------------+--------+---------+------+
       | method        | direction      | object | acronym | Body |
       +---------------+----------------+--------+---------+------+
       | DESCRIBE      | C -> S         | P,S    | DES     | r    |
       |               |                |        |         |      |
       | GET_PARAMETER | C -> S, S -> C | P,S    | GPR     | R,r  |
       |               |                |        |         |      |
       | OPTIONS       | C -> S, S -> C | P,S    | OPT     |      |
       |               |                |        |         |      |
       | PAUSE         | C -> S         | P,S    | PSE     |      |
       |               |                |        |         |      |
       | PLAY          | C -> S         | P,S    | PLY     |      |
       |               |                |        |         |      |
       | PLAY_NOTIFY   | S -> C         | P,S    | PNY     | R    |
       |               |                |        |         |      |
       | REDIRECT      | S -> C         | P,S    | RDR     |      |
       |               |                |        |         |      |
       | SETUP         | C -> S         | S      | STP     |      |
       |               |                |        |         |      |
       | SET_PARAMETER | C -> S, S -> C | P,S    | SPR     | R,r  |
       |               |                |        |         |      |
       | TEARDOWN      | C -> S         | P,S    | TRD     |      |
       |               |                |        |         |      |
       |               | S -> C         | P      | TRD     |      |
       +---------------+----------------+--------+---------+------+

   Table 8: Overview of RTSP methods, their significance to that application,
   since the directives may be applicable to all recipients along the
   request/response chain.  It direction, and what objects
   (P: presentation, S: stream) they operate on. Body notes if a method
       is not possible allowed to specify a cache-
   directive for a specific cache.

   Cache-Control should only be specified in a DESCRIBE, GET_PARAMETER,
   SET_PARAMETER and SETUP request carry body and its response. in which direction, R = Request,
   r=response. Note: Cache-
   Control does not govern only the caching of responses as It is allowed for HTTP,
   instead it also applies all error messages 4xx and 5xx to the media stream identified by the SETUP
   request.
                                have a body

   The RTSP requests are generally not cacheable, general syntax for further
   information see Section 18.  Below header fields is the description of the cache
   directives that can be included covered in the Cache-Control header.

   no-cache:  Indicates that the media stream MUST NOT be cached
         anywhere. Section 5.2.  This allows an origin server to prevent caching even
         by caches that have been configured to return stale responses
         to client requests.  Note, there is no security function
         enforcing that the content can't be cached.

   public:  Indicates that the media stream is cacheable by any cache.

   private:  Indicates that the media stream is intended for a single
         user and MUST NOT be cached by a shared cache.  A private (non-
         shared) cache may cache the media streams.

   no-transform:  An intermediate cache (proxy) may find it useful to
         convert the media type of a certain stream.  A proxy might, for
         example, convert between video formats to save cache space or
         to reduce
   section lists the amount full set of traffic header fields along with notes on a slow link.  Serious
         operational problems may occur, however, when these
         transformations have been applied to streams intended for
         certain kinds of applications.  For example, applications for
         medical imaging, scientific data analysis
   meaning, and those using end-
         to-end authentication all depend on receiving a stream that is
         bit-for-bit identical to the original media stream.  Therefore,
         if a response includes the no-transform directive, an
         intermediate cache or proxy MUST NOT change the encoding of the
         stream.  Unlike HTTP, RTSP does not provide usage.  The syntax definition for partial
         transformation at header fields are
   present in Section 20.2.3.  Throughout this point, e.g., allowing translation into a
         different language.

   only-if-cached:  In some cases, such as times of extremely poor
         network connectivity, a client may want a cache section, we use [HX.Y] to return only
         those media streams that it currently has stored, and not
   informational refer to
         receive these from the origin server.  To do this, the client
         may include the only-if-cached directive in a request.  If it
         receives this directive, a cache SHOULD either respond using a
         cached media stream that is consistent with the other
         constraints Section X.Y of the request, or respond with a 504 (Gateway
         Timeout) status.  However, if a group of caches is being
         operated as a unified system with good internal connectivity,
         such a request MAY be forwarded within that group current HTTP/1.1
   specification RFC 2616 [RFC2616].  Examples of caches.

   max-stale:  Indicates that the client is willing each header field are
   given.

   Information about header fields in relation to accept a media
         stream that has exceeded its expiration time.  If max-stale methods and proxy
   processing is
         assigned a value, then summarized in Table 9, Table 10, Table 11, and
   Table 12.

   The "where" column describes the client is willing to accept a request and response that has exceeded its expiration time by no more than types in which
   the specified number of seconds.  If no header field can be used.  Values in this column are:

   R:    header field may only appear in requests;

   r:    header field may only appear in responses;

   2xx, 4xx, etc.:  A numerical value is assigned to
         max-stale, then the client is willing to accept a stale or range indicates response of any age.

   min-fresh:  Indicates that codes
         with which the client header field can be used;

   c:    header field is willing copied from the request to accept a media
         stream whose freshness lifetime is no less than its current age
         plus the specified time response.

   An empty entry in seconds.  That is, the client wants
         a response "where" column indicates that will still be fresh for at least the specified
         number of seconds.

   must-revalidate:  When the must-revalidate directive is header field
   may be present in both requests and responses.

   The "proxy" column describes the operations a
         SETUP response received by proxy may perform on a cache,
   header field.  An empty proxy column indicates that cache the proxy MUST
   NOT use do any changes to that header, all allowed operations are
   explicitly stated:

   a:    A proxy can add or concatenate the
         entry after it becomes stale header field if not present.

   m:    A proxy can modify an existing header field value.

   d:    A proxy can delete a header field value.

   r:    A proxy needs to respond be able to a subsequent request
         without first revalidating it with read the origin server.  That is, header field, and thus
         this header field cannot be encrypted.

   The rest of the cache is required columns relate to do an end-to-end revalidation every
         time, if, based solely the presence of a header field in a
   method.  The method names when abbreviated, are according to Table 8:

   c:    Conditional; requirements on the origin server's Expires, header field depend on the
         cached response
         context of the message.

   m:    The header field is stale.

   proxy-revalidate: mandatory.

   m*:   The proxy-revalidate directive has the same
         meaning as the must-revalidate directive, except that it does
         not apply to non-shared user agent caches.  It can header field SHOULD be used on a
         response to an authenticated request sent, but clients/servers need to permit the user's cache be
         prepared to store and later return the response receive messages without needing to
         revalidate it (since it has already been authenticated once by
         that user), while still requiring proxies that service many
         users to revalidate each time (in order to make sure that each
         user has been authenticated).  Note header field.

   o:    The header field is optional.

   *:    The header field MUST be present if the message body is not
         empty.  See Section 18.16, Section 18.18 and Section 5.3 for
         details.

   -:    The header field is not applicable.

   "Optional" means that a Client/Server MAY include the header field in
   a request or response.  The Client/Server behavior when receiving
   such authenticated
         responses also need headers varies, for some it may ignore the public cache control directive header field, in order
         to allow them
   other cases it is a request to be cached at all.

   max-age:  When an intermediate cache process the header.  This is forced, regulated
   by means the method and header descriptions.  Example of headers that
   require processing are the Require and Proxy-Require header fields
   discussed in Section 18.41 and Section 18.35.  A "mandatory" header
   field MUST be present in a max-
         age=0 directive, to revalidate its own cache entry, request, and MUST be understood by the
         client has supplied its own validator
   Client/Server receiving the request.  A mandatory response header
   field MUST be present in the request, response, and the
         supplied validator might differ from header field MUST be
   understood by the validator currently
         stored with Client/Server processing the cache entry.  In this case, response.  "Not
   applicable" means that the cache MAY use
         either validator header field MUST NOT be present in making its own request without affecting
         semantic transparency.

   However, the choice of validator might affect performance.  The best
   approach is for the intermediate cache to use its own validator when
   making its a
   request.  If one is placed in a request by mistake, it MUST be
   ignored by the server replies with 304 (Not Modified),
   then the cache can return its now validated copy to Client/Server receiving the client with request.  Similarly, a
   200 (OK) response.  If the server replies with
   header field labeled "not applicable" for a new message body and
   cache validator, however, the intermediate cache can compare response means that the
   returned validator with
   Client/Server MUST NOT place the one provided header field in the client's request,
   using the strong comparison function.  If the client's validator is
   equal to the origin server's, then response, and
   the intermediate cache simply
   returns 304 (Not Modified).  Otherwise, it returns Client/Server MUST ignore the new message
   body with a 200 (OK) response.

16.11.  Connection

   The Connection general-header header field allows in the sender to specify
   options response.

   An RTSP agent MUST ignore extension headers that are desired for that particular connection not understood.

   The From and Location header fields contain an URI.  If the URI
   contains a comma, or semicolon, the URI MUST NOT be communicated by proxies over further connections.

   RTSP 2.0 proxies MUST parse enclosed in double
   quotes (").  Any URI parameters are contained within these quotes.
   If the Connection header field before a
   message URI is forwarded and, for each connection-token not enclosed in this field,
   remove double quote, any header field(s) from the message with the same name as the
   connection-token. semicolon-delimited
   parameters are header-parameters, not URI parameters.

   +------------------+-------+-----+----+-----+-----+-----+-----+-----+
   | Header           | Where | Pro | DE | OPT | STP | PLY | PSE | TRD |
   |                  |       | xy  | S  |     |     |     |     |     |
   +------------------+-------+-----+----+-----+-----+-----+-----+-----+
   | Accept           | R     |     | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Credentia | R     | rm  | o  | o   | o   | o   | o   | o   |
   | ls               |       |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Encoding  | R     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Language  | R     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | R     | r   | -  | -   | m   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | r     | r   | -  | -   | m   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Accept-Ranges    | 456   | r   | -  | -   | -   | m   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Allow            | r     | am  | c  | c   | c   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Allow            | 405   | am  | m  | m   | m   | m   | m   | m   |
   |                  |       |     |    |     |     |     |     |     |
   | Authorization    | R     |     | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | Bandwidth        | R     |     | o  | o   | o   | o   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Blocksize        | R     |     | o  | -   | o   | o   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Cache-Control    |       | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Connection options are signaled by the presence       |       | ad  | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | Connection-Crede | 470,4 | ar  | o  | o   | o   | o   | o   | o   |
   | ntials           | 07    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Base     | r     |     | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Base     | 4xx,5 |     | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | R     | r   | -  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Encoding | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | R     | r   | -  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Language | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Length   | r     | r   | *  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Length   | 4xx,5 | r   | *  | *   | *   | *   | *   | *   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Location | r     | r   | o  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Location | 4xx,5 | r   | o  | o   | o   | o   | o   | o   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Type     | r     | r   | *  | -   | -   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Content-Type     | 4xx,5 | ar  | *  | *   | *   | *   | *   | *   |
   |                  | xx    |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | CSeq             | Rc    | rm  | m  | m   | m   | m   | m   | m   |
   |                  |       |     |    |     |     |     |     |     |
   | Date             |       | am  | o/ | o/* | o/* | o/* | o/* | o/* |
   |                  |       |     | *  |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | Expires          | r     | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | From             | R     | r   | o  | o   | o   | o   | o   | o   |
   |                  |       |     |    |     |     |     |     |     |
   | If-Match         | R     | r   | -  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | If-Modified-Sinc | R     | r   | o  | -   | o   | -   | -   | -   |
   | e                |       |     |    |     |     |     |     |     |
   |                  |       |     |    |     |     |     |     |     |
   | If-None-Match    | R     | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Last-Modified    | r     | r   | o  | -   | o   | -   | -   | -   |
   |                  |       |     |    |     |     |     |     |     |
   | Location         | 3rr   |     | o  | o   | o   | o   | o   | o   |
   +------------------+-------+-----+----+-----+-----+-----+-----+-----+

     Table 9: Overview of
   a connection-token in the Connection header field, not by any
   corresponding additional header field(s), since the additional header
   field may not be sent if there are no parameters associated with that
   connection option.

   Message headers listed in the Connection header MUST NOT include end-
   to-end headers, such as Cache-Control. RTSP 2.0 defines the "close" connection option for the sender to
   signal that the connection will be closed after completion of the
   response.  For example, Connection: close in either the request or
   the response header fields indicates that the connection SHOULD NOT
   be considered `persistent' (Section 10.2) after the current request/
   response is complete.

   The use of the connection option "close" in RTSP messages SHOULD be
   limited to error messages when the server is unable (A-L) related to recover methods
           DESCRIBE, OPTIONS, SETUP, PLAY, PAUSE, and
   therefore see it necessary to close the connection.  The reason is
   that the client has the choice of continuing using a connection
   indefinitely, as long as it sends valid messages.

16.12.  Connection-Credentials

   The Connection-Credentials response header is used to carry the chain
   of credentials TEARDOWN.

   +----------------+-------+------+-----+-----+-----+-----+-----+-----+
   | Header         | Where | Prox | DES | OPT | STP | PLY | PSE | TRD |
   |                |       | y    |     |     |     |     |     |     |
   +----------------+-------+------+-----+-----+-----+-----+-----+-----+
   | Media-         |       |      | -   | -   | m   | m   | m   | -   |
   | Properties     |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Media-Range    |       |      | -   | -   | m   | m   | m   | -   |
   |                |       |      |     |     |     |     |     |     |
   | MTag           | r     | r    | o   | -   | o   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Pipelined-Requ |       | amdr | -   | o   | o   | o   | o   | o   |
   | ests           |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | 407   | amr  | m   | m   | m   | m   | m   | m   |
   | Authenticate   |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | R     | rd   | o   | o   | o   | o   | o   | o   |
   | Authorization  |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Proxy- Require | R     | ar   | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Proxy- Require | r     | r    | c   | c   | c   | c   | c   | c   |
   |                |       |      |     |     |     |     |     |     |
   | Proxy-         | R     | amr  | c   | c   | c   | c   | c   | c   |
   | Supported      |       |      |     |     |     |     |     |     |
   | Proxy-         | r     |      | c   | c   | c   | c   | c   | c   |
   | Supported      |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Public         | r     | amr  | -   | m   | -   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Public         | 501   | amr  | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Range          | R     |      | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Range          | r     |      | -   | -   | c   | m   | m   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Referrer       | R     |      | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Request-       | R     |      | -   | -   | -   | -   | -   | -   |
   | Status         |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Require        | R     |      | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Retry-After    | 3rr,5 |      | o   | o   | o   | o   | o   | -   |
   |                | 03    |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Retry-After    | 413   |      | o   | -   | -   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | RTP-Info       | r     |      | -   | -   | c   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Scale          | R     | r    | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Scale          | r     | amr  | -   | -   | -   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Seek-Style     | R     |      | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Seek-Style     | r     |      | -   | -   | -   | m   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Server         | R     | r    | -   | o   | -   | -   | -   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Server         | r     | r    | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Session        | R     | r    | -   | o   | o   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Session        | r     | r    | -   | c   | m   | m   | m   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Speed          | R     | admr | -   | -   | -   | o   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Speed          | r     | admr | -   | -   | -   | c   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Supported      | R     | amr  | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Supported      | r     | amr  | c   | c   | c   | c   | c   | c   |
   | Terminate-Reas | R     | r    | -   | -   | -   | -   | -   | -   |
   | on             |       |      |     |     |     |     |     |     |
   |                |       |      |     |     |     |     |     |     |
   | Timestamp      | R     | admr | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Timestamp      | c     | admr | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | Transport      |       | mr   | -   | -   | m   | -   | -   | -   |
   |                |       |      |     |     |     |     |     |     |
   | Unsupported    | r     |      | c   | c   | c   | c   | c   | c   |
   |                |       |      |     |     |     |     |     |     |
   | User-Agent     | R     |      | m*  | m*  | m*  | m*  | m*  | m*  |
   |                |       |      |     |     |     |     |     |     |
   | Via            | R     | amr  | o   | o   | o   | o   | o   | o   |
   |                |       |      |     |     |     |     |     |     |
   | Via            | c     | dr   | m   | m   | m   | m   | m   | m   |
   |                |       |      |     |     |     |     |     |     |
   | WWW-           | 401   |      | m   | m   | m   | m   | m   | m   |
   | Authenticate   |       |      |     |     |     |     |     |     |
   +----------------+-------+------+-----+-----+-----+-----+-----+-----+

     Table 10: Overview of any next hop that need to be approved by the
   requester.  It MUST only be used in server to client responses.

   The Connection-Credentials header in an RTSP response MUST, if
   included, contain the credential information (in form of a list of
   certificates providing the chain of certification) of the next hop
   that an intermediary needs to securely connect to.  The header MUST
   include the URI of the next hop (proxy or server) and a base64
   [RFC4648] encoded binary structure containing a sequence of DER
   encoded X.509v3 certificates[RFC5280] .

   The binary structure starts with the number of certificates
   (NR_CERTS) included as a 16 bit unsigned integer.  This is followed
   by NR_CERTS number of 16 bit unsigned integers providing the size in
   octets of each DER encoded certificate.  This is followed by NR_CERTS
   number of DER encoded X.509v3 certificates in a sequence (chain).
   The proxy or server's certificate must come first in the structure.
   Each following certificate must directly certify the one preceding
   it.  Because certificate validation requires that root keys be
   distributed independently, the self-signed certificate which
   specifies the root certificate authority may optionally be omitted
   from the chain, under the assumption that the remote end must already
   possess it in order fields (M-W) related to validate it in any case.

   Example:

   Connection-Credentials:"rtsps://proxy2.example.com/";MIIDNTCC... methods
           DESCRIBE, OPTIONS, SETUP, PLAY, PAUSE, and TEARDOWN.

   +------------------------+---------+-------+-----+-----+-----+-----+
   | Header                 | Where MIIDNTCC... is   | Proxy | GPR | SPR | RDR | PNY |
   +------------------------+---------+-------+-----+-----+-----+-----+
   | Accept                 | R       | arm   | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Credentials     | R       | rm    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Encoding        | R       | r     | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Language        | R       | r     | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Accept-Ranges          |         | rm    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Allow                  | 405     | amr   | m   | m   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Authorization          | R       |       | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Bandwidth              | R       |       | -   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Blocksize              | R       |       | -   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Cache-Control          |         | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Connection             |         |       | o   | o   | o   | o   |
   | Connection-Credentials | 470,407 | ar    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | R       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | r       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Base           | 4xx,5xx |       | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | R       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | r       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Encoding       | 4xx,5xx | r     | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | R       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | r       | r     | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Language       | 4xx,5xx | r     | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | R       | r     | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | r       | r     | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Length         | 4xx,5xx | r     | *   | *   | *   | *   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | R       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | r       |       | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Location       | 4xx,5xx |       | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | R       |       | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | r       |       | *   | *   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Content-Type           | 4xx,5xx |       | *   | *   | *   | *   |
   |                        |         |       |     |     |     |     |
   | CSeq                   | R,c     | mr    | m   | m   | m   | m   |
   |                        |         |       |     |     |     |     |
   | Date                   | R       | a BASE64 encoding of the following structure:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Number of certificates o   | o   | m   | o   |
   |                        |         |       |     |     |     |     |
   | Date                   | r       | am    | o   | o   | o   | o   |
   |                        |         |       |     |     |     |     |
   | Expires                | r       | r     | -   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | From                   | R       | r     | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | If-Match               | R       | r     | -   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | If-Modified-Since      | R       | am    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | If-None-Match          | R       | am    | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Last-Modified          | R       | r     | -   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Last-Modified          | r       | r     | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Location               | 3rr     |       | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Location               | R       |       | -   | -   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Media-Properties       | R       | amr   | o   | -   | -   | c   |
   |                        |         |       |     |     |     |     |
   | Media-Properties       | r       | mr    | c   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Media-Range            | R       |       | o   | -   | -   | c   |
   |                        |         |       |     |     |     |     |
   | Media-Range            | r       |       | c   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | MTag                   | r       | r     | o   | -   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Notify-Reason          | R       |       | -   | -   | -   | m   |
   |                        |         |       |     |     |     |     |
   | Pipelined-Requests     | R       | amdr  | o   | o   | -   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Authenticate     | 407     | amr   | m   | m   | m   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Authorization    | R       | rd    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Require          | R       | ar    | o   | o   | o   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Require          | r       | r     | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Supported        | R       | amr   | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Proxy-Supported        | r       |       | c   | c   | c   | -   |
   |                        |         |       |     |     |     |     |
   | Public                 | 501     | admr  | m   | m   | m   | -   |
   +------------------------+---------+-------+-----+-----+-----+-----+

     Table 11: Overview of RTSP header fields (A-P) related to methods
         GET_PARAMETER, SET_PARAMETER, REDIRECT, and PLAY_NOTIFY.

      +------------------+---------+-------+-----+-----+-----+-----+
      | Header           | Where   | Proxy | GPR | SPR | RDR | PNY |
      +------------------+---------+-------+-----+-----+-----+-----+
      | Range            | R       |       | o   | -   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Referrer         | R       |       | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Request-Status   | R       |       | -   | -   | -   | c   |
      |                  |         |       |     |     |     |     |
      | Require          | R       | r     | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Retry-After      | 3rr,503 |       | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Retry-After      | 413     |       | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | RTP-Info         | R       | r     | o   | -   | -   | C   |
      |                  |         |       |     |     |     |     |
      | RTP-Info         | r       | r     | c   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Scale            |         |       | -   | -   | -   | c   |
      |                  |         |       |     |     |     |     |
      | Seek-Style       |         |       | -   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Server           | R       | r     | o   | o   | o   | o   |
      |                  |         |       |     |     |     |     |
      | Server           | r       | r     | o   | o   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Session          | R       | r     | o   | o   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Session          | r       | r     | c   | c   | o   | m   |
      |                  |         |       |     |     |     |     |
      | Speed            |         |       | -   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Supported        | R       | adrm  | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Supported        | r       | adrm  | c   | c   | c   | -   |
      |                  |         |       |     |     |     |     |
      | Terminate-Reason | R       | r     | -   | -   | m   | -   |
      |                  |         |       |     |     |     |     |
      | Timestamp        | R       | adrm  | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Timestamp        | c       | adrm  | m   | m   | m   | -   |
      |                  |         |       |     |     |     |     |
      | Transport        |         | mr    | -   | -   | -   | -   |
      |                  |         |       |     |     |     |     |
      | Size of certificate #1 Unsupported      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ r       | Size of certificate #2 arm   | Size of certificate #3 c   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #1                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #2                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #3                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

16.13.  Content-Base

   The Content-Base message-header field may be used to specify the base
   URI for resolving relative URIs within the message body.

   Content-Base: rtsp://media.example.com/movie/twister/

   If no Content-Base field is present, the base URI of an message body
   is defined either by its Content-Location (if that Content-Location
   URI is an absolute URI) or the URI used to initiate the request, in
   that order of precedence.  Note, however, that the base URI of the
   contents within the message-body may be redefined within that
   message-body.

16.14.  Content-Encoding

   The Content-Encoding header field is used as a modifier to the media-
   type.  When present, its value indicates what additional content
   codings have been applied to the message body, and thus what decoding
   mechanisms must be applied in order to obtain the media-type
   referenced by the Content-Type header field.  Content-Encoding is
   primarily used to allow a document to be compressed without losing
   the identity of its underlying media type.

   The content-coding is a characteristic of the message body identified
   by the Request-URI.  Typically, the message body is stored with this
   encoding and is only decoded before rendering or analogous usage.
   However, a non-transparent proxy MAY modify the content-coding if the
   new coding is known to be acceptable to the recipient, unless the
   "no-transform" cache-control directive is present in the message.

   If the content-coding of a message body is not "identity", then the
   response MUST include a Content-Encoding Message-body header that
   lists the non-identity content-coding(s) used.

   If the content-coding of a message body in a request message is not
   acceptable to the origin server, the server SHOULD respond with a
   status code of 415 (Unsupported Media Type).

   If multiple encodings have been applied to a message body, the
   content codings MUST be listed in the order in which they were
   applied, first to last from left to right.  Additional information
   about the encoding parameters MAY be provided by other header fields
   not defined by this specification.

16.15.  Content-Language

   The Content-Language header field describes the natural language(s)
   of the intended audience for the enclosed message body.  Note that
   this might not be equivalent to all the languages used within the
   message body.

   Language tags are mentioned in Section 16.4.  The primary purpose c   | c   | -   |
      |                  |         |       |     |     |     |     |
      | User-Agent       | R       | r     | m*  | m*  | -   | -   |
      | User-Agent       | r       | r     | m*  | m*  | m*  | m*  |
      |                  |         |       |     |     |     |     |
      | Via              | R       | amr   | o   | o   | o   | -   |
      |                  |         |       |     |     |     |     |
      | Via              | c       | dr    | m   | m   | m   | -   |
      |                  |         |       |     |     |     |     |
      | WWW-Authenticate | 401     |       | m   | m   | m   | -   |
      +------------------+---------+-------+-----+-----+-----+-----+

     Table 12: Overview of
   Content-Language is to allow a user RTSP header fields (R-W) related to identify methods
         GET_PARAMETER, SET_PARAMETER,  REDIRECT, and differentiate
   entities according to the user's own preferred language.  Thus, if
   the body content is intended only for a Danish-literate audience, the
   appropriate PLAY_NOTIFY.

18.1.  Accept

   The Accept request-header field is

      Content-Language: da

   If no Content-Language is specified, the default is that the content
   is intended for all language audiences.  This might mean that the
   sender does not consider it to can be specific used to any natural language,
   or that the sender does not know for specify certain
   presentation description and parameter media types [RFC4288] which language it is intended.

   Multiple languages MAY be listed for content that is intended
   are acceptable for
   multiple audiences.  For example, a rendition of the "Treaty of
   Waitangi," presented simultaneously in the original Maori response to DESCRIBE and English
   versions, would call GET_PARAMETER
   requests.

   See Section 20.2.3 for

      Content-Language: mi, en

   However, just because multiple languages are present within a message
   body does not mean that it the syntax.

   Example of use:
     Accept: application/example ;q=1.0, application/sdp

18.2.  Accept-Credentials

   The Accept-Credentials header is intended for multiple linguistic
   audiences.  An example would be a beginner's language primer, such as
   "A First Lesson in Latin," which is clearly intended to be request header used by an
   English-literate audience.  In this case, the Content-Language would
   properly only include "en".

   Content-Language MAY be applied to indicate to
   any media type -- it is not
   limited trusted intermediary how to textual documents.

16.16.  Content-Length

   The Content-Length general-header field contains the length of handle further secured connections to
   proxies or servers.  See Section 19 for the
   message body usage of the RTSP message (i.e. after the double CRLF
   following the last header).  Unlike HTTP, it this header.  It
   MUST NOT be included in all
   messages that carry server to client requests.

   In a message body beyond request the header portion of MUST contain the
   RTSP message.  If it is missing, a default value of zero is assumed.
   Any Content-Length greater than method (User, Proxy, or equal to zero Any)
   for approving credentials selected by the requester.  The method MUST
   NOT be changed by any proxy, unless it is "Proxy" when a valid value.

16.17.  Content-Location

   The Content-Location header field proxy MAY be used
   change it to supply the resource
   location for "user" to take the message body enclosed in role of user approving each further
   hop.  If the message when that body method is accessible from a location separate from the requested resource's
   URI.  A server SHOULD provide a Content-Location for "User" the variant
   corresponding to header contains zero or more of
   credentials that the response message body; especially client accepts.  The header may contain zero
   credentials in the case
   where first RTSP request to a resource has multiple variants associated with it, and those
   entities actually have separate locations by which they might be
   individually accessed, the RTSP server SHOULD provide a Content-Location
   for when using the particular variant which is returned.

   The Content-Location value is not a replacement for
   "User" method.  This as the original
   requested URI; it is only a statement client has not yet received any
   credentials to accept.  Each credential MUST consist of one URI
   identifying the location of proxy or server, the hash algorithm identifier, and
   the resource
   corresponding to this particular variant at hash over that agent's DER encoded certificate [RFC5280] in
   Base64 [RFC4648].  All RTSP clients and proxies MUST implement the time
   SHA-256[FIPS-pub-180-2] algorithm for computation of the request.
   Future requests MAY specify the Content-Location URI as hash of the request
   URI if
   DER encoded certificate.  The SHA-256 algorithm is identified by the desire
   token "sha-256".

   The intention with allowing for other hash algorithms is to identify enable
   the source future retirement of algorithms that particular
   variant.  This is useful if the RTSP agent desires to verify if are not implemented
   somewhere else than here.  Thus the
   resource variant definition of future algorithms
   for this purpose is current through a conditional request.

   A cache cannot assume that a message body with a Content-Location
   different from the URI used intended to retrieve it can be used to respond to
   later requests on that Content-Location URI.  However, the Content-
   Location extremely limited.  A feature tag
   can be used to differentiate between multiple variants
   retrieved from a single requested resource.

   If the Content-Location is a relative URI, ensure that support for the relative URI replacement algorithm
   exist.

   Example:
   Accept-Credentials:User
     "rtsps://proxy2.example.com/";sha-256;exaIl9VMbQMOFGClx5rXnPJKVNI=,
     "rtsps://server.example.com/";sha-256;lurbjj5khhB0NhIuOXtt4bBRH1M=

18.3.  Accept-Encoding

   The Accept-Encoding request-header field is
   interpreted relative similar to Accept, but
   restricts the Request-URI.

   Note, content-codings (see Section 18.14),i.e. transformation
   codings of the message body, such as gzip compression, that Content-Location can be used are
   acceptable in some cases to derive the
   base-URI for relative URI present in session description formats.
   This needs to be taken into account when Content-Location response.

   A server tests whether a content-coding is used.
   The easiest way to avoid needing acceptable, according to consider that issue
   an Accept-Encoding field, using these rules:

   1.  If the content-coding is to include one of the Content-Base whenever content-codings listed in the Content-Location
       Accept-Encoding field, then it is included.

   Note also, when using Media Tags in conjunction with Content-Location acceptable, unless it is important that the different versions have different MTags,
   even if provided under different Content-Location URIs.  This as they
   have still been provided under the same request URI.

   Note also, as
       accompanied by a qvalue of 0.  (As defined in most cases the URI used [H3.9], a qvalue of
       0 means "not acceptable.")

   2.  The special "*" symbol in an Accept-Encoding field matches any
       available content-coding not explicitly listed in the DESCRIBE and the
   SETUP requests header
       field.

   3.  If multiple content-codings are different, the URI provided in a DESCRIBE Content-
   Location response can't directly be used in a SETUP request.  Instead acceptable, then the extra step of resolving URIs combined acceptable
       content-coding with the media descriptions
   indication, like with SDP's a=control attribute.

16.18.  Content-Type highest non-zero qvalue is preferred.

   4.  The Content-Type header indicates "identity" content-coding is always acceptable, i.e. no
       transformation at all, unless specifically refused because the media type of
       Accept-Encoding field includes "identity;q=0", or because the message body
   sent to
       field includes "*;q=0" and does not explicitly include the recipient.  Note that
       "identity" content-coding.  If the content types suitable for RTSP
   are likely to be restricted in practice to presentation descriptions
   and parameter-value types.

16.19.  CSeq

   The CSeq general-header field specifies Accept-Encoding field-value is
       empty, then only the sequence number for "identity" encoding is acceptable.

   If an
   RTSP request-response pair.  This Accept-Encoding field MUST be is present in all
   requests a request, and responses.  For every RTSP request containing the given
   sequence number, if the corresponding
   server cannot send a response will have the same
   number.  Any retransmitted request MUST contain which is acceptable according to the same sequence
   number as
   Accept-Encoding header, then the original (i.e., server SHOULD send an error response
   with the sequence number 406 (Not Acceptable) status code.

   If no Accept-Encoding field is not incremented
   for retransmissions of the same request).  For each new RTSP request present in a request, the CSeq value MUST be incremented by one.  The initial sequence
   number server MAY be any number, however, it is RECOMMENDED to start at 0.
   Each sequence number series is unique between each requester and
   responder, i.e.,
   assume that the client has will accept any content coding.  In this case,
   if "identity" is one series for its request to a
   server and of the available content-codings, then the
   server SHOULD use the "identity" content-coding, unless it has another when sending request
   additional information that a different content-coding is meaningful
   to the client.
   Each requester and responder

18.4.  Accept-Language

   The Accept-Language request-header field is identified with its socket address
   (IP address and port number).

   Proxies that aggregate several sessions on the same transport will
   have similar to ensure that Accept, but
   restricts the requests sent towards a particular server
   have set of natural languages that are preferred as a joint sequence number space, i.e., they will regularly need
   response to
   renumber the CSeq header field in requests (from proxy to server) and
   responses (from server to proxy) to fulfill request.  Note that the rules for language specified applies to
   the header.
   The proxy MUST increase presentation description and any reason phrases, but not the CSeq
   media content.

   A language tag identifies a natural language spoken, written, or
   otherwise conveyed by one human beings for each request it
   transmits, without regard communication of different sessions.

   Example:
   CSeq: 239

16.20.  Date information
   to other human beings.  Computer languages are explicitly excluded.
   The Date header field represents the date syntax and time at which the
   message was originated.  The inclusion registry of the Date header in RTSP
   message follows these rules:

   o  An RTSP message, sent either by 2.0 language tags is the client or same as that
   defined by [RFC5646].

   Each language-range MAY be given an associated quality value which
   represents an estimate of the server,
      containing a body MUST include a Date header, if user's preference for the sending host
      has a clock;

   o  Clients and servers are RECOMMENDED languages
   specified by that range.  The quality value defaults to include a Date header in
      all "q=1".  For
   example:

      Accept-Language: da, en-gb;q=0.8, en;q=0.7

   would mean: "I prefer Danish, but will accept British English and
   other RTSP messages, if the sending host has a clock;

   o  If the server does not have a clock that can provide a reasonable
      approximation types of the current time, its responses MUST NOT include
      a Date header field.  In this case, this rule MUST be followed:
      Some origin server implementations might not have a clock
      available.  An origin server without a clock MUST NOT assign
      Expires or Last-Modified values to English."  A language-range matches a response, unless these values
      were associated with language-tag if
   it exactly equals the resource by a system full tag, or user with if it exactly equals a
      reliable clock.  It MAY assign an Expires value prefix of
   the tag, i.e., the primary-tag in the ABNF, such that the character
   following primary-tag is known, at
      or before server configuration time, to be "-".  The special range "*", if present in
   the past (this
      allows "pre-expiration" Accept-Language field, matches every tag not matched by any other
   range present in the Accept-Language field.

      Note: This use of responses without storing separate
      Expires values for each resource).

   A received message that a prefix matching rule does not have a Date header field MUST be imply that
      language tags are assigned one by the recipient if the message will be cached by to languages in such a way that
   recipient .  An RTSP implementation without it is
      always true that if a clock MUST NOT cache
   responses without revalidating them on every use.  An RTSP cache,
   especially user understands a shared cache, SHOULD use language with a mechanism, such as NTP, to
   synchronize its clock certain
      tag, then this user will also understand all languages with tags
      for which this tag is a reliable external standard. prefix.  The RTSP-date sent in a Date header SHOULD NOT represent a date and
   time subsequent to prefix rule simply allows the generation
      use of prefix tags if this is the message.  It SHOULD
   represent case.

   In the best available approximation process of selecting a language, each language-tag is assigned
   a qualification factor, i.e., if a language being supported by the date
   client is actually supported by the server and time of
   message generation, unless what "preference"
   level the implementation has no means language achieves.  The quality value (q-value) of
   generating a reasonably accurate date and time.  In theory, the date
   ought to represent
   longest language-range in the moment just before field that matches the message body language-tag is
   generated.  In practice,
   assigned as the date can be generated at any time during qualification factor for a particular language-tag.
   If no language-range in the message origination without affecting its semantic value.

16.21.  Expires

   The Expires message-header field gives a date and time after which matches the description or media-stream should be considered stale.  The
   interpretation depends on tag, the method:

   DESCRIBE response:  The Expires language
   qualification factor assigned is 0.  If no Accept-Language header indicates a date and time
         after which is
   present in the presentation description (body) SHOULD be
         considered stale.

   SETUP response:  The Expires header indicate a date and time after
         which request, the media stream server SHOULD be considered stale.

   A stale cache entry may not normally be returned by a cache (either a
   proxy cache or assume that all languages
   are equally acceptable.  If an user agent cache) unless it Accept-Language header is first validated with
   the origin server (or with an intermediate cache that has present,
   then all languages which are assigned a fresh
   copy qualification factor greater
   than 0 are acceptable.

18.5.  Accept-Ranges

   The Accept-Ranges general-header field allows indication of the message body).  See Section 18 for further discussion of
   format supported in the expiration model. Range header.  The presence of an Expires field does not imply that client MUST include the original
   resource will change or cease
   header in SETUP requests to exist at, before, or after that
   time.

   The format is an absolute date and time as defined by RTSP-date.  An
   example of its use is
     Expires: Thu, 01 Dec 1994 16:00:00 GMT

   RTSP/2.0 clients indicate which formats it support to
   receive in PLAY and caches PAUSE responses, and REDIRECT requests.  The
   server MUST treat other invalid date formats,
   especially including include the value "0", as having occurred header in the past
   (i.e., already expired).

   To mark a response as "already expired," an origin server should use
   an Expires date that is equal SETUP and 456 error responses to
   indicate the Date header value.  To mark a
   response as "never expires," an origin server SHOULD use an Expires
   date approximately one year from formats supported for the time resource indicated by the response is sent.
   RTSP/2.0 servers SHOULD NOT send Expires dates more than one year
   request URI.  The header MAY be included in
   the future.

16.22.  From GET_PARAMETER request and
   response pairs.  The From request-header field, if given, SHOULD GET_PARAMETER request MUST contain an Internet
   e-mail address for a Session
   header to identify the human user who controls session context the requesting user
   agent. request is related to.
   The address SHOULD be machine-usable, as requester and responder will indicate their capabilities
   regarding Range formats respectively.

      Accept-Ranges: NPT, SMPTE

   The syntax is defined by "mailbox" in [RFC1123].

   This header Section 20.2.3.

18.6.  Allow

   The Allow message-header field MAY be used for logging purposes and as a means for
   identifying lists the source of invalid or unwanted requests.  It SHOULD
   NOT be used as an insecure form of access protection. methods supported by the
   resource identified by the Request-URI.  The
   interpretation purpose of this field is that
   to strictly inform the request is being performed
   on behalf recipient of valid methods associated with the person given, who accepts responsibility for
   resource.  An Allow header field MUST be present in a 405 (Method Not
   Allowed) response.  The Allow header MUST also be present in all
   OPTIONS responses where the content of the
   method performed.  In particular, robot agents SHOULD include this header so that will not include
   exactly the person responsible for running same methods as listed in the robot can Public header.

   The Allow MUST also be
   contacted included in SETUP and DESCRIBE responses, if problems occur on
   the receiving end.

   The Internet e-mail address methods allowed for the resource is different than the complete
   set of methods defined in this field MAY be separate memo.

   Example of use:
      Allow: SETUP, PLAY, SET_PARAMETER, DESCRIBE

18.7.  Authorization

   An RTSP client that wishes to authenticate itself with a server using
   authentication mechanism from the
   Internet host which issued HTTP [RFC2617] , usually, but not
   necessarily, after receiving a 401 response, does so by including an
   Authorization request-header field with the request.  For example, when  The
   Authorization field value consists of credentials containing the
   authentication information of the user agent for the realm of the
   resource being requested.

   If a request is passed through authenticated and a proxy realm specified, the original issuer's address same
   credentials SHOULD be
   used.

   The client SHOULD NOT send the From header field without valid for all other requests within this realm
   (assuming that the user's
   approval, authentication scheme itself does not require
   otherwise, such as credentials that vary according to a challenge
   value or using synchronized clocks).

   When a shared cache (see Section 16) receives a request containing an
   Authorization field, it might conflict with MUST NOT return the user's privacy interests or
   their site's security policy.  It is strongly recommended that corresponding response as
   a reply to any other request, unless one of the
   user be able to disable, enable, and modify following specific
   exceptions holds:

   1.  If the value of this field
   at any time prior response includes the "max-age" cache-control directive,
       the cache MAY use that response in replying to a subsequent
       request.

16.23.  If-Match

   The If-Match request-header field is especially useful for ensuring
   the integrity of the presentation description, independent of how  But (if the
   presentation description was received.  The presentation description
   can be fetched via means external to RTSP (such as HTTP) or via specified maximum age has passed) a proxy
       cache MUST first revalidate it with the
   DESCRIBE message.  In origin server, using the case of retrieving
       request-headers from the presentation
   description via RTSP, new request to allow the origin server implementation
       to authenticate the new request.  (This is guaranteeing the
   integrity of defined behavior
       for max-age.)  If the description between response includes "max-age=0", the time of proxy
       MUST always revalidate it before re-using it.

   2.  If the DESCRIBE message
   and response includes the SETUP message.  By including "must-revalidate" cache-control
       directive, the MTag given cache MAY use that response in or with replying to a
       subsequent request.  But if the
   session description in an If-Match header part of response is stale, all caches
       MUST first revalidate it with the SETUP request, origin server, using the client ensures that resources set up are matching
       request-headers from the
   description.  A SETUP new request with to allow the If-Match header for which origin server
       to authenticate the new request.

   3.  If the
   MTag validation check fails, MUST response using 412 (Precondition
   Failed).

   This validation check is also very useful if a session has been
   redirected from one server includes the "public" cache-control directive, it
       MAY be returned in reply to another.

16.24.  If-Modified-Since any subsequent request.

18.8.  Bandwidth

   The If-Modified-Since Bandwidth request-header field is used with describes the DESCRIBE
   and SETUP methods estimated bandwidth
   available to make them conditional.  If the requested variant
   has not been modified since the time specified in this field, client, expressed as a
   description will positive integer and measured
   in kilobits per second.  The bandwidth available to the client may
   change during an RTSP session, e.g., due to mobility, congestion,
   etc.

   Clients may not be returned from able to accurately determine the server (DESCRIBE) or available
   bandwidth, for example due to that first hop is not a
   stream bottleneck.
   For example most local area networks (LAN) will not be set up (SETUP).  Instead, a 304 (Not Modified)
   response MUST be returned without any message-body.

   An example of the field is:
     If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

16.25.  If-None-Match

   This request header can be used with one or several message body tags
   to make DESCRIBE requests conditional.  A client that has one or more
   message bodies previously obtained from bottleneck
   if the resource, can verify that
   none of those entities server is current by including a list of their
   associated message body tags not in the If-None-Match header field.  The
   purpose of this feature is to allow efficient updates of cached
   information with a minimum amount same LAN.  Thus link speeds of transaction overhead.  As WLAN or
   Ethernet networks are normally not a
   special case, the value "*" matches any current entity of the
   resource.

   If any of the message body tags match the message body tag of the
   message body that would have been returned in basis for estimating the response
   available bandwidth.  Cellular devices or other devices directly
   connected to a
   similar DESCRIBE request (without the If-None-Match header) on that
   resource, modem or if "*" is given connection enabling device may more
   accurately estimate the bottleneck bandwidth and any current entity exists what is reasonable
   share of it for that
   resource, then the server MUST NOT perform the requested method,
   unless required RTSP controlled media.  The client will also need to do so because
   take into account other traffic sharing the resource's modification date
   fails bottleneck.  For example
   by only assigning a certain fraction to match RTSP and its media streams.
   It is RECOMMENDED that supplied in an If-Modified-Since only clients that has accurate and explicit
   information about bandwidth bottlenecks uses this header.

   This header is not a substitute for proper congestion control.  Only
   a method providing an initial estimate and coarsely determine if the
   selected content can be delivered at all.

   Example:
     Bandwidth: 62360

18.9.  Blocksize

   The Blocksize request-header field in is sent from the request.  Instead, if client to the request method was DESCRIBE,
   media server asking the server
   SHOULD respond with for a 304 (Not Modified) response, including particular media packet size.
   This packet size does not include lower-layer headers such as IP,
   UDP, or RTP.  The server is free to use a blocksize which is lower
   than the
   cache-related header fields (particularly MTag) of one of the message
   bodies that matched.  For all other request methods, the requested.  The server MUST
   respond with a status of 412 (Precondition Failed).

   See Section 18.1.3 for rules on how MAY truncate this packet size to determine if two message body
   tags match.

   If none of
   the message body tags match, then closest multiple of the server MAY perform minimum, media-specific block size, or
   override it with the requested method as media-specific size if the If-None-Match header field did not
   exist, but necessary.  The block
   size MUST also ignore any If-Modified-Since header field(s) be a positive decimal number, measured in
   the request.  That is, octets.  The
   server only returns an error (4xx) if no message body tags match, then the server value is syntactically
   invalid.

18.10.  Cache-Control

   The Cache-Control general-header field is used to specify directives
   that MUST NOT return a 304 (Not Modified) response.

   If the request would, without be obeyed by all caching mechanisms along the If-None-Match header field, result
   in anything other than request/
   response chain.

   Cache directives MUST be passed through by a 2xx proxy or 304 status, then gateway
   application, regardless of their significance to that application,
   since the If-None-Match
   header MUST directives may be ignored.  (See Section 18.1.4 applicable to all recipients along the
   request/response chain.  It is not possible to specify a cache-
   directive for a discussion of
   server behavior when both If-Modified-Since and If-None-Match appear specific cache.

   Cache-Control should only be specified in the same request.)

   The result of a DESCRIBE, GET_PARAMETER,
   SET_PARAMETER and SETUP request having both an If-None-Match header field and
   an If-Match header field its response.  Note: Cache-
   Control does not govern only the caching of responses as for HTTP,
   instead it also applies to the media stream identified by the SETUP
   request.  The RTSP requests are generally not cacheable, for further
   information see Section 16.  Below is unspecified and the description of the cache
   directives that can be included in the Cache-Control header.

   no-cache:  Indicates that the media stream MUST NOT be considered cached
         anywhere.  This allows an
   illegal request.

16.26.  Last-Modified

   The Last-Modified message-header field indicates the date and time at
   which the origin server believes to prevent caching even
         by caches that have been configured to return stale responses
         to client requests.  Note, there is no security function
         enforcing that the content can't be cached.

   public:  Indicates that the presentation description or media stream was last modified.  For is cacheable by any cache.

   private:  Indicates that the method DESCRIBE, media stream is intended for a single
         user and MUST NOT be cached by a shared cache.  A private (non-
         shared) cache may cache the header
   field indicates media streams.

   no-transform:  An intermediate cache (proxy) may find it useful to
         convert the last modification date and time media type of a certain stream.  A proxy might, for
         example, convert between video formats to save cache space or
         to reduce the
   description, amount of traffic on a slow link.  Serious
         operational problems may occur, however, when these
         transformations have been applied to streams intended for SETUP that
         certain kinds of applications.  For example, applications for
         medical imaging, scientific data analysis and those using end-
         to-end authentication all depend on receiving a stream that is
         bit-for-bit identical to the original media stream.

   An origin server MUST NOT send  Therefore,
         if a Last-Modified date which is later
   than the server's time of message origination.  In such cases, where
   the resource's last modification would indicate some time in the
   future, response includes the server no-transform directive, an
         intermediate cache or proxy MUST replace that date with the message
   origination date.

   An origin server SHOULD obtain NOT change the Last-Modified value encoding of the message
   body as close
         stream.  Unlike HTTP, RTSP does not provide for partial
         transformation at this point, e.g., allowing translation into a
         different language.

   only-if-cached:  In some cases, such as possible times of extremely poor
         network connectivity, a client may want a cache to the time return only
         those media streams that it generates the Date
   value of its response.  This allows a recipient currently has stored, and not to make an accurate
   assessment of the message body's modification time, especially if
         receive these from the
   message body changes near origin server.  To do this, the time that client
         may include the response is generated.

   RTSP servers only-if-cached directive in a request.  If it
         receives this directive, a cache SHOULD send Last-Modified whenever feasible.

16.27.  Location

   The Location response-header field either respond using a
         cached media stream that is used to redirect consistent with the recipient
   to a location other than the Request-URI for completion
         constraints of the
   request request, or identification respond with a 504 (Gateway
         Timeout) status.  However, if a group of caches is being
         operated as a new resource.  For 3xx responses, the
   location SHOULD indicate unified system with good internal connectivity,
         such a request MAY be forwarded within that group of caches.

   max-stale:  Indicates that the server's preferred URI for automatic
   redirection client is willing to accept a media
         stream that has exceeded its expiration time.  If max-stale is
         assigned a value, then the resource.  The field value consists of client is willing to accept a single
   absolute URI.

   Note: The Content-Location header field (Section 16.17) differs from
   Location in
         response that has exceeded its expiration time by no more than
         the Content-Location identifies specified number of seconds.  If no value is assigned to
         max-stale, then the original
   location client is willing to accept a stale
         response of any age.

   min-fresh:  Indicates that the message body enclosed client is willing to accept a media
         stream whose freshness lifetime is no less than its current age
         plus the specified time in seconds.  That is, the request.  It is
   therefore possible for client wants
         a response to contain header fields for both
   Location and Content-Location.  Also, see Section 18.2 that will still be fresh for cache
   requirements at least the specified
         number of some methods.

16.28.  Media-Properties

   This general header seconds.

   must-revalidate:  When the must-revalidate directive is used present in a
         SETUP response or PLAY_NOTIFY requests
   to indicate the media's properties received by a cache, that currently are applicable to cache MUST NOT use the RTSP session.  PLAY_NOTIFY MAY be used
         entry after it becomes stale to modify these properties
   at any point.  However, respond to a subsequent request
         without first revalidating it with the client SHOULD have received origin server.  That is,
         the update
   prior to any action related cache is required to do an end-to-end revalidation every
         time, if, based solely on the new media properties take effect.
   For aggregated sessions, the Media-Properties header will be returned
   in each SETUP response.  The header received in origin server's Expires, the latest
         cached response is stale.

   proxy-revalidate:  The proxy-revalidate directive has the one same
         meaning as the must-revalidate directive, except that applies it does
         not apply to non-shared user agent caches.  It can be used on a
         response to an authenticated request to permit the whole session from this point until
   any future update.  The header MAY be included user's cache
         to store and later return the response without value in
   GET_PARAMETER requests needing to
         revalidate it (since it has already been authenticated once by
         that user), while still requiring proxies that service many
         users to revalidate each time (in order to make sure that each
         user has been authenticated).  Note that such authenticated
         responses also need the server with public cache control directive in order
         to allow them to be cached at all.

   max-age:  When an intermediate cache is forced, by means of a Session header included max-
         age=0 directive, to query revalidate its own cache entry, and the current Media-Properties for
         client has supplied its own validator in the session.  The responder
   MUST include request, the current session's media properties.

   The media properties expressed by
         supplied validator might differ from the validator currently
         stored with the cache entry.  In this header case, the cache MAY use
         either validator in making its own request without affecting
         semantic transparency.

   However, the choice of validator might affect performance.  The best
   approach is for the one applicable intermediate cache to all media in use its own validator when
   making its request.  If the RTSP session.  For aggregated sessions, server replies with 304 (Not Modified),
   then the
   header expressed cache can return its now validated copy to the combined media-properties.  As a result,
   aggregation of media MAY result in client with a change of
   200 (OK) response.  If the media properties, server replies with a new message body and thus the content of
   cache validator, however, the Media-Properties header contained in
   subsequent SETUP responses.

   The header contains a list of property values that are applicable to intermediate cache can compare the currently setup media or aggregate of media as indicated by
   returned validator with the
   RTSP URI one provided in the request.  No ordering client's request,
   using the strong comparison function.  If the client's validator is enforced within
   equal to the header.
   Property values should be grouped into origin server's, then the intermediate cache simply
   returns 304 (Not Modified).  Otherwise, it returns the new message
   body with a single group 200 (OK) response.

18.11.  Connection

   The Connection general-header field allows the sender to specify
   options that handles a
   particular orthogonal property.  Values or groups are desired for that express
   multiple properties SHOULD particular connection and MUST NOT
   be used.  The list of properties that
   can be expressed MAY be extended at any time.  Unknown property
   values communicated by proxies over further connections.

   RTSP 2.0 proxies MUST be ignored.

   This specification defines parse the following 4 groups and their property
   values:

   Random Access:

      Random-Access:  Indicates that random access is possible.  May
         optionally include Connection header field before a floating point value
   message is forwarded and, for each connection-token in seconds indicating
         the longest duration between this field,
   remove any two random access points in header field(s) from the media.

      Begining-Only:  Seeking is limited to message with the beginning only.

      No-Seeking:  No seeking is possible.

   Content Modifications:

      Immutable:  The content will not be changed during same name as the life-time
   connection-token.  Connection options are signaled by the presence of
   a connection-token in the RTSP session.

      Dynamic:  The content Connection header field, not by any
   corresponding additional header field(s), since the additional header
   field may not be changed based on external methods or
         triggers

      Time-Progressing  The media accessible progresses sent if there are no parameters associated with that
   connection option.

   Message headers listed in the Connection header MUST NOT include end-
   to-end headers, such as wallclock
         time progresses.

   Retention:

      Unlimited:  Content will be retained for Cache-Control.

   RTSP 2.0 defines the duration of "close" connection option for the life-
         time of sender to
   signal that the RTSP session.

      Time-Limited:  Content connection will be retained at least until closed after completion of the
         specified wallclock time.  The time must be provided
   response.  For example, Connection: close in either the
         absolute time format specified in Section 4.6.

      Time-Duration  Each individual media unit is retained for at least request or
   the specified time duration.  This definition allows for
         retaining data with a time based sliding window.  The time
         duration is expressed as floating point number in seconds. 0.0
         is a valid value as this response header fields indicates that no data the connection SHOULD NOT
   be considered `persistent' (Section 10.2) after the current request/
   response is retained in
         a time-progressing session.

   Supported Scale:

      Scales:  A quoted comma separated list of one or more decimal
         values or ranges complete.

   The use of scale values supported by the content connection option "close" in
         arbitrary order.  A range has a start RTSP messages SHOULD be
   limited to error messages when the server is unable to recover and stop value separated
         by a colon.  A range indicates that
   therefore see it necessary to close the content supports fine
         grained selection of scale values.  Fine grained allows for
         steps at least as small as one tenth of a scale value.
         Negative values are supported. connection.  The value 0 reason is
   that the client has no meaning and
         MUST NOT be used.

   Examples the choice of this header for on-demand content and continuing using a live stream
   without recording are:

   On-demand:
   Media-Properties: Random-Access=2.5s, Unlimited, Immutable,
        Scales="-20, -10, -4, 0.5:1.5, 4, 8, 10, 15, 20"

   Live stream without recording/timeshifting:
   Media-Properties: No-Seeking, Time-Progressing, Time-Duration=0.0

16.29.  Media-Range connection
   indefinitely, as long as it sends valid messages.

18.12.  Connection-Credentials

   The Media-Range general Connection-Credentials response header is used to give carry the range chain
   of the media
   at the time credentials of sending the RTSP message.  This header MUST be
   included in SETUP response, and PLAY and PAUSE response for media
   that are Time-Progressing, and PLAY and PAUSE response after any
   change for media that are Dynamic, and in PLAY_NOTIFY request next hop that
   are sent due need to Media-Property-Update.  Media-Range header without
   any range specifications MAY be included in GET_PARAMETER requests to approved by the
   requester.  It MUST only be used in server to request the current range. client responses.

   The server MUST Connection-Credentials header in this
   case include an RTSP response MUST, if
   included, contain the current range at credential information (in form of a list of
   certificates providing the time chain of certification) of sending the response. next hop
   that an intermediary needs to securely connect to.  The header MUST
   include range specifications for all time formats
   supported for the media, URI of the next hop (proxy or server) and a base64
   [RFC4648] encoded binary structure containing a sequence of DER
   encoded X.509v3 certificates[RFC5280] .

   The binary structure starts with the number of certificates
   (NR_CERTS) included as indicated in Accept-Ranges header
   (Section 16.5) when setting up a 16 bit unsigned integer.  This is followed
   by NR_CERTS number of 16 bit unsigned integers providing the media. size in
   octets of each DER encoded certificate.  This is followed by NR_CERTS
   number of DER encoded X.509v3 certificates in a sequence (chain).
   The server MAY include
   more than proxy or server's certificate must come first in the structure.
   Each following certificate must directly certify the one range specification of any given time format to
   indicate media that has non-continuous range.

   For media preceding
   it.  Because certificate validation requires that has root keys be
   distributed independently, the Time-Progressing property, self-signed certificate which
   specifies the Media-Range
   values will only root certificate authority may optionally be valid for omitted
   from the particular point in time when it
   was issued.  As wallclock progresses so will also chain, under the media range.
   However, it shall be assumed assumption that media time progresses the remote end must already
   possess it in direct
   relationship order to wallclock time (with the exception of clock skew) so
   that validate it in any case.

   Example:

   Connection-Credentials:"rtsps://proxy2.example.com/";MIIDNTCC...

   Where MIIDNTCC... is a reasonably accurate estimation BASE64 encoding of the media range can be
   calculated.

16.30.  MTag

   The MTag response header MAY be included in DESCRIBE, GET_PARAMETER
   or SETUP responses. following structure:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Number of certificates       | Size of certificate #1        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Size of certificate #2        | Size of certificate #3        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #1                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #2                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : DER Encoding of Certificate #3                                :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

18.13.  Content-Base

   The message body tags (Section 4.8) returned in
   a DESCRIBE response, and the one in SETUP refers Content-Base message-header field may be used to specify the presentation,
   i.e. both the returned session description and the media stream.
   This allows base
   URI for verification that one has resolving relative URIs within the right session
   description to a media resource at message body.

   Content-Base: rtsp://media.example.com/movie/twister/

   If no Content-Base field is present, the time base URI of an message body
   is defined either by its Content-Location (if that Content-Location
   URI is an absolute URI) or the SETUP request.
   However, it has URI used to initiate the disadvantage that a change request, in any
   that order of precedence.  Note, however, that the parts
   results in invalidation base URI of all the parts.

   If the MTag is provided both inside the message body, e.g.
   contents within the
   "a=mtag" attribute in SDP, and in the response message, then both
   tags MUST message-body may be identical.  It is RECOMMENDED redefined within that the MTag
   message-body.

18.14.  Content-Encoding

   The Content-Encoding header field is primarily
   given in the RTSP response message, used as a modifier to ensure that caches can use the
   MTag without requiring media-
   type.  When present, its value indicates what additional content inspection.  However, for session
   descriptions that are distributed outside of RTSP, for example using
   HTTP, etc. it will be necessary
   codings have been applied to include the message body tag in
   the session description as specified in Appendix D.1.9.

   SETUP body, and DESCRIBE requests can thus what decoding
   mechanisms must be made conditional upon the MTag
   using the headers If-Match (Section 16.23) and If-None-Match (
   Section 16.25).

16.31.  Notify-Reason

   The Notify Reason header is solely used applied in order to obtain the PLAY_NOTIFY method.
   It indicates the reason why the server has sent media-type
   referenced by the asynchronous
   PLAY_NOTIFY request (see Section 13.5).

16.32.  Pipelined-Requests

   The Pipelined-Requests general Content-Type header field.  Content-Encoding is
   primarily used to indicate that allow a
   request is document to be executed in compressed without losing
   the context created by a previous
   request(s).  The primary usage of this header is to allow pipelining identity of SETUP requests so that any additional SETUP request after the
   first one does not need to wait for the session ID to be sent back to
   the requesting agent. its underlying media type.

   The header contains a unique identifier that content-coding is scoped by the persistent connection used to send the requests.

   Upon receiving a request with the Pipelined-Requests characteristic of the responding
   agent MUST look up if there exists a binding between this Pipelined-
   Requests identifier for message body identified
   by the current persistent connection and an RTSP
   session ID.  If that exists then Request-URI.  Typically, the received request message body is processed
   the same way as if it contained the Session header stored with the found
   session ID.  If there does not exist a mapping this
   encoding and no Session header is included in the request, the responding agent MUST create a
   binding upon the successful completion of a session creating request,
   i.e.  SETUP.  A binding MUST NOT be created, if the request failed to
   create an RTSP session.  In case the request contains both a Session
   header and the Pipelined-Requests header the Pipelined-Requests MUST
   be ignored.

   Note: Based on the above definition at least the first request
   containing only decoded before rendering or analogous usage.
   However, a non-transparent proxy MAY modify the content-coding if the
   new unique Pipelined-Requests will be required coding is known to be a
   SETUP request (unless acceptable to the protocol recipient, unless the
   "no-transform" cache-control directive is extended with new methods present in the message.

   If the content-coding of
   creating a session).  After that first one, additional SETUP requests
   or request of any type using message body is not "identity", then the RTSP session context may
   response MUST include a Content-Encoding Message-body header that
   lists the
   Pipelined-Requests header.

   When responding to any non-identity content-coding(s) used.

   If the content-coding of a message body in a request that contained message is not
   acceptable to the Pipelined-Requests
   header origin server, the server MUST also include the Session header when SHOULD respond with a binding
   status code of 415 (Unsupported Media Type).

   If multiple encodings have been applied to a session context exist.  An RTSP agent that knows the session ID
   SHOULD NOT use message body, the Pipelined-Requests header
   content codings MUST be listed in any request and only
   use the Session header.  This as the Session identifier is persistent
   across transport contexts, like TCP connections, order in which they were
   applied, first to last from left to right.  Additional information
   about the Pipelined-
   Requests identifier is not. encoding parameters MAY be provided by other header fields
   not defined by this specification.

18.15.  Content-Language

   The RTSP agent sending the request with a Pipelined-Requests Content-Language header
   has field describes the responsibility natural language(s)
   of the intended audience for using the enclosed message body.  Note that
   this might not be equivalent to all the languages used within the
   message body.

   Language tags are mentioned in Section 18.4.  The primary purpose of
   Content-Language is to allow a unique user to identify and previously unused
   identifier within differentiate
   entities according to the transport context.  Currently user's own preferred language.  Thus, if
   the body content is intended only for a TCP
   connection Danish-literate audience, the
   appropriate field is defined as such transport context.  A server MUST
   delete

      Content-Language: da

   If no Content-Language is specified, the Pipelined-Requests identifier and its binding default is that the content
   is intended for all language audiences.  This might mean that the
   sender does not consider it to be specific to any natural language,
   or that the sender does not know for which language it is intended.

   Multiple languages MAY be listed for content that is intended for
   multiple audiences.  For example, a session
   upon rendition of the termination "Treaty of that session.  Despite
   Waitangi," presented simultaneously in the previous mandate,
   RTSP agents original Maori and English
   versions, would call for

      Content-Language: mi, en

   However, just because multiple languages are RECOMMENDED to present within a message
   body does not reuse identifiers to allow mean that it is intended for
   better error handling and logging.

   RTSP Proxies may need multiple linguistic
   audiences.  An example would be a beginner's language primer, such as
   "A First Lesson in Latin," which is clearly intended to translate Pipelined-Requests identifier
   values from incoming request be used by an
   English-literate audience.  In this case, the Content-Language would
   properly only include "en".

   Content-Language MAY be applied to outgoing any media type -- it is not
   limited to allow for aggregation of
   requests onto a persistent connection.

16.33.  Proxy-Authenticate textual documents.

18.16.  Content-Length

   The Proxy-Authenticate response-header Content-Length general-header field contains the length of the
   message body of the RTSP message (i.e. after the double CRLF
   following the last header).  Unlike HTTP, it MUST be included as part in all
   messages that carry a message body beyond the header portion of the
   RTSP message.  If it is missing, a 407 (Proxy Authentication Required) response.  The field default value
   consists of zero is assumed.
   Any Content-Length greater than or equal to zero is a challenge that indicates the authentication scheme and
   parameters applicable valid value.

18.17.  Content-Location

   The Content-Location header field MAY be used to supply the proxy resource
   location for this Request-URI.

   The HTTP access authentication process is described the message body enclosed in [RFC2617].
   Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
   only to message when that body
   is accessible from a location separate from the current connection and requested resource's
   URI.  A server SHOULD NOT be passed on to
   downstream agents.  However, an intermediate proxy might need provide a Content-Location for the variant
   corresponding to
   obtain its own credentials by requesting them from the downstream
   agent, which response message body; especially in some circumstances will appear as if the proxy is
   forwarding case
   where a resource has multiple variants associated with it, and those
   entities actually have separate locations by which they might be
   individually accessed, the Proxy-Authenticate header field.

16.34.  Proxy-Authorization

   The Proxy-Authorization request-header field allows server SHOULD provide a Content-Location
   for the particular variant which is returned.

   As example, if an RTSP client to
   identify itself (or its user) to performs a proxy which requires
   authentication.  The Proxy-Authorization field value consists DESCRIBE request on a given
   resource, e.g., "rtsp://a.example.com/movie/Plan9FromOuterSpace",
   then the server may use additional information, such as the User-
   Agent header, to determine the capabilities of
   credentials containing the authentication information agent.  The server
   will then return a media description tailored to that class of RTSP
   agents.  To indicate which specific description the user agent for the proxy and/or realm of receives
   the resource being requested.

   The HTTP access authentication process identifier
   ("rtsp://a.example.com/movie/Plan9FromOuterSpace/FullHD.sdp") is described
   provided in [RFC2617].
   Unlike Authorization, the Proxy-Authorization header field applies
   only to Content-Location, while the next outbound proxy that demanded authentication using description is still a valid
   response for the Proxy-Authenticate field.  When multiple proxies are used in generic resource identifier.  Thus enabling both
   debugging and cache operation as discussed below.

   The Content-Location value is not a
   chain, replacement for the Proxy-Authorization header field original
   requested URI; it is consumed by only a statement of the first
   outbound proxy that was expecting location of the resource
   corresponding to receive credentials.  A proxy this particular variant at the time of the request.
   Future requests MAY relay specify the credentials from Content-Location URI as the client request
   URI if the desire is to identify the next proxy
   if source of that particular
   variant.  This is useful if the mechanism by which RTSP agent desires to verify if the proxies cooperatively
   authenticate
   resource variant is current through a given conditional request.

16.35.  Proxy-Require

   The Proxy-Require request-header field is used to indicate proxy-
   sensitive features that MUST be supported by the proxy.  Any Proxy-
   Require header features

   A cache cannot assume that are not supported by the proxy MUST be
   negatively acknowledged by a message body with a Content-Location
   different from the proxy URI used to the client using the
   Unsupported header.  The proxy MUST use the 551 (Option Not
   Supported) status code in the response.  Any feature-tag included in
   the Proxy-Require does not apply retrieve it can be used to the end-point (server or client).
   To ensure respond to
   later requests on that Content-Location URI.  However, the Content-
   Location can be used to differentiate between multiple variants
   retrieved from a feature single requested resource.

   If the Content-Location is supported by both proxies and servers a relative URI, the
   tag needs relative URI is
   interpreted relative to the Request-URI.

   Note, that Content-Location can be included used in also a Require header.

   See Section 16.41 for more details on some cases to derive the mechanics of this message
   and a usage example.  See discussion
   base-URI for relative URI present in the proxies section
   (Section 17.1) about session description formats.
   This needs to be taken into account when Content-Location is used.
   The easiest way to avoid needing to consider that a feature requires proxy
   support.

   Example of use:
      Proxy-Require: play.basic

16.36.  Proxy-Supported

   The Proxy-Supported header field enumerates all issue is to include
   the extensions
   supported by Content-Base whenever the proxy Content-Location is included.

   Note also, when using feature-tags.  The header carries Media Tags in conjunction with Content-Location
   it is important that the
   intersection of extensions supported by different versions have different MTags,
   even if provided under different Content-Location URIs.  This as they
   have still been provided under the forwarding proxies.  The
   Proxy-Supported header MAY be included in any same request by a proxy.  It
   MUST be added by any proxy if URI.

   Note also, as in most cases the Supported header is present URI used in a
   request.  When present the DESCRIBE and the
   SETUP requests are different, the URI provided in a request, the receiver MUST DESCRIBE Content-
   Location response can't directly be used in a SETUP request.  Instead
   the
   response copy extra step of resolving URIs combined with the received Proxy-Supported header. media descriptions
   indication, like with SDP's a=control attribute.

18.18.  Content-Type

   The Proxy-Supported Content-Type header field contains a list indicates the media type of feature-tags
   applicable the message body
   sent to proxies, as described the recipient.  Note that the content types suitable for RTSP
   are likely to be restricted in Section 4.7. practice to presentation descriptions
   and parameter-value types.

18.19.  CSeq

   The list is CSeq general-header field specifies the
   intersection of sequence number for an
   RTSP request-response pair.  This field MUST be present in all feature-tags understood by
   requests and responses.  For every RTSP request containing the proxies.  To
   achieve an intersection, given
   sequence number, the proxy adding corresponding response will have the Proxy-Supported header
   includes all proxy feature-tags it understands. same
   number.  Any proxy receiving
   a retransmitted request with the header, MUST check contain the list and removes any
   feature-tag(s) it does same sequence
   number as the original (i.e., the sequence number is not support.  A Proxy-Supported header present
   in incremented
   for retransmissions of the response same request).  For each new RTSP request
   the CSeq value MUST NOT be touched incremented by the proxies.

   Example:
     C->P1: OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            User-Agent: PhonyClient/1.2

    P1->P2: OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            Proxy-Supported: proxy-foo, proxy-bar, proxy-blech
            Via: 2.0 pro.example.com

    P2->S:  OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            Proxy-Supported: proxy-foo, proxy-blech
            Via: 2.0 pro.example.com, 2.0 prox2.example.com

     S->C:  RTSP/2.0 200 OK
            Supported: foo, bar, baz
            Proxy-Supported: proxy-foo, proxy-blech
            Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN
            Via: 2.0 pro.example.com, 2.0 prox2.example.com

16.37.  Public one.  The Public response header field lists the set of methods supported
   by initial sequence
   number MAY be any number, however, it is RECOMMENDED to start at 0.
   Each sequence number series is unique between each requester and
   responder, i.e., the response sender.  This header applies client has one series for its request to a
   server and the general
   capabilities of server has another when sending request to the sender client.
   Each requester and its only purpose responder is to indicate identified with its socket address
   (IP address and port number).

   Proxies that aggregate several sessions on the
   sender's capabilities same transport will
   have to ensure that the recipient.  The methods listed may or
   may not be applicable requests sent towards a particular server
   have a joint sequence number space, i.e., they will regularly need to
   renumber the Request-URI; the Allow CSeq header field
   (Section 16.6) MAY be used in requests (from proxy to indicate methods allowed for a
   particular URI.

   Example of use:
      Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN

   In the event that there are proxies between the sender server) and
   responses (from server to proxy) to fulfill the
   recipient of a response, each intervening rules for the header.
   The proxy MUST modify increase the
   Public header field to remove any methods that are not supported via
   that proxy. CSeq by one for each request it
   transmits, without regard of different sessions.

   Example:
   CSeq: 239

18.20.  Date

   The resulting Public Date header field will contain an
   intersection of represents the sender's methods date and time at which the methods allowed through
   message was originated.  The inclusion of the Date header in RTSP
   message follows these rules:

   o  An RTSP message, sent either by the intervening proxies.

      In general, proxies should allow all methods to transparently pass
      through from client or the server,
      containing a body MUST include a Date header, if the sending RTSP agent host
      has a clock;

   o  Clients and servers are RECOMMENDED to the receiving RTSP agent,
      but there may be cases where this is not desirable for include a given
      proxy.  Modification of the Public response Date header field by the
      intervening proxies ensures that in
      all other RTSP messages, if the request sender gets an
      accurate response indicating sending host has a clock;

   o  If the methods server does not have a clock that can be used on the
      target agent via provide a reasonable
      approximation of the proxy chain.

16.38.  Range

   The Range current time, its responses MUST NOT include
      a Date header specifies field.  In this case, this rule MUST be followed:
      Some origin server implementations might not have a time range in PLAY (Section 13.4), PAUSE
   (Section 13.6), SETUP (Section 13.3), REDIRECT (Section 13.10), and
   PLAY_NOTIFY (Section 13.5) requests and responses. clock
      available.  An origin server without a clock MUST NOT assign
      Expires or Last-Modified values to a response, unless these values
      were associated with the resource by a system or user with a
      reliable clock.  It MAY assign an Expires value that is known, at
      or before server configuration time, to be
   included in GET_PARAMETER requests from the client past (this
      allows "pre-expiration" of responses without storing separate
      Expires values for each resource).

   A received message that does not have a Date header field MUST be
   assigned one by the recipient if the message will be cached by that
   recipient .  An RTSP implementation without a clock MUST NOT cache
   responses without revalidating them on every use.  An RTSP cache,
   especially a shared cache, SHOULD use a mechanism, such as NTP, to the server
   synchronize its clock with
   only a Range format reliable external standard.

   The RTSP-date sent in a Date header SHOULD NOT represent a date and no value
   time subsequent to request the current media
   position, whether the session is in Play or Ready state in generation of the
   included format.  The server SHALL, if supporting message.  It SHOULD
   represent the range format,
   respond with best available approximation of the current playing point or pause point as date and time of
   message generation, unless the start implementation has no means of
   generating a reasonably accurate date and time.  In theory, the range.  If an explicit stop point was used in date
   ought to represent the previous PLAY
   request, then that value shall be included as stop point.  Note that
   if moment just before the server message body is currently under any type of media playback
   manipulation affecting
   generated.  In practice, the interpretation of Range, like Scale, that
   is also required to date can be included in generated at any GET_PARAMETER response to
   provide complete information. time during
   the message origination without affecting its semantic value.

18.21.  Expires

   The range can be specified in Expires message-header field gives a number of units.  This specification
   defines smpte (Section 4.4), npt (Section 4.5), and clock
   (Section 4.6) range units.  While byte ranges [H14.35.1] date and other
   extended units MAY time after which
   the description or media-stream should be used, their behavior is unspecified since they
   are not normally meaningful in RTSP.  Servers supporting considered stale.  The
   interpretation depends on the Range method:

   DESCRIBE response:  The Expires header MUST understand the NPT range format indicates a date and SHOULD understand the
   SMPTE range format.  If time
         after which the Range presentation description (body) SHOULD be
         considered stale.

   SETUP response:  The Expires header is sent in indicate a date and time format
   that is not understood, after
         which the recipient media stream SHOULD return 456 (Header Field
   Not Valid for Resource) and include be considered stale.

   A stale cache entry may not normally be returned by a cache (either a
   proxy cache or an Accept-Ranges header
   indicating user agent cache) unless it is first validated with
   the supported time formats origin server (or with an intermediate cache that has a fresh
   copy of the message body).  See Section 16 for further discussion of
   the given resource.

   Example:
     Range: clock=19960213T143205Z- expiration model.

   The Range header contains a range presence of one single range format.  A
   range is a half-open interval with a start and an end point,
   including the start point, but excluding Expires field does not imply that the end point.  A range may
   either be fully specified with explicit values for start point and
   end point, original
   resource will change or have either start cease to exist at, before, or end point be implicit. after that
   time.

   The format is an absolute date and time as defined by RTSP-date.  An
   implicit start point indicates the session's pause point,
   example of its use is
     Expires: Thu, 01 Dec 1994 16:00:00 GMT

   RTSP/2.0 clients and if no
   pause point caches MUST treat other invalid date formats,
   especially including the value "0", as having occurred in the past
   (i.e., already expired).

   To mark a response as "already expired," an origin server should use
   an Expires date that is set the start of equal to the content.  An implicit end point
   indicates Date header value.  To mark a
   response as "never expires," an origin server SHOULD use an Expires
   date approximately one year from the end of time the content.  The usage of both implicit start
   and end point response is not allowed sent.
   RTSP/2.0 servers SHOULD NOT send Expires dates more than one year in
   the same range header, however, future.

18.22.  From

   The From request-header field, if given, SHOULD contain an Internet
   e-mail address for the
   exclusion of human user who controls the range requesting user
   agent.  The address SHOULD be machine-usable, as defined by "mailbox"
   in [RFC1123].

   This header has that meaning, i.e. from pause point
   (or start) until end of content.

      Regarding the half-open intervals; field MAY be used for logging purposes and as a range of A-B starts exactly
      at time A, but ends just before B. Only means for
   identifying the start time source of a media
      unit such as a video invalid or audio frame unwanted requests.  It SHOULD
   NOT be used as an insecure form of access protection.  The
   interpretation of this field is relevant.  For example,
      assume that video frames are generated every 40 ms.  A range of
      10.0-10.1 would include a video frame starting at 10.0 or later
      time and would include a video frame starting at 10.08, even
      though it lasted beyond the interval.  A range of 10.0-10.08, request is being performed
   on behalf of the other hand, would exclude the frame at 10.08.

      Please note the difference between NPT time scales' "now" and an
      implicit start value.  Implicit value reference the current pause-
      point.  While "now" is person given, who accepts responsibility for the currently ongoing time.
   method performed.  In a time-
      progressing session with recording (retention particular, robot agents SHOULD include this
   header so that the person responsible for some or full
      time) running the pause point may robot can be 2 min into
   contacted if problems occur on the session while now
      could receiving end.

   The Internet e-mail address in this field MAY be 1 hour into the session.

   By default, range intervals increase, where the second point is
   larger than separate from the first point.

   Example:
       Range: npt=10-15

   However, range intervals can also decrease if
   Internet host which issued the Scale header (see
   Section 16.44) indicates a negative scale value. request.  For example, this
   would be the case when a playback in reverse is desired.

   Example:
       Scale: -1
       Range: npt=15-10

   Decreasing ranges are still half open intervals as described above.
   Thus, for range A-B, A is closed and B request
   is open.  In passed through a proxy the above
   example, 15 is closed and 10 is open.  An exception to this rule is original issuer's address SHOULD be
   used.

   The client SHOULD NOT send the case when B=0 in a decreasing range.  In this case, From header field without the range is
   closed on both ends, user's
   approval, as otherwise there would be no way to reach 0 on
   a reverse playback for formats that have such a notion, like NPT and
   SMPTE.

   Example:
       Scale: -1
       Range: npt=15-0

   In this range both 15 it might conflict with the user's privacy interests or
   their site's security policy.  It is strongly recommended that the
   user be able to disable, enable, and 0 are closed.

   A decreasing range interval without modify the value of this field
   at any time prior to a corresponding negative Scale
   header is not valid.

16.39.  Referrer request.

18.23.  If-Match

   The Referrer If-Match request-header field allows the client to specify, is especially useful for ensuring
   the server's benefit, the address (URI) integrity of the resource from which presentation description, independent of how the Request-URI
   presentation description was obtained. received.  The URI refers presentation description
   can be fetched via means external to that RTSP (such as HTTP) or via the
   DESCRIBE message.  In the case of retrieving the presentation description, typically retrieved
   description via HTTP.  The Referrer
   request-header allows a RTSP, the server to generate lists implementation is guaranteeing the
   integrity of back-links to the description between the time of the DESCRIBE message
   and the SETUP message.  By including the MTag given in or with the
   session description in an If-Match header part of the SETUP request,
   the client ensures that resources set up are matching the
   description.  A SETUP request with the If-Match header for interest, logging, optimized caching, etc.  It which the
   MTag validation check fails, MUST response using 412 (Precondition
   Failed).

   This validation check is also
   allows obsolete or mistyped links very useful if a session has been
   redirected from one server to be traced for maintenance. another.

18.24.  If-Modified-Since

   The
   Referrer If-Modified-Since request-header field MUST NOT be sent if is used with the Request-URI was obtained from DESCRIBE
   and SETUP methods to make them conditional.  If the requested variant
   has not been modified since the time specified in this field, a source that does
   description will not have its own URI, such as input be returned from the user
   keyboard.

   If server (DESCRIBE) or a
   stream will not be set up (SETUP).  Instead, a 304 (Not Modified)
   response MUST be returned without any message-body.

   An example of the field value is a relative URI, it SHOULD is:
     If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

18.25.  If-None-Match

   This request header can be interpreted
   relative used with one or several message body tags
   to make DESCRIBE requests conditional.  A client that has one or more
   message bodies previously obtained from the Request-URI.  The URI MUST NOT include resource, can verify that
   none of those entities is current by including a fragment.

   Because list of their
   associated message body tags in the source If-None-Match header field.  The
   purpose of a link might be private information or might
   reveal an otherwise private information source, it this feature is strongly
   recommended to allow efficient updates of cached
   information with a minimum amount of transaction overhead.  As a
   special case, the value "*" matches any current entity of the
   resource.

   If any of the message body tags match the message body tag of the
   message body that would have been returned in the user be able response to select whether or not a
   similar DESCRIBE request (without the
   Referrer field If-None-Match header) on that
   resource, or if "*" is sent.  For example, a streaming client could have a
   toggle switch given and any current entity exists for openly/anonymously, which would respectively
   enable/disable that
   resource, then the sending of Referrer and From information.

   Clients SHOULD server MUST NOT include a Referrer perform the requested method,
   unless required to do so because the resource's modification date
   fails to match that supplied in an If-Modified-Since header field in a (non-secure)
   RTSP request
   the request.  Instead, if the referring page request method was transferred DESCRIBE, the server
   SHOULD respond with a secure
   protocol.

16.40.  Request-Status

   This request 304 (Not Modified) response, including the
   cache-related header is used to indicate fields (particularly MTag) of one of the end result for requests message
   bodies that takes time to complete, such a PLAY (Section 13.4).  It is sent
   in PLAY_NOTIFY (Section 13.5) with the end-of-stream reason to report
   how the PLAY matched.  For all other request concluded, either in success or in failure.  The
   header carries methods, the server MUST
   respond with a reference status of 412 (Precondition Failed).

   See Section 16.1.3 for rules on how to determine if two message body
   tags match.

   If none of the request it reports on using message body tags match, then the
   CSeq number for server MAY perform
   the session indicated by requested method as if the Session If-None-Match header in the
   request.  It provides both a numerical status code (according to
   Section 8.1.1) and a human readable reason phrase.

   Example:
   Request-Status: cseq=63 status=500 reason="Media data unavailable"

16.41.  Require

   The Require request-header field is used by clients or servers to
   ensure that the other end-point supports features that are required did not
   exist, but MUST also ignore any If-Modified-Since header field(s) in respect to this
   the request.  It can also be used to query  That is, if no message body tags match, then the
   other end-point supports certain features, however, the use of the
   Supported (Section 16.49) is much more effective in this purpose.
   The server
   MUST respond to this header by using the Unsupported
   header to negatively acknowledge those feature-tags which are NOT
   supported.  The response MUST use return a 304 (Not Modified) response.

   If the error code 551 (Option Not
   Supported).  This header does not apply to proxies, for request would, without the same
   functionality in respect to proxies see Proxy-Require If-None-Match header
   (Section 16.35) with the exception of media modifying proxies.  Media
   modifying proxies, due to their nature of handling media field, result
   in anything other than a way
   that is very similar to a server, do need to understand also 2xx or 304 status, then the If-None-Match
   header MUST be ignored.  (See Section 16.1.4 for a discussion of
   server features to correctly serve the client.

      This is to make sure that the client-server interaction will
      proceed without delay behavior when all features are understood by both
      sides, If-Modified-Since and only slow down if features are not understood (as If-None-Match appear
   in the example below).  For a well-matched client-server pair, the
      interaction proceeds quickly, saving same request.)

   The result of a round-trip often required
      by negotiation mechanisms.  In addition, it also removes state
      ambiguity when the client requires features that the server does
      not understand.

   Example (Not complete):

   C->S:   SETUP rtsp://server.com/foo/bar/baz.rm RTSP/2.0
           CSeq: 302
           Require: funky-feature
           Funky-Parameter: funkystuff

   S->C:   RTSP/2.0 551 Option not supported
           CSeq: 302
           Unsupported: funky-feature

   In this example, "funky-feature" request having both an If-None-Match header field and
   an If-Match header field is unspecified and MUST be considered an
   illegal request.

18.26.  Last-Modified

   The Last-Modified message-header field indicates the feature-tag date and time at
   which indicates
   to the client that origin server believes the fictional Funky-Parameter field is required.
   The relationship between "funky-feature" presentation description or
   media stream was last modified.  For the method DESCRIBE, the header
   field indicates the last modification date and Funky-Parameter is not
   communicated via time of the RTSP exchange, since
   description, for SETUP that relationship is an
   immutable property of "funky-feature" and thus should not be
   transmitted with every exchange.

   Proxies and other intermediary devices the media stream.

   An origin server MUST ignore this header.  If NOT send a
   particular extension requires that intermediate devices support it, Last-Modified date which is later
   than the extension should be tagged in server's time of message origination.  In such cases, where
   the Proxy-Require field instead
   (see Section 16.35).  See discussion resource's last modification would indicate some time in the proxies section
   (Section 17.1) about when to consider
   future, the server MUST replace that a feature requires proxy
   support.

16.42.  Retry-After

   The Retry-After response-header field can be used date with a 503 (Service
   Unavailable) response to indicate how long the service is expected to
   be unavailable to message
   origination date.

   An origin server SHOULD obtain the requesting client.  This field MAY also be used
   with any 3xx (Redirection) response Last-Modified value of the message
   body as close as possible to indicate the minimum time that it generates the
   user-agent is asked to wait before issuing the redirected request.
   The Date
   value of this field can be either an RTSP-date or its response.  This allows a recipient to make an integer
   number accurate
   assessment of seconds (in decimal) after the time of message body's modification time, especially if the response.

   Example:
   Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
   Retry-After: 120

   In
   message body changes near the latter example, time that the delay response is 2 minutes.

16.43.  RTP-Info generated.

   RTSP servers SHOULD send Last-Modified whenever feasible.

18.27.  Location

   The RTP-Info general header Location response-header field is used to set RTP-specific
   parameters in redirect the PLAY and GET_PARAMETER responses recipient
   to a location other than the Request-URI for completion of the
   request or identification of a PLAY_NOTIFY
   and GET_PARAMETER requests. new resource.  For streams using RTP as transport
   protocol 3xx responses, the RTP-Info header
   location SHOULD be part indicate the server's preferred URI for automatic
   redirection to the resource.  The field value consists of a 200 response to
   PLAY. single
   absolute URI.

   Note: The exclusion Content-Location header field (Section 18.17) differs from
   Location in that the Content-Location identifies the original
   location of the RTP-Info message body enclosed in the request.  It is
   therefore possible for a PLAY response to contain header fields for RTP
      transported media will result both
   Location and Content-Location.  Also, see Section 16.2 for cache
   requirements of some methods.

18.28.  Media-Properties

   This general header is used in that a client needs SETUP response or PLAY_NOTIFY requests
   to
      synchronize indicate the media streams using RTCP.  This may have negative
      impact as media's properties that currently are applicable to
   the RTCP can RTSP session.  PLAY_NOTIFY MAY be lost, and does not need used to be
      particularly timely in its arrival.  Also functionality as
      informing modify these properties
   at any point.  However, the client from which packet a seek has occurred is
      affected.

   The RTP-Info MAY SHOULD have received the update
   prior to any action related to the new media properties take effect.
   For aggregated sessions, the Media-Properties header will be included returned
   in each SETUP responses to provide
   synchronization information when changing transport parameters, see
   Section 13.3. response.  The header received in the latest response
   is the one that applies on the whole session from this point until
   any future update.  The RTP-Info header and the Range header MAY be included without value in a
   GET_PARAMETER request from client requests to the server without any
   values with a Session header included
   to request query the current playback point and corresponding RTP
   synchronization information.  When the RTP-Info header is included in
   a Request also Media-Properties for the Range header MUST be included (Note, Range header
   only MAY be used). session.  The server response SHALL responder
   MUST include both the Range current session's media properties.

   The media properties expressed by this header and the RTP-Info header.  If the session is the one applicable
   to all media in Play state,
   then the value of RTSP session.  For aggregated sessions, the Range
   header SHALL be filled expressed the combined media-properties.  As a result,
   aggregation of media MAY result in with a change of the
   current playback point media properties,
   and with thus the corresponding RTP-Info values.
   If content of the server is another state, no values are included Media-Properties header contained in the RTP-
   Info header.
   subsequent SETUP responses.

   The header is included in PLAY_NOTIFY requests with the
   Notify-Reason contains a list of end-of-stream property values that are applicable to provide RTP information about
   the
   end currently setup media or aggregate of media as indicated by the stream.

   The header can carry the following parameters:

   url:  Indicates the stream URI for which the following RTP parameters
         correspond, this
   RTSP URI MUST be the same as used in the SETUP
         request for this media stream.  Any relative URI MUST use request.  No ordering is enforced within the
         Request-URI as base URI.  This parameter MUST header.
   Property values should be present.

   ssrc: The Synchronization source (SSRC) grouped into a single group that the RTP timestamp and
         sequence number provided applies to.  This parameter MUST be
         present.

   seq:  Indicates the sequence number of the first packet of the stream handles a
   particular orthogonal property.  Values or groups that is direct result of the request.  This allows clients to
         gracefully deal with packets when seeking. express
   multiple properties SHOULD NOT be used.  The client uses
         this value to differentiate packets that originated before the
         seek from packets that originated after the seek.  Note list of properties that a
         client may not receive the packet with the
   can be expressed sequence
         number, and instead packets with a higher sequence number, due
         to packet loss or reordering.  This parameter is RECOMMENDED to MAY be present.

   rtptime: extended at any time.  Unknown property
   values MUST indicate be ignored.

   This specification defines the RTP timestamp following 4 groups and their property
   values:

   Random Access:

      Random-Access:  Indicates that random access is possible.  May
         optionally include a floating point value corresponding to in seconds indicating
         the
         start time value longest duration between any two random access points in
         the Range response header, or if not
         explicitly given media.

      Begining-Only:  Seeking is limited to the implied start point. beginning only.

      No-Seeking:  No seeking is possible.

   Content Modifications:

      Immutable:  The client uses this
         value to calculate content will not be changed during the mapping life-time
         of RTP time to NPT the RTSP session.

      Dynamic:  The content may be changed based on external methods or other
         triggers

      Time-Progressing  The media timescale.  This parameter SHOULD be present to ensure
         inter-media synchronization is achieved.  There exists no
         requirement that any received RTP packet accessible progresses as wallclock
         time progresses.

   Retention:

      Unlimited:  Content will have be retained for the duration of the life-
         time of the same RTP
         timestamp value as RTSP session.

      Time-Limited:  Content will be retained at least until the one
         specified wallclock time.  The time must be provided in the parameter used to establish
         synchronization.

      A mapping from RTP timestamps to NTP timestamps (wallclock) is
      available via RTCP.  However, this information is not sufficient
      to generate a mapping from RTP timestamps to media clock
         absolute time
      (NPT, etc.).  Furthermore, format specified in order to ensure that this
      information Section 4.6.

      Time-Duration  Each individual media unit is available retained for at least
         the necessary specified time (immediately at
      startup or after duration.  This definition allows for
         retaining data with a seek), and that it is delivered reliably, this
      mapping time based sliding window.  The time
         duration is placed expressed as floating point number in the RTSP control channel.

      In order to compensate for drift for long, uninterrupted
      presentations, RTSP clients should additionally map NPT to NTP,
      using initial RTCP sender reports to do the mapping, and later
      reports to check drift against the mapping.

   Example:
   Range:npt=3.25-15
   RTP-Info:url="rtsp://example.com/foo/audio" ssrc=0A13C760:seq=45102;
            rtptime=12345678,url="rtsp://example.com/foo/video"
            ssrc=9A9DE123:seq=30211;rtptime=29567112

   Lets assume that Audio uses a 16kHz RTP timestamp clock and Video seconds. 0.0
         is a 90kHz RTP timestamp clock. Then the media synchronization valid value as this indicates that no data is
   depicted retained in the following way.

   NPT    3.0---3.1---3.2-X-3.3---3.4---3.5---3.6
   Audio               PA
         a time-progressing session.

   Supported Scale:

      Scales:  A
   Video                  V    PV

   X: NPT time value = 3.25, from Range header.
   A: RTP timestamp value for Audio from RTP-Info header (12345678).
   V: RTP timestamp value for Video from RTP-Info header (29567112).
   PA: RTP audio packet carrying an RTP timestamp quoted comma separated list of 12344878. Which
       corresponds to NPT = (12344878 - A) / 16000 + 3.25 = 3.2
   PV: RTP video packet carrying an RTP timestamp one or more decimal
         values or ranges of 29573412. Which
       corresponds to NPT = (29573412 - V) / 90000 + 3.25 = 3.32

16.44.  Scale

   A scale value of 1 indicates normal play at the normal forward
   viewing rate.  If not 1, the value corresponds to values supported by the rate with
   respect to normal viewing rate.  For example, content in
         arbitrary order.  A range has a ratio of 2 indicates
   twice the normal viewing rate ("fast forward") start and stop value separated
         by a ratio of 0.5 colon.  A range indicates half that the normal viewing rate.  In other words, a ratio of 2
   has content time increase at twice the playback time.  For every
   second supports fine
         grained selection of elapsed (wallclock) time, 2 seconds scale values.  Fine grained allows for
         steps at least as small as one tenth of content time will be
   delivered. a scale value.  A negative value indicates reverse direction.  For
   certain media transports this may require certain considerations
         content is considered to
   work consistent, see Appendix C.1 for description on how RTP handles
   this.

   The transmitted data rate SHOULD NOT be changed by support fine grained selection of when
         the server in response to a
   different given scale value can produce
         content with an actual scale that is less than 1 tenth of scale
         unit, i.e., 0.1, from the requested value.  Negative values are
         supported.  The resulting bit-rate should value 0 has no meaning and MUST NOT be reasonably
   close to the nominal bit-rate used.

   Examples of the content this header for Scale = 1. on-demand content and a live stream
   without recording are:

   On-demand:
   Media-Properties: Random-Access=2.5s, Unlimited, Immutable,
        Scales="-20, -10, -4, 0.5:1.5, 4, 8, 10, 15, 20"

   Live stream without recording/timeshifting:
   Media-Properties: No-Seeking, Time-Progressing, Time-Duration=0.0

18.29.  Media-Range

   The
   server has to actively manipulate the data when needed Media-Range general header is used to meet give the
   bitrate constraints.  Implementation range of scale changes depends on the
   server and media type.  For video, a server may, for example, deliver
   only key frames or selected frames.  For audio, it may time-scale
   at the
   audio while preserving pitch or, less desirably, deliver fragments time of
   audio, or completely mute sending the audio.

   The server RTSP message.  This header MUST be
   included in SETUP response, and content may restrict the range of scale values PLAY and PAUSE response for media
   that it
   supports.  The supported values are indicated by the Media-Properties
   header (Section 16.28).  The client SHOULD only indicate values
   indicated to be supported.  However, as the values may Time-Progressing, and PLAY and PAUSE response after any
   change as the
   content progresses a requested value may no longer be valid when the
   request arrives.  Thus, a non-supported value for media that are Dynamic, and in a PLAY_NOTIFY request does not
   generate an error, only forces that
   are sent due to Media-Property-Update.  Media-Range header without
   any range specifications MAY be included in GET_PARAMETER requests to
   the server to choose request the closest
   value. current range.  The response MUST always contain the actual scale value
   chosen by the server.

   If the server does not implement the possibility to scale, it will
   not return a Scale header.  A server supporting Scale operations for
   PLAY MUST indicate in this with
   case include the use of current range at the "play.scale" feature-tag.

   When indicating a negative scale for a reverse playback, time of sending the Range response.

   The header MUST indicate a decreasing include range specifications for all time formats
   supported for the media, as described in
   Section 16.38.

   Example of playing indicated in reverse at 3.5 times normal rate:
     Scale: -3.5
     Range: npt=15-10

16.45.  Seek-Style

   When a client sends a PLAY request with a Range Accept-Ranges header to perform a
   random access to
   (Section 18.5) when setting up the media, media.  The server MAY include
   more than one range specification of any given time format to
   indicate media that has non-continuous range.

   For media that has the client does not know if Time-Progressing property, the server Media-Range
   values will pick the first media samples or only be valid for the first random access particular point
   prior to in time when it
   was issued.  As wallclock progresses so will also the request media range.  Depending on use case, the client may
   have a strong preference.  To express this preference and provide the
   client with information on how the server actually acted on
   However, it shall be assumed that
   preference media time progresses in direct
   relationship to wallclock time (with the Seek-Style header is defined.

   Seek-Style is exception of clock skew) so
   that a general reasonably accurate estimation of the media range can be
   calculated.

18.30.  MTag

   The MTag response header that MAY be included in any PLAY
   request to indicate the client's preference for any media stream that
   has random access properties. DESCRIBE, GET_PARAMETER
   or SETUP responses.  The server MUST always include message body tags (Section 4.8) returned in
   a DESCRIBE response, and the
   header one in any PLAY response for media with random access properties SETUP refers to indicate what policy was applied.  A server that receives an
   unknown Seek-Style policy MUST ignore it and select the server
   default policy.  A client receiving an unknown policy MUST ignore it
   and use presentation,
   i.e. both the Range header returned session description and any media synchronization information as
   basis to determine what the server did. media stream.
   This specification defines the following seek policies allows for verification that may be
   requested (see also Section 4.9.1):

   RAP:  Random Access Point (RAP) is the behavior of requesting one has the
      server right session
   description to locate the closest previous random access point that
      exists in the media aggregate and deliver from that.  By
      requesting a RAP, media quality will be resource at the best possible as all
      media will be delivered from time of the SETUP request.
   However, it has the disadvantage that a point where full media state can be
      established change in any of the media decoder.

   CoRAP:  Conditional Random Access Point (CoRAP) is a variant parts
   results in invalidation of all the
      above RAP behavior.  This policy is primarily intended for cases
      where there parts.

   If the MTag is larger distance between provided both inside the random access points message body, e.g. within the
   "a=mtag" attribute in SDP, and in the media.  CoRAP response message, then both
   tags MUST be identical.  It is conditioned on RECOMMENDED that there the MTag is a Random Access
      Point closer to primarily
   given in the requested start point than RTSP response message, to the current
      pause point.  This policy assumes ensure that caches can use the media state existing
      prior
   MTag without requiring content inspection.  However, for session
   descriptions that are distributed outside of RTSP, for example using
   HTTP, etc. it will be necessary to include the pause is usable if delivery message body tag in
   the session description as specified in Appendix D.1.9.

   SETUP and DESCRIBE requests can be made conditional upon the MTag
   using the headers If-Match (Section 18.23) and If-None-Match (
   Section 18.25).

18.31.  Notify-Reason

   The Notify Reason header is continued.  If solely used in the PLAY_NOTIFY method.
   It indicates the reason why the
      client or server knows has sent the asynchronous
   PLAY_NOTIFY request (see Section 13.5).

18.32.  Pipelined-Requests

   The Pipelined-Requests general header is used to indicate that this a
   request is not the fact the RAP policy
      should to be used.  In other words: executed in most cases when the client
      requests context created by a start point prior previous
   request(s).  The primary usage of this header is to allow pipelining
   of SETUP requests so that any additional SETUP request after the current pause point, a valid
      decoding dependency chain from the media delivered prior
   first one does not need to wait for the
      pause and session ID to be sent back to
   the requested media unit will not exist.  If requesting agent.  The header contains a unique identifier that
   is scoped by the
      server searched persistent connection used to send the requests.

   Upon receiving a random access point request with the server Pipelined-Requests the responding
   agent MUST return look up if there exists a binding between this Pipelined-
   Requests identifier for the CoRAP policy in current persistent connection and an RTSP
   session ID.  If that exists then the Seek-Style received request is processed
   the same way as if it contained the Session header and adjust with the Range found
   session ID.  If there does not exist a mapping and no Session header to reflect
   is included in the position request, the responding agent MUST create a
   binding upon the successful completion of a session creating request,
   i.e.  SETUP.  A binding MUST NOT be created, if the picked RAP. request failed to
   create an RTSP session.  In case the
      random access point is further away request contains both a Session
   header and the server selects to
      continue from Pipelined-Requests header the current pause point it Pipelined-Requests MUST include the "Next"
      policy in
   be ignored.

   Note: Based on the Seek-Style header and adjust above definition at least the Range header start
      point first request
   containing a new unique Pipelined-Requests will be required to be a
   SETUP request (unless the current pause point.

   First-Prior:  The first-prior policy will start delivery protocol is extended with the
      media unit that has new methods of
   creating a playout time session).  After that first prior to one, additional SETUP requests
   or request of any type using the requested
      time.  For discrete media that would only RTSP session context may include media units that
      would still be rendered at the
   Pipelined-Requests header.

   When responding to any request time.  For continuous media
      that is media that will be rendered during the requested start
      time of contained the range.

   Next:  The next media units after Pipelined-Requests
   header the provided start time of server MUST also include the
      range.  For continuous framed media Session header when a binding
   to a session context exist.  An RTSP agent that would mean knows the first next
      frame after session ID
   SHOULD NOT use the provided time.  For discrete media Pipelined-Requests header in any request and only
   use the first unit
      that Session header.  This as the Session identifier is to be rendered after persistent
   across transport contexts, like TCP connections, which the provided time.  The main usage
      for this case Pipelined-
   Requests identifier is when not.

   The RTSP agent sending the client knows it request with a Pipelined-Requests header
   has all media up to the responsibility for using a
      certain point unique and would like previously unused
   identifier within the transport context.  Currently only a TCP
   connection is defined as such transport context.  A server MUST
   delete the Pipelined-Requests identifier and its binding to continue delivery so that a
      complete non-interrupted media playback can be achieved.  Example session
   upon the termination of such scenarios include switching that session.  Despite the previous mandate,
   RTSP agents are RECOMMENDED to not reuse identifiers to allow for
   better error handling and logging.

   RTSP Proxies may need to translate Pipelined-Requests identifier
   values from a broadcast/multicast
      delivery incoming request to outgoing to allow for aggregation of
   requests onto a unicast based delivery.  This policy persistent connection.

18.33.  Proxy-Authenticate

   The Proxy-Authenticate response-header field MUST only be
      used on the client's explicit request.

   Please note that these expressed preferences exist for optimizing the
   startup time or the media quality. included as part
   of a 407 (Proxy Authentication Required) response.  The "Next" policy breaks the
   normal definition field value
   consists of the Range header to enable a client challenge that indicates the authentication scheme and
   parameters applicable to request
   media with minimal overlap, although some may still occur the proxy for
   aggregated sessions.  RAP and First-Prior both fulfill this Request-URI.

   The HTTP access authentication process is described in [RFC2617].
   Unlike WWW-Authenticate, the
   requirement of providing media from Proxy-Authenticate header field applies
   only to the requested range current connection and forward. SHOULD NOT be passed on to
   downstream agents.  However, unless RAP is used, an intermediate proxy might need to
   obtain its own credentials by requesting them from the media quality for many media codecs
   using predictive methods can be severely degraded unless additional
   data downstream
   agent, which in some circumstances will appear as if the proxy is available as, for example, already buffered, or through other
   side channels.

16.46.  Server
   forwarding the Proxy-Authenticate header field.

18.34.  Proxy-Authorization

   The Server response-header Proxy-Authorization request-header field contains information about the
   software used by allows the origin server client to handle the request.
   identify itself (or its user) to a proxy which requires
   authentication.  The Proxy-Authorization field
   can contain multiple product tokens and comments identifying value consists of
   credentials containing the
   server and any significant subproducts.  The product tokens are
   listed in order authentication information of their significance the user
   agent for identifying the
   application.

   Example:
   Server: PhonyServer/1.0

   If proxy and/or realm of the response is resource being forwarded through a proxy, requested.

   The HTTP access authentication process is described in [RFC2617].
   Unlike Authorization, the Proxy-Authorization header field applies
   only to the next outbound proxy
   application MUST NOT modify that demanded authentication using
   the Server response-header.  Instead, it
   SHOULD include Proxy-Authenticate field.  When multiple proxies are used in a Via field (Section 16.56).  If
   chain, the response Proxy-Authorization header field is
   generated consumed by the proxy, first
   outbound proxy that was expecting to receive credentials.  A proxy
   MAY relay the credentials from the client request to the next proxy application MUST return
   if that is the Server
   response-header as previously returned mechanism by which the server.

16.47.  Session proxies cooperatively
   authenticate a given request.

18.35.  Proxy-Require

   The Session Proxy-Require request-header and response-header field identifies an
   RTSP session.  An RTSP session is created by the server as a result
   of a successful SETUP request and in the response the session
   identifier is given used to the client.  The RTSP session exists until
   destroyed by a TEARDOWN, REDIRECT or timed out indicate proxy-
   sensitive features that MUST be supported by the server.

   The session identifier is chosen proxy.  Any Proxy-
   Require header features that are not supported by the server (see Section 4.3) and proxy MUST be returned in
   negatively acknowledged by the SETUP response.  Once a client receives a
   session identifier, it MUST be included in any request related proxy to
   that session.  This means that the Session header MUST be included in
   a request, client using the following methods: PLAY, PAUSE, and TEARDOWN,
   and MAY be included in SETUP, OPTIONS, SET_PARAMETER, GET_PARAMETER,
   and REDIRECT, and MUST NOT be included in DESCRIBE.
   Unsupported header.  The Session
   header proxy MUST NOT be included in the following methods, if these
   requests are pipelined and if the session identifier is not yet
   known: PLAY, PAUSE, TEARDOWN, SETUP, OPTIONS SET_PARAMETER, and
   GET_PARAMETER.

   In an RTSP response use the session header MUST be included in methods,
   SETUP, PLAY, and PAUSE, and MAY be included in methods, TEARDOWN, and
   REDIRECT, and if included 551 (Option Not
   Supported) status code in the request of the following methods it
   MUST also be response.  Any feature-tag included in
   the response, OPTIONS, GET_PARAMETER, and
   SET_PARAMETER, Proxy-Require does not apply to the end-point (server or client).
   To ensure that a feature is supported by both proxies and MUST NOT servers the
   tag needs to be included in DESCRIBE responses.

   Note that also a session identifier identifies an RTSP session across
   transport sessions or connections.  RTSP requests Require header.

   See Section 18.41 for a given session
   can use different URIs (Presentation and media URIs).  Note, that
   there are restrictions depending more details on the session which URIs mechanics of this message
   and a usage example.  See discussion in the proxies section
   (Section 15.1) about when to consider that are
   acceptable for a given method.  However, multiple "user" sessions for feature requires proxy
   support.

   Example of use:
      Proxy-Require: play.basic

18.36.  Proxy-Supported

   The Proxy-Supported header field enumerates all the same URI from extensions
   supported by the same client will require use of different
   session identifiers. proxy using feature-tags.  The session identifier is needed to distinguish several delivery
      requests for header carries the same URI coming from
   intersection of extensions supported by the same client. forwarding proxies.  The response 454 (Session Not Found)
   Proxy-Supported header MAY be included in any request by a proxy.  It
   MUST be returned added by any proxy if the session
   identifier is invalid.

   The Supported header MAY include the session timeout period.  If not explicitly
   provided this value is set to 60 seconds.  As this affects how often
   session keep-alives are needed values smaller than 30 seconds are not
   recommended.  However, larger than default values can be useful in
   applications of RTSP that have inactive but established sessions for
   longer time periods.

      60 seconds was chosen as session timeout value due to: Resulting present in not too frequent keep-alive messages and having low sensitivity
      to variations a
   request.  When present in request response timing.  If one reduces a request, the
      timeout value to below 30 seconds receiver MUST in the corresponding request
   response timeout becomes a significant part of copy the session
      timeout. 60 seconds also allows for reasonably rapid recovery received Proxy-Supported header.

   The Proxy-Supported header field contains a list of
      committed server resources feature-tags
   applicable to proxies, as described in case of client failure.

16.48.  Speed Section 4.7.  The Speed request-header field requests list is the server to deliver
   specific amounts of nominal media time per unit
   intersection of delivery time,
   contingent on the server's ability and desire to serve all feature-tags understood by the media
   stream at proxies.  To
   achieve an intersection, the given speed.  The client requests proxy adding the delivery speed to
   be within Proxy-Supported header
   includes all proxy feature-tags it understands.  Any proxy receiving
   a given range request with a lower and upper bound.  The server
   SHALL deliver at the highest possible speed within the range, but not
   faster than the upper-bound, for which the underlying network path
   can support header, MUST check the resulting transport data rates.  As long as list and removes any speed
   value within the given range can be provided
   feature-tag(s) it does not support.  A Proxy-Supported header present
   in the server SHALL response MUST NOT
   modify the media quality.  Only if be touched by the server is unable to deliver
   media at proxies.

   Example:

     C->P1: OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            User-Agent: PhonyClient/1.2

    P1->P2: OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            Proxy-Supported: proxy-foo, proxy-bar, proxy-blech
            Via: 2.0 pro.example.com

    P2->S:  OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            Proxy-Supported: proxy-foo, proxy-blech
            Via: 2.0 pro.example.com, 2.0 prox2.example.com

     S->C:  RTSP/2.0 200 OK
            Supported: foo, bar, baz
            Proxy-Supported: proxy-foo, proxy-blech
            Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN
            Via: 2.0 pro.example.com, 2.0 prox2.example.com

18.37.  Public

   The Public response header field lists the speed value provided set of methods supported
   by the lower bound shall it reduce response sender.  This header applies to the media quality.

   Implementation general
   capabilities of the Speed functionality by the server sender and its only purpose is OPTIONAL.
   The server can to indicate its support through a feature-tag,
   play.speed.  The lack of a Speed header in the response is an
   indication of lack of support of this functionality.

   The speed parameter values are expressed as a positive decimal value,
   e.g., a value of 2.0 indicates that data is
   sender's capabilities to be delivered twice as
   fast as normal.  A speed value of zero is invalid.  The range is
   specified in the form "lower bound - upper bound". recipient.  The lower bound
   value methods listed may be smaller or equal to the upper bound.  All speeds
   may not be possible applicable to support.  Therefore the server MAY modify the
   requested values to Request-URI; the closest supported.  The actual supported
   speed MUST Allow header field
   (Section 18.6) MAY be included in used to indicate methods allowed for a
   particular URI.

   Example of use:
      Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN

   In the response.  Note, however, event that there are proxies between the use
   cases may vary sender and that Speed value ranges such as 0.7 - 0.8,
   0.3-2.0, 1.0-2.5, 2.5-2.5 all have their usage.

   Example:

     Speed: 1.0-2.5

   Use of this header changes the bandwidth used for data delivery.  It
   is meant for use in specific circumstances where delivery
   recipient of the
   presentation at a higher or lower rate is desired.  The main use
   cases response, each intervening proxy MUST modify the
   Public header field to remove any methods that are buffer operations or local scale operations.  Implementors
   should keep in mind not supported via
   that bandwidth for proxy.  The resulting Public header field will contain an
   intersection of the session may be negotiated
   beforehand (by means other than RTSP), sender's methods and therefore re-negotiation the methods allowed through
   by the intervening proxies.

      In general, proxies should allow all methods to transparently pass
      through from the sending RTSP agent to the receiving RTSP agent,
      but there may be necessary.  To perform Speed operations cases where this is not desirable for a given
      proxy.  Modification of the server needs to
   ensure Public response header field by the
      intervening proxies ensures that the network path request sender gets an
      accurate response indicating the methods that can support be used on the resulting bit-rate.
   Thus
      target agent via the media transport needs proxy chain.

18.38.  Range

   The Range header specifies a time range in PLAY (Section 13.4), PAUSE
   (Section 13.6), SETUP (Section 13.3), REDIRECT (Section 13.10), and
   PLAY_NOTIFY (Section 13.5) requests and responses.  It MAY be
   included in GET_PARAMETER requests from the client to support feedback so that the server
   can react with
   only a Range format and adapt no value to request the available bitrate.

16.49.  Supported current media
   position, whether the session is in Play or Ready state in the
   included format.  The Supported header enumerates all server SHALL, if supporting the extensions supported by range format,
   respond with the current playing point or pause point as the start of
   the range.  If an explicit stop point was used in the previous PLAY
   request, then that value shall be included as stop point.  Note that
   if the
   client or server using feature tags.  The header carries the
   extensions supported by is currently under any type of media playback
   manipulation affecting the message sending client or server.  The
   Supported header MAY interpretation of Range, like Scale, that
   is also required to be included in any request.  When present GET_PARAMETER response to
   provide complete information.

   The range can be specified in a
   request, number of units.  This specification
   defines smpte (Section 4.4), npt (Section 4.5), and clock
   (Section 4.6) range units.  While byte ranges [H14.35.1] and other
   extended units MAY be used, their behavior is unspecified since they
   are not normally meaningful in RTSP.  Servers supporting the receiver Range
   header MUST respond with its corresponding Supported
   header.  Note that understand the Supported NPT range format and SHOULD understand the
   SMPTE range format.  If the Range header is also included sent in 4xx and
   5xx responses.

   The Supported header contains a list of feature-tags, described in
   Section 4.7, time format
   that are understood by is not understood, the client or server. recipient SHOULD return 456 (Header Field
   Not Valid for Resource) and include an Accept-Ranges header
   indicating the supported time formats for the given resource.

   Example:

     C->S:  OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            User-Agent: PhonyClient/1.2

     S->C:  RTSP/2.0 200 OK
            Supported: bar, blech, baz

16.50.  Terminate-Reason
     Range: clock=19960213T143205Z-

   The Terminate-Reason request Range header allows the server when sending contains a
   REDIRECT or TEARDOWN request to provide range of one single range format.  A
   range is a reason for the session
   termination half-open interval with a start and any additional information.  This specification
   identifies three reasons an end point,
   including the start point, but excluding the end point.  A range may
   either be fully specified with explicit values for Redirections start point and may
   end point, or have either start or end point be extended in implicit.  An
   implicit start point indicates the
   future:

   Server-Admin:  The server needs to be shutdown for some
      administrative reason.

   Session-Timeout:  A client's session is kept alive for extended
      periods of time session's pause point, and if no
   pause point is set the server has determined that it needs to
      reclaim start of the resources associated with this session.

   Internal-Error content.  An internal error that is impossible to recover from
      has occurred forcing implicit end point
   indicates the server to terminate end of the session. content.  The Server may provide additional parameters containing information
   around usage of both implicit start
   and end point is not allowed in the redirect.  This specification defines same range header, however, the following ones.

   time:  Provides a wallclock time when
   exclusion of the server will stop provide
      any service.

   user-msg:  An UTF-8 text string with a message range header has that meaning, i.e. from pause point
   (or start) until end of content.

      Regarding the server to half-open intervals; a range of A-B starts exactly
      at time A, but ends just before B. Only the
      user.  This message SHOULD be displayed to start time of a media
      unit such as a video or audio frame is relevant.  For example,
      assume that video frames are generated every 40 ms.  A range of
      10.0-10.1 would include a video frame starting at 10.0 or later
      time and would include a video frame starting at 10.08, even
      though it lasted beyond the user.

16.51.  Timestamp

   The Timestamp general-header describes when interval.  A range of 10.0-10.08, on
      the agent sent other hand, would exclude the
   request.  The frame at 10.08.

      Please note the difference between NPT time scales' "now" and an
      implicit start value.  Implicit value of reference the timestamp current pause-
      point.  While "now" is of significance only to the
   agent and may use any timescale.  The responding agent MUST echo the
   exact same value and MAY, if it has accurate information about this,
   add currently ongoing time.  In a floating point number indicating time-
      progressing session with recording (retention for some or full
      time) the number of seconds that has
   elapsed since it has received pause point may be 2 min into the request.  The timestamp can session while now
      could be used
   by 1 hour into the agent to compute session.

   By default, range intervals increase, where the round-trip time to second point is
   larger than the responding agent
   so that it first point.

   Example:
       Range: npt=10-15

   However, range intervals can adjust the timeout value for retransmissions when
   running over an unreliable protocol.  It also resolves retransmission
   ambiguities for unreliable transport of RTSP.

   Note that the present specification provides only for reliable
   transport of RTSP messages.  The Timestamp general-header is
   specified in case the protocol is extended in decrease if the future to use
   unreliable transport.

16.52.  Transport

   The Transport request and response Scale header (see
   Section 18.44) indicates which transport
   protocol is to a negative scale value.  For example, this
   would be used and configures its parameters such the case when a playback in reverse is desired.

   Example:
       Scale: -1
       Range: npt=15-10

   Decreasing ranges are still half open intervals as
   destination address, compression, multicast time-to-live and
   destination port described above.
   Thus, for a single stream.  It sets those values not
   already determined by a presentation description. range A-B, A Transport request header MAY contain a list of transport options
   acceptable to is closed and B is open.  In the client, in above
   example, 15 is closed and 10 is open.  An exception to this rule is
   the form of multiple transport
   specification entries.  Transport specifications are comma separated,
   listed case when B=0 in a decreasing order of preference.  Parameters may range.  In this case, the range is
   closed on both ends, as otherwise there would be added no way to
   each transport specification, separated by reach 0 on
   a semicolon.  The server
   MUST return reverse playback for formats that have such a Transport response-header in the response to indicate
   the values actually chosen if any.  If the transport specification is
   not supported, no transport notion, like NPT and
   SMPTE.

   Example:
       Scale: -1
       Range: npt=15-0

   In this range both 15 and 0 are closed.

   A decreasing range interval without a corresponding negative Scale
   header is returned and the request MUST
   be responded using not valid.

18.39.  Referrer

   The Referrer request-header field allows the status code 461 (Unsupported Transport)
   (Section 15.4.26).  In case more than one transport specification was
   present in client to specify, for
   the request, server's benefit, the server MUST return address (URI) of the single (transport-
   spec) resource from which
   the Request-URI was actually chosen, if any. obtained.  The number of transport-
   spec entries is expected URI refers to be limited as the client will get
   guidance on what configurations that are possible from of the
   presentation description. description, typically retrieved via HTTP.  The Transport header MAY also be used in subsequent SETUP requests to
   change transport parameters.  A Referrer
   request-header allows a server MAY refuse to change
   parameters of an existing stream.

   A transport specification may only contain one of any given parameter
   within it.  Parameters MAY be given in any order.  Additionally, it
   may only contain either generate lists of the unicast back-links to
   resources for interest, logging, optimized caching, etc.  It also
   allows obsolete or the multicast transport
   type parameter.  All parameters need mistyped links to be understood in a transport
   specification, if not, the transport specification traced for maintenance.  The
   Referrer field MUST NOT be ignored.
   RTSP proxies of any type that uses or modifies sent if the transport
   specification, e.g. access proxy or security proxy, MUST remove
   specifications with unknown parameters before forwarding Request-URI was obtained from
   a source that does not have its own URI, such as input from the RTSP
   message. user
   keyboard.

   If that result in no remaining transport specification the
   proxy SHALL send a 461 (Unsupported Transport) (Section 15.4.26)
   response without any Transport header.

      The Transport header field value is restricted to describing a single media
      stream.  (RTSP can also control multiple streams as a single
      entity.)  Making relative URI, it part of RTSP rather than relying on SHOULD be interpreted
   relative to the Request-URI.  The URI MUST NOT include a
      multitude of session description formats greatly simplifies
      designs fragment.

   Because the source of firewalls.

   The general syntax for a link might be private information or might
   reveal an otherwise private information source, it is strongly
   recommended that the transport specifier user be able to select whether or not the
   Referrer field is sent.  For example, a list of slash
   separated tokens:
   Value1/Value2/Value3...
   Which streaming client could have a
   toggle switch for RTP transports take openly/anonymously, which would respectively
   enable/disable the form:
   RTP/profile/lower-transport.

   The default value for sending of Referrer and From information.

   Clients SHOULD NOT include a Referrer header field in a (non-secure)
   RTSP request if the "lower-transport" parameters referring page was transferred with a secure
   protocol.

18.40.  Request-Status

   This request header is specific used to indicate the profile.  For RTP/AVP, the default is UDP.

   There are two different methods end result for how requests
   that takes time to specify where complete, such a PLAY (Section 13.4).  It is sent
   in PLAY_NOTIFY (Section 13.5) with the media
   should be delivered for unicast transport:

   dest_addr:  The presence of this parameter and its values indicates end-of-stream reason to report
   how the destination address PLAY request concluded, either in success or addresses (host address and port
         pairs for IP flows) necessary in failure.  The
   header carries a reference to the request it reports on using the
   CSeq number for the media transport.

   No dest_addr:  The lack of session indicated by the dest_addr parameter indicates Session header in the
   request.  It provides both a numerical status code (according to
   Section 8.1.1) and a human readable reason phrase.

   Example:
   Request-Status: cseq=63 status=500 reason="Media data unavailable"

18.41.  Require

   The Require request-header field is used by clients or servers to
   ensure that the
         server MUST send media other end-point supports features that are required
   in respect to same address for which this request.  It can also be used to query if the
   other end-point supports certain features, however, the RTSP
         messages originates.

   The choice use of method for indicating where the media
   Supported (Section 18.49) is much more effective in this purpose.
   The server MUST respond to be
   delivered depends on the use case.  In some cases this header by using the only allowed
   method will be Unsupported
   header to negatively acknowledge those feature-tags which are NOT
   supported.  The response MUST use no explicit address indication and have the
   server deliver media error code 551 (Option Not
   Supported).  This header does not apply to the source of the RTSP messages.

   For Multicast there is several methods proxies, for specifying addresses but
   they are different the same
   functionality in how they work compared with unicast:

   dest_addr respect to proxies see Proxy-Require header
   (Section 18.35) with client picked address:  The address and relevant
         parameters like TTL (scope) for the actual multicast group exception of media modifying proxies.  Media
   modifying proxies, due to
         deliver the their nature of handling media to.  There are security implications
         (Section 21) with this method in a way
   that needs is very similar to be addressed if
         using this method because a RTSP server can be used as a DoS
         attacker on an existing multicast group.

   dest_addr using Session Description Information:  The information
         included in server, do need to understand also the transport header can all be coming from
   server features to correctly serve the
         session description, e.g. client.

      This is to make sure that the SDP c= client-server interaction will
      proceed without delay when all features are understood by both
      sides, and m= line.  This
         mitigates some of only slow down if features are not understood (as in
      the security issues of example below).  For a well-matched client-server pair, the previous methods
         as
      interaction proceeds quickly, saving a round-trip often required
      by negotiation mechanisms.  In addition, it is also removes state
      ambiguity when the session provider client requires features that picks the multicast group
         and scope.  The server does
      not understand.

   Example (Not complete):
   C->S:   SETUP rtsp://server.com/foo/bar/baz.rm RTSP/2.0
           CSeq: 302
           Require: funky-feature
           Funky-Parameter: funkystuff

   S->C:   RTSP/2.0 551 Option not supported
           CSeq: 302
           Unsupported: funky-feature

   In this example, "funky-feature" is the feature-tag which indicates
   to the client MUST include that the information if it fictional Funky-Parameter field is
         available in the session description.

   No dest_addr: required.
   The behavior when no explicit multicast group is
         present in a request relationship between "funky-feature" and Funky-Parameter is not defined.

   An RTSP proxy will need to take care.  If
   communicated via the media RTSP exchange, since that relationship is an
   immutable property of "funky-feature" and thus should not desired to be routed through the proxy, the proxy will need to introduce the
   destination indication.

   Below are the configuration parameters associated
   transmitted with transport:

   General parameters:

   unicast / multicast:  This parameter is every exchange.

   Proxies and other intermediary devices MUST ignore this header.  If a mutually exclusive
         indication of whether unicast or multicast delivery will be
         attempted.  One of
   particular extension requires that intermediate devices support it,
   the two values MUST extension should be specified.  Clients
         that are capable of handling both unicast and multicast
         transmission needs tagged in the Proxy-Require field instead
   (see Section 18.35).  See discussion in the proxies section
   (Section 15.1) about when to indicate such capability by including two
         full transport-specs consider that a feature requires proxy
   support.

18.42.  Retry-After

   The Retry-After response-header field can be used with separate parameters for each.

   layers:  The number of multicast layers a 503 (Service
   Unavailable) response to indicate how long the service is expected to
   be unavailable to the requesting client.  This field MAY also be used for this media
         stream.  The layers are sent
   with any 3xx (Redirection) response to consecutive addresses starting
         at indicate the dest_addr address.  If minimum time the parameter
   user-agent is not included, it
         defaults asked to a single layer.

   dest_addr:  A general destination address parameter that wait before issuing the redirected request.
   The value of this field can contain
         one be either an RTSP-date or more address specifications.  Each combination an integer
   number of
         protocol/profile/lower transport needs to have seconds (in decimal) after the format and
         interpretation time of its address specification defined.  For RTP/
         AVP/UDP and RTP/AVP/TCP, the address specification response.

   Example:

   Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
   Retry-After: 120

   In the latter example, the delay is a tuple
         containing a host address 2 minutes.

18.43.  RTP-Info

   The RTP-Info general header field is used to set RTP-specific
   parameters in the PLAY and port.  Note, only GET_PARAMETER responses or a single
         destination parameter per PLAY_NOTIFY
   and GET_PARAMETER requests.  For streams using RTP as transport spec is intended.  The
         usage
   protocol the RTP-Info header SHOULD be part of multiple destinations to distribute a single media 200 response to
         multiple entities is unspecified.
   PLAY.

      The client originating the RTSP request MAY specify the
         destination address of the stream recipient with the host
         address part exclusion of the tuple.  When the destination address is
         specified, the recipient may be RTP-Info in a different party than PLAY response for RTP
      transported media will result in that a client needs to
      synchronize the
         originator of media streams using RTCP.  This may have negative
      impact as the request.  To avoid becoming RTCP can be lost, and does not need to be
      particularly timely in its arrival.  Also functionality as
      informing the unwitting
         perpetrator of a remote-controlled denial-of-service attack, client from which packet a
         server MUST perform security checks (see seek has occurred is
      affected.

   The RTP-Info MAY be included in SETUP responses to provide
   synchronization information when changing transport parameters, see
   Section 21.1) 13.3.  The RTP-Info header and
         SHOULD log such attempts before allowing the Range header MAY be
   included in a GET_PARAMETER request from client to direct a
         media stream server without any
   values to request the current playback point and corresponding RTP
   synchronization information.  When the RTP-Info header is included in
   a recipient address not chosen by Request also the server.
         Implementations cannot rely on TCP as reliable means of client
         identification. Range header MUST be included (Note, Range header
   only MAY be used).  The server response SHALL include both the Range
   header and the RTP-Info header.  If the server does not allow session is in Play state,
   then the host address
         part value of the tuple to Range header SHALL be set, it MUST return 463 (Destination
         Prohibited).

         The host address part of filled in with the tuple MAY be empty, for example
         ":58044",
   current playback point and with the corresponding RTP-Info values.
   If the server is another state, no values are included in cases when only destination port the RTP-
   Info header.  The header is desired to be
         specified.  Responses to included in PLAY_NOTIFY requests including with the
   Notify-Reason of end-of-stream to provide RTP information about the
   end of the Transport stream.

   The header with a dest_addr parameter SHOULD include can carry the full
         destination address that is actually used by following parameters:

   url:  Indicates the server.  The
         server stream URI for which the following RTP parameters
         correspond, this URI MUST NOT remove address information present already be the same as used in the SETUP
         request when responding unless for this media stream.  Any relative URI MUST use the protocol requires it.

   src_addr:  A general source address
         Request-URI as base URI.  This parameter MUST be present.

   ssrc: The Synchronization source (SSRC) that can contain one or
         more address specifications.  Each combination of protocol/
         profile/lower transport needs to have the format and
         interpretation of its address specification defined.  For RTP/
         AVP/UDP and RTP/AVP/TCP, the address specification is a tuple
         containing a host address RTP timestamp and port.
         sequence number provided applies to.  This parameter MUST be specified by
         present.

   seq:  Indicates the server if it transmits
         media packets from another address than sequence number of the one RTSP messages
         are sent to.  This will allow first packet of the client to verify source
         address and give it a destination address for its RTCP feedback
         packets, if RTP stream
         that is used.  The address or addresses indicated in
         the src_addr parameter SHOULD be used both for sending and
         receiving direct result of the media streams data packets. request.  This allows clients to
         gracefully deal with packets when seeking.  The main reasons
         are threefold: First, indicating the port and source address(s)
         lets client uses
         this value to differentiate packets that originated before the receiver know where
         seek from packets that originated after the seek.  Note that a
         client may not receive the packet with the expressed sequence
         number, and instead packets is expected with a higher sequence number, due
         to
         originate.  Secondly, traversal of NATs is greatly simplified
         when traffic packet loss or reordering.  This parameter is flowing symmetrically over an NAT binding.
         Thirdly, certain NAT traversal mechanisms, needs to know to
         which address and port RECOMMENDED to send so called "binding packets" from
         be present.

   rtptime:  MUST indicate the receiver RTP timestamp value corresponding to the sender, thus creating an address binding
         start time value in the NAT that Range response header, or if not
         explicitly given the sender implied start point.  The client uses this
         value to receiver packet flow can use. calculate the mapping of RTP time to NPT or other
         media timescale.  This information may also parameter SHOULD be available through SDP.
               However, since this present to ensure
         inter-media synchronization is more a feature of transport than
               media initialization, achieved.  There exists no
         requirement that any received RTP packet will have the authoritative source for this
               information should be same RTP
         timestamp value as the one in the SETUP response.

   mode: The mode parameter indicates the methods used to be supported for
         this session.  Currently defined valid values are "PLAY".  If
         not provided, the default is "PLAY".  The "RECORD" value was
         defined in RFC 2326 and establish
         synchronization.

      A mapping from RTP timestamps to NTP timestamps (wallclock) is in
      available via RTCP.  However, this specification unspecified
         but reserved.  RECORD and other values may be specified in the
         future.

   interleaved:  The interleaved parameter implies mixing the information is not sufficient
      to generate a mapping from RTP timestamps to media
         stream with the control stream clock time
      (NPT, etc.).  Furthermore, in whatever protocol order to ensure that this
      information is being
         used by available at the necessary time (immediately at
      startup or after a seek), and that it is delivered reliably, this
      mapping is placed in the RTSP control stream, channel.

      In order to compensate for drift for long, uninterrupted
      presentations, RTSP clients should additionally map NPT to NTP,
      using initial RTCP sender reports to do the mechanism defined in
         Section 14.  The argument provides the channel number mapping, and later
      reports to be
         used in check drift against the $ block Section 14 mapping.

   Example:

   Range:npt=3.25-15
   RTP-Info:url="rtsp://example.com/foo/audio" ssrc=0A13C760:seq=45102;
            rtptime=12345678,url="rtsp://example.com/foo/video"
            ssrc=9A9DE123:seq=30211;rtptime=29567112

   Lets assume that Audio uses a 16kHz RTP timestamp clock and MUST be present.  This
         parameter MAY be specified as Video
   a interval, e.g., interleaved=4-5
         in cases where the transport choice for 90kHz RTP timestamp clock. Then the media stream
         requires it, e.g., for RTP with RTCP.  The channel number given synchronization is
   depicted in the request is only a guidance following way.

   NPT    3.0---3.1---3.2-X-3.3---3.4---3.5---3.6
   Audio               PA A
   Video                  V    PV

   X: NPT time value = 3.25, from the client Range header.
   A: RTP timestamp value for Audio from RTP-Info header (12345678).
   V: RTP timestamp value for Video from RTP-Info header (29567112).
   PA: RTP audio packet carrying an RTP timestamp of 12344878. Which
       corresponds to the server
         on what channel number(s) NPT = (12344878 - A) / 16000 + 3.25 = 3.2
   PV: RTP video packet carrying an RTP timestamp of 29573412. Which
       corresponds to use.  The server MAY set any valid
         channel number in the response.  The declared channel(s) are
         bi-directional, so both end-parties MAY send data on the given
         channel.  One example NPT = (29573412 - V) / 90000 + 3.25 = 3.32

18.44.  Scale

   A scale value of such usage is 1 indicates normal play at the second channel used
         for RTCP, where both server and client send RTCP packets on normal forward
   viewing rate.  If not 1, the
         same channel.

               This allows RTP/RTCP to be handled similarly value corresponds to the way
               that it is done rate with UDP, i.e., one channel for RTP
   respect to normal viewing rate.  For example, a ratio of 2 indicates
   twice the normal viewing rate ("fast forward") and a ratio of 0.5
   indicates half the normal viewing rate.  In other for RTCP.

   MIKEY:  This parameter is used in conjunction with transport
         specifications that can utilize MIKEY for security context
         establishment.  So far only words, a ratio of 2
   has content time increase at twice the SRTP based RTP profiles SAVP
         and SAVPF can utilize MIKEY and playback time.  For every
   second of elapsed (wallclock) time, 2 seconds of content time will be
   delivered.  A negative value indicates reverse direction.  For
   certain media transports this is defined in may require certain considerations to
   work consistent, see Appendix C.1.4.1.  This parameter can C.1 for description on how RTP handles
   this.

   The transmitted data rate SHOULD NOT be included both in
         request and response messages. changed by selection of a
   different scale value.  The binary MIKEY message SHALL resulting bit-rate should be BASE64 [RFC4648] encoded before being included in reasonably
   close to the value
         part nominal bit-rate of the parameter.

   Multicast-specific:

   ttl:  multicast time-to-live content for IPv4.  When included in requests the
         value indicate Scale = 1.  The
   server has to actively manipulate the TTL value that data when needed to meet the client request
   bitrate constraints.  Implementation of scale changes depends on the
   server
         to use.  In and media type.  For video, a response, server may, for example, deliver
   only key frames or selected frames.  For audio, it may time-scale the value actually being used by
   audio while preserving pitch or, less desirably, deliver fragments of
   audio, or completely mute the audio.

   The server is returned.  A server will need to consider what values
         that are reasonable and also content may restrict the authority range of scale values that it
   supports.  The supported values are indicated by the user Media-Properties
   header (Section 18.28).  The client SHOULD only indicate values
   indicated to set
         this value.  Corresponding functions are not needed for IPv6 be supported.  However, as the scoping is part of values may change as the address.

   RTP-specific:

   These parameters MAY only
   content progresses a requested value may no longer be used if valid when the media transport protocol is
   RTP.

   ssrc: The ssrc parameter, if included
   request arrives.  Thus, a non-supported value in a SETUP response, indicates
         the RTP SSRC [RFC3550] value(s) that will be used by request does not
   generate an error, only forces the media server for RTP packets within to choose the stream.  It is expressed as
         an eight digit hexadecimal closest
   value.  The ssrc parameter response MUST NOT be specified in requests.  The
         functionality of specifying always contain the ssrc parameter in a SETUP
         request is deprecated as it is incompatible with actual scale value
   chosen by the
         specification of RTP in RFC 3550[RFC3550]. server.

   If the parameter is
         included in server does not implement the Transport header of possibility to scale, it will
   not return a SETUP request, the Scale header.  A server
         SHOULD ignore it, and choose appropriate SSRCs supporting Scale operations for
   PLAY MUST indicate this with the stream.
         The server SHOULD set the ssrc parameter in the Transport
         header use of the response.

   RTCP-mux:  Use to negotiate "play.scale" feature-tag.

   When indicating a negative scale for a reverse playback, the usage of RTP and RTCP multiplexing
         [RFC5761] on Range
   header MUST indicate a single underlying transport stream / flow.  The
         presence decreasing range as described in
   Section 18.38.

   Example of this parameter playing in reverse at 3.5 times normal rate:
     Scale: -3.5
     Range: npt=15-10

18.45.  Seek-Style

   When a SETUP client sends a PLAY request indicates with a Range header to perform a
   random access to the
         clients support and requires media, the client does not know if the server
   will pick the first media samples or the first random access point
   prior to the request range.  Depending on use RTP and RTCP
         multiplexing.  The client SHALL only include one transport
         stream in case, the Transport header specification. client may
   have a strong preference.  To express this preference and provide the
         server
   client with information on how the server actually acted on that
   preference the Seek-Style header is defined.

   Seek-Style is a choice between using RTP/RTCP multiplexing or
         not, two different transport general header specifications must be
         included.

   The parameters setup and connection defined below that MAY only be used if included in any PLAY
   request to indicate the client's preference for any media transport protocol of the lower-level transport is
   connection-oriented (such as TCP).  However, these parameters MUST
   NOT be used when interleaving data over the RTSP control connection.

   setup:  Clients use the setup parameter on stream that
   has random access properties.  The server MUST always include the Transport line
   header in a
         SETUP request, any PLAY response for media with random access properties
   to indicate what policy was applied.  A server that receives an
   unknown Seek-Style policy MUST ignore it and select the roles server
   default policy.  A client receiving an unknown policy MUST ignore it wishes
   and use the Range header and any media synchronization information as
   basis to play in a TCP
         connection. determine what the server did.

   This parameter specification defines the following seek policies that may be
   requested (see also Section 4.9.1):

   RAP:  Random Access Point (RAP) is adapted from [RFC4145].  We
         discuss the use behavior of this parameter in RTP/AVP/TCP non-
         interleaved transport in Appendix C.2.2; requesting the discussion below
         is limited
      server to syntactic issues.  Clients may specify locate the
         following values for closest previous random access point that
      exists in the setup parameter: ["active":] The
         client will initiate an outgoing connection. ["passive":] The
         client will accept an incoming connection. ["actpass":] The
         client is willing to accept an incoming connection or to
         initiate an outgoing connection.

         If a client does not specify media aggregate and deliver from that.  By
      requesting a setup value, RAP, media quality will be the "active" value
         is assumed.

         In response to best possible as all
      media will be delivered from a client SETUP request point where full media state can be
      established in the setup parameter media decoder.

   CoRAP:  Conditional Random Access Point (CoRAP) is set to "active", a server's 2xx reply MUST assign the setup
         parameter to "passive" on variant of the Transport header line.

         In response to a client SETUP request
      above RAP behavior.  This policy is primarily intended for cases
      where there is larger distance between the setup parameter random access points in
      the media.  CoRAP is conditioned on that there is set to "passive", a server's 2xx reply MUST assign Random Access
      Point closer to the setup
         parameter requested start point than to "active" on the Transport header line.

         In response current
      pause point.  This policy assumes that the media state existing
      prior to a client SETUP request where the setup parameter pause is set to "actpass", a server's 2xx reply MUST assign usable if delivery is continued.  If the setup
         parameter to "active"
      client or "passive" on the Transport header
         line.

         Note server knows that the "holdconn" value for setup this is not defined for
         RTSP use, and MUST NOT appear on a Transport line.

   connection:  Clients use the setup parameter on fact the Transport line RAP policy
      should be used.  In other words: in most cases when the client
      requests a SETUP request, start point prior to indicate the SETUP request prefers the
         reuse of an existing connection between client and server (in
         which case current pause point, a valid
      decoding dependency chain from the client sets media delivered prior to the "connection" parameter
      pause and to
         "existing"), or that the client requires requested media unit will not exist.  If the creation of
      server searched to a new
         connection between client and random access point the server (in which cast MUST return
      the client
         sets CoRAP policy in the "connection" parameter Seek-Style header and adjust the Range
      header to "new").  Typically, clients
         use reflect the "new" value for position of the first SETUP request for a URL, picked RAP.  In case the
      random access point is further away and
         "existing" for subsequent SETUP requests for a URL.

         If a client SETUP request assigns the "new" value server selects to
         "connection",
      continue from the server response current pause point it MUST also assign include the "new"
         value to "connection" on "Next"
      policy in the Transport line.

         If a client SETUP request assigns Seek-Style header and adjust the "existing" value Range header start
      point to
         "connection", the server response MUST assign current pause point.

   First-Prior:  The first-prior policy will start delivery with the
      media unit that has a value of
         "existing" or "new" playout time first prior to "connection" on the Transport line, requested
      time.  For discrete media that would only include media units that
      would still be rendered at
         its discretion. the request time.  For continuous media
      that is media that will be rendered during the requested start
      time of the range.

   Next:  The default value next media units after the provided start time of "connection" the
      range.  For continuous framed media that would mean the first next
      frame after the provided time.  For discrete media the first unit
      that is "existing", to be rendered after the provided time.  The main usage
      for this case is when the client knows it has all SETUP
         requests (initial and subsequent).

   The combination of transport protocol, profile media up to a
      certain point and lower transport
   needs would like to continue delivery so that a
      complete non-interrupted media playback can be defined.  A number achieved.  Example
      of combinations are defined in the
   Appendix C.

   Below is a usage example, showing such scenarios include switching from a client advertising the capability broadcast/multicast
      delivery to handle multicast or unicast, preferring multicast.  Since this is a unicast-only stream, the server responds with unicast based delivery.  This policy MUST only be
      used on the proper transport
   parameters client's explicit request.

   Please note that these expressed preferences exist for unicast.

     C->S: SETUP rtsp://example.com/foo/bar/baz.rm RTSP/2.0
           CSeq: 302
           Transport: RTP/AVP;multicast;mode="PLAY",
               RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/
               "192.0.2.5:3457";mode="PLAY"
           Accept-Ranges: NPT, SMPTE, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 302
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Session: 47112344
           Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/
              "192.0.2.5:3457";src_addr="192.0.2.224:6256"/
              "192.0.2.224:6257";mode="PLAY"
           Accept-Ranges: NPT
           Media-Properties: Random-Access=0.6, Dynamic,
                             Time-Limited=20081128T165900

16.53.  Unsupported

   The Unsupported response-header lists the features not supported by optimizing the responding RTSP agent.  In
   startup time or the case where media quality.  The "Next" policy breaks the feature was
   specified via
   normal definition of the Proxy-Require field (Section 16.35), if there is Range header to enable a
   proxy on the path between the client to request
   media with minimal overlap, although some may still occur for
   aggregated sessions.  RAP and First-Prior both fulfill the server, the proxy MUST
   send a response message with a status code
   requirement of 551 (Option Not
   Supported).  The request MUST NOT providing media from the requested range and forward.
   However, unless RAP is used, the media quality for many media codecs
   using predictive methods can be forwarded.

   See Section 16.41 severely degraded unless additional
   data is available as, for a usage example.

16.54.  User-Agent example, already buffered, or through other
   side channels.

18.46.  Server

   The User-Agent general-header Server response-header field contains information about the
   user agent originating the request.  This is for statistical
   purposes, the tracing of protocol violations, and automated
   recognition of user agents for
   software used by the sake of tailoring responses origin server to
   avoid particular user agent limitations.  User agents SHOULD include
   this field with requests. handle the request.  The field
   can contain multiple product tokens and comments identifying the agent
   server and any subproducts which
   form a significant part of the user agent.  By convention, the subproducts.  The product tokens are
   listed in order of their significance for identifying the
   application.

   Example:

   User-Agent: PhonyClient/1.2

16.55.  Vary

   The Vary field value indicates the set of request-header fields that
   fully determines, while
   Server: PhonyServer/1.0

   If the response is fresh, whether a cache is
   permitted to use the response to reply to a subsequent request
   without revalidation.  For uncacheable or stale responses, the Vary
   field value advises the user agent about the criteria that were used
   to select the representation.  A Vary field value of "*" implies that being forwarded through a cache cannot determine from proxy, the request headers of a subsequent
   request whether this response is proxy
   application MUST NOT modify the appropriate representation.

   An RTSP server Server response-header.  Instead, it
   SHOULD include a Vary header Via field with any cacheable
   response that is subject to server-driven negotiation.  Doing so
   allows a cache to properly interpret future requests on that resource
   and informs the user agent about (Section 18.55).  If the presence of negotiation on that
   resource.  A server MAY include a Vary header field with a non-
   cacheable response that is subject to server-driven negotiation,
   since this might provide the user agent with useful information about
   generated by the dimensions over which proxy, the response varies at proxy application MUST return the time of Server
   response-header as previously returned by the
   response.

   A Vary server.

18.47.  Session

   The Session request-header and response-header field value consisting of identifies an
   RTSP session.  An RTSP session is created by the server as a list result
   of field-names signals that
   the representation selected for the response is based on a selection
   algorithm which considers ONLY the listed request-header field values successful SETUP request and in selecting the most appropriate representation.  A cache MAY assume
   that the same selection will be made for future requests with the
   same values for the listed field names, for the duration of time for
   which the response the session
   identifier is fresh.

   The field-names given are not limited to the set of standard request-
   header fields defined by this specification.  Field names are case-
   insensitive.

   A Vary field value of "*" signals that unspecified parameters not
   limited to the request-headers (e.g., the network address of the
   client), play a role in the selection of the response representation. client.  The "*" value MUST NOT be generated RTSP session exists until
   destroyed by a proxy server; it may only be
   generated TEARDOWN, REDIRECT or timed out by an origin the server.

16.56.  Via

   The Via general-header field MUST be used session identifier is chosen by proxies to indicate the
   intermediate protocols and recipients between the user agent and the
   server on requests, and between the origin server (see Section 4.3) and
   MUST be returned in the SETUP response.  Once a client on
   responses.  The field is intended to receives a
   session identifier, it MUST be used for tracking message
   forwards, avoiding included in any request loops, and identifying the protocol
   capabilities of all senders along the request/response chain.

   Multiple Via field values represents each proxy related to
   that session.  This means that has forwarded the message.  Each recipient Session header MUST append its information such that be included in
   a request, using the end result is ordered according to following methods: PLAY, PAUSE, and TEARDOWN,
   and MAY be included in SETUP, OPTIONS, SET_PARAMETER, GET_PARAMETER,
   and REDIRECT, and MUST NOT be included in DESCRIBE.  The Session
   header MUST NOT be included in the sequence of forwarding
   applications.

   Proxies (e.g., Access Proxy or Translator Proxy) SHOULD NOT, by
   default, forward following methods, if these
   requests are pipelined and if the names session identifier is not yet
   known: PLAY, PAUSE, TEARDOWN, SETUP, OPTIONS SET_PARAMETER, and ports of hosts within
   GET_PARAMETER.

   In an RTSP response the private/
   protected region.  This information SHOULD only session header MUST be propagated included in methods,
   SETUP, PLAY, and PAUSE, and MAY be included in methods, TEARDOWN, and
   REDIRECT, and if
   explicitly enabled.  If not enabled, included in the via-received request of any host
   behind the firewall/NAT SHOULD following methods it
   MUST also be replaced by included in the response, OPTIONS, GET_PARAMETER, and
   SET_PARAMETER, and MUST NOT be included in DESCRIBE responses.

   Note that a session identifier identifies an appropriate
   pseudonym RTSP session across
   transport sessions or connections.  RTSP requests for a given session
   can use different URIs (Presentation and media URIs).  Note, that host.

   For organizations
   there are restrictions depending on the session which URIs that have strong privacy requirements are
   acceptable for hiding
   internal structures, a proxy MAY combine an ordered subsequence given method.  However, multiple "user" sessions for
   the same URI from the same client will require use of
   Via header field entries with identical sent-protocol values into a
   single such entry.  Applications MUST NOT combine entries which have different received-protocol values.

16.57.  WWW-Authenticate

   The WWW-Authenticate response-header field MUST be included in 401
   (Unauthorized) response messages.
   session identifiers.

      The field value consists of at
   least one challenge that indicates the authentication scheme(s) and
   parameters applicable session identifier is needed to distinguish several delivery
      requests for the Request-URI. same URI coming from the same client.

   The HTTP access authentication process response 454 (Session Not Found) MUST be returned if the session
   identifier is described in [RFC2617].
   User agents are advised to take special care in parsing invalid.

   The header MAY include the WWW-
   Authenticate field session timeout period.  If not explicitly
   provided this value as it might contain more is set to 60 seconds.  As this affects how often
   session keep-alives are needed values smaller than one challenge,
   or if more 30 seconds are not
   recommended.  However, larger than one WWW-Authenticate header field is provided, the
   contents of a challenge itself default values can contain a comma-separated list be useful in
   applications of
   authentication parameters.

17.  Proxies

   RTSP Proxies are RTSP agents that are located have inactive but established sessions for
   longer time periods.

      60 seconds was chosen as session timeout value due to: Resulting
      in between a client not too frequent keep-alive messages and
   a server.  A proxy can take on both having low sensitivity
      to variations in request response timing.  If one reduces the role as
      timeout value to below 30 seconds the corresponding request
      response timeout becomes a significant part of the session
      timeout. 60 seconds also allows for reasonably rapid recovery of
      committed server resources in case of client and as failure.

18.48.  Speed

   The Speed request-header field requests the server depending on what it tries to accomplish.  Proxies are also
   introduced for several different reasons deliver
   specific amounts of nominal media time per unit of delivery time,
   contingent on the server's ability and desire to serve the below listed are
   often combined.

   In general there are two categories of RTSP proxies, transparent (of
   which media
   stream at the given speed.  The client is not aware) requests the delivery speed to
   be within a given range with a lower and upper bound.  The server
   SHALL deliver at the non-transparent proxies (of
   which highest possible speed within the client is aware).  Transparent proxies are range, but not visible to
   the client in terms of that
   faster than the transport layer connection, e.g., TCP upper-bound, for RTSP, as there is only a single transport connection which is
   terminated at the RTSP client and the RTSP server.  In underlying network path
   can support the case of
   non-transparent proxies, there are two resulting transport layer connections,
   one from data rates.  As long as any speed
   value within the RTSP client to given range can be provided the RTSP proxy and a second from server SHALL NOT
   modify the RTSP
   proxy to media quality.  Only if the RTSP server.

   There are these types of RTSP proxies:

   Caching Proxy:  This type of proxy server is used unable to reduce the workload on
         servers and connections.  By caching the description and deliver
   media
         streams, i.e., the presentation, at the proxy can serve a client
         with content, but without requesting it from speed value provided by the server once lower bound shall it
         has been cached and has not become stale.  See reduce
   the caching
         Section 18.  This type media quality.

   Implementation of proxy is also expected to understand
         RTSP end-point functionality, i.e., the Speed functionality identified in by the Require server is OPTIONAL.
   The server can indicate its support through a feature-tag,
   play.speed.  The lack of a Speed header in addition to what Proxy-Require demands.

   Translator Proxy:  This type of proxy the response is used to ensure that an RTSP
         client gets access
   indication of lack of support of this functionality.

   The speed parameter values are expressed as a positive decimal value,
   e.g., a value of 2.0 indicates that data is to servers and content on an external
         network be delivered twice as
   fast as normal.  A speed value of zero is invalid.  The range is
   specified in the form "lower bound - upper bound".  The lower bound
   value may be smaller or using content encodings equal to the upper bound.  All speeds may not supported by
   be possible to support.  Therefore the client.
         The proxy performs server MAY modify the necessary translation of addresses,
         protocols or encodings.  This type of proxy is expected
   requested values to also
         understand RTSP end-point functionality, i.e. functionality
         identified the closest supported.  The actual supported
   speed MUST be included in the Require response.  Note, however, that the use
   cases may vary and that Speed value ranges such as 0.7 - 0.8,
   0.3-2.0, 1.0-2.5, 2.5-2.5 all have their usage.

   Example:

     Speed: 1.0-2.5

   Use of this header changes the bandwidth used for data delivery.  It
   is meant for use in addition to what Proxy-
         Require demands.

   Access Proxy:  This type specific circumstances where delivery of proxy the
   presentation at a higher or lower rate is used desired.  The main use
   cases are buffer operations or local scale operations.  Implementors
   should keep in mind that bandwidth for the session may be negotiated
   beforehand (by means other than RTSP), and therefore re-negotiation
   may be necessary.  To perform Speed operations the server needs to
   ensure that an RTSP
         clients get access to servers on an external network. the network path can support the resulting bit-rate.
   Thus
         this proxy is placed on the border between two domains, e.g. a
         private address space media transport needs to support feedback so that the server
   can react and adapt to the public Internet. available bitrate.

18.49.  Supported

   The proxy
         performs Supported header enumerates all the necessary translation, usually addresses.  This
         type of proxy is required to redirect extensions supported by the media to itself
   client or a
         controlled gateway that performs the translation before server using feature tags.  The header carries the
         media can reach
   extensions supported by the client.

   Security Proxy:  This type of proxy is used to help facilitate
         security functions around RTSP.  For example when having message sending client or server.  The
   Supported header MAY be included in any request.  When present in a
         firewalled network,
   request, the security proxy request receiver MUST respond with its corresponding Supported
   header.  Note that the
         necessary pinholes Supported header is also included in the firewall are opened when 4xx and
   5xx responses.

   The Supported header contains a client list of feature-tags, described in
   Section 4.7, that are understood by the protected network wants client or server.

   Example:

     C->S:  OPTIONS rtsp://example.com/ RTSP/2.0
            Supported: foo, bar, blech
            User-Agent: PhonyClient/1.2

     S->C:  RTSP/2.0 200 OK
            Supported: bar, blech, baz

18.50.  Terminate-Reason

   The Terminate-Reason request header allows the server when sending a
   REDIRECT or TEARDOWN request to access media streams on provide a reason for the
         external side. session
   termination and any additional information.  This proxy can also limit specification
   identifies three reasons for Redirections and may be extended in the clients access
   future:

   Server-Admin:  The server needs to
         certain types be shutdown for some
      administrative reason.

   Session-Timeout:  A client's session is kept alive for extended
      periods of content.  This proxy can perform its function
         without redirecting the media between time and the server and client.
         However, in deployments has determined that it needs to
      reclaim the resources associated with private address spaces this proxy session.

   Internal-Error  An internal error that is likely impossible to be combined with recover from
      has occurred forcing the access proxy.  Anyway, server to terminate the
         functionality of this proxy is usually closely tied into
         understanding all aspects of session.

   The Server may provide additional parameters containing information
   around the media transport.

   Auditing Proxy:  RTSP proxies can also redirect.  This specification defines the following ones.

   time:  Provides a wallclock time when the server will stop provide network owners
      any service.

   user-msg:  An UTF-8 text string with a
         logging and audit point for RTSP sessions, e.g. for
         corporations that track their employees usage of message from the network.
         This type of proxy can perform its function without inserting
         itself or any other node in server to the media transport.
      user.  This proxy
         type can also accept unknown methods as it doesn't interfere
         with the clients' requests.

   All types of proxies can message SHOULD be used also displayed to the user.

18.51.  Timestamp

   The Timestamp general-header describes when using secured
   communication with TLS as RTSP 2.0 allows the client agent sent the
   request.  The value of the timestamp is of significance only to approve
   certificate chains used for connection establishment from a proxy,
   see Section 19.3.2.  However, that trust model the
   agent and may not be suitable
   for all types of deployment.  In those cases, use any timescale.  The responding agent MUST echo the secured sessions do
   by-pass
   exact same value and MAY, if it has accurate information about this,
   add a floating point number indicating the number of seconds that has
   elapsed since it has received the proxies.

   Access proxies SHOULD NOT request.  The timestamp can be used in equipment like NATs and
   firewalls that aren't expected
   by the agent to be regularly maintained, like home
   or small office equipment.  In these cases it is better compute the round-trip time to use the
   NAT traversal procedures defined responding agent
   so that it can adjust the timeout value for RTSP 2.0
   [I-D.ietf-mmusic-rtsp-nat].  The reason retransmissions when
   running over an unreliable protocol.  It also resolves retransmission
   ambiguities for these recommendations is unreliable transport of RTSP.

   Note that any extensions the present specification provides only for reliable
   transport of RTSP resulting messages.  The Timestamp general-header is
   specified in new media transport
   protocols or profiles, new parameters, etc. may fail case the protocol is extended in a proxy that
   isn't maintained.  This would impede RTSP's the future development and
   usage.

17.1.  Proxies and Protocol Extensions

   The existence of proxies must always be considered when developing
   new RTSP extensions.  Most types of proxies will need to implement
   any new method use
   unreliable transport.

18.52.  Transport

   The Transport request and response header indicates which transport
   protocol is to operate correctly in the presence of that
   extension.  New headers can be introduced used and will configures its parameters such as
   destination address, compression, multicast time-to-live and
   destination port for a single stream.  It sets those values not be blocked
   already determined by
   older proxies.  However, it is important to consider if this a presentation description.

   A Transport request header
   and its function is required MAY contain a list of transport options
   acceptable to be understood by the proxy or can be
   forwarded.  If client, in the header needs to form of multiple transport
   specification entries.  Transport specifications are comma separated,
   listed in decreasing order of preference.  Parameters may be understood, added to
   each transport specification, separated by a feature-tag
   representing the functionality semicolon.  The server
   MUST be included return a Transport response-header in the Proxy-Require
   header.  Below are guidelines for analysis response to indicate
   the values actually chosen if any.  If the header needs to be
   understood.  The transport specification is
   not supported, no transport header is returned and its parameters also shows that
   headers that are extensible and require correct interpretation the request MUST
   be responded using the status code 461 (Unsupported Transport)
   (Section 17.4.26).  In case more than one transport specification was
   present in the
   proxy also require handling rules.

   Whether a proxy needs to understand a header is not easy to
   determine, as they serve a broad variety of functions.  When
   evaluating request, the server MUST return the single (transport-
   spec) which was actually chosen, if a header needs any.  The number of transport-
   spec entries is expected to be understood, one can divide limited as the
   functionality into three main categories:

   Media modifying:  The caching and translator proxies client will get
   guidance on what configurations that are modifying possible from the actual media and therefore needs to understand
   presentation description.

   The Transport header MAY also request
      directed be used in subsequent SETUP requests to the
   change transport parameters.  A server that affects how the media is rendered.
      Thus, this type MAY refuse to change
   parameters of an existing stream.

   A transport specification may only contain one of any given parameter
   within it.  Parameters MAY be given in any order.  Additionally, it
   may only contain either of proxy needs to also understand the server side
      functionality.

   Transport modifying:  The access and unicast or the security proxy both multicast transport
   type parameter.  All parameters need to
      understand how be understood in a transport
   specification, if not, the transport is performed, either for opening
      pinholes specification MUST be ignored.
   RTSP proxies of any type that uses or to translate modifies the outer headers, transport
   specification, e.g.  IP and UDP.

   Non-modifying:  The audit access proxy is special in that it does not modify
      the messages in other ways than to insert or security proxy, MUST remove
   specifications with unknown parameters before forwarding the Via header.  That
      makes it possible for this type to forward RTSP messages
   message.  If that
      contain different types of unknown methods, headers or header
      parameters.

   Based on the above classification, one should evaluate if the new
   functionality requires result in no remaining transport specification the
   proxy SHALL send a 461 (Unsupported Transport) (Section 17.4.26)
   response without any Transport modifying type of proxies header.

      The Transport header is restricted to
   understand describing a single media
      stream.  (RTSP can also control multiple streams as a single
      entity.)  Making it or not.

17.2.  Multiplexing and Demultiplexing part of Messages

   RTSP proxies may have to multiplex multiple RTSP sessions from their
   clients towards RTSP servers.  This requires that RTSP requests from
   multiple clients are multiplexed onto rather than relying on a common connection
      multitude of session description formats greatly simplifies
      designs of firewalls.

   The general syntax for
   requests outgoing to an RTSP server and on the way back the responses
   are demultiplexed from the server to per client responses.  On the
   protocol level this requires that request and response messages are
   handled in both ways, requiring that there transport specifier is a mechanism to
   correlate what request/response pair exchanged between proxy and
   server is mapped to what client (or client request).

   This multiplexing of requests and demultiplexing list of responses is done
   by using slash
   separated tokens:

   Value1/Value2/Value3...
   Which for RTP transports take the CSeq header field (see Section 16.19). form:
   RTP/profile/lower-transport.

   The proxy has to
   rewrite default value for the CSeq in requests "lower-transport" parameters is specific to
   the server and responses from profile.  For RTP/AVP, the
   server and remember what CSeq default is mapped to what client.

18.  Caching

   In HTTP, request-response pairs are cached.  RTSP differs
   significantly in that respect.  Responses UDP.

   There are not cacheable, with two different methods for how to specify where the
   exception media
   should be delivered for unicast transport:

   dest_addr:  The presence of this parameter and its values indicates
         the presentation description returned by DESCRIBE.
   (Since the responses for anything but DESCRIBE destination address or addresses (host address and GET_PARAMETER do
   not return any data, caching is not really an issue port
         pairs for these
   requests.)  However, it is desirable IP flows) necessary for the continuous media data,
   typically delivered out-of-band with respect to RTSP, to be cached,
   as well as the session description.

   On receiving a SETUP or PLAY request, a proxy ascertains whether it
   has an up-to-date copy transport.

   No dest_addr:  The lack of the continuous media content and its
   description.  It can determine whether dest_addr parameter indicates that the copy is up-to-date by
   issuing a SETUP or DESCRIBE request, respectively, and comparing
         server MUST send media to same address for which the
   Last-Modified header with that RTSP
         messages originates.

   The choice of method for indicating where the cached copy.  If the copy media is
   not up-to-date, it modifies the SETUP transport parameters as
   appropriate and forwards the request to be
   delivered depends on the origin server.
   Subsequent control commands such as PLAY or PAUSE then pass use case.  In some cases the proxy
   unmodified.  The proxy delivers only allowed
   method will be to use no explicit address indication and have the continuous
   server deliver media data to the
   client, while possibly making a local copy for later reuse.  The
   exact allowed behavior source of the cache RTSP messages.

   For Multicast there is given by the cache-response
   directives described several methods for specifying addresses but
   they are different in Section 16.10.  A cache MUST answer any
   DESCRIBE requests if it is currently serving how they work compared with unicast:

   dest_addr with client picked address:  The address and relevant
         parameters like TTL (scope) for the stream actual multicast group to
         deliver the
   requester, as it is possible media to.  There are security implications
         (Section 21) with this method that low-level details of the stream
   description may have changed needs to be addressed if
         using this method because a RTSP server can be used as a DoS
         attacker on the origin-server.

   Note that an RTSP cache, is of the "cut-through" variety.  Rather
   than retrieving existing multicast group.

   dest_addr using Session Description Information:  The information
         included in the whole resource transport header can all be coming from the origin server,
         session description, e.g. the cache
   simply copies SDP c= and m= line.  This
         mitigates some of the streaming data security issues of the previous methods
         as it passes by on its way to is the
   client.  Thus, session provider that picks the multicast group
         and scope.  The client MUST include the information if it does not introduce additional latency.

   To is
         available in the client, an session description.

   No dest_addr:  The behavior when no explicit multicast group is
         present in a request is not defined.

   An RTSP proxy cache appears like a regular media
   server, will need to take care.  If the media origin server like a client.  Just as an HTTP
   cache has is not desired to store
   be routed through the content type, content language, and so on for proxy, the objects it caches, a media cache has proxy will need to store the presentation
   description.  Typically, a cache eliminates all transport-references
   (e.g., multicast information) from introduce the presentation description,
   since these
   destination indication.

   Below are independent of the data delivery from the cache to
   the client.  Information on the encodings remains the same.  If the
   cache configuration parameters associated with transport:

   General parameters:

   unicast / multicast:  This parameter is able to translate the cached media data, it would create a
   new presentation description with all mutually exclusive
         indication of whether unicast or multicast delivery will be
         attempted.  One of the encoding possibilities it
   can offer.

18.1.   Validation Model

   When a cache has a stale entry two values MUST be specified.  Clients
         that it would like to use as a
   response to a client's request, it first has are capable of handling both unicast and multicast
         transmission needs to check with the origin
   server (or possibly an intermediate cache indicate such capability by including two
         full transport-specs with a fresh response) separate parameters for each.

   layers:  The number of multicast layers to
   see if its cached entry is still usable.  We call be used for this "validating" media
         stream.  The layers are sent to consecutive addresses starting
         at the cache entry.  Since we do dest_addr address.  If the parameter is not want included, it
         defaults to have a single layer.

   dest_addr:  A general destination address parameter that can contain
         one or more address specifications.  Each combination of
         protocol/profile/lower transport needs to pay have the overhead format and
         interpretation of
   retransmitting the full response if its address specification defined.  For RTP/
         AVP/UDP and RTP/AVP/TCP, the cached entry address specification is good, a tuple
         containing a host address and we
   do not want to pay the overhead port.  Note, only a single
         destination parameter per transport spec is intended.  The
         usage of an extra round trip if the cached
   entry multiple destinations to distribute a single media to
         multiple entities is invalid, unspecified.

         The client originating the RTSP protocol supports request MAY specify the use
         destination address of conditional
   methods.

   The key protocol features for supporting conditional methods are
   those concerned the stream recipient with "cache validators."  When an origin server
   generates a full response, it attaches some sort the host
         address part of validator to it,
   which is kept with the cache entry. tuple.  When the destination address is
         specified, the recipient may be a client (user agent or
   proxy cache) makes a conditional request for a resource for which it
   has a cache entry, it includes different party than the associated validator in
         originator of the request.

   The  To avoid becoming the unwitting
         perpetrator of a remote-controlled denial-of-service attack, a
         server then MUST perform security checks that validator against the current validator
   for the requested resource, and, if they match (see Section 18.1.3),
   it responds with a special status code (usually, 304 (Not Modified)) 21.2.1) and no message body.  Otherwise, it returns
         SHOULD log such attempts before allowing the client to direct a full response
   (including message body).  Thus, we avoid transmitting
         media stream to a recipient address not chosen by the full
   response if server.
         Implementations cannot rely on TCP as reliable means of client
         identification.  If the validator matches, and we avoid an extra round trip
   if it server does not match.

   In RTSP, a conditional request looks exactly allow the same as a normal
   request for host address
         part of the same resource, except that tuple to be set, it carries a special
   header (which includes the validator) that implicitly turns the
   method (usually DESCRIBE or SETUP) into a conditional. MUST return 463 (Destination
         Prohibited).

         The protocol includes both positive and negative senses host address part of cache-
   validating conditions.  That is, it is possible to request either
   that a method the tuple MAY be performed if and only if a validator matches or if
   and empty, for example
         ":58044", in cases when only if no validators match.

      Note: a response that lacks a validator may still be cached, and
      served from cache until it expires, unless this destination port is explicitly
      prohibited by a cache-control directive (see Section 16.10).
      However, a cache cannot do a conditional retrieval if it does not
      have a validator for the resource, which means it will not desired to be
      refreshable after it expires.

   Media streams that are being adapted based on
         specified.  Responses to requests including the transport capacity
   between Transport
         header with a dest_addr parameter SHOULD include the full
         destination address that is actually used by the server.  The
         server and MUST NOT remove address information present already in
         the cache makes caching more difficult. request when responding unless the protocol requires it.

   src_addr:  A
   server general source address parameter that can contain one or
         more address specifications.  Each combination of protocol/
         profile/lower transport needs to consider how it views caching have the format and
         interpretation of media streams that
   it adapts its address specification defined.  For RTP/
         AVP/UDP and potentially instruct any caches to not cache such
   streams.

18.1.1.  Last-Modified Dates

   The Last-Modified header (Section 16.26) value RTP/AVP/TCP, the address specification is often used as a
   cache validator.  In simple terms, tuple
         containing a cache entry is considered to host address and port.

         This parameter MUST be
   valid if specified by the content has not been modified since server if it transmits
         media packets from another address than the Last-Modified
   value.

18.1.2.  Message Body Tag Cache Validators

   The MTag response-header field value, a message body tag, provides
   for an "opaque" cache validator. one RTSP messages
         are sent to.  This might will allow more reliable
   validation in situations where the client to verify source
         address and give it a destination address for its RTCP feedback
         packets, if RTP is inconvenient to store
   modification dates, where used.  The address or addresses indicated in
         the one-second resolution src_addr parameter SHOULD be used both for sending and
         receiving of RTSP-date
   values is not sufficient, or where the origin server wishes to avoid
   certain paradoxes that might arise media streams data packets.  The main reasons
         are threefold: First, indicating the port and source address(s)
         lets the receiver know where from the use packets is expected to
         originate.  Secondly, traversal of modification
   dates.

   Message body tags are described in Section 4.8

18.1.3.  Weak and Strong Validators

   Since both origin servers NATs is greatly simplified
         when traffic is flowing symmetrically over an NAT binding.
         Thirdly, certain NAT traversal mechanisms, needs to know to
         which address and caches will compare two validators port to
   decide if they represent the same or different entities, one normally
   would expect that if send so called "binding packets" from
         the message body (i.e., receiver to the presentation
   description) or any associated message body headers changes sender, thus creating an address binding in any
   way, then
         the associated validator would change as well.  If NAT that the sender to receiver packet flow can use.

               This information may also be available through SDP.
               However, since this is
   true, then we call this validator more a "strong validator."  We call
   message body (i.e., feature of transport than
               media initialization, the presentation description) or any associated
   message body headers an entity authoritative source for a better understanding.

   However, there might this
               information should be cases when a server prefers in the SETUP response.

   mode: The mode parameter indicates the methods to change be supported for
         this session.  Currently defined valid values are "PLAY".  If
         not provided, the
   validator only on semantically significant changes, default is "PLAY".  The "RECORD" value was
         defined in RFC 2326 and not when
   insignificant aspects of is in this specification unspecified
         but reserved.  RECORD and other values may be specified in the
         future.

   interleaved:  The interleaved parameter implies mixing the entity change.  A validator that does
   not always change when media
         stream with the resource changes control stream in whatever protocol is a "weak validator."

   Message body tags are normally "strong validators," but being
         used by the control stream, using the protocol
   provides a mechanism defined in
         Section 14.  The argument provides the channel number to tag a message body tag be
         used in the $ block Section 14 and MUST be present.  This
         parameter MAY be specified as "weak."  One can
   think of a strong validator as one that changes whenever interval, e.g., interleaved=4-5
         in cases where the bits of
   an entity changes, while a weak value changes whenever transport choice for the meaning of
   an entity changes.  Alternatively, one can think of a strong
   validator as part of an identifier media stream
         requires it, e.g., for a specific entity, while a
   weak validator RTP with RTCP.  The channel number given
         in the request is part of an identifier for only a guidance from the client to the server
         on what channel number(s) to use.  The server MAY set of semantically
   equivalent entities.

      Note: any valid
         channel number in the response.  The declared channel(s) are
         bi-directional, so both end-parties MAY send data on the given
         channel.  One example of a strong validator is an integer that is
      incremented in stable storage every time an entity such usage is changed.

      An entity's modification time, if represented with one-second
      resolution, could the second channel used
         for RTCP, where both server and client send RTCP packets on the
         same channel.

               This allows RTP/RTCP to be a weak validator, since handled similarly to the way
               that it is possible that done with UDP, i.e., one channel for RTP and
               the resource might be modified twice during a single second.

      Support other for weak validators RTCP.

   MIKEY:  This parameter is optional.  However, weak validators
      allow used in conjunction with transport
         specifications that can utilize MIKEY [RFC3830] for more efficient caching of equivalent objects.

   A "use" of a validator security
         context establishment.  So far only the SRTP based RTP profiles
         SAVP and SAVPF can utilize MIKEY and this is either when a client generates a defined in
         Appendix C.1.4.1.  This parameter can be included both in
         request and includes response messages.  The binary MIKEY message SHALL
         be BASE64 [RFC4648] encoded before being included in the validator value
         part of the parameter.

   Multicast-specific:

   ttl:  multicast time-to-live for IPv4.  When included in requests the
         value indicate the TTL value that the client request the server
         to use.  In a validating header field, or when a response, the value actually being used by the
         server compares two validators.

   Strong validators is returned.  A server will need to consider what values
         that are usable in any context.  Weak validators reasonable and also the authority of the user to set
         this value.  Corresponding functions are
   only usable in contexts that do not depend on exact equality of an
   entity.  For example, either kind is usable needed for a conditional
   DESCRIBE IPv6 as
         the scoping is part of a full entity.  However, the IPv6 multicast address [RFC4291].

   RTP-specific:

   These parameters MAY only a strong validator be used if the media transport protocol is
   usable
   RTP.

   ssrc: The ssrc parameter, if included in a SETUP response, indicates
         the RTP SSRC [RFC3550] value(s) that will be used by the media
         server for a sub-range retrieval, since otherwise RTP packets within the client might
   end up with stream.  It is expressed as
         an internally inconsistent entity.

   Clients MAY issue DESCRIBE requests with either weak validators or
   strong validators.  Clients eight digit hexadecimal value.

         The ssrc parameter MUST NOT use weak validators be specified in other
   forms of requests.  The only function that
         functionality of specifying the RTSP protocol defines on validators ssrc parameter in a SETUP
         request is
   comparison.  There are two validator comparison functions, depending
   on whether deprecated as it is incompatible with the comparison context allows
         specification of RTP in RFC 3550[RFC3550].  If the use parameter is
         included in the Transport header of weak validators
   or not:

   o a SETUP request, the server
         SHOULD ignore it, and choose appropriate SSRCs for the stream.
         The strong comparison function: server SHOULD set the ssrc parameter in order the Transport
         header of the response.

   RTCP-mux:  Use to be considered equal,
      both validators MUST be identical in every way, negotiate the usage of RTP and both MUST NOT
      be weak.

   o RTCP multiplexing
         [RFC5761] on a single underlying transport stream / flow.  The weak comparison function:
         presence of this parameter in order a SETUP request indicates the
         clients support and requires the server to be considered equal,
      both validators MUST be identical use RTP and RTCP
         multiplexing.  The client SHALL only include one transport
         stream in every way, but either the Transport header specification.  To provide the
         server with a choice between using RTP/RTCP multiplexing or both
      of them
         not, two different transport header specifications must be
         included.

   The parameters setup and connection defined below MAY only be tagged as "weak" without affecting used if
   the result.

   A message body tag is strong unless it media transport protocol of the lower-level transport is explicitly tagged
   connection-oriented (such as weak.

   A Last-Modified time, when TCP).  However, these parameters MUST
   NOT be used as a validator when interleaving data over the RTSP control connection.

   setup:  Clients use the setup parameter on the Transport line in a
         SETUP request, is
   implicitly weak unless it is possible to deduce that indicate the roles it wishes to play in a TCP
         connection.  This parameter is strong,
   using adapted from [RFC4145].  We
         discuss the following rules:

   o  The validator use of this parameter in RTP/AVP/TCP non-
         interleaved transport in Appendix C.2.2; the discussion below
         is being compared by an origin server limited to syntactic issues.  Clients may specify the actual
      current validator
         following values for the entity and,

   o  That origin server reliably knows that the associated entity did
      not change more than once during the second covered by the
      presented validator.

   OR

   o setup parameter: ["active":] The validator is about to be used by a
         client in will initiate an If-Modified-
      Since, because the outgoing connection. ["passive":] The
         client has will accept an incoming connection. ["actpass":] The
         client is willing to accept an incoming connection or to
         initiate an outgoing connection.

         If a cache entry for the associated
      entity, and

   o  That cache entry includes client does not specify a Date setup value, which gives the time when
      the origin server sent the original response, and

   o  The presented Last-Modified time "active" value
         is at least 60 seconds before the
      Date value.

   OR

   o  The validator assumed.

         In response to a client SETUP request where the setup parameter
         is being compared by an intermediate cache set to "active", a server's 2xx reply MUST assign the
      validator stored in its cache entry for setup
         parameter to "passive" on the entity, and

   o  That cache entry includes Transport header line.

         In response to a Date value, which gives client SETUP request where the time when setup parameter
         is set to "passive", a server's 2xx reply MUST assign the origin server sent setup
         parameter to "active" on the original response, and

   o  The presented Last-Modified time Transport header line.

         In response to a client SETUP request where the setup parameter
         is at least 60 seconds before set to "actpass", a server's 2xx reply MUST assign the
      Date value.

   This method relies setup
         parameter to "active" or "passive" on the fact Transport header
         line.

         Note that if two different responses were
   sent by the origin server during "holdconn" value for setup is not defined for
         RTSP use, and MUST NOT appear on a Transport line.

   connection:  Clients use the same second, but both had setup parameter on the
   same Last-Modified time, then at least one of those responses would
   have Transport line in
         a Date value equal SETUP request, to its Last-Modified time.  The arbitrary 60-
   second limit guards against indicate the possibility that SETUP request prefers the Date
         reuse of an existing connection between client and Last-
   Modified values are generated from different clocks, or at somewhat
   different times during server (in
         which case the preparation of client sets the response.  An
   implementation MAY use a value larger than 60 seconds, if it is
   believed "connection" parameter to
         "existing"), or that 60 seconds is too short.

   If the client requires the creation of a new
         connection between client wishes and server (in which cast the client
         sets the "connection" parameter to perform a sub-range retrieval on a "new").  Typically, clients
         use the "new" value for
   which it has only a Last-Modified time and no opaque validator, it
   MAY do this only if the Last-Modified time is strong in the sense
   described here.

18.1.4.  Rules first SETUP request for When to Use Message Body Tags and Last-Modified Dates

   We adopt a set of rules URL, and recommendations
         "existing" for origin servers,
   clients, and caches regarding when various validator types ought to
   be used, and subsequent SETUP requests for what purposes.

   RTSP origin servers:

   o  SHOULD send a message body tag validator unless it is not feasible
      to generate one.

   o  MAY send a weak message body tag instead of URL.

         If a strong message body
      tag, if performance considerations support client SETUP request assigns the use of weak message
      body tags, or if it is unfeasible to send a strong message body
      tag.

   o  SHOULD send a Last-Modified "new" value if it is feasible to send one,
      unless the risk of a breakdown in semantic transparency that could
      result from using this date in an If-Modified-Since header would
      lead to serious problems.

   In other words,
         "connection", the preferred behavior for an RTSP origin server is
   to send both a strong message body tag and a Last-Modified value.

   In order to be legal, a strong message body tag response MUST change whenever also assign the associated entity "new"
         value changes in any way.  A weak message body
   tag SHOULD change whenever to "connection" on the associated entity changes in Transport line.

         If a
   semantically significant way.

      Note: in order client SETUP request assigns the "existing" value to provide semantically transparent caching, an
      origin
         "connection", the server response MUST avoid reusing assign a specific strong message body
      tag value for two different entities, of
         "existing" or reusing a specific weak
      message body tag "new" to "connection" on the Transport line, at
         its discretion.

         The default value of "connection" is "existing", for two semantically different entities.
      Cache entries might persist for arbitrarily long periods,
      regardless all SETUP
         requests (initial and subsequent).

   The combination of expiration times, so it might be inappropriate to
      expect that a cache will never again attempt transport protocol, profile and lower transport
   needs to validate an entry
      using a validator that it obtained at some point be defined.  A number of combinations are defined in the past.

   RTSP clients:

   o  If
   Appendix C.

   Below is a message body tag has been provided by usage example, showing a client advertising the origin server, MUST
      use that message body tag in any cache-conditional request (using
      If-Match capability
   to handle multicast or If-None-Match).

   o  If only unicast, preferring multicast.  Since this is
   a Last-Modified value has been provided by unicast-only stream, the origin
      server, SHOULD use that value in non-subrange cache-conditional
      requests (using If-Modified-Since).

   o  If both a message body tag and a Last-Modified value have been
      provided server responds with the proper transport
   parameters for unicast.

     C->S: SETUP rtsp://example.com/foo/bar/baz.rm RTSP/2.0
           CSeq: 302
           Transport: RTP/AVP;multicast;mode="PLAY",
               RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/
               "192.0.2.5:3457";mode="PLAY"
           Accept-Ranges: NPT, SMPTE, UTC
           User-Agent: PhonyClient/1.2

     S->C: RTSP/2.0 200 OK
           CSeq: 302
           Date: Thu, 23 Jan 1997 15:35:06 GMT
           Session: 47112344
           Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/
              "192.0.2.5:3457";src_addr="192.0.2.224:6256"/
              "192.0.2.224:6257";mode="PLAY"
           Accept-Ranges: NPT
           Media-Properties: Random-Access=0.6, Dynamic,
                             Time-Limited=20081128T165900

18.53.  Unsupported

   The Unsupported response-header lists the features not supported by
   the origin server, SHOULD use both validators in
      cache-conditional requests.

   An responding RTSP origin server, upon receiving a conditional request that
   includes both agent.  In the case where the feature was
   specified via the Proxy-Require field (Section 18.35), if there is a Last-Modified date (e.g., in an If-Modified-Since
   header)
   proxy on the path between the client and one or more message body tags (e.g., in an If-Match, If-
   None-Match, or If-Range header field) as cache validators, the server, the proxy MUST NOT
   return
   send a response status of 304 (Not Modified) unless doing so is
   consistent message with all a status code of the conditional header fields in the request.

      Note: 551 (Option Not
   Supported).  The general principle behind these rules is that RTSP
      servers and clients should transmit as much non-redundant
      information as is available in their responses and requests.  RTSP
      systems receiving this request MUST NOT be forwarded.

   See Section 18.41 for a usage example.

18.54.  User-Agent

   The User-Agent general-header field contains information will make the most conservative
      assumptions about the validators they receive.

18.1.5.  Non-validating Conditionals

   The principle behind message body tags is that only
   user agent originating the service
   author knows request.  This is for statistical
   purposes, the semantics tracing of a resource well enough to select an
   appropriate cache validation mechanism, protocol violations, and automated
   recognition of user agents for the specification sake of any
   validator comparison function more complex than byte-equality would
   open up tailoring responses to
   avoid particular user agent limitations.  User agents SHOULD include
   this field with requests.  The field can contain multiple product
   tokens and comments identifying the agent and any subproducts which
   form a can of worms.  Thus, comparisons significant part of any other headers the user agent.  By convention, the
   product tokens are
   never used for purposes listed in order of validating a cache entry.

18.2.  Invalidation After Updates or Deletions their significance for
   identifying the application.

   Example:
   User-Agent: PhonyClient/1.2

18.55.  Via

   The effect of certain methods performed on a resource at Via general-header field MUST be used by proxies to indicate the
   intermediate protocols and recipients between the user agent and the origin
   server might cause one or more existing cache entries to become non-
   transparently invalid.  That is, although they might continue to be
   "fresh," they do not accurately reflect what on requests, and between the origin server would
   return for a new request and the client on that resource.

   There
   responses.  The field is no way intended to be used for tracking message
   forwards, avoiding request loops, and identifying the RTSP protocol to guarantee that
   capabilities of all such
   cache entries are marked invalid.  For example, senders along the request request/response chain.

   Multiple Via field values represents each proxy that
   caused the change at has forwarded
   the origin server might not have gone through message.  Each recipient MUST append its information such that
   the proxy where a cache entry end result is stored.  However, several rules help
   reduce the likelihood of erroneous behavior.

   In this section, the phrase "invalidate an entity" means that ordered according to the
   cache will either remove all instances sequence of that entity from its
   storage, forwarding
   applications.

   Proxies (e.g., Access Proxy or will mark these as "invalid" Translator Proxy) SHOULD NOT, by
   default, forward the names and in need ports of a mandatory
   revalidation before they can be returned in response to a subsequent
   request.

   Some RTSP methods MUST cause a cache to invalidate an entity. hosts within the private/
   protected region.  This
   is either information SHOULD only be propagated if
   explicitly enabled.  If not enabled, the entity referred to by via-received of any host
   behind the Request-URI, or firewall/NAT SHOULD be replaced by the
   Location or Content-Location headers (if present).  These methods
   are:

   o  DESCRIBE
   o  SETUP

   In order to prevent denial of service attacks, an invalidation based
   on the URI in appropriate
   pseudonym for that host.

   For organizations that have strong privacy requirements for hiding
   internal structures, a Location or Content-Location proxy MAY combine an ordered subsequence of
   Via header field entries with identical sent-protocol values into a
   single such entry.  Applications MUST NOT combine entries which have
   different received-protocol values.

18.56.  WWW-Authenticate

   The WWW-Authenticate response-header field MUST only be
   performed if included in 401
   (Unauthorized) response messages.  The field value consists of at
   least one challenge that indicates the host part is authentication scheme(s) and
   parameters applicable to the same as Request-URI.

   The HTTP access authentication process is described in [RFC2617].
   User agents are advised to take special care in parsing the Request-URI.

   A cache that passes through requests for methods WWW-
   Authenticate field value as it does not
   understand SHOULD invalidate any entities referred to by might contain more than one challenge,
   or if more than one WWW-Authenticate header field is provided, the Request-
   URI.
   contents of a challenge itself can contain a comma-separated list of
   authentication parameters.

19.  Security Framework

   The RTSP security framework consists of two high level components:
   the pure authentication mechanisms based on HTTP authentication, and
   the message transport protection based on TLS, which is independent
   of RTSP.  Because of the similarity in syntax and usage between RTSP
   servers and HTTP servers, the security for HTTP is re-used to a large
   extent.

19.1.  RTSP and HTTP Authentication

   RTSP and HTTP share common authentication schemes, and thus follow
   the same usage guidelines as specified in [RFC2617] and also in
   [H15].  Servers SHOULD implement both basic and digest [RFC2617]
   authentication.  Clients MUST implement both basic and digest
   authentication [RFC2617] so that a server that requires the client to
   authenticate can trust that the capability is present.

   It should be stressed that using the HTTP authentication alone does
   not provide full control message security.  Therefore, in
   environments requiring tighter security for the control messages, TLS
   SHOULD be used, see Section 19.2.

19.2.  RTSP over TLS

   RTSP agents MUST implement RTSP over TLS as defined in this section
   and the next Section 19.3.  RTSP MUST follow the same guidelines with
   regards to TLS [RFC5246] usage as specified for HTTP, see [RFC2818].
   RTSP over TLS is separated from unsecured RTSP both on URI level and
   port level.  Instead of using the "rtsp" scheme identifier in the
   URI, the "rtsps" scheme identifier MUST be used to signal RTSP over
   TLS.  If no port is given in a URI with the "rtsps" scheme, port 322
   MUST be used for TLS over TCP/IP.

   When a client tries to setup an insecure channel to the server (using
   the "rtsp" URI), and the policy for the resource requires a secure
   channel, the server MUST redirect the client to the secure service by
   sending a 301 redirect response code together with the correct
   Location URI (using the "rtsps" scheme).  A user or client MAY
   upgrade a non secured URI to a secured by changing the scheme from
   "rtsp" to "rtsps".  A server implementing support for "rtsps" MUST
   allow this.

   It should be noted that TLS allows for mutual authentication (when
   using both server and client certificates).  Still, one of the more
   common ways TLS is used is to only provide server side authentication
   (often to avoid client certificates).  TLS is then used in addition
   to HTTP authentication, providing transport security and server
   authentication, while HTTP Authentication is used to authenticate the
   client.

   RTSP includes the possibility to keep a TCP session up between the
   client and server, throughout the RTSP session lifetime.  It may be
   convenient to keep the TCP session, not only to save the extra setup
   time for TCP, but also the extra setup time for TLS (even if TLS uses
   the resume function, there will be almost two extra round trips).
   Still, when TLS is used, such behavior introduces extra active state
   in the server, not only for TCP and RTSP, but also for TLS.  This may
   increase the vulnerability to DoS attacks.

   In addition to these recommendations, Section 19.3 gives further
   recommendations of TLS usage with proxies.

19.3.  Security and Proxies

   The nature of a proxy is often to act as a "man-in-the-middle", while
   security is often about preventing the existence of a "man-in-the-
   middle".  This section provides clients with the possibility to use
   proxies even when applying secure transports (TLS) between the RTSP
   agents.  The TLS proxy mechanism allows for server and proxy
   identification using certificates.  However, the client can not be
   identified based on certificates.  The client needs to select between
   using the procedure specified below or using a TLS connection
   directly (by-passing any proxies) to the server.  The choice may be
   dependent on policies.

   There are basically two categories of proxies, the transparent
   proxies (of which the client is not aware) and the non-transparent
   proxies (of which the client is aware), see Section Section 17 15 for an
   introduction to RTSP proxies.  An infrastructure based on proxies
   requires that the trust model is such that both client and servers
   can trust the proxies to handle the RTSP messages correctly.  To be
   able to trust a proxy, the client and server also needs to be aware
   of the proxy.  Hence, transparent proxies cannot generally be seen as
   trusted and will not work well with security (unless they work only
   at transport layer).  In the rest of this section any reference to
   proxy will be to a non-transparent proxy, which inspects or
   manipulate the RTSP messages.

   HTTP Authentication is built on the assumption of proxies and can
   provide user-proxy authentication and proxy-proxy/server
   authentication in addition to the client-server authentication.

   When TLS is applied and a proxy is used, the client will connect to
   the proxy's address when connecting to any RTSP server.  This implies
   that for TLS, the client will authenticate the proxy server and not
   the end server.  Note that when the client checks the server
   certificate in TLS, it MUST check the proxy's identity (URI or
   possibly other known identity) against the proxy's identity as
   presented in the proxy's Certificate message.

   The problem is that for a proxy accepted by the client, the proxy
   needs to be provided information on which grounds it should accept
   the next-hop certificate.  Both the proxy and the user may have rules
   for this, and the user have the possibility to select the desired
   behavior.  To handle this case, the Accept-Credentials header (See
   Section 16.2) 18.2) is used, where the client can force the proxy/proxies
   to relay back the chain of certificates used to authenticate any
   intermediate proxies as well as the server.  Given the assumption
   that the proxies are viewed as trusted, it gives the user a
   possibility to enforce policies to each trusted proxy of whether it
   should accept the next agent in the chain.  However, it should be
   noted that not all deployments will return the chain of certificates
   used to authenticate any intermediate proxies as well as the server.
   An operator of such a deployment may want to hide its topology from
   the client.

   A proxy MUST use TLS for the next hop if the RTSP request includes a
   "rtsps" URI.  TLS MAY be applied on intermediate links (e.g. between
   client and proxy, or between proxy and proxy), even if the resource
   and the end server are not required to use it.  The proxy MUST, when
   initiating the next hop TLS connection, use the incoming TLS
   connections cipher suite list, only modified by removing any cipher
   suits that the proxy does not support.  In case a proxy fails to
   establish a TLS connection due to cipher suite mismatch between proxy
   and next hop proxy or server, this is indicated using error code 472
   (Failure to establish secure connection).

19.3.1.  Accept-Credentials

   The Accept-Credentials header can be used by the client to distribute
   simple authorization policies to intermediate proxies.  The client
   includes the Accept-Credentials header to dictate how the proxy
   treats the server/next proxy certificate.  There are currently three
   methods defined:

   Any,  which means that the proxy (or proxies) MUST accept whatever
         certificate presented.  This is of course not a recommended
         option to use, but may be useful in certain circumstances (such
         as testing).

   Proxy,  which means that the proxy (or proxies) MUST use its own
         policies to validate the certificate and decide whether to
         accept it or not.  This is convenient in cases where the user
         has a strong trust relation with the proxy.  Reason why a
         strong trust relation may exist are; personal/company proxy,
         proxy has a out-of-band policy configuration mechanism.

   User, which means that the proxy (or proxies) MUST send credential
         information about the next hop to the client for authorization.
         The client can then decide whether the proxy should accept the
         certificate or not.  See Section 19.3.2 for further details.

   If the Accept-Credentials header is not included in the RTSP request
   from the client, then the "Proxy" method MUST be used as default.  If
   another method than the "Proxy" is to be used, then the Accept-
   Credentials header MUST be included in all of the RTSP requests from
   the client.  This is because it cannot be assumed that the proxy
   always keeps the TLS state or the users previous preference between
   different RTSP messages (in particular if the time interval between
   the messages is long).

   With the "Any" and "Proxy" methods the proxy will apply the policy as
   defined for each method.  If the policy does not accept the
   credentials of the next hop, the proxy MUST respond with a message
   using status code 471 (Connection Credentials not accepted).

   An RTSP request in the direction server to client MUST NOT include
   the Accept-Credentials header.  As for the non-secured communication,
   the possibility for these requests depends on the presence of a
   client established connection.  However, if the server to client
   request is in relation to a session established over a TLS secured
   channel, it MUST be sent in a TLS secured connection.  That secured
   connection MUST also be the one used by the last client to server
   request.  If no such transport connection exist at the time when the
   server desires to send the request, the server MUST discard the
   message.

   Further policies MAY be defined and registered, but should be done so
   with caution.

19.3.2.  User approved TLS procedure

   For the "User" method, each proxy MUST perform the following
   procedure for each RTSP request:

   o  Setup the TLS session to the next hop if not already present (i.e.
      run the TLS handshake, but do not send the RTSP request).

   o  Extract the peer certificate chain for the TLS session.

   o  Check if a matching identity and hash of the peer certificate is
      present in the Accept-Credentials header.  If present, send the
      message to the next hop, and conclude these procedures.  If not,
      go to the next step.

   o  The proxy responds to the RTSP request with a 470 or 407 response
      code.  The 407 response code MAY be used when the proxy requires
      both user and connection authorization from user or client.  In
      this message the proxy MUST include a Connection-Credentials
      header, see Section 16.12 18.12 with the next hop's identity and
      certificate.

   The client MUST upon receiving a 470 or 407 response with Connection-
   Credentials header take the decision on whether to accept the
   certificate or not (if it cannot do so, the user SHOULD be
   consulted).  If the certificate is accepted, the client has to again
   send the RTSP request.  In that request the client has to include the
   Accept-Credentials header including the hash over the DER encoded
   certificate for all trusted proxies in the chain.

   Example:

   C->P: SETUP rtsps://test.example.org/secret/audio RTSP/2.0
         CSeq: 2
         Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:4588"/
                    "192.0.2.5:4589"
         Accept-Ranges: NPT, SMPTE, UTC
         Accept-Credentials: User

   P->C: RTSP/2.0 470 Connection Authorization Required
         CSeq: 2
         Connection-Credentials: "rtsps://test.example.org";
         MIIDNTCCAp...

   C->P: SETUP rtsps://test.example.org/secret/audio RTSP/2.0
         CSeq: 3
         Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:4588"/
                    "192.0.2.5:4589"
         Accept-Credentials: User "rtsps://test.example.org";sha-256;
         dPYD7txpoGTbAqZZQJ+vaeOkyH4=
         Accept-Ranges: NPT, SMPTE, UTC

   P->S: SETUP rtsps://test.example.org/secret/audio RTSP/2.0
         CSeq: 3
         Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:4588"/
                    "192.0.2.5:4589"
         Via: RTSP/2.0 proxy.example.org
         Accept-Credentials: User "rtsps://test.example.org";sha-256;
         dPYD7txpoGTbAqZZQJ+vaeOkyH4=
         Accept-Ranges: NPT, SMPTE, UTC

   One implication of this process is that the connection for secured
   RTSP messages may take significantly more round-trip times for the
   first message.  A complete extra message exchange between the proxy
   connecting to the next hop and the client results because of the
   process for approval for each hop.  However, if each message contains
   the chain of proxies that the requester accepts, the remaining
   message exchange should not be delayed.  The procedure of including
   the credentials in each request rather than building state in each
   proxy, avoids the need for revocation procedures.

20.  Syntax

   The RTSP syntax is described in an Augmented Backus-Naur Form (ABNF)
   as defined in RFC 5234 [RFC5234].  It uses the basic definitions
   present in RFC 5234.

   Please note that ABNF strings, e.g.  "Accept", are case insensitive
   as specified in section 2.3 of RFC 5234.

20.1.  Base Syntax

   RTSP header values can be folded onto multiple lines if the
   continuation line begins with a space or horizontal tab.  All linear
   white space, including folding, has the same semantics as SP.  A
   recipient MAY replace any linear white space with a single SP before
   interpreting the field value or forwarding the message downstream.
   This is intended to behave exactly as HTTP/1.1 as described in RFC
   2616 [RFC2616].  The SWS construct is used when linear white space is
   optional, generally between tokens and separators.

   To separate the header name from the rest of value, a colon is used,
   which, by the above rule, allows whitespace before, but no line
   break, and whitespace after, including a line break.  The HCOLON
   defines this construct.

   OCTET           =  %x00-FF ; any 8-bit sequence of data
   CHAR            =  %x01-7F ; any US-ASCII character (octets 1 - 127)
   UPALPHA         =  %x41-5A ; any US-ASCII uppercase letter "A".."Z"
   LOALPHA         =  %x61-7A ;any US-ASCII lowercase letter "a".."z"
   ALPHA           =  UPALPHA / LOALPHA
   DIGIT           =  %x30-39 ; any US-ASCII digit "0".."9"
   CTL             =  %x00-1F / %x7F  ; any US-ASCII control character
                      ; (octets 0 - 31) and DEL (127)
   CR              =  %x0D ; US-ASCII CR, carriage return (13)
   LF              =  %x0A  ; US-ASCII LF, linefeed (10)
   SP              =  %x20  ; US-ASCII SP, space (32)
   HT              =  %x09  ; US-ASCII HT, horizontal-tab (9)
   DQ              =  %x22  ; US-ASCII double-quote mark (34)
   BACKSLASH       =  %x5C  ; US-ASCII backslash (92)
   CRLF            =  CR LF
   LWS             =  [CRLF] 1*( SP / HT ) ; Line-breaking White Space
   SWS             =  [LWS] ; Separating White Space
   HCOLON          =  *( SP / HT ) ":" SWS
   TEXT            =  %x20-7E / %x80-FF  ; any OCTET except CTLs
   tspecials       =  "(" / ")" / "<" / ">" / "@"
                   /  "," / ";" / ":" / BACKSLASH / DQ
                   /  "/" / "[" / "]" / "?" / "="
                   /  "{" / "}" / SP / HT
   token           =  1*(%x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
                   /  %x41-5A / %x5E-7A / %x7C / %x7E)
                      ; 1*<any CHAR except CTLs or tspecials>
   quoted-string   =  ( DQ *qdtext DQ )
   qdtext          =  %x20-21 / %x23-7E / %x80-FF / UTF8-NONASCII
                      ; any UTF-8 TEXT except <">
   quoted-pair     =  BACKSLASH CHAR
   ctext           =  %x20-27 / %x2A-7E
                   /  %x80-FF  ; any OCTET except CTLs, "(" and ")"
   generic-param   =  token [ EQUAL gen-value ]
   gen-value       =  token / host / quoted-string

   safe            =  "$" / "-" / "_" / "." / "+"
   extra           =  "!" / "*" / "'" / "(" / ")" / ","
   rtsp-extra      =  "!" / "*" / "'" / "(" / ")"

   HEX             =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
                   /  "a" / "b" / "c" / "d" / "e" / "f"
   LHEX            =  DIGIT /  "a" / "b" / "c" / "d" / "e" / "f"
                      ; lowercase "a-f" Hex
   reserved        =  ";" / "/" / "?" / ":" / "@" / "&" / "="

   unreserved      =  ALPHA / DIGIT / safe / extra
   rtsp-unreserved  =  ALPHA / DIGIT / safe / rtsp-extra

   base64          =  *base64-unit [base64-pad]
   base64-unit     =  4base64-char
   base64-pad      =  (2base64-char "==") / (3base64-char "=")
   base64-char     =  ALPHA / DIGIT / "+" / "/"
   SLASH    =  SWS "/" SWS ; slash
   EQUAL    =  SWS "=" SWS ; equal
   LPAREN   =  SWS "(" SWS ; left parenthesis
   RPAREN   =  SWS ")" SWS ; right parenthesis
   COMMA    =  SWS "," SWS ; comma
   SEMI     =  SWS ";" SWS ; semicolon
   COLON    =  SWS ":" SWS ; colon
   MINUS    =  SWS "-" SWS ; minus/dash
   LDQUOT   =  SWS DQ ; open double quotation mark
   RDQUOT   =  DQ SWS ; close double quotation mark
   RAQUOT   =  ">" SWS ; right angle quote
   LAQUOT   =  SWS "<" ; left angle quote

   TEXT-UTF8char    =  %x21-7E / UTF8-NONASCII
   UTF8-NONASCII    =  %xC0-DF 1UTF8-CONT
                    /  %xE0-EF 2UTF8-CONT
                    /  %xF0-F7 3UTF8-CONT
                    /  %xF8-FB 4UTF8-CONT
                    /  %xFC-FD 5UTF8-CONT
   UTF8-CONT        =  %x80-BF

   POS-FLOAT        = 1*12DIGIT ["." 1*9DIGIT]
   FLOAT            = ["-"] POS-FLOAT

20.2.  RTSP Protocol Definition

20.2.1.  Generic Protocol elements
   RTSP-IRI       =  schemes ":" IRI-rest
   IRI-rest       =  ihier-part [ "?" iquery ] [ "#" ifragment ]
   ihier-part     =  "//" iauthority ipath-abempty
   RTSP-IRI-ref   =  RTSP-IRI / irelative-ref
   irelative-ref  =  irelative-part [ "?" iquery ] [ "#" ifragment ]
   irelative-part =  "//" iauthority ipath-abempty
                     / ipath-absolute
                     / ipath-noscheme
                     / ipath-empty

   iauthority     =  < As defined in RFC 3987>
   ipath          =  ipath-abempty   ; begins with "/" or is empty
                     / ipath-absolute  ; begins with "/" but not "//"
                     / ipath-noscheme  ; begins with a non-colon segment
                     / ipath-rootless  ; begins with a segment
                     / ipath-empty     ; zero characters

   ipath-abempty   =  *( "/" isegment )
   ipath-absolute  =  "/" [ isegment-nz *( "/" isegment ) ]
   ipath-noscheme  =  isegment-nz-nc *( "/" isegment )
   ipath-rootless  =  isegment-nz *( "/" isegment )
   ipath-empty     =  0<ipchar>

   isegment        =  *ipchar [";" *ipchar]
   isegment-nz     =  1*ipchar [";" *ipchar]
                      / ";" *ipchar
   isegment-nz-nc  =  (1*ipchar-nc [";" *ipchar-nc])
                      / ";" *ipchar-nc
                      ; non-zero-length segment without any colon ":"

   ipchar         =  iunreserved / pct-encoded / sub-delims / ":" / "@"
   ipchar-nc      =  iunreserved / pct-encoded / sub-delims / "@"

   iquery         =  < As defined in RFC 3987>
   ifragment      =  < As defined in RFC 3987>
   iunreserved    =  < As defined in RFC 3987>
   pct-encoded    =  < As defined in RFC 3987>
   RTSP-URI       =  schemes ":" URI-rest
   RTSP-REQ-URI   =  schemes ":" URI-req-rest
   RTSP-URI-Ref   =  RTSP-URI / RTSP-Relative
   RTSP-REQ-Ref   =  RTSP-REQ-URI / RTSP-REQ-Rel
   schemes        =  "rtsp" / "rtsps" / scheme
   scheme         =  < As defined in RFC 3986>
   URI-rest       =  hier-part [ "?" query ] [ "#" fragment ]
   URI-req-rest   =  hier-part [ "?" query ]
                     ; Note fragment part not allowed in requests
   hier-part      =  "//" authority path-abempty

   RTSP-Relative  =  relative-part [ "?" query ] [ "#" fragment ]
   RTSP-REQ-Rel   =  relative-part [ "?" query ]
   relative-part  =  "//" authority path-abempty
                     / path-absolute
                     / path-noscheme
                     / path-empty

   authority      =  < As defined in RFC 3986>
   query          =  < As defined in RFC 3986>
   fragment       =  < As defined in RFC 3986>

   path           =  path-abempty    ; begins with "/" or is empty
                     / path-absolute ; begins with "/" but not "//"
                     / path-noscheme ; begins with a non-colon segment
                     / path-rootless ; begins with a segment
                     / path-empty    ; zero characters

   path-abempty   =  *( "/" segment )
   path-absolute  =  "/" [ segment-nz *( "/" segment ) ]
   path-noscheme  =  segment-nz-nc *( "/" segment )
   path-rootless  =  segment-nz *( "/" segment )
   path-empty     =  0<pchar>

   segment        =  *pchar [";" *pchar]
   segment-nz     =  ( 1*pchar [";" *pchar]) / (";" *pchar)
   segment-nz-nc  =  ( 1*pchar-nc [";" *pchar-nc]) / (";" *pchar-nc)
                     ; non-zero-length segment without any colon ":"

   pchar          =  unreserved / pct-encoded / sub-delims / ":" / "@"
   pchar-nc       =  unreserved / pct-encoded / sub-delims / "@"

   sub-delims     =  "!" / "$" / "&" / "'" / "(" / ")"
                     / "*" / "+" / "," / "="

   smpte-range        =  smpte-type ["=" smpte-range-spec]
                         ; See section 3.4
   smpte-range-spec   =  ( smpte-time "-" [ smpte-time ] )
                      /  ( "-" smpte-time )
   smpte-type         =  "smpte" / "smpte-30-drop"
                      /  "smpte-25" / smpte-type-extension
                      ; other timecodes may be added
   smpte-type-extension  =  "smpte" token
   smpte-time         =  1*2DIGIT ":" 1*2DIGIT ":" 1*2DIGIT
                         [ ":" 1*2DIGIT [ "." 1*2DIGIT ] ]

   npt-range        =  "npt" ["=" npt-range-spec]
   npt-range-spec   =  ( npt-time "-" [ npt-time ] ) / ( "-" npt-time )
   npt-time         =  "now" / npt-sec / npt-hhmmss
   npt-sec          =  1*19DIGIT [ "." 1*9DIGIT ]
   npt-hhmmss       =  npt-hh ":" npt-mm ":" npt-ss [ "." 1*9DIGIT ]
   npt-hh           =  1*19DIGIT   ; any positive number
   npt-mm           =  1*2DIGIT  ; 0-59
   npt-ss           =  1*2DIGIT  ; 0-59

   utc-range        =  "clock" ["=" utc-range-spec]
   utc-range-spec   =  ( utc-time "-" [ utc-time ] ) / ( "-" utc-time )
   utc-time         =  utc-date "T" utc-clock "Z"
   utc-date         =  8DIGIT
   utc-clock        =  6DIGIT [ "." 1*9DIGIT ]

   feature-tag       =  token

   session-id        =  1*256( ALPHA / DIGIT / safe )

   extension-header  =  header-name HCOLON header-value
   header-name       =  token
   header-value      =  *(TEXT-UTF8char / UTF8-CONT / LWS)

20.2.2.  Message Syntax
   RTSP-message  = Request / Response  ; RTSP/2.0 messages

   Request       = Request-Line
                   *((general-header
                   /  request-header
                   /  message-header) CRLF)
                   CRLF
                   [ message-body-data ]

   Response     = Status-Line
                  *((general-header
                  /  response-header
                  /  message-header) CRLF)
                  CRLF
                  [ message-body-data ]

   Request-Line = Method SP Request-URI SP RTSP-Version CRLF

   Status-Line  = RTSP-Version SP Status-Code SP Reason-Phrase CRLF
   Method  =  "DESCRIBE"
           /  "GET_PARAMETER"
           /  "OPTIONS"
           /  "PAUSE"
           /  "PLAY"
           /  "PLAY_NOTIFY"
           /  "REDIRECT"
           /  "SETUP"
           /  "SET_PARAMETER"
           /  "TEARDOWN"
           /  extension-method

   extension-method  =  token

   Request-URI  =  "*" / RTSP-REQ-URI
   RTSP-Version =  "RTSP/" 1*DIGIT "." 1*DIGIT

   message-body-data = 1*OCTET

   Status-Code  =  "100"  ; Continue
                /  "200"  ; OK
                /  "301"  ; Moved Permanently
                /  "302"  ; Found
                /  "303"  ; See Other
                /  "304"  ; Not Modified
                /  "305"  ; Use Proxy
                /  "400"  ; Bad Request
                /  "401"  ; Unauthorized
                /  "402"  ; Payment Required
                /  "403"  ; Forbidden
                /  "404"  ; Not Found
                /  "405"  ; Method Not Allowed
                /  "406"  ; Not Acceptable
                /  "407"  ; Proxy Authentication Required
                /  "408"  ; Request Time-out
                /  "410"  ; Gone
                /  "411"  ; Length Required
                /  "412"  ; Precondition Failed
                /  "413"  ; Request Message Body Too Large
                /  "414"  ; Request-URI Too Large
                /  "415"  ; Unsupported Media Type
                /  "451"  ; Parameter Not Understood
                /  "452"  ; reserved
                /  "453"  ; Not Enough Bandwidth
                /  "454"  ; Session Not Found
                /  "455"  ; Method Not Valid in This State
                /  "456"  ; Header Field Not Valid for Resource
                /  "457"  ; Invalid Range
                /  "458"  ; Parameter Is Read-Only
                /  "459"  ; Aggregate operation not allowed
                /  "460"  ; Only aggregate operation allowed
                /  "461"  ; Unsupported Transport
                /  "462"  ; Destination Unreachable
                /  "463"  ; Destination Prohibited
                /  "464"  ; Data Transport Not Ready Yet
                /  "465"  ; Notification Reason Unknown
                /  "466"  ; Key Management Error
                /  "470"  ; Connection Authorization Required
                /  "471"  ; Connection Credentials not accepted
                /  "472"  ; Failure to establish secure connection
                /  "500"  ; Internal Server Error
                /  "501"  ; Not Implemented
                /  "502"  ; Bad Gateway
                /  "503"  ; Service Unavailable
                /  "504"  ; Gateway Time-out
                /  "505"  ; RTSP Version not supported
                /  "551"  ; Option not supported
                /  extension-code

   extension-code  =  3DIGIT

   Reason-Phrase   =  1*(TEXT-UTF8char / HT / SP)
   general-header  =  Cache-Control
                   /  Connection
                   /  CSeq
                   /  Date
                   /  Media-Properties
                   /  Media-Range
                   /  Pipelined-Requests
                   /  Proxy-Supported
                   /  Seek-Style
                   /  Server
                   /  Supported
                   /  Timestamp
                   /  User-Agent
                   /  Via
                   /  extension-header

   request-header  =  Accept
                   /  Accept-Credentials
                   /  Accept-Encoding
                   /  Accept-Language
                   /  Authorization
                   /  Bandwidth
                   /  Blocksize
                   /  From
                   /  If-Match
                   /  If-Modified-Since
                   /  If-None-Match
                   /  Notify-Reason
                   /  Proxy-Require
                   /  Range
                   /  Referrer
                   /  Request-Status
                   /  Require
                   /  Scale
                   /  Session
                   /  Speed
                   /  Supported
                   /  Terminate-Reason
                   /  Transport
                   /  extension-header

   response-header  =  Accept-Credentials
                    /  Accept-Ranges
                    /  Connection-Credentials
                    /  MTag
                    /  Location
                    /  Proxy-Authenticate
                    /  Public
                    /  Range
                    /  Retry-After
                    /  RTP-Info
                    /  Scale
                    /  Session
                    /  Speed
                    /  Transport
                    /  Unsupported
                    /  Vary
                    /  WWW-Authenticate
                    /  extension-header

   message-header    =  Allow
                    /  Content-Base
                    /  Content-Encoding
                    /  Content-Language
                    /  Content-Length
                    /  Content-Location
                    /  Content-Type
                    /  Expires
                    /  Last-Modified
                    /  extension-header

20.2.3.  Header Syntax

   Accept            =  "Accept" HCOLON
                        [ accept-range *(COMMA accept-range) ]
   accept-range      =  media-type-range [SEMI accept-params]
   media-type-range  =  ( "*/*"
                        / ( m-type SLASH "*" )
                        / ( m-type SLASH m-subtype )
                       ) *( SEMI m-parameter )
   accept-params     =  "q" EQUAL qvalue *(SEMI generic-param )
   qvalue            =  ( "0" [ "." *3DIGIT ] )
                     /  ( "1" [ "." *3("0") ] )
   Accept-Credentials =  "Accept-Credentials" HCOLON cred-decision
   cred-decision     =  ("User" [LWS cred-info])
                     /  "Proxy"
                     /  "Any"
                     /  (token [LWS 1*header-value])
                                     ; For future extensions

   cred-info         =  cred-info-data *(COMMA cred-info-data)

   cred-info-data    =  DQ RTSP-REQ-URI DQ SEMI hash-alg SEMI base64
   hash-alg          =  "sha-256" / extension-alg
   extension-alg     =  token
   Accept-Encoding   =  "Accept-Encoding" HCOLON
                        [ encoding *(COMMA encoding) ]
   encoding          =  codings [SEMI accept-params]
   codings           =  content-coding / "*"
   content-coding    =  token
   Accept-Language   =  "Accept-Language" HCOLON
                        language *(COMMA language)
   language          =  language-range [SEMI accept-params]
   language-range    =  language-tag / "*"
   language-tag      =  primary-tag *( "-" subtag )
   primary-tag       =  1*8ALPHA
   subtag            =  1*8ALPHA
   Accept-Ranges     =  "Accept-Ranges" HCOLON acceptable-ranges
   acceptable-ranges =  (range-unit *(COMMA range-unit))
   range-unit        =  "NPT" / "SMPTE" / "UTC" / extension-format
   extension-format  =  token
   Allow             =  "Allow" HCOLON Method *(COMMA Method)
   Authorization     =  "Authorization" HCOLON credentials
   credentials       =  ("Digest" LWS digest-response)
                     /  other-response
   digest-response   =  dig-resp *(COMMA dig-resp)
   dig-resp          =  username / realm / nonce / digest-uri
                     /  dresponse / algorithm / cnonce
                     /  opaque / message-qop
                     /  nonce-count / auth-param
   username          =  "username" EQUAL username-value
   username-value    =  quoted-string
   digest-uri        =  "uri" EQUAL LDQUOT digest-uri-value RDQUOT
   digest-uri-value  =  RTSP-REQ-URI
   message-qop       =  "qop" EQUAL qop-value
   cnonce            =  "cnonce" EQUAL cnonce-value
   cnonce-value      =  nonce-value
   nonce-count       =  "nc" EQUAL nc-value
   nc-value          =  8LHEX
   dresponse         =  "response" EQUAL request-digest
   request-digest    =  LDQUOT 32LHEX RDQUOT
   auth-param        =  auth-param-name EQUAL
                        ( token / quoted-string )
   auth-param-name   =  token
   other-response    =  auth-scheme LWS auth-param
                        *(COMMA auth-param)
   auth-scheme       =  token
   Bandwidth         =  "Bandwidth" HCOLON 1*19DIGIT

   Blocksize         =  "Blocksize" HCOLON 1*9DIGIT

   Cache-Control     =  "Cache-Control" HCOLON cache-directive
                        *(COMMA cache-directive)
   cache-directive   =  cache-rqst-directive
                     /  cache-rspns-directive

   cache-rqst-directive =  "no-cache"
                        /  "max-stale" [EQUAL delta-seconds]
                        /  "min-fresh" EQUAL delta-seconds
                        /  "only-if-cached"
                        /  cache-extension

   cache-rspns-directive =  "public"
                            /  "private"
                            /  "no-cache"
                            /  "no-transform"
                            /  "must-revalidate"
                            /  "proxy-revalidate"
                            /  "max-age" EQUAL delta-seconds
                            /  cache-extension

   cache-extension   =  token [EQUAL (token / quoted-string)]
   delta-seconds     =  1*19DIGIT

   Connection         =  "Connection" HCOLON connection-token
                         *(COMMA connection-token)
   connection-token   =  "close" / token

   Connection-Credentials = "Connection-Credentials" HCOLON cred-chain
   cred-chain         =  DQ RTSP-REQ-URI DQ SEMI base64

   Content-Base       =  "Content-Base" HCOLON RTSP-URI
   Content-Encoding   =  "Content-Encoding" HCOLON
                         content-coding *(COMMA content-coding)
   Content-Language   =  "Content-Language" HCOLON
                         language-tag *(COMMA language-tag)
   Content-Length     =  "Content-Length" HCOLON 1*19DIGIT
   Content-Location   =  "Content-Location" HCOLON RTSP-REQ-Ref
   Content-Type       =  "Content-Type" HCOLON media-type
   media-type         =  m-type SLASH m-subtype *(SEMI m-parameter)
   m-type             =  discrete-type / composite-type
   discrete-type      =  "text" / "image" / "audio" / "video"
                      /  "application" / extension-token
   composite-type   =  "message" / "multipart" / extension-token
   extension-token  =  ietf-token / x-token
   ietf-token       =  token
   x-token          =  "x-" token
   m-subtype        =  extension-token / iana-token
   iana-token       =  token
   m-parameter      =  m-attribute EQUAL m-value
   m-attribute      =  token
   m-value          =  token / quoted-string

   CSeq           =  "CSeq" HCOLON cseq-nr
   cseq-nr        =  1*9DIGIT
   Date           =  "Date" HCOLON RTSP-date
   RTSP-date      =  rfc1123-date ; HTTP-date
   rfc1123-date   =  wkday "," SP date1 SP time SP "GMT"
   date1          =  2DIGIT SP month SP 4DIGIT
                     ; day month year (e.g., 02 Jun 1982)
   time           =  2DIGIT ":" 2DIGIT ":" 2DIGIT
                     ; 00:00:00 - 23:59:59
   wkday          =  "Mon" / "Tue" / "Wed"
                  /  "Thu" / "Fri" / "Sat" / "Sun"
   month          =  "Jan" / "Feb" / "Mar" / "Apr"
                  /  "May" / "Jun" / "Jul" / "Aug"
                  /  "Sep" / "Oct" / "Nov" / "Dec"

   Expires        =  "Expires" HCOLON RTSP-date
   From           =  "From" HCOLON from-spec
   from-spec      =  ( name-addr / addr-spec ) *( SEMI from-param )
   name-addr      =  [ display-name ] LAQUOT addr-spec RAQUOT
   addr-spec      =  RTSP-REQ-URI / absolute-URI
   absolute-URI   =  < As defined in RFC 3986>
   display-name   =  *(token LWS) / quoted-string
   from-param     =  tag-param / generic-param
   tag-param      =  "tag" EQUAL token
   If-Match       =  "If-Match" HCOLON ("*" / message-tag-list)
   message-tag-list =  message-tag *(COMMA message-tag)
   message-tag      =  [ weak ] opaque-tag
   weak             =  "W/"
   opaque-tag       =  quoted-string
   If-Modified-Since  =  "If-Modified-Since" HCOLON RTSP-date
   If-None-Match    =  "If-None-Match" HCOLON ("*" / message-tag-list)
   Last-Modified    =  "Last-Modified" HCOLON RTSP-date
   Location         =  "Location" HCOLON RTSP-REQ-URI
   Media-Properties = "Media-Properties" HCOLON [media-prop-list]
   media-prop-list  = media-prop-value *(COMMA media-prop-value)
   media-prop-value = ("Random-Access" [EQUAL POS-FLOAT])
                    / "Begining-Only"
                    / "No-Seeking"
                    / "Immutable"
                    / "Dynamic"
                    / "Time-Progressing"
                    / "Unlimited"
                    / ("Time-Limited" EQUAL utc-time)
                    / ("Time-Duration" EQUAL POS-FLOAT)
                    / ("Scales" EQUAL scale-value-list)
                    / media-prop-ext
   media-prop-ext   = token [EQUAL (1*rtsp-unreserved / quoted-string)]
   scale-value-list = DQ scale-entry *(COMMA scale-entry) DQ
   scale-entry      = scale-value / (scale-value COLON scale-value)
   scale-value      = FLOAT
   Media-Range      = "Media-Range" HCOLON [ranges-list]
   ranges-list      =  ranges-spec *(COMMA ranges-spec)
   MTag             =  "MTag" HCOLON message-tag
   Notify-Reason    = "Notify-Reason" HCOLON Notify-Reas-val
   Notify-Reas-val  = "end-of-stream"
                    / "media-properties-update"
                    / "scale-change"
                    / Notify-Reason-extension
   Notify-Reason-extension  = token
   Pipelined-Requests = "Pipelined-Requests" HCOLON startup-id
   startup-id  = 1*8DIGIT

 Proxy-Authenticate   =  "Proxy-Authenticate" HCOLON challenge-list
 challenge-list       =  challenge *(COMMA challenge)
 challenge            =  ("Digest" LWS digest-cln *(COMMA digest-cln))
                      /  other-challenge
 other-challenge      =  auth-scheme LWS auth-param
                         *(COMMA auth-param)
 digest-cln           =  realm / domain / nonce
                      /  opaque / stale / algorithm
                      /  qop-options / auth-param
 realm                =  "realm" EQUAL realm-value
 realm-value          =  quoted-string
 domain               =  "domain" EQUAL LDQUOT RTSP-REQ-Ref
                         *(1*SP RTSP-REQ-Ref ) RDQUOT
 nonce                =  "nonce" EQUAL nonce-value
 nonce-value          =  quoted-string
 opaque               =  "opaque" EQUAL quoted-string
 stale                =  "stale" EQUAL ( "true" / "false" )
 algorithm            =  "algorithm" EQUAL ("MD5" / "MD5-sess" / token)
 qop-options          =  "qop" EQUAL LDQUOT qop-value
                         *("," qop-value) RDQUOT
 qop-value            =  "auth" / "auth-int" / token
 Proxy-Require        =  "Proxy-Require" HCOLON feature-tag-list
 feature-tag-list     =  feature-tag *(COMMA feature-tag)
 Proxy-Supported      =  "Proxy-Supported" HCOLON [feature-tag-list]

 Public               =  "Public" HCOLON Method *(COMMA Method)

 Range                =  "Range" HCOLON ranges-spec

 ranges-spec          =  npt-range / utc-range / smpte-range
                      /  range-ext
 range-ext            =  extension-format ["=" range-value]
 range-value          =  1*(rtsp-unreserved / quoted-string / ":" )

 Referrer             =  "Referrer" HCOLON (absolute-URI / RTSP-URI-Ref)
 Request-Status       =  "Request-Status" HCOLON req-status-info
 req-status-info      =  cseq-info LWS status-info LWS reason-info
 cseq-info            =  "cseq" EQUAL cseq-nr
 status-info          =  "status" EQUAL Status-Code
 reason-info          =  "reason" EQUAL DQ Reason-Phrase DQ
 Require              =  "Require" HCOLON feature-tag-list
  RTP-Info         =  "RTP-Info" HCOLON [rtsp-info-spec
                      *(COMMA rtsp-info-spec)]
  rtsp-info-spec   =  stream-url 1*ssrc-parameter
  stream-url       =  "url" EQUAL DQ RTSP-REQ-Ref DQ
  ssrc-parameter   =  LWS "ssrc" EQUAL ssrc HCOLON
                      ri-parameter *(SEMI ri-parameter)
  ri-parameter     =  ("seq" EQUAL 1*5DIGIT)
                   /  ("rtptime" EQUAL 1*10DIGIT)
                   /  generic-param

  Retry-After      =  "Retry-After" HCOLON ( RTSP-date / delta-seconds )
  Scale            =  "Scale" HCOLON scale-value
  Seek-Style       =  "Seek-Style" HCOLON Seek-S-values
  Seek-S-values    =  "RAP"
                   /  "CoRAP"
                   /  "First-Prior"
                   /  "Next"
                   /  Seek-S-value-ext
  Seek-S-value-ext =  token

  Server           =  "Server" HCOLON ( product / comment )
                      *(LWS (product / comment))
  product          =  token [SLASH product-version]
  product-version  =  token
  comment          =  LPAREN *( ctext / quoted-pair) RPAREN

  Session          =  "Session" HCOLON session-id
                      [ SEMI "timeout" EQUAL delta-seconds ]

  Speed            =  "Speed" HCOLON lower-bound MINUS upper-bound
  lower-bound      =  POS-FLOAT
  upper-bound      =  POS-FLOAT

  Supported        =  "Supported" HCOLON [feature-tag-list]
   Terminate-Reason      =  "Terminate-Reason" HCOLON TR-Info
   TR-Info              =  TR-Reason *(SEMI TR-Parameter)
   TR-Reason            =  "Session-Timeout"
                        /  "Server-Admin"
                        /  "Internal-Error"
                        /  token
   TR-Parameter         =  TR-time / TR-user-msg / generic-param
   TR-time              =  "time" EQUAL utc-time
   TR-user-msg          =  "user-msg" EQUAL quoted-string

   Timestamp        =  "Timestamp" HCOLON timestamp-value [LWS delay]
   timestamp-value  =  *19DIGIT [ "." *9DIGIT ]
   delay            =  *9DIGIT [ "." *9DIGIT ]

   Transport        =  "Transport" HCOLON transport-spec
                       *(COMMA transport-spec)
   transport-spec   =  transport-id *trns-parameter
   transport-id     =  trans-id-rtp / other-trans
   trans-id-rtp     =  "RTP/" profile ["/" lower-transport]
                       ; no LWS is allowed inside transport-id
   other-trans      =  token *("/" token)

profile             = "AVP" / "SAVP" / "AVPF" / "SAVPF" / token
lower-transport     = "TCP" / "UDP" / token
trns-parameter      = (SEMI ( "unicast" / "multicast" ))
                    / (SEMI "interleaved" EQUAL channel [ "-" channel ])
                    / (SEMI "ttl" EQUAL ttl)
                    / (SEMI "layers" EQUAL 1*DIGIT)
                    / (SEMI "ssrc" EQUAL ssrc *(SLASH ssrc))
                    / (SEMI "mode" EQUAL mode-spec)
                    / (SEMI "dest_addr" EQUAL addr-list)
                    / (SEMI "src_addr" EQUAL addr-list)
                    / (SEMI "setup" EQUAL contrans-setup)
                    / (SEMI "connection" EQUAL contrans-con)
                    / (SEMI "RTCP-mux")
                    / (SEMI "MIKEY" EQUAL MIKEY-Value)
                    / (SEMI trn-param-ext)
contrans-setup      = "active" / "passive" / "actpass"
contrans-con        = "new" / "existing"
trn-param-ext       = par-name [EQUAL trn-par-value]
par-name            = token
trn-par-value       = *(rtsp-unreserved / quoted-string)
ttl                 = 1*3DIGIT ; 0 to 255
ssrc                = 8HEX
channel             = 1*3DIGIT ; 0 to 255
MIKEY-Value         = base64
mode-spec           = ( DQ mode *(COMMA mode) DQ )
mode                = "PLAY" / token
addr-list           = quoted-addr *(SLASH quoted-addr)
quoted-addr         = DQ (host-port / extension-addr) DQ
host-port           = ( host [":" port] )
                    / ( ":" port )
extension-addr      = 1*qdtext
host                = < As defined in RFC 3986>
port                = < As defined in RFC 3986>
   Unsupported     = "Unsupported" HCOLON feature-tag-list

   User-Agent      = "User-Agent" HCOLON ( product / comment )
                     *(LWS (product / comment))

   Vary            = "Vary" HCOLON ( "*" / field-name-list)

   field-name-list = field-name *(COMMA field-name)
   field-name      = token
   Via             = "Via" HCOLON via-parm *(COMMA via-parm)
   via-parm        = sent-protocol LWS sent-by *( SEMI via-params )
   via-params      = via-ttl / via-maddr
                   / via-received / via-extension
   via-ttl         = "ttl" EQUAL ttl
   via-maddr       = "maddr" EQUAL host
   via-received    = "received" EQUAL (IPv4address / IPv6address)
   IPv4address     = < As defined in RFC 3986>
   IPv6address     = < As defined in RFC 3986>
   via-extension   = generic-param
   sent-protocol   = protocol-name SLASH protocol-version
                     SLASH transport-prot
   protocol-name   = "RTSP" / token
   protocol-version = token
   transport-prot  = "UDP" / "TCP" / "TLS" / other-transport
   other-transport = token
   sent-by         = host [ COLON port ]

   WWW-Authenticate = "WWW-Authenticate" HCOLON challenge-list

20.3.  SDP extension Syntax

   This section defines in ABNF the SDP extensions defined for RTSP.
   See Appendix D for the definition definition of the extensions in text.

   control-attribute   =  "a=control:" *SP RTSP-REQ-Ref CRLF

   a-range-def         =  "a=range:" ranges-spec CRLF

   a-mtag-def          =  "a=mtag:" message-tag CRLF

21.  Security Considerations

   The security considerations and threats around RTSP and its usage can
   be divided to considerations around the signaling protocol itself and
   the issues related to the media stream delivery.  However, when it
   comes to mitigations of security threats, a threat depending on the
   media stream delivery may in fact be mitigated by a mechanism in the
   signaling protocol.

   There are several chapters and appendix in this document that defines
   security solutions for the protocol.  We will reference them when
   discussing the threats below.  But the reader should take special
   notice of the Security Framework (Section 19) and the specification
   of how to use SRTP and its key-mangement (Appendix C.1.4) to achieve
   certain aspects of the media security.

21.1.  Signaling Protocol Threats

   This section focus on issues related to the signaling protocol.
   Because of the similarity in syntax and usage between RTSP servers
   and HTTP servers, the security considerations outlined in [H15] apply
   also.

   Specifically, please note the following:

   Abuse of Server Log Information:  RTSP and HTTP servers will
         presumably have similar logging mechanisms, and thus should be
         equally guarded in protecting the contents of those logs, thus
         protecting the privacy of the users of the servers.  See
         [H15.1.1] for HTTP server recommendations regarding server
         logs.

   Transfer of Sensitive Information:  There is no reason to believe
         that information transferred or controlled via RTSP may be any
         less sensitive than that normally transmitted via HTTP.
         Therefore, all of the precautions regarding the protection of
         data privacy and user privacy apply to implementors of RTSP
         clients, servers, and proxies.  See [H15.1.2] for further
         details.

   Attacks Based On File and Path Names:  Though RTSP URIs are opaque
         handles that do not necessarily have file system semantics, it
         is anticipated that many implementations will translate
         portions of the Request-URIs directly to file system calls.  In
         such cases, file systems SHOULD follow the precautions outlined
         in [H15.5], such as checking for ".." in path components.

   Personal Information:  RTSP clients are often privy to the same
         information that HTTP clients are (user name, location, etc.)
         and thus should be equally sensitive.  See [H15.1] for further
         recommendations.

   Privacy Issues Connected to Accept Headers:  Since may of the same
         "Accept" headers exist in RTSP as in HTTP, the same caveats
         outlined in [H15.1.4] with regards to their use should be
         followed.

   DNS Spoofing:  Presumably, given the longer connection times
         typically associated to RTSP sessions relative to HTTP
         sessions, RTSP client DNS optimizations should be less
         prevalent.  Nonetheless, the recommendations provided in
         [H15.3] are still relevant to any implementation which attempts
         to rely on a DNS-to-IP mapping to hold beyond a single use of
         the mapping.

   Location Headers and Spoofing:  If a single server supports multiple
         organizations that do not trust each another, then it needs to
         check the values of the extensions Location and Content-Location header fields
         in text.

   control-attribute   =  "a=control:" *SP RTSP-REQ-Ref CRLF

   a-range-def         =  "a=range:" ranges-spec CRLF

   a-mtag-def          =  "a=mtag:" message-tag CRLF

21.  Security Considerations

   Because responses that are generated under control of said
         organizations to make sure that they do not attempt to
         invalidate resources over which they have no authority.
         ([H15.4])

   In addition to the similarity recommendations in syntax the current HTTP specification
   (RFC 2616 [RFC2616], as of this writing) and usage also of the previous RFC
   2068 [RFC2068], future HTTP specifications may provide additional
   guidance on security issues.

   The following are added considerations for RTSP implementations.

   Session hijacking:  Since there is no or little relation between a
         transport layer connection and an RTSP servers session, it is possible
         for a malicious client to issue requests with random session
         identifiers which would affect unsuspecting clients.  To
         mitigate this the server SHALL use a large, random and HTTP servers, non-
         sequential session identifier to minimize the possibility of
         this kind of attack.  However, unless the RTSP signaling is
         always confidentiality protected, e.g. using TLS, an on-path
         attacker will be able to hijack a session.  To prevent session
         hijacking client authentication needs to be performed and only
         the authenticated client creating the session SHALL be able to
         access that session.

   Authentication:  Servers SHOULD implement both basic and digest
         [RFC2617] authentication.  In environments requiring tighter
         security considerations outlined in [H15] apply
   also.

   Specifically, please note for the following:

   Abuse control messages, the transport layer
         mechanism TLS [RFC5246] SHOULD be used.

   Persistently suspicious behavior:  RTSP servers SHOULD return error
         code 403 (Forbidden) upon receiving a single instance of Server Log Information:
         behavior which is deemed a security risk.  RTSP and HTTP servers will
         presumably have similar logging mechanisms, SHOULD
         also be aware of attempts to probe the server for weaknesses
         and thus should entry points and MAY arbitrarily disconnect and ignore
         further requests from clients which are deemed to be
         equally guarded in protecting the contents
         violation of those logs, thus
         protecting local security policy.

   TLS through proxies:  If one uses the privacy possibility to connect TLS in
         multiple legs (Section 19.3) one really needs to be aware of
         the users trust model.  That procedure requires full faith and trust
         in all proxies, which will be identified, that one allows to
         connect through.  They are men in the middle and have access to
         all that goes on over the TLS connection.  Thus it is important
         to consider if that trust model is acceptable in the actual
         application.  Further discussion of the servers.  See
         [H15.1.1] for HTTP actual trust model in
         Section 19.3.

   Resource Exhaustion:  As RTSP is a stateful protocol and establish
         resource usage on the server recommendations regarding there is a clear possibility to
         attack the server
         logs.

   Transfer by trying to overbook these resources to
         perform a denial of Sensitive Information:  There is no reason service attack.  This attack can be both
         against ongoing sessions and to believe
         that information transferred or controlled via prevent others from
         establishing sessions.  RTSP may be any
         less sensitive than that normally transmitted via HTTP.
         Therefore, all agents will need to have
         mechanisms to prevent single peers from consuming extensive
         amounts of resources.  The methods for guarding against this
         are varied and depends on the precautions agents role and capabilities and
         policies.  Each implementation have to careful consider their
         methods and policies to mitigate this threat.  For example
         regarding the protection handling of
         data privacy connections there is recommendations in
         Section 10.7.

   The above threats and user privacy apply to implementors consideration has resulted in a set of RTSP
         clients, servers, security
   function and proxies.  See [H15.1.2] for further
         details.

   Attacks Based On File mechanism built into or used by the protocol.  The
   signaling protocol relies on two security features defined in the
   Security Framework (Section 19) namely client authentication using
   HTTP authentication and Path Names:  Though RTSP URIs are opaque
         handles that do not necessarily have file system semantics, it
         is anticipated that many implementations will translate
         portions TLS based transport protection of the Request-URIs directly to file system calls.  In
         such cases, file systems SHOULD follow the precautions outlined
         in [H15.5], such as checking for ".." in path components.

   Personal Information:  RTSP clients
   signaling messages.  Both these there mechanism are often privy required to be
   implemented by any RTSP agent.

   A number of different security mitigations has been designed into the same
         information that HTTP clients are (user name, location, etc.)
   protocol and thus should will be equally sensitive.  See [H15.1] for further
         recommendations.

   Privacy Issues Connected to Accept Headers:  Since may of present by following the same
         "Accept" headers exist in RTSP specification as
   written, for example by ensuring sufficient amount of entropy in HTTP, the same caveats
         outlined in [H15.1.4] with regards
   randomly generated session identifiers when not using client
   authentication to their use should prevent session hijacking.  When client
   authentication is used the protection against hijacking will be
         followed.

   DNS Spoofing:  Presumably, given
   strongly improved by scoping the longer connection times
         typically associated to RTSP accessible sessions relative to HTTP
         sessions, RTSP the one this
   client DNS optimizations should be less
         prevalent.  Nonetheless, identity has created.  Some of the recommendations provided in
         [H15.3] above threats are still relevant to any such that
   the implementation which attempts
         to rely on a DNS-to-IP mapping to hold beyond a single use of the mapping.

   Location Headers RTSP functionality itself needs to consider
   which policy and Spoofing:  If a single server supports multiple
         organizations that do not trust each another, then strategy it needs uses to
         check the values of Location mitigate them.

21.2.  Media Stream Delivery Threats

   The fact that RTSP establish and Content-Location header fields controls a media stream delivery
   results in responses that are generated under control a set of said
         organizations security issues related to make sure that they do not the media streams.
   This section will attempt to
         invalidate resources over which they have no authority.
         ([H15.4])

   In addition to analyze general threats, however the recommendations
   choice of media stream transport protocol, like RTP will result in the current HTTP
   some difference in threats and what mechanisms that exist to mitigate
   them.  Thus it becomes important that each specification
   (RFC 2616 [RFC2616], as of this writing) a new
   media stream transport and also of the previous RFC
   2068 [RFC2068], future HTTP specifications may provide additional
   guidance on delivery protocol usable by RTSP requires
   its own security issues.

   The following are added considerations analyses.  This section will include such a one for RTSP implementations.
   RTP.

   The set of general threats from or by the media stream delivery
   itself are:

   Concentrated denial-of-service attack:  The protocol offers the
      opportunity for a remote-controlled denial-of-service (DoS)
      attack.  Where the media stream is the hammer in that DoS attack.
      See Section 21.1.

   Session hijacking:  Since there is no or little relation between a
         transport layer connection 21.2.1.

   Media Confidentiality:  The media delivery may contain content of any
      type and an RTSP session, it is not possible
         for a malicious client in general to issue requests with random session
         identifiers which would affect unsuspecting clients.  The
         server SHOULD use determine how sensitive
      this content is from a large, random and non-sequential session
         identifier confidentiality point.  Thus it is a strong
      requirement that any media delivery protocol provides method for
      providing confidentiality of the actual media content.  In
      addition to minimize the possibility of this kind of attack.
         However, unless media level confidentiality it becomes critical
      that no resource identifier used in the RTSP signaling is always confidentiality
         protected, e.g. using TLS, are exposed to
      an on-path attacker will as they may have human understandable names, or may be able to
         hijack a session.  For real session security, client
         authentication needs
      also available to be performed.

   Authentication:  Servers SHOULD implement both basic and digest
         [RFC2617] authentication.  In environments requiring tighter
         security for the control messages, attacker so they can determine the transport layer
         mechanism TLS [RFC5246] SHOULD be used.

   Stream issues:  RTSP only provides for stream control.  Stream
         delivery issues are not covered in this section, nor in content
      they user was delivered.  Thus also the
         rest signaling protocol must
      provide confidentiality protection of this draft.  RTSP implementations will most likely rely
         on other protocols any information related to
      the media resource.

   Media Integrity and Authentication:  There exist several reasons,
      such as RTP, IP multicast, RSVP and IGMP,
         and should address security considerations brought up in those
         and other applicable specifications.

   Persistently suspicious behavior:  RTSP servers SHOULD return error
         code 403 (Forbidden) upon receiving a single instance discrediting the target, misinformation of
         behavior which is deemed a security risk. the target, why
      an attacker will have interest to substitute the media stream sent
      out from the RTSP servers SHOULD
         also be aware server with one of attempts the attackers creation or
      selection.  Therefore it is important that the media protocol
      provides mechanism to probe verify the server for weaknesses
         and entry points and MAY arbitrarily disconnect source authentication, integrity
      and ignore
         further requests from clients which are deemed to be in
         violation of local security policy. prevent replay attacks on the media stream.

   Scope of Multicast:  If RTSP is used to control the transmission of
      media onto a multicast network it is needed to consider the scope
      that delivery has.  RTSP supports the TTL Transport header
      parameter to indicate this scope for IPv4.  IPv6 has a different
      mechanism for scope boundary.  However, such scope control is has
      risks, as it may be set too large and distribute media beyond the
      intended scope.

   TLS through proxies:  If one uses the possibility to connect TLS in
         multiple legs

   Below (Section 19.3) one really needs to be aware of
         the trust model.  That procedure requires full faith and trust
         in all proxies that one allows to connect through.  They are
         men in the middle and have access to all that goes on over the
         TLS connection.  Thus it is important to consider if that trust
         model is acceptable in the actual application.

   Resource Exhaustion:  As RTSP is 21.2.2) we do a stateful protocol and establish
         resource usage on the server there is a specific analysis of security
   considerations for RTP based media transport.  In that section we
   also make clear possibility to
         attack the server by trying to overbook these resources to
         perform a denial of service attack.  This attack can be both
         against ongoing sessions and to prevent others from
         establishing sessions. requirements on implementing security functions
   for RTSP agents will need to have
         mechanisms to prevent single peers from consuming extensive
         amounts of resources.

21.1. supporting media delivery over RTP.

21.2.1.  Remote denial of Service Attack

   The attacker may initiate traffic flows to one or more IP addresses
   by specifying them as the destination in SETUP requests.  While the
   attacker's IP address may be known in this case, this is not always
   useful in prevention of more attacks or ascertaining the attackers
   identity.  Thus, an RTSP server MUST only allow client-specified
   destinations for RTSP-initiated traffic flows if the server has
   ensured that the specified destination address accepts receiving
   media through different security mechanisms.  Security mechanisms
   that are acceptable in an increased generality are:

   o  Verification of the client's identity against a database of known
      users using RTSP authentication mechanisms (preferably digest
      authentication or stronger)

   o  A list of addresses that accept to be media destinations,
      especially considering user identity

   o  Media path based verification

   The server SHOULD NOT allow the destination field to be set unless a
   mechanism exists in the system to authorize the request originator to
   direct streams to the recipient.  It is preferred that this
   authorization be performed by the media recipient (destination)
   itself and the credentials passed along to the server.  However, in
   certain cases, such as when recipient address is a multicast group,
   or when the recipient is unable to communicate with the server in an
   out-of-band manner, this may not be possible.  In these cases the
   server may chose another method such as a server-resident
   authorization list to ensure that the request originator has the
   proper credentials to request stream delivery to the recipient.

   One solution that performs the necessary verification of acceptance
   of media suitable for unicast based delivery is the ICE based NAT
   traversal method described in [I-D.ietf-mmusic-rtsp-nat].  By using  This
   mechanism uses random passwords and username so that the probability
   of unintended indication as a valid media destination is very low.  If
   In addition the server
   include includes in its STUN requests a cookie
   (consisting of random material) that the destination echoes back back,
   thus the solution is also safe safe-guards against having a off-path attacker
   being able to spoof the STUN checks.  This leaves this solution
   vulnerable only to on-path attackers that can see the STUN requests
   go to the target of attack. attack and thus forge a response.

   For delivery to multicast addresses there is a need for another
   solution which is not specified in this memo.

21.2.2.  RTP Security analysis

   RTP is a commonly used media transport protocol and has been the most
   common choice for RTSP 1.0 implementations.  The core RTP protocol
   has been in use for a long time and it has well-known security
   properties and the RTP security consideration (Section 9 of
   [RFC3550]) needs to be reviewed.  In perspective of the usage of RTP
   in context of RTSP the following properties should be noted:

   Stream Additions:  RTP has support for multiple simultaneous media
      streams in each RTP session.  As some use case require support for
      non-synchronized adding and removal of media streams and their
      identifiers an attacker can easily insert additional media streams
      into a session context that according to protocol design is
      intended to be played out.  Another threat vector is that one of
      denial of service by exhausting the resources of the RTP session
      receiver, for example by using a large number of SSRC identifier
      simultaneously.  The strong mitigation of this is to ensure that
      one cryptographically authenticates any incoming packet flow to
      the RTP session.  Weak mitigations like blocking additional media
      streams in session contexts easily lead to a denial of service
      vulnerability in addition to preventing certain RTP extensions or
      use cases which rely on multiple media streams, such as RTP
      retransmission [RFC4588] to function.

   Forged Feedback:  The built in RTP control Protocol (RTCP) also
      offers a large attack surface for a couple of different types of
      attacks.  One venue is to send RTCP feedback to the media sender
      indicating large amounts of packet loss and thus trigger an media
      bit-rate adaptation response from the sender resulting in lowered
      media quality and potentially shut down of the media stream.
      Another attack is to perform a resource exhaustion attack on the
      receiver by using many SSRC identifiers to create large state
      tables and increase the RTCP related processing demands.

   RTP/RTCP Extensions:  RTP and RTCP extensions generally provide
      additional and sometimes extremely powerful tools to do denial of
      service or service disruption.  For example the Code Control
      Message [RFC5104] RTCP extensions enables both locking down the
      bit-rate to low values and disrupt video quality by requesting
      Intra frames.

   Taking into account the above general discussion in Section 21.2 and
   the RTP specific discussion in this section it is clear that strong
   security mechanism to protect RTP is necessary to support.  Therefore
   this specification has the following requirements on RTP security
   functions for all RTSP agents that handles media streams and where
   the media stream transport is done using RTP.

   RTSP agents supporting RTP MUST implement SRTP [RFC3711] and thus the
   SAVP profile, in addition the secure profile SAVPF MUST also be
   supported if the AVPF profile is implemented.  This specification
   requires no additional crypto transforms or configuration values
   beyond the mandatory to implement in RFC3711, i.e.  AES-CM and HMAC-
   SHA1.  The default key-management mechanism which MUST be implemented
   is the one defined in the MIKEY Key Establishment (Appendix C.1.4.1).
   The MIKEY implementation MUST implement the necessary functions for
   MIKEY-RSA-R mode [RFC4738] and in addition the SRTP parameter
   negotiation necessary to negotiate the supported SRTP transforms and
   parameters.

22.  IANA Considerations

   This section sets up a number of registries for RTSP 2.0 that should
   be maintained by IANA.  These registries are separate from any
   registries existing for RTSP 1.0.  For each registry there is a
   description on what it is required to contain, what specification is
   needed when adding an entry with IANA, and finally the entries that
   this document needs to register.  See also the Section 2.7 "Extending
   RTSP".  There is also an IANA registration of two SDP attributes.

   Registries or entries in registries which have been made for RTSP 1.0
   are not moved to RTSP 2.0.  The registries and entries in registries
   of RTSP 1.0 and RTSP 2.0 are indenpendent.  If any registry or entry
   in a registry is also required in RTSP 2.0, it must follow the below
   defined procedure to allocated the registry or entry in a registry.

   The sections describing how to register an item uses some of the
   requirements level described in RFC 5226 [RFC5226], namely "First
   Come, First Served", "Expert Review, "Specification Required", and
   "Standards Action".

   In case a registry requires a contact person, the authors are the
   contact person for any entries created by this document.

   A registration request to IANA MUST contain the following
   information:

   o  A name of the item to register according to the rules specified by
      the intended registry.

   o  Indication of who has change control over the feature (for
      example, IETF, ISO, ITU-T, other international standardization
      bodies, a consortium, a particular company or group of companies,
      or an individual);

   o  A reference to a further description, if available, for example
      (in decreasing order of preference) an RFC, a published standard,
      a published paper, a patent filing, a technical report, documented
      source code or a computer manual;

   o  For proprietary features, contact information (postal and email
      address);

22.1.  Feature-tags
22.1.1.  Description

   When a client and server try to determine what part and functionality
   of the RTSP specification and any future extensions that its counter
   part implements there is need for a namespace.  This registry
   contains named entries representing certain functionality.

   The usage of feature-tags is explained in Section 11 and
   Section 13.1.

22.1.2.  Registering New Feature-tags with IANA

   The registering of feature-tags is done on a first come, first served
   basis.

   The name of the feature MUST follow these rules: The name may be of
   any length, but SHOULD be no more than twenty characters long.  The
   name MUST NOT contain any spaces, or control characters.  The
   registration MUST indicate if the feature-tag applies to clients,
   servers, or proxies only or any combinations of these.  Any
   proprietary feature MUST have as the first part of the name a vendor
   tag, which identifies the organization.  The registry entries
   consists of the feature tag, a one paragraph description of what it
   represents, its applicability (server, client, proxy, any
   combination) and a reference to its specification where applicable.

   Examples for a vendor tag describing a proprietary feature are:

         vendorA.specfeat01

         vendorA.specfeat02

22.1.3.  Registered entries

   The following feature-tags are defined in this specification and
   hereby registered.  The change control belongs to the IETF.

   play.basic:  The implementation for delivery and playback operations
         according to the core RTSP specification, as defined in this
         memo.  Applies for both clients, servers and proxies.

   play.scale:  Support of scale operations for media playback.  Applies
         only for servers.

   play.speed:  Support of the speed functionality for media delivery.
         Applies only for servers.

   setup.rtp.rtcp.mux  Support of the RTP and RTCP multiplexing as
         discussed in Appendix C.1.6.4.  Applies for both client and
         servers and any media caching proxy.

   This should be represented by IANA as table with the feature tags,
   contact person and their references.

22.2.  RTSP Methods

22.2.1.  Description

   What a method is, is described in Section Section 13.  Extending the
   protocol with new methods allow for totally new functionality.

22.2.2.  Registering New Methods with IANA

   A new method MUST be registered through an IETF Standards Action.
   The reason is that new methods may radically change the protocol's
   behavior and purpose.

   A specification for a new RTSP method MUST consist of the following
   items:

   o  A method name which follows the ABNF rules for methods.

   o  A clear specification what a request using the method does and
      what responses are expected.  Which directions the method is used,
      C->S or S->C or both.  How the use of headers, if any, modifies
      the behavior and effect of the method.

   o  A list or table specifying which of the IANA registered headers
      that are allowed to be used with the method in request or/and
      response.  The list or table SHOULD follow the format of tables in
      Section Section 16. 18.

   o  Describe how the method relates to network proxies.

22.2.3.  Registered Entries

   This specification, RFCXXXX, registers 10 methods: DESCRIBE,
   GET_PARAMETER, OPTIONS, PAUSE, PLAY, PLAY_NOTIFY, REDIRECT, SETUP,
   SET_PARAMETER, and TEARDOWN.  The initial table of the registry is
   below provided.

   Method         Directionality           Reference
   -----------------------------------------------------
   DESCRIBE       C->S                     [RFCXXXX]
   GET_PARAMETER  C->S, S->C               [RFCXXXX]
   OPTIONS        C->S, S->C               [RFCXXXX]
   PAUSE          C->S                     [RFCXXXX]
   PLAY           C->S                     [RFCXXXX]
   PLAY_NOTIFY    S->C                     [RFCXXXX]
   REDIRECT       S->C                     [RFCXXXX]
   SETUP          C->S                     [RFCXXXX]
   SET_PARAMETER  C->S, S->C               [RFCXXXX]
   TEARDOWN       C->S, S->C               [RFCXXXX]

22.3.  RTSP Status Codes

22.3.1.  Description

   A status code is the three digit numbers used to convey information
   in RTSP response messages, see Section 8.  The number space is
   limited and care should be taken not to fill the space.

22.3.2.  Registering New Status Codes with IANA

   A new status code registration follows the policy of IETF Review.  A
   specification for a new status code MUST specify the following:

   o  The registered number.

   o  A description what the status code means and the expected behavior
      of the sender and receiver of the code.

22.3.3.  Registered Entries

   RFCXXXX, registers the numbered status code defined in the ABNF entry
   "Status-Code" except "extension-code" (that defines the syntax
   allowed for future extensions) in Section 20.2.2.

22.4.  RTSP Headers

22.4.1.  Description

   By specifying new headers a method(s) can be enhanced in many
   different ways.  An unknown header will be ignored by the receiving
   agent.  If the new header is vital for a certain functionality, a
   feature-tag for the functionality can be created and demanded to be
   used by the counter-part with the inclusion of a Require header
   carrying the feature-tag.

22.4.2.  Registering New Headers with IANA

   Registrations in the registry can be done following the Expert Review
   policy.  A specification SHOULD be provided, preferably an IETF RFC
   or other Standards Developing Organization specification.  The
   minimal information in a registration request is the header name and
   the contact information.

   The specification SHOULD contain the following information:

   o  The name of the header.

   o  An ABNF specification of the header syntax.

   o  A list or table specifying when the header may be used,
      encompassing all methods, their request or response, the direction
      (C->S or S->C).

   o  How the header is to be handled by proxies.

   o  A description of the purpose of the header.

22.4.3.  Registered entries

   All headers specified in Section 16 18 in RFCXXXX are to be registered.
   The Registry is to include header name, description, and reference.

   Furthermore the following legacy RTSP headers defined in other
   specifications are registered: registered with header name, reference and
   description according to below list.  Note: These references may not
   fulfill all of the above rules for registrations due to their legacy
   status.

   o  x-wap-profile defined in [3gpp-26234]. [TS-26234].  The x-wap-profile request
      header contains one or more absolute URLs to the requesting agents
      device capability profile.

   o  x-wap-profile-diff defined in [3gpp-26234]. [TS-26234].  The x-wap-profile-diff
      request header contains a subset of an device capability profile.

   o  x-wap-profile-warning defined in [3gpp-26234]. [TS-26234].  The x-wap-profile-
      warning is a response header that contains error codes explaining
      to what extent the server has been able to match the terminal
      request in regards to device capability profile as described using
      x-wap-profile and x-wap-profile-diff headers.

   o  x-predecbufsize defined in [3gpp-26234]. [TS-26234].  This response header
      provides an RTSP agent with the TS 26.234 Annex G hypothetical
      pre-decoder buffer size.

   o  x-initpredecbufperiod defined in [3gpp-26234]. [TS-26234].  This response header
      provides an RTSP agent with the TS 26.234 Annex G hypothetical
      pre-decoder buffering period.

   o  x-initpostdecbufperiod defined in [3gpp-26234]. [TS-26234].  This response
      header provides an RTSP agent with the TS 26.234 Annex G post-
      decoder buffering period.

   o  3gpp-videopostdecbufsize defined in [3gpp-26234]. [TS-26234].  This response
      header provides an RTSP agent with the TS 26.234 defined post-
      decoder buffer size usable for H.264 (AVC) video streams.

   o  3GPP-Link-Char defined in [3gpp-26234]. [TS-26234].  This request header
      provides the RTSP server with the RTSP client's link
      charateristics as deterimined from the raido interface.  The
      information that can be provided are guararnteed bit-rate, maximum
      bit-rate and maximum transfer delay.

   o  3GPP-Adaptation defined in [3gpp-26234]. [TS-26234].  This general header is
      part of the bit-rate adaptation solution specified for PSS.  It
      provides the RTSP clients buffer sizes and target buffer levels to
      the server and responses are used to acknowledge the support and
      values.

   o  3GPP-QoE-Metrics defined in [3gpp-26234]. [TS-26234].  This general header is
      used by PSS RTSP agents to negotiate the quality of experince
      metrics that a client should gather and report to the server.

   o  3GPP-QoE-Feedback defined in [3gpp-26234]. [TS-26234].  This request header is
      used by RTSP clients supporting PSS to report the actual values of
      the metrics gathered in its quality of experince metering.

   The use of "x-" is NOT RECOMMENDED but the above headers in the
   register list was defined prior to the clarification.

22.5.  Accept-Credentials

   The security framework's TLS connection mechanism has two registrable
   entities.

22.5.1.  Accept-Credentials policies

   In Section 19.3.1 three policies for how to handle certificates are
   specified.  Further policies may be defined and MUST be registered
   with IANA using the following rules:

   o  Registering requires an IETF Standards Action

   o  A registration is required to name a contact person.

   o  Name of the policy.

   o  A describing text that explains how the policy works for handling
      the certificates.

   This specification registers the following values:

   Any

   Proxy

   User

22.5.2.  Accept-Credentials hash algorithms

   The Accept-Credentials header (See Section 16.2) 18.2) allows for the usage
   of other algorithms for hashing the DER records of accepted entities.
   The registration of any future algorithm is expected to be extremely
   rare and could also cause interoperability problems.  Therefore the
   bar for registering new algorithms is intentionally placed high.

   Any registration of a new hash algorithm MUST fulfill the following
   requirement:

   o  Follow the IETF Standards Action policy.

   o  A definition of the algorithm and its identifier meeting the
      "token" ABNF requirement.

   The registered value is:
   Hash Alg. Id   Reference
   ------------------------
   sha-256        [RFCXXXX]

22.6.  Cache-Control Cache Directive Extensions

   There exists a number of cache directives which can be sent in the
   Cache-Control header.  A registry for these cache directives MUST be
   defined with the following rules:

   o  Registering requires an IETF Standards Action or IESG Approval.

   o  A registration is required to contain a contact person.

   o  Name of the directive and a definition of the value, if any.

   o  Specification if it is a request or response directive.

   o  A describing text that explains how the cache directive is used
      for RTSP controlled media streams.

   This specification registers the following values:

   no-cache:

   public:

   private:

   no-transform:

   only-if-cached:

   max-stale:

   min-fresh:

   must-revalidate:

   proxy-revalidate:

   max-age:

   The registry should be represented as: Name of the directive, contact
   person and reference.

22.7.  Media Properties

22.7.1.  Description

   The media streams being controlled by RTSP can have many different
   properties.  The media properties required to cover the use cases
   that was in mind when writing the specification are defined.
   However, it can be expected that further innovation will result in
   new use cases or media streams with properties not covered by the
   ones specified here.  Thus new media properties can be specified.  As
   new media properties may need a substantial amount of new definitions
   to correctly specify behavior for this property the bar is intended
   to be high.

22.7.2.  Registration Rules

   Registering new media property MUST fulfill the following
   requirements

   o  Follow the Specification Required policy and get the approval of
      the designated Expert.

   o  Have an ABNF definition of the media property value name that
      meets "media-prop-ext" definition

   o  A Contact Person for the Registration

   o  Description of all changes to the behavior of the RTSP protocol as
      result of these changes.

22.7.3.  Registered Values

   This specification registers the 9 values listed in Section 16.28. 18.28.
   The registry should be represented as: Name of the media property,
   contact person and reference.

22.8.  Notify-Reason header

22.8.1.  Description

   Notify-Reason values are used for indicating the reason the
   notification was sent.  Each reason has its associated rules on what
   headers and information that may or must be included in the
   notification.  New notification behaviors need to be specified to
   enable interoperable usage, thus a specification of each new value is
   required.

22.8.2.  Registration Rules

   Registrations for new Notify-Reason value MUST fulfill the following
   requirements

   o  Follow the Specification Required policy and get the approval of
      the designated Expert.

   o  An ABNF definition of the Notify reason value name that meets
      "Notify-Reason-extension" definition

   o  A Contact Person for the Registration

   o  Description of which headers shall be included in the request and
      response, when it should be sent, and any effect it has on the
      server client state.

22.8.3.  Registered Values

   This specification registers 3 values defined in the Notify-Reas-val
   ABNFSection 20.2.3:

   o  end-of-stream

   o  media-properties-update

   o  scale-change

   end-of-stream:  This Notify-Reason header indicates the end of a
      media stream.

   media-properties-update:  This Notify-Reason header allows the server
      to indicate that the properties of the media has changed during
      the playout.

   scale-change:  This Notify-Reason header allows the server to notify
      the client about a change in the Scale of the media.

   The registry entries should be represented in the registry as: Name,
   short description, contact and reference.

22.9.  Range header formats

22.9.1.  Description

   The Range header (Section 16.38) 18.38) allows for different range formats.
   New ones may be registered, but moderation should be applied as it
   makes interoperability more difficult.

22.9.2.  Registration Rules

   A registration MUST fulfill the following requirements:

   o  Follow the Specification Required policy.

   o  An ABNF definition of the range format that fulfills the "range-
      ext" definition.

   o  A Contact person for the registration.

   o  Rules for how one handles the range when using a negative Scale.

22.9.3.  Registered Values

   The registry should be represented as: Name of the range format,
   contact person and reference.  This specification registers the
   following values.

   npt:  Normal Play Time

   clock:  UTC Clock format

   smpte:  SMPTE Timestamps

22.10.  Terminate-Reason Header

   The Terminate-Reason header (Section 16.50) 18.50) has two registries for
   extensions.

22.10.1.  Redirect Reasons

   Registrations are done under the policy of Expert Review.  The
   registered value needs to follow syntax, i.e. be a token.  The
   specification needs to provide a definition of what procedures are to
   be followed when a client receives this redirect reason.  This
   specification registers two values:

   o  Session-Timeout

   o  Server-Admin

   The registry should be represented as: Name of the Redirect Reason,
   contact person and reference.

22.10.2.  Terminate-Reason Header Parameters

   Registrations are done under the policy of Specification Required.
   The registrations must define a syntax for the parameter that also
   follows the syntax allowed by the RTSP 2.0 specification.  A contact
   person is also required.  This specification registers:

   o  time

   o  user-msg

   The registry should be represented as: Name of the Terminate Reason,
   contact person and reference.

22.11.  RTP-Info header parameters

22.11.1.  Description

   The RTP-Info header (Section 16.43) 18.43) carries one or more parameter
   value pairs with information about a particular point in the RTP
   stream.  RTP extensions or new usages may need new types of
   information.  As RTP information that could be needed is likely to be
   generic enough and to maximize the interoperability registration
   requires Specification Required.

22.11.2.  Registration Rules

   Registrations for new RTP-Info value MUST fulfill the following
   requirements

   o  Follow the Specification Required policy and get the approval of
      the designated Expert.

   o  Have an ABNF definition that meets the "generic-param" definition

   o  A Contact Person for the Registration

22.11.3.  Registered Values

   This specification registers 2 the following parameter value pairs:

   o  url

   o  ssrc

   o  seq

   o  rtptime

   The registry should be represented as: Name of the parameter, contact
   person and reference.

22.12.  Seek-Style Policies

22.12.1.  Description

   New seek policies may be registered, however, a large number of these
   will complicate implementation substantially.  The impact of unknown
   policies is that the server will not honor the unknown and use the
   server default policy instead.

22.12.2.  Registration Rules

   Registrations of new Seek-Style polices MUST fulfill the following
   requirements

   o  Follow the Specification Required policy.

   o  Have an ABNF definition of the Seek-Style policy name that meets
      "Seek-S-value-ext" definition

   o  A Contact Person for the Registration

   o  Description of which headers shall be included in the request and
      response, when it should be sent, and any affect it has on the
      server client state.

22.12.3.  Registered Values

   This specification registers 4 values:

   o  RAP

   o  CoRAP

   o  First-Prior

   o  Next

   The registry should be represented as: Name of the Seek-Style Policy,
   short description, contact person and reference.

22.13.  Transport Header Registries

   The transport header contains a number of parameters which have
   possibilities for future extensions.  Therefore registries for these
   need to be defined.

22.13.1.  Transport Protocol Specification

   A registry for the parameter transport-protocol specification MUST be
   defined with the following rules:

   o  Registering uses the policy of Specification Required.

   o  A contact person or organization with address and email.

   o  A value definition that are following the ABNF syntax definition
      of "transport-id" Section 20.2.3.

   o  A describing text that explains how the registered value are used
      in RTSP.

   The registry should be represented as: The protocol ID string,
   contact person and reference.

   This specification registers the following values:

   RTP/AVP:  Use of the RTP [RFC3550] protocol for media transport in
         combination with the "RTP profile for audio and video
         conferences with minimal control" [RFC3551] over UDP.  The
         usage is explained in RFC XXXX, Appendix C.1.

   RTP/AVP/UDP:  the same as RTP/AVP.

   RTP/AVPF:  Use of the RTP [RFC3550] protocol for media transport in
         combination with the "Extended RTP Profile for RTCP-based
         Feedback (RTP/AVPF)" [RFC4585] over UDP.  The usage is
         explained in RFC XXXX, Appendix C.1.

   RTP/AVPF/UDP:  the same as RTP/AVPF.

   RTP/SAVP:  Use of the RTP [RFC3550] protocol for media transport in
         combination with the "The Secure Real-time Transport Protocol
         (SRTP)" [RFC3711] over UDP.  The usage is explained in RFC
         XXXX, Appendix C.1.

   RTP/SAVP/UDP:  the same as RTP/SAVP.

   RTP/SAVPF:  Use of the RTP[RFC3550] protocol for media transport in
         combination with the Extended Secure RTP Profile for Real-time
         Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)
         [RFC5124] over UDP.  The usage is explained in RFC XXXX,
         Appendix C.1.

   RTP/SAVPF/UDP:  the same as RTP/SAVPF.

   RTP/AVP/TCP:  Use of the RTP [RFC3550] protocol for media transport
         in combination with the "RTP profile for audio and video
         conferences with minimal control" [RFC3551] over TCP.  The
         usage is explained in RFC XXXX, Appendix C.2.2.

   RTP/AVPF/TCP:  Use of the RTP [RFC3550] protocol for media transport
         in combination with the "Extended RTP Profile for RTCP-based
         Feedback (RTP/AVPF)" [RFC4585] over TCP.  The usage is
         explained in RFC XXXX, Appendix C.2.2.

   RTP/SAVP/TCP:  Use of the RTP [RFC3550] protocol for media transport
         in combination with the "The Secure Real-time Transport
         Protocol (SRTP)" [RFC3711] over TCP.  The usage is explained in
         RFC XXXX, Appendix C.2.2.

   RTP/SAVPF/TCP:  Use of the RTP [RFC3550] protocol for media transport
         in combination with the "Extended Secure RTP Profile for Real-
         time Transport Control Protocol (RTCP)-Based Feedback (RTP/
         SAVPF)" [RFC5124] over TCP.  The usage is explained in RFC
         XXXX, Appendix C.2.2.

22.13.2.  Transport modes

   A registry for the transport parameter mode MUST be defined with the
   following rules:

   o  Registering requires an IETF Standards Action.

   o  A contact person or organization with address and email.

   o  A value definition that are following the ABNF "token" definition
      Section 20.2.3.

   o  A describing text that explains how the registered value are used
      in RTSP.

   This specification registers 1 value:

   PLAY: See RFC XXXX.

22.13.3.  Transport Parameters

   A registry for parameters that may be included in the Transport
   header MUST be defined with the following rules:

   o  Registering uses the Specification Required policy.

   o  A value definition that are following the ABNF "token" definition
      Section 20.2.3.

   o  A describing text that explains how the registered value are used
      in RTSP.

   This specification registers all the transport parameters defined in
   Section 16.52. 18.52.  This is a copy of this list:

   o  unicast

   o  multicast

   o  interleaved

   o  ttl

   o  layers
   o  ssrc

   o  mode

   o  dest_addr

   o  src_addr

   o  setup

   o  connection

   o  RTCP-mux

   o  MIKEY

22.14.  URI Schemes

   This specification defines two URI schemes ("rtsp" and "rtsps") and
   reserves a third one ("rtspu").  These URI schemes are defined in
   existing registries which are not created by RTSP.  Registrations are
   following RFC 4395[RFC4395].

22.14.1.  The rtsp URI Scheme

   URI scheme name:  rtsp

   Status:  Permanent

   URI scheme syntax:  See Section 20.2.1 of RFC XXXX.

   URI scheme semantics:  The rtsp scheme is used to indicate resources
         accessible through the usage of the Real-time Streaming
         Protocol (RTSP).  RTSP allows different operations on the
         resource identified by the URI, but the primary purpose is the
         streaming delivery of the resource to a client.  However, the
         operations that are currently defined are: DESCRIBE,
         GET_PARAMETER, OPTIONS, PLAY, PLAY_NOTIFY, PAUSE, SETUP,
         SET_PARAMETER, and TEARDOWN.

   Encoding considerations:  IRIs in this scheme are defined and needs
         to be encoded as RTSP URIs when used within the RTSP protocol.
         That encoding is done according to RFC 3987.

   Applications/protocols that use this URI scheme name:  RTSP 1.0 (RFC
         2326), RTSP 2.0 (RFC XXXX)

   Interoperability considerations:  The change in URI syntax performed
         between RTSP 1.0 and 2.0 can create interoperability issues.

   Security considerations:  All the security threats identified in
         Section 7 of RFC 3986 applies also to this scheme.  They need
         to be reviewed and considered in any implementation utilizing
         this scheme.

   Contact:  Magnus Westerlund, magnus.westerlund@ericsson.com

   Author/Change controller:  IETF

   References:  RFC 2326, RFC 3986, RFC 3987, RFC XXXX

22.14.2.  The rtsps URI Scheme

   URI scheme name:  rtsps

   Status:  Permanent

   URI scheme syntax:  See Section 20.2.1 of RFC XXXX.

   URI scheme semantics:  The rtsps scheme is used to indicate resources
         accessible through the usage of the Real-time Streaming
         Protocol (RTSP) over TLS.  RTSP allows different operations on
         the resource identified by the URI, but the primary purpose is
         the streaming delivery of the resource to a client.  However,
         the operations that are currently defined are: DESCRIBE,
         GET_PARAMETER, OPTIONS, PLAY, PLAY_NOTIFY, PAUSE, SETUP,
         SET_PARAMETER, and TEARDOWN.

   Encoding considerations:  IRIs in this scheme are defined and needs
         to be encoded as RTSP URIs when used within the RTSP protocol.
         That encoding is done according to RFC 3987.

   Applications/protocols that use this URI scheme name:  RTSP 1.0 (RFC
         2326), RTSP 2.0 (RFC XXXX)

   Interoperability considerations:  The change in URI syntax performed
         between RTSP 1.0 and 2.0 can create interoperability issues.

   Security considerations:  All the security threats identified in
         Section 7 of RFC 3986 applies also to this scheme.  They need
         to be reviewed and considered in any implementation utilizing
         this scheme.

   Contact:  Magnus Westerlund, magnus.westerlund@ericsson.com

   Author/Change controller:  IETF

   References:  RFC 2326, RFC 3986, RFC 3987, RFC XXXX

22.14.3.  The rtspu URI Scheme

   URI scheme name:  rtspu

   Status:  Permanent

   URI scheme syntax:  See Section 3.2 of RFC 2326.

   URI scheme semantics:  The rtspu scheme is used to indicate resources
         accessible through the usage of the Real-time Streaming
         Protocol (RTSP) over unreliable datagram transport.  RTSP
         allows different operations on the resource identified by the
         URI, but the primary purpose is the streaming delivery of the
         resource to a client.  However, the operations that are
         currently defined are: DESCRIBE, GET_PARAMETER, OPTIONS, PLAY,
         PLAY_NOTIFY, PAUSE, SETUP, SET_PARAMETER, and TEARDOWN.

   Encoding considerations:  IRIs in this scheme are not defined.

   Applications/protocols that use this URI scheme name:  RTSP 1.0 (RFC
         2326)

   Interoperability considerations:  The definition of the transport
         mechanism of RTSP over UDP has interoperability issues.  That
         makes the usage of this scheme problematic.

   Security considerations:  All the security threats identified in
         Section 7 of RFC 3986 applies also to this scheme.  They needs
         to be reviewed and considered in any implementation utilizing
         this scheme.

   Contact:  Magnus Westerlund, magnus.westerlund@ericsson.com

   Author/Change controller:  IETF

   References:  RFC 2326

22.15.  SDP attributes

   This specification defines three SDP [RFC4566] attributes that it is
   requested that IANA register.

   SDP Attribute ("att-field"):

        Attribute name:     range
        Long form:          Media Range Attribute
        Type of name:       att-field
        Type of attribute:  Media and session level
        Subject to charset: No
        Purpose:            RFC XXXX
        Reference:          RFC XXXX, RFC 2326
        Values:             See ABNF definition.

        Attribute name:     control
        Long form:          RTSP control URI
        Type of name:       att-field
        Type of attribute:  Media and session level
        Subject to charset: No
        Purpose:            RFC XXXX
        Reference:          RFC XXXX, RFC 2326
        Values:             Absolute or Relative URIs.

        Attribute name:     mtag
        Long form:          Message Tag
        Type of name:       att-field
        Type of attribute:  Media and session level
        Subject to charset: No
        Purpose:            RFC XXXX
        Reference:          RFC XXXX
        Values:             See ABNF definition

22.16.  Media Type Registration for text/parameters

   Type name:  text

   Subtype name:  parameters

   Required parameters:

   Optional parameters:

   Encoding considerations:

   Security considerations:  This format may carry any type of
      parameters.  Some can have security requirements, like privacy,
      confidentiality or integrity requirements.  The format has no
      built in security protection.  For the usage it was defined the
      transport can be protected between server and client using TLS.
      However, care must be take to consider if also the proxies are
      trusted with the parameters in case hop-by-hop security is used.
      If stored as file in file system the necessary precautions needs
      to be taken in relation to the parameters requirements including
      object security such as S/MIME [RFC5751].

   Interoperability considerations:  This media type was mentioned as a
      fictional example in RFC 2326 but was not formally specified.
      This has resulted in usage of this media type which may not match
      its formal definition.

   Published specification:  RFC XXXX, Appendix F.

   Applications that use this media type:  Applications that use RTSP
      and have additional parameters they like to read and set using the
      RTSP GET_PARAMETER and SET_PARAMETER methods.

   Additional information:

   Magic number(s):

   File extension(s):

   Macintosh file type code(s):

   Person & email address to contact for further information:  Magnus
      Westerlund (magnus.westerlund@ericsson.com)

   Intended usage:   Common

   Restrictions on usage:   None

   Author:  Magnus Westerlund (magnus.westerlund@ericsson.com)

   Change controller:  IETF

   Addition Notes:

23.  References

23.1.  Normative References

   [3gpp-26234]
              Third Generation Partnership Project (3GPP), "Transparent
              end-to-end Packet-switched Streaming Service (PSS);
              Protocols and codecs; Technical Specification 26.234",
              December 2002.

   [FIPS-pub-180-2]
              National Institute of Standards and Technology (NIST),
              "Federal Information Processing Standards Publications
              (FIPS PUBS) 180-2: Secure Hash Standard", August 2002.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC3830]  Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
              Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
              August 2004.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4567]  Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E.
              Carrara, "Key Management Extensions for Session
              Description Protocol (SDP) and Real Time Streaming
              Protocol (RTSP)", RFC 4567, July 2006.

   [RFC4571]  Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
              and RTP Control Protocol (RTCP) Packets over Connection-
              Oriented Transport", RFC 4571, July 2006.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC4738]  Ignjatic, D., Dondeti, L., Audet, F., and P. Lin, "MIKEY-
              RSA-R: An Additional Mode of Key Distribution in
              Multimedia Internet KEYing (MIKEY)", RFC 4738,
              November 2006.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, February 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port", RFC 5761, April 2010.

   [TS-26234]
              Third Generation Partnership Project (3GPP), "Transparent
              end-to-end Packet-switched Streaming Service (PSS);
              Protocols and codecs; Technical Specification 26.234",
              December 2002.

23.2.  Informative References

   [I-D.ietf-mmusic-rtsp-nat]
              Goldberg, J., Westerlund, M., and T. Zeng, "A Network
              Address Translator (NAT) Traversal mechanism for media
              controlled by Real-Time Streaming Protocol (RTSP)",
              draft-ietf-mmusic-rtsp-nat-11 (work in progress),
              October 2011.

   [ISO.13818-6.1995]
              International Organization for Standardization,
              "Information technology - Generic coding of moving
              pictures and associated audio information - part 6:
              Extension for digital storage media and control",
              ISO Draft Standard 13818-6, November 1995.

   [ISO.8601.2000]
              International Organization for Standardization, "Data
              elements and interchange formats - Information interchange
              - Representation of dates and times", ISO/IEC Standard
              8601, December 2000.

   [RFC1123]  Braden, R., "Requirements for Internet Hosts - Application
              and Support", STD 3, RFC 1123, October 1989.

   [RFC1644]  Braden, B., "T/TCP -- TCP Extensions for Transactions
              Functional Specification", RFC 1644, July 1994.

   [RFC2068]  Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
              Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
              RFC 2068, January 1997.

   [RFC2326]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
              Streaming Protocol (RTSP)", RFC 2326, April 1998.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822,
              April 2001.

   [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
              Announcement Protocol", RFC 2974, October 2000.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4588]  Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
              Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
              July 2006.

   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
              "Codec Control Messages in the RTP Audio-Visual Profile
              with Feedback (AVPF)", RFC 5104, February 2008.

   [RFC5583]  Schierl, T. and S. Wenger, "Signaling Media Decoding
              Dependency in the Session Description Protocol (SDP)",
              RFC 5583, July 2009.

   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description
              Protocol (SDP) Grouping Framework", RFC 5888, June 2010.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [Stevens98]
              Stevens, W., "Unix Networking Programming - Volume 1,
              second edition", 1998.

Appendix A.  Examples

   This section contains several different examples trying to illustrate
   possible ways of using RTSP.  The examples can also help with the
   understanding of how functions of RTSP work.  However, remember that
   these are examples and the normative and syntax description in the
   other sections takes precedence.  Please also note that many of the
   examples contain syntax illegal line breaks to accommodate the
   formatting restriction that the RFC series impose.

A.1.  Media on Demand (Unicast)

   This is an example of media on demand streaming of a media stored in
   a container file.  For purposes of this example, a container file is
   a storage entity in which multiple continuous media types pertaining
   to the same end-user presentation are present.  In effect, the
   container file represents an RTSP presentation, with each of its
   components being RTSP controlled media streams.  Container files are
   a widely used means to store such presentations.  While the
   components are transported as independent streams, it is desirable to
   maintain a common context for those streams at the server end.

      This enables the server to keep a single storage handle open
      easily.  It also allows treating all the streams equally in case
      of any priorization of streams by the server.

   It is also possible that the presentation author may wish to prevent
   selective retrieval of the streams by the client in order to preserve
   the artistic effect of the combined media presentation.  Similarly,
   in such a tightly bound presentation, it is desirable to be able to
   control all the streams via a single control message using an
   aggregate URI.

   The following is an example of using a single RTSP session to control
   multiple streams.  It also illustrates the use of aggregate URIs.  In
   a container file it is also desirable to not write any URI parts
   which is not kept, when the container is distributed, like the host
   and most of the path element.  Therefore this example also uses the
   "*" and relative URI in the delivered SDP.

   Also this presentation description (SDP) is not cachable, as the
   Expires header is set to an equal value with date indicating
   immediate expiration of its valididty.

   Client C requests a presentation from media server M. The movie is
   stored in a container file.  The client has obtained an RTSP URI to
   the container file.

   C->M: DESCRIBE rtsp://example.com/twister.3gp RTSP/2.0
         CSeq: 1
         User-Agent: PhonyClient/1.2

   M->C: RTSP/2.0 200 OK
         CSeq: 1
         Server: PhonyServer/1.0
         Date: Thu, 24 Jan 1997 15:35:06 GMT
         Content-Type: application/sdp
         Content-Length: 271
         Content-Base: rtsp://example.com/twister.3gp/
         Expires: 24 Jan 1997 15:35:06 GMT

         v=0
         o=- 2890844256 2890842807 IN IP4 198.51.100.5
         s=RTSP Session
         i=An Example of RTSP Session Usage
         e=adm@example.com
         c=IN IP4 0.0.0.0
         a=control: *
         a=range: npt=0-0:10:34.10
         t=0 0
         m=audio 0 RTP/AVP 0
         a=control: trackID=1
         m=video 0 RTP/AVP 26
         a=control: trackID=4

   C->M: SETUP rtsp://example.com/twister.3gp/trackID=1 RTSP/2.0
         CSeq: 2
         User-Agent: PhonyClient/1.2
         Require: play.basic
         Transport: RTP/AVP;unicast;dest_addr=":8000"/":8001"
         Accept-Ranges: NPT, SMPTE, UTC

   M->C: RTSP/2.0 200 OK
         CSeq: 2
         Server: PhonyServer/1.0
         Transport: RTP/AVP;unicast; ssrc=93CB001E;
                    dest_addr="192.0.2.53:8000"/"192.0.2.53:8001";
                    src_addr="198.51.100.5:9000"/"198.51.100.5:9001"
         Session: 12345678
         Expires: 24 Jan 1997 15:35:12 GMT
         Date: 24 Jan 1997 15:35:12 GMT
         Accept-Ranges: NPT
         Media-Properties: Random-Access=0.02, Immutable, Unlimited

   C->M: SETUP rtsp://example.com/twister.3gp/trackID=4 RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Require: play.basic
         Transport: RTP/AVP;unicast;dest_addr=":8002"/":8003"
         Session: 12345678
         Accept-Ranges: NPT, SMPTE, UTC

   M->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/1.0
         Transport: RTP/AVP;unicast; ssrc=A813FC13;
                    dest_addr="192.0.2.53:8002"/"192.0.2.53:8003";
                    src_addr="198.51.100.5:9002"/"198.51.100.5:9003";

         Session: 12345678
         Expires: 24 Jan 1997 15:35:13 GMT
         Date: 24 Jan 1997 15:35:13 GMT
         Accept-Range: NPT
         Media-Properties: Random-Access=0.8, Immutable, Unlimited

   C->M: PLAY rtsp://example.com/twister.3gp/ RTSP/2.0
         CSeq: 4
         User-Agent: PhonyClient/1.2
         Range: npt=30-
         Seek-Style: RAP
         Session: 12345678

   M->C: RTSP/2.0 200 OK
         CSeq: 4
         Server: PhonyServer/1.0
         Date: 24 Jan 1997 15:35:14 GMT
         Session: 12345678
         Range: npt=30-634.10
         Seek-Style: RAP
         RTP-Info: url="rtsp://example.com/twister.3gp/trackID=4"
            ssrc=0D12F123:seq=12345;rtptime=3450012,
           url="rtsp://example.com/twister.3gp/trackID=1"
            ssrc=4F312DD8:seq=54321;rtptime=2876889

   C->M: PAUSE rtsp://example.com/twister.3gp/ RTSP/2.0
         CSeq: 5
         User-Agent: PhonyClient/1.2
         Session: 12345678

   # Pause happens 0.87 seconds after starting to play

   M->C: RTSP/2.0 200 OK
         CSeq: 5
         Server: PhonyServer/1.0
         Date: 24 Jan 1997 15:36:01 GMT
         Session: 12345678
         Range: npt=30.87-634.10

   C->M: PLAY rtsp://example.com/twister.3gp/ RTSP/2.0
         CSeq: 6
         User-Agent: PhonyClient/1.2
         Range: npt=30.87-634.10
         Seek-Style: Next
         Session: 12345678

   M->C: RTSP/2.0 200 OK
         CSeq: 6
         Server: PhonyServer/1.0
         Date: 24 Jan 1997 15:36:01 GMT
         Session: 12345678
         Range: npt=30.87-634.10
         Seek-Style: Next
         RTP-Info: url="rtsp://example.com/twister.3gp/trackID=4"
            ssrc=0D12F123:seq=12555;rtptime=6330012,
           url="rtsp://example.com/twister.3gp/trackID=1"
            ssrc=4F312DD8:seq=55021;rtptime=3132889

   C->M: TEARDOWN rtsp://example.com/twister.3gp/ RTSP/2.0
         CSeq: 7
         User-Agent: PhonyClient/1.2
         Session: 12345678

   M->C: RTSP/2.0 200 OK
         CSeq: 7
         Server: PhonyServer/1.0
         Date: 24 Jan 1997 15:49:34 GMT

A.2.  Media on Demand using Pipelining

   This example is basically the example above (Appendix A.1), but now
   utilizing pipelining to speed up the setup.  It requires only two
   round trip times until the media starts flowing.  First of all, the
   session description is retrieved to determine what media resources
   need to be setup.  In the second step, one sends the necessary SETUP
   requests and the PLAY request to initiate media delivery.

   Client C requests a presentation from media server M. The movie is
   stored in a container file.  The client has obtained an RTSP URI to
   the container file.

   C->M: DESCRIBE rtsp://example.com/twister.3gp RTSP/2.0
         CSeq: 1
         User-Agent: PhonyClient/1.2

   M->C: RTSP/2.0 200 OK
         CSeq: 1
         Server: PhonyServer/1.0
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Content-Type: application/sdp
         Content-Length: 271
         Content-Base: rtsp://example.com/twister.3gp/
         Expires: 24 Jan 1997 15:35:06 GMT

         v=0
         o=- 2890844256 2890842807 IN IP4 192.0.2.5
         s=RTSP Session
         i=An Example of RTSP Session Usage
         e=adm@example.com
         c=IN IP4 0.0.0.0
         a=control: *
         a=range: npt=0-0:10:34.10
         t=0 0
         m=audio 0 RTP/AVP 0
         a=control: trackID=1
         m=video 0 RTP/AVP 26
         a=control: trackID=4

   C->M: SETUP rtsp://example.com/twister.3gp/trackID=1 RTSP/2.0
         CSeq: 2
         User-Agent: PhonyClient/1.2
         Require: play.basic
         Transport: RTP/AVP;unicast;dest_addr=":8000"/":8001"
         Accept-Ranges: NPT, SMPTE, UTC
         Pipelined-Requests: 7654

   C->M: SETUP rtsp://example.com/twister.3gp/trackID=4 RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Require: play.basic
         Transport: RTP/AVP;unicast;dest_addr=":8002"/":8003"
         Accept-Ranges: NPT, SMPTE, UTC
         Pipelined-Requests: 7654

   C->M: PLAY rtsp://example.com/twister.3gp/ RTSP/2.0
         CSeq: 4
         User-Agent: PhonyClient/1.2
         Range: npt=0-
         Seek-Style: RAP
         Pipelined-Requests: 7654

   M->C: RTSP/2.0 200 OK
         CSeq: 2
         Server: PhonyServer/1.0
         Transport: RTP/AVP;unicast;
                    dest_addr="192.0.2.53:8000"/"192.0.2.53:8001";
                    src_addr="198.51.100.5:9000"/"198.51.100.5:9001";
                    ssrc=93CB001E
         Session: 12345678
         Expires: 24 Jan 1997 15:35:12 GMT
         Date: 23 Jan 1997 15:35:12 GMT
         Accept-Ranges: NPT
         Pipelined-Requests: 7654
         Media-Properties: Random-Access=0.2, Immutable, Unlimited

   M->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/1.0
         Transport: RTP/AVP;unicast;
                    dest_addr="192.0.2.53:8002"/"192.0.2.53:8003;
                    src_addr="198.51.100.5:9002"/"198.51.100.5:9003";
                    ssrc=A813FC13
         Session: 12345678
         Expires: 24 Jan 1997 15:35:13 GMT
         Date: 23 Jan 1997 15:35:13 GMT
         Accept-Range: NPT
         Pipelined-Requests: 7654
         Media-Properties: Random-Access=0.8, Immutable, Unlimited

   M->C: RTSP/2.0 200 OK
         CSeq: 4
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:35:14 GMT
         Session: 12345678
         Range: npt=0-623.10
         Seek-Style: RAP
         RTP-Info: url="rtsp://example.com/twister.3gp/trackID=4"
            ssrc=0D12F123:seq=12345;rtptime=3450012,
           url="rtsp://example.com/twister.3gp/trackID=1"
            ssrc=4F312DD8:seq=54321;rtptime=2876889
         Pipelined-Requests: 7654

A.3.  Media on Demand (Unicast)

   An alternative example of media on demand with a bit more tweaks is
   the following.  Client C requests a movie distributed from two
   different media servers A (audio.example.com) and V (
   video.example.com).  The media description is stored on a web server
   W. The media description contains descriptions of the presentation
   and all its streams, including the codecs that are available, dynamic
   RTP payload types, the protocol stack, and content information such
   as language or copyright restrictions.  It may also give an
   indication about the timeline of the movie.

   In this example, the client is only interested in the last part of
   the movie.

   C->W: GET /twister.sdp HTTP/1.1
         Host: www.example.com
         Accept: application/sdp

   W->C: HTTP/1.0 200 OK
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Content-Type: application/sdp
         Content-Length: 278
         Expires: 23 Jan 1998 15:35:06 GMT

         v=0
         o=- 2890844526 2890842807 IN IP4 198.51.100.5
         s=RTSP Session
         e=adm@example.com
         c=IN IP4 0.0.0.0
         a=range:npt=0-1:49:34
         t=0 0
         m=audio 0 RTP/AVP 0
         a=control:rtsp://audio.example.com/twister/audio.en
         m=video 0 RTP/AVP 31
         a=control:rtsp://video.example.com/twister/video

   C->A: SETUP rtsp://audio.example.com/twister/audio.en RTSP/2.0
         CSeq: 1
         User-Agent: PhonyClient/1.2
         Transport: RTP/AVP/UDP;unicast;dest_addr=":3056"/":3057",
                    RTP/AVP/TCP;unicast;interleaved=0-1
         Accept-Ranges: NPT, SMPTE, UTC

   A->C: RTSP/2.0 200 OK
         CSeq: 1
         Session: 12345678
         Transport: RTP/AVP/UDP;unicast;
                    dest_addr="192.0.2.53:3056"/"192.0.2.53:3057";
                    src_addr="198.51.100.5:5000"/"198.51.100.5:5001"
         Date: 23 Jan 1997 15:35:12 GMT
         Server: PhonyServer/1.0
         Expires: 24 Jan 1997 15:35:12 GMT
         Cache-Control: public
         Accept-Ranges: NPT, SMPTE
         Media-Properties: Random-Access=0.02, Immutable, Unlimited

   C->V: SETUP rtsp://video.example.com/twister/video RTSP/2.0
         CSeq: 1
         User-Agent: PhonyClient/1.2
         Transport: RTP/AVP/UDP;unicast;
                    dest_addr="192.0.2.53:3058"/"192.0.2.53:3059",
                    RTP/AVP/TCP;unicast;interleaved=0-1
         Accept-Ranges: NPT, SMPTE, UTC

   V->C: RTSP/2.0 200 OK
         CSeq: 1
         Session: 23456789
         Transport: RTP/AVP/UDP;unicast;
            dest_addr="192.0.2.53:3058"/"192.0.2.53:3059";
            src_addr="198.51.100.5:5002"/"198.51.100.5:5003"
         Date: 23 Jan 1997 15:35:12 GMT
         Server: PhonyServer/1.0
         Cache-Control: public
         Expires: 24 Jan 1997 15:35:12 GMT
         Accept-Ranges: NPT, SMPTE
         Media-Properties: Random-Access=1.2, Immutable, Unlimited

   C->V: PLAY rtsp://video.example.com/twister/video RTSP/2.0
         CSeq: 2
         User-Agent: PhonyClient/1.2
         Session: 23456789
         Range: smpte=0:10:00-

   V->C: RTSP/2.0 200 OK
         CSeq: 2
         Session: 23456789
         Range: smpte=0:10:00-1:49:23
         Seek-Style: First-Prior
         RTP-Info: url="rtsp://video.example.com/twister/video"
                   ssrc=A17E189D:seq=12312232;rtptime=78712811
         Server: PhonyServer/2.0
         Date: 23 Jan 1997 15:35:13 GMT

   C->A: PLAY rtsp://audio.example.com/twister/audio.en RTSP/2.0
         CSeq: 2
         User-Agent: PhonyClient/1.2
         Session: 12345678
         Range: smpte=0:10:00-

   A->C: RTSP/2.0 200 OK
         CSeq: 2
         Session: 12345678
         Range: smpte=0:10:00-1:49:23
         Seek-Style: First-Prior
         RTP-Info: url="rtsp://audio.example.com/twister/audio.en"
                   ssrc=3D124F01:seq=876655;rtptime=1032181
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:35:13 GMT

   C->A: TEARDOWN rtsp://audio.example.com/twister/audio.en RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Session: 12345678

   A->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:36:52 GMT

   C->V: TEARDOWN rtsp://video.example.com/twister/video RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Session: 23456789

   V->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/2.0
         Date: 23 Jan 1997 15:36:52 GMT

   Even though the audio and video track are on two different servers
   that may start at slightly different times and may drift with respect
   to each other over time, the client can perform initial
   synchronization of the two media using RTP-Info and Range received in
   the PLAY responses.  If the two servers are time synchronized the
   RTCP packets can also be used to maintain synchronization.

A.4.  Single Stream Container Files

   Some RTSP servers may treat all files as though they are "container
   files", yet other servers may not support such a concept.  Because of
   this, clients needs to use the rules set forth in the session
   description for Request-URIs, rather than assuming that a consistent
   URI may always be used throughout.  Below is an example of how a
   multi-stream server might expect a single-stream file to be served:

   C->S: DESCRIBE rtsp://foo.example.com/test.wav RTSP/2.0
         Accept: application/x-rtsp-mh, application/sdp
         CSeq: 1
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 1
         Content-base: rtsp://foo.example.com/test.wav/
         Content-type: application/sdp
         Content-length: 163
         Server: PhonyServer/1.0
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Expires: 23 Jan 1997 17:00:00 GMT

         v=0
         o=- 872653257 872653257 IN IP4 192.0.2.5
         s=mu-law wave file
         i=audio test
         c=IN IP4 0.0.0.0
         t=0 0
         a=control: *
         m=audio 0 RTP/AVP 0
         a=control:streamid=0

   C->S: SETUP rtsp://foo.example.com/test.wav/streamid=0 RTSP/2.0
         Transport: RTP/AVP/UDP;unicast;
            dest_addr=":6970"/":6971";mode="PLAY"
         CSeq: 2
         User-Agent: PhonyClient/1.2
         Accept-Ranges: NPT, SMPTE, UTC

   S->C: RTSP/2.0 200 OK
         Transport: RTP/AVP/UDP;unicast;
             dest_addr="192.0.2.53:6970"/"192.0.2.53:6971";
             src_addr="198.51.100.5:6970"/"198.51.100.5:6971";
             mode="PLAY";ssrc=EAB98712
         CSeq: 2
         Session: 2034820394
         Expires: 23 Jan 1997 16:00:00 GMT
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:35:07 GMT
         Accept-Ranges: NPT
         Media-Properties: Random-Acces=0.5, Immutable, Unlimited

   C->S: PLAY rtsp://foo.example.com/test.wav/ RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Session: 2034820394

   S->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:35:08 GMT
         Session: 2034820394
         Range: npt=0-600
         Seek-Style: RAP
         RTP-Info: url="rtsp://foo.example.com/test.wav/streamid=0"
            ssrc=0D12F123:seq=981888;rtptime=3781123

   Note the different URI in the SETUP command, and then the switch back
   to the aggregate URI in the PLAY command.  This makes complete sense
   when there are multiple streams with aggregate control, but is less
   than intuitive in the special case where the number of streams is
   one.  However, the server has declared the aggregated control URI in
   the SDP and therefore this is legal.

   In this case, it is also required that servers accept implementations
   that use the non-aggregated interpretation and use the individual
   media URI, like this:

   C->S: PLAY rtsp://example.com/test.wav/streamid=0 RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Session: 2034820394

A.5.  Live Media Presentation Using Multicast

   The media server M chooses the multicast address and port.  Here, it
   is assumed that the web server only contains a pointer to the full
   description, while the media server M maintains the full description.

   C->W: GET /sessions.html HTTP/1.1
         Host: www.example.com

   W->C: HTTP/1.1 200 OK
         Content-Type: text/html

         <html>
           ...
           <a href "rtsp://live.example.com/concert/audio">
              Streamed Live Music performance </a>
           ...
         </html>

   C->M: DESCRIBE rtsp://live.example.com/concert/audio RTSP/2.0
         CSeq: 1
         Supported: play.basic, play.scale
         User-Agent: PhonyClient/1.2

   M->C: RTSP/2.0 200 OK
         CSeq: 1
         Content-Type: application/sdp
         Content-Length: 183
         Server: PhonyServer/1.0
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Supported: play.basic

         v=0
         o=- 2890844526 2890842807 IN IP4 192.0.2.5
         s=RTSP Session
         t=0 0
         m=audio 3456 RTP/AVP 0
         c=IN IP4 233.252.0.54/16
         a=control: rtsp://live.example.com/concert/audio
         a=range:npt=0-

   C->M: SETUP rtsp://live.example.com/concert/audio RTSP/2.0
         CSeq: 2
         Transport: RTP/AVP;multicast;
              dest_addr="233.252.0.54:3456"/"233.252.0.54:3457";ttl=16
         Accept-Ranges: NPT, SMPTE, UTC
         User-Agent: PhonyClient/1.2

   M->C: RTSP/2.0 200 OK
         CSeq: 2
         Server: PhonyServer/1.0
         Date: Thu, 23 Jan 1997 15:35:06 GMT
         Transport: RTP/AVP;multicast;
              dest_addr="233.252.0.54:3456"/"233.252.0.54:3457";ttl=16
              ;ssrc=4D12AB92/0DF876A3
         Session: 0456804596
         Accept-Ranges: NPT, UTC
         Media-Properties: No-Seeking, Time-Progressing, Time-Duration=0

   C->M: PLAY rtsp://live.example.com/concert/audio RTSP/2.0
         CSeq: 3
         Session: 0456804596
         User-Agent: PhonyClient/1.2

   M->C: RTSP/2.0 200 OK
         CSeq: 3
         Server: PhonyServer/1.0
         Date: 23 Jan 1997 15:35:07 GMT
         Session: 0456804596
         Seek-Style: Next
         Range:npt=1256-
         RTP-Info: url="rtsp://live.example.com/concert/audio"
                   ssrc=0D12F123:seq=1473; rtptime=80000

A.6.  Capability Negotiation

   This example illustrates how the client and server determines their
   capability to support a special feature, in this case "play.scale".
   The server, through the clients request and the included Supported
   header, learns the client supports RTSP 2.0, and also supports the
   playback time scaling feature of RTSP.  The server's response
   contains the following feature related information to the client; it
   supports the basic media delivery functions (play.basic), the
   extended functionality of time scaling of content (play.scale), and
   one "example.com" proprietary feature (com.example.flight).  The
   client also learns the methods supported (Public header) by the
   server for the indicated resource.

  C->S: OPTIONS rtsp://media.example.com/movie/twister.3gp RTSP/2.0
        CSeq: 1
        Supported: play.basic, play.scale
        User-Agent: PhonyClient/1.2

  S->C: RTSP/2.0 200 OK
        CSeq: 1
        Public: OPTIONS,SETUP,PLAY,PAUSE,TEARDOWN,DESCRIBE,GET_PARAMETER
        Allow: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN, DESCRIBE
        Server: PhonyServer/2.0
        Supported: play.basic, play.scale, com.example.flight

   When the client sends its SETUP request it tells the server that it
   requires support of the play.scale feature for this session by
   including the Require header.

   C->S: SETUP rtsp://media.example.com/twister.3gp/trackID=1 RTSP/2.0
         CSeq: 3
         User-Agent: PhonyClient/1.2
         Transport: RTP/AVP/UDP;unicast;
                    dest_addr="192.0.2.53:3056"/"192.0.2.53:3057",
                    RTP/AVP/TCP;unicast;interleaved=0-1
         Require: play.scale
         Accept-Ranges: NPT, SMPTE, UTC
         User-Agent: PhonyClient/1.2

   S->C: RTSP/2.0 200 OK
         CSeq: 3
         Session: 12345678
         Transport: RTP/AVP/UDP;unicast;
            dest_addr="192.0.2.53:3056"/"192.0.2.53:3057";
            src_addr="198.51.100.5:5000"/"198.51.100.5:5001"
         Server: PhonyServer/2.0
         Accept-Ranges: NPT, SMPTE
         Media-Properties: Random-Access=0.8, Immutable, Unlimited

Appendix B.  RTSP Protocol State Machine

   The RTSP session state machine describes the behavior of the protocol
   from RTSP session initialization through RTSP session termination.

   The State machine is defined on a per session basis which is uniquely
   identified by the RTSP session identifier.  The session may contain
   one or more media streams depending on state.  If a single media
   stream is part of the session it is in non-aggregated control.  If
   two or more is part of the session it is in aggregated control.

   The below state machine is an informative description of the
   protocols behavior.  In case of ambiguity with the earlier parts of
   this specification, the description in the earlier parts take
   precedence.

B.1.  States

   The state machine contains three states, described below.  For each
   state there exist a table which shows which requests and events are
   allowed and whether they will result in a state change.

   Init: Initial state no session exists.

   Ready:  Session is ready to start playing.

   Play: Session is playing, i.e. sending media stream data in the
         direction S->C.

B.2.  State variables

   This representation of the state machine needs more than its state to
   work.  A small number of variables is also needed and they are
   explained below.

   NRM:  The number of media streams part of this session.

   RP:   Resume point, the point in the presentation time line at which
         a request to continue playing will resume from.  A time format
         for the variable is not mandated.

B.3.  Abbreviations

   To make the state tables more compact a number of abbreviations are
   used, which are explained below.

   IFI:  IF Implemented.

   md:   Media

   PP:   Pause Point, the point in the presentation time line at which
         the presentation was paused.

   Prs:  Presentation, the complete multimedia presentation.

   RedP: Redirect Point, the point in the presentation time line at
         which a REDIRECT was specified to occur.

   SES:  Session.

B.4.  State Tables

   This section contains a table for each state.  The table contains all
   the requests and events that this state is allowed to act on.  The
   events which are method names are, unless noted, requests with the
   given method in the direction client to server (C->S).  In some cases
   there exist one or more requisite.  The response column tells what
   type of response actions should be performed.  Possible actions that
   are requested for an event includes: response codes, e.g. 200,
   headers that needs to be included in the response, setting of state
   variables, or setting of other session related parameters.  The new
   state column tells which state the state machine changes to.

   The response to a valid request meeting the requisites is normally a
   2xx (SUCCESS) unless other noted in the response column.  The
   exceptions need to be given a response according to the response
   column.  If the request does not meet the requisite, is erroneous or
   some other type of error occur, the appropriate response code is to
   be sent.  If the response code is a 4xx the session state is
   unchanged.  A response code of 3rr will result in that the session is
   ended and its state is changed to Init.  A response code of 304
   results in no state change.  However, there are restrictions to when
   a 3rr response may be used.  A 5xx response does not result in any
   change of the session state, except if the error is not possible to
   recover from.  A unrecoverable error results in the ending of the
   session.  As it in the general case can't be determined if it was a
   unrecoverable error or not the client will be required to test.  In
   the case that the next request after a 5xx is responded with 454
   (Session Not Found) the client knows that the session has ended.  For
   any request message that cannot be responded to within the time
   defined in Section 10.4, a 100 response must be sent.

   The server will timeout the session after the period of time
   specified in the SETUP response, if no activity from the client is
   detected.  Therefore there exists a timeout event for all states
   except Init.

   In the case that NRM = 1 the presentation URI is equal to the media
   URI or a specified presentation URI.  For NRM > 1 the presentation
   URI needs to be other than any of the medias that are part of the
   session.  This applies to all states.

   +---------------+-----------------+---------------------------------+
   | Event         | Prerequisite    | Response                        |
   +---------------+-----------------+---------------------------------+
   | DESCRIBE      | Needs REDIRECT  | 3rr, Redirect                   |
   |               |                 |                                 |
   | DESCRIBE      |                 | 200, Session description        |
   |               |                 |                                 |
   | OPTIONS       | Session ID      | 200, Reset session timeout      |
   |               |                 | timer                           |
   |               |                 |                                 |
   | OPTIONS       |                 | 200                             |
   |               |                 |                                 |
   | SET_PARAMETER | Valid parameter | 200, change value of parameter  |
   |               |                 |                                 |
   | GET_PARAMETER | Valid parameter | 200, return value of parameter  |
   +---------------+-----------------+---------------------------------+

               Table 13: None state-machine changing events

   The methods in Table 13 do not have any effect on the state machine
   or the state variables.  However, some methods do change other
   session related parameters, for example SET_PARAMETER which will set
   the parameter(s) specified in its body.  Also all of these methods
   that allow Session header will also update the keep-alive timer for
   the session.

   +------------------+----------------+-----------+-------------------+
   | Action           | Requisite      | New State | Response          |
   +------------------+----------------+-----------+-------------------+
   | SETUP            |                | Ready     | NRM=1, RP=0.0     |
   |                  |                |           |                   |
   | SETUP            | Needs Redirect | Init      | 3rr Redirect      |
   |                  |                |           |                   |
   | S -> C: REDIRECT | No Session hdr | Init      | Terminate all SES |
   +------------------+----------------+-----------+-------------------+

                           Table 14: State: Init

   The initial state of the state machine, see Table 14 can only be left
   by processing a correct SETUP request.  As seen in the table the two
   state variables are also set by a correct request.  This table also
   shows that a correct SETUP can in some cases be redirected to another
   URI and/or server by a 3rr response.

   +-------------+------------------------+---------+------------------+
   | Action      | Requisite              | New     | Response         |
   |             |                        | State   |                  |
   +-------------+------------------------+---------+------------------+
   | SETUP       | New URI                | Ready   | NRM +=1          |
   |             |                        |         |                  |
   | SETUP       | URI Setup prior        | Ready   | Change transport |
   |             |                        |         | param            |
   |             |                        |         |                  |
   | TEARDOWN    | Prs URI,               | Init    | No session hdr,  |
   |             |                        |         | NRM = 0          |
   |             |                        |         |                  |
   | TEARDOWN    | md URI,NRM=1           | Init    | No Session hdr,  |
   |             |                        |         | NRM = 0          |
   |             |                        |         |                  |
   | TEARDOWN    | md URI,NRM>1           | Ready   | Session hdr, NRM |
   |             |                        |         | -= 1             |
   |             |                        |         |                  |
   | PLAY        | Prs URI, No range      | Play    | Play from RP     |
   |             |                        |         |                  |
   | PLAY        | Prs URI, Range         | Play    | According to     |
   |             |                        |         | range            |
   |             |                        |         |                  |
   | PLAY        | md URI, NRM=1, Range   | Play    | According to     |
   |             |                        |         | range            |
   |             |                        |         |                  |
   | PLAY        | md URI, NRM=1          | Play    | Play from RP     |
   |             |                        |         |                  |
   | PAUSE       | Prs URI                | Ready   | Return PP        |
   |             |                        |         |                  |
   | SC:REDIRECT | Terminate-Reason       | Ready   | Set RedP         |
   |             |                        |         |                  |
   | SC:REDIRECT | No Terminate-Reason    | Init    | Session is       |
   |             | time parameter         |         | removed          |
   |             |                        |         |                  |
   | Timeout     |                        | Init    |                  |
   |             |                        |         |                  |
   | RedP        |                        | Init    | TEARDOWN of      |
   | reached     |                        |         | session          |
   +-------------+------------------------+---------+------------------+

                          Table 15: State: Ready

   In the Ready state, see Table 15, some of the actions are depending
   on the number of media streams (NRM) in the session, i.e., aggregated
   or non-aggregated control.  A SETUP request in the Ready state can
   either add one more media stream to the session or, if the media
   stream (same URI) already is part of the session, change the
   transport parameters.  TEARDOWN is depending on both the Request-URI
   and the number of media stream within the session.  If the Request-
   URI is the presentations URI the whole session is torn down.  If a
   media URI is used in the TEARDOWN request and more than one media
   exists in the session, the session will remain and a session header
   is returned in the response.  If only a single media stream remains
   in the session when performing a TEARDOWN with a media URI the
   session is removed.  The number of media streams remaining after
   tearing down a media stream determines the new state.

   +----------------+-----------------------+--------+-----------------+
   | Action         | Requisite             | New    | Response        |
   |                |                       | State  |                 |
   +----------------+-----------------------+--------+-----------------+
   | PAUSE          | Prs URI               | Ready  | Set RP to       |
   |                |                       |        | present point   |
   |                |                       |        |                 |
   | End of media   | All media             | Play   | Set RP = End of |
   |                |                       |        | media           |
   |                |                       |        |                 |
   | End of range   |                       | Play   | Set RP = End of |
   |                |                       |        | range           |
   |                |                       |        |                 |
   | PLAY           | Prs URI, No range     | Play   | Play from       |
   |                |                       |        | present point   |
   |                |                       |        |                 |
   | PLAY           | Prs URI, Range        | Play   | According to    |
   |                |                       |        | range           |
   |                |                       |        |                 |
   | SC:PLAY_NOTIFY |                       | Play   | 200             |
   |                |                       |        |                 |
   | SETUP          | New URI               | Play   | 455             |
   |                |                       |        |                 |
   | SETUP          | Setuped URI           | Play   | 455             |
   |                |                       |        |                 |
   | SETUP          | Setuped URI, IFI      | Play   | Change          |
   |                |                       |        | transport       |
   |                |                       |        | param.          |
   |                |                       |        |                 |
   | TEARDOWN       | Prs URI               | Init   | No session hdr  |
   |                |                       |        |                 |
   | TEARDOWN       | md URI,NRM=1          | Init   | No Session hdr, |
   |                |                       |        | NRM=0           |
   |                |                       |        |                 |
   | TEARDOWN       | md URI                | Play   | 455             |
   |                |                       |        |                 |
   | SC:REDIRECT    | Terminate Reason with | Play   | Set RedP        |
   |                | Time parameter        |        |                 |
   |                |                       |        |                 |
   | SC:REDIRECT    |                       | Init   | Session is      |
   |                |                       |        | removed         |
   |                |                       |        |                 |
   | RedP reached   |                       | Init   | TEARDOWN of     |
   |                |                       |        | session         |
   |                |                       |        |                 |
   | Timeout        |                       | Init   | Stop Media      |
   |                |                       |        | playout         |
   +----------------+-----------------------+--------+-----------------+
                           Table 16: State: Play

   The Play state table, see Table 16, contains a number of requests
   that need a presentation URI (labeled as Prs URI) to work on (i.e.,
   the presentation URI has to be used as the Request-URI).  This is due
   to the exclusion of non-aggregated stream control in sessions with
   more than one media stream.

   To avoid inconsistencies between the client and server, automatic
   state transitions are avoided.  This can be seen at for example "End
   of media" event when all media has finished playing, the session
   still remains in Play state.  An explicit PAUSE request needs to be
   sent to change the state to Ready.  It may appear that there exist
   automatic transitions in "RedP reached" and "PP reached".  However,
   they are requested and acknowledged before they take place.  The time
   at which the transition will happen is known by looking at the range
   header.  If the client sends a request close in time to these
   transitions it needs to be prepared for receiving error messages, as
   the state may or may not have changed.

Appendix C.  Media Transport Alternatives

   This section defines how certain combinations of protocols, profiles
   and lower transports are used.  This includes the usage of the
   Transport header's source and destination address parameters
   "src_addr" and "dest_addr".

C.1.  RTP

   This section defines the interaction of RTSP with respect to the RTP
   protocol [RFC3550].  It also defines any necessary media transport
   signalling
   signaling with regards to RTP.

   The available RTP profiles and lower layer transports are described
   below along with rules on signalling signaling the available combinations.

C.1.1.  AVP

   The usage of the "RTP Profile for Audio and Video Conferences with
   Minimal Control" [RFC3551] when using RTP for media transport over
   different lower layer transport protocols is defined below in regards
   to RTSP.

   One such case is defined within this document, the use of embedded
   (interleaved) binary data as defined in Section 14.  The usage of
   this method is indicated by including the "interleaved" parameter.

   When using embedded binary data the "src_addr" and "dest_addr" MUST
   NOT be used.  This addressing and multiplexing is used as defined
   with use of channel numbers and the interleaved parameter.

C.1.2.  AVP/UDP

   This part describes sending of RTP [RFC3550] over lower transport
   layer UDP [RFC0768] according to the profile "RTP Profile for Audio
   and Video Conferences with Minimal Control" defined in RFC 3551
   [RFC3551].  This profile requires one or two uni- or bi-directional
   UDP flows per media stream.  The first UDP flow is for RTP and the
   second is for RTCP.  Embedding of RTP data with the RTSP messages, in
   accordance with Section 14, SHOULD NOT be performed when RTSP
   messages are transported over unreliable transport protocols, like
   UDP [RFC0768].

   The RTP/UDP and RTCP/UDP flows can be established using the Transport
   header's "src_addr", and "dest_addr" parameters.

   In RTSP PLAY mode, the transmission of RTP packets from client to
   server is unspecified.  The behavior in regards to such RTP packets
   MAY be defined in future.

   The "src_addr" and "dest_addr" parameters are used in the following
   way for media delivery and playback mode, i.e.  Mode=PLAY:

   o  The "src_addr" and "dest_addr" parameters MUST contain either 1 or
      2 address specifications.

   o  Each address specification for RTP/AVP/UDP or RTP/AVP/TCP MUST
      contain either:

      *  both an address and a port number, or

      *  a port number without an address.

   o  The first address and port pair given in either of the parameters
      applies to the RTP stream.  The second address and port pair if
      present applies to the RTCP stream.

   o  The RTP/UDP packets from the server to the client MUST be sent to
      the address and port given by the first address and port pair of
      the "dest_addr" parameter.

   o  The RTCP/UDP packets from the server to the client MUST be sent to
      the address and port given by the second address and port pair of
      the "dest_addr" parameter.  If no second pair is specified RTCP
      MUST NOT be sent.

   o  The RTCP/UDP packets from the client to the server MUST be sent to
      the address and port given by the second address and port pair of
      the "src_addr" parameter.  If no second pair is given RTCP MUST
      NOT be sent.

   o  The RTP/UDP packets from the client to the server MUST be sent to
      the address and port given by the first address and port pair of
      the "src_addr" parameter.

   o  RTP and RTCP Packets SHOULD be sent from the corresponding
      receiver port, i.e.  RTCP packets from the server should be sent
      from the "src_addr" parameters second address port pair.

C.1.3.  AVPF/UDP

   The RTP profile "Extended RTP Profile for RTCP-based Feedback (RTP/
   AVPF)" [RFC4585] MAY be used as RTP profiles in sessions using RTP.
   All that is defined for AVP MUST also apply for AVPF.

   The usage of AVPF is indicated by the media initialization protocol
   used.  In the case of SDP it is indicated by media lines (m=)
   containing the profile RTP/AVPF.  That SDP MAY also contain further
   AVPF related SDP attributes configuring the AVPF session regarding
   reporting interval and feedback messages to be used.  This
   configuration MUST be followed.

C.1.4.  SAVP/UDP

   The RTP profile "The Secure Real-time Transport Protocol (SRTP)"
   [RFC3711] is an RTP profile (SAVP) that MAY be used in RTSP sessions
   using RTP.  All that is defined for AVP MUST also apply for SAVP.

   The usage of SRTP requires that a security context is established.
   The default key-management unless otherwise signalled shall be MIKEY
   in RSA-R mode as defined in Appendix C.1.4.1, and not according to
   the procedure defined in "Key Management Extensions for Session
   Description Protocol (SDP) and Real Time Streaming Protocol (RTSP)"
   [RFC4567].  The reason is that RFC 4567 sends the initial MIKEY
   message in SDP, thus both requiring the usage of the DESCRIBE method
   and forcing the server to keep state for clients performing DESCRIBE
   in anticipation that they might require key management.

   MIKEY is selected as default method for establishing SRTP
   cryptographic context within an RTSP session as it can be embedded in
   the RTSP messages, while still ensuring confidentiality of content of
   the keying material, even when using hop-by-hop TLS security for the
   RTSP messages.  This method does also support pipelining of the RTSP
   messages.

C.1.4.1.  MIKEY Key Establishment

   This method for using MIKEY [RFC3830] to establish the SRTP
   cryptographic context is initiated in the client's SETUP request, and
   the servers response to the SETUP carries the MIKEY response.  Thus
   ensuring that the crypto context establishment happens simultaneously
   with the establishment of the media stream being protected.  By using
   MIKEY's RSA-R mode [RFC4738] the client can be the initiator and
   still allow the server to set the parameters in accordance with the
   actual media stream.

   The SRTP cryptographic context establishment is done according to the
   following process:

   1.   The client determines that SAVP or SAVPF shall be used from
        media description format, e.g.  SDP.  If no other key management
        method is explicitly signalled, then MIKEY SHALL be used as
        defined herein.  This specification does not specify an explicit
        method for indicating this SRTP cryptographic context
        establishment method, but future specifications may.

   2.   The client SHALL establish a TLS connection for RTSP messages,
        directly or hop by hop with the server.  If hop-by-hop TLS
        security is used, the User method SHALL be indicated in the
        Accept-Credentials header.  We do note that using hop-by-hop
        does allow the proxy to insert itself as a man in the middle
        also in the MIKEY exchange by providing one of its certificates,
        rather than the server's in the Connection-Credentials header.
        The client SHALL therefore validate the server certificate.

   3.   The client retrieves the servers certificate from a direct TLS
        connection, or if hop by hop from Connection-Credentials header.
        The client then checks that the server certificate is valid and
        belongs to the server.

   4.   The client forms the MIKEY Initiator message using RSA-R mode in
        unicast mode as specified in [RFC4738].  The client SHOULD use
        the same certificate for TLS and in MIKEY to enable the server
        to bind the two together.  The client's certificate SHALL be
        included in the MIKEY message.  The client SHALL indicate its
        SRTP capabilities in the message.

   5.   The MIKEY message from the previous step is base64 [RFC4648]
        encoded and becomes the value of the MIKEY parameter that is
        included in the transport specification(s) that specifies a SRTP
        based profile (SAVP, SAVPF) in the SETUP request.

   6.   Any proxy encountering the MIKEY parameter SHALL forward it
        without modification.  A proxy requiring to understand transport
        specification which doesn't support SAVP/SAVPF with MIKEY will
        discard the whole transport specification.  Most types of proxy
        can easily support SAVP and SAVPF with MIKEY.  If possible
        bypassing the proxy should be tried.

   7.   The server upon receiving the SETUP request, will need to decide
        upon the transport specification to use, if multiple are
        included by the client.  In the determination of which transport
        specifications that are supported and preferred, the server
        SHOULD decode the MIKEY message to take the embedded SRTP
        parameters into account.  If all transport specs require SRTP
        but no MIKEY parameter or other supported keying method is
        included, the server SHALL respond with 403.

   8.   Upon generating a response the following outcomes can occur:

        *  A transport spec not using SRTP and MIKEY is selected.  Thus
           the response will not contain any MIKEY parameter.

        *  A transport spec using SRTP and MIKEY is selected but an
           error is encountered in the MIKEY processing.  In that case
           an RTSP error response code of 466 "Key Management Error"
           SHALL be used.  A MIKEY message describing the error MAY be
           included.

        *  A transport spec using SRTP and MIKEY is selected and a MIKEY
           response message can be created.  The server SHOULD use the
           same certificate for TLS and in MIKEY to enable client to
           bind the two together.  If a different certificate is used it
           SHALL be included in the MIKEY message.  It is RECOMMENDED
           that the envelope key cache type is set to 'Cache' and that a
           single envelope key is reused for all MIKEY messages to the
           client.  That message is included in the MIKEY parameter part
           of the single selected transport specification in the SETUP
           response.  The server will set the SRTP parameters as
           preferred for this media stream within the supported range by
           the client.

   9.   The server transmits the SETUP response back to the client.

   10.  The client receives the SETUP response and if the response code
        indicates a successful request it decodes the MIKEY message and
        establish the SRTP cryptographic context from the parameters in
        the MIKEY response.

   In the above method the client's certificate may be self-signed in
   cases where the client's identity is not necessary to establish and
   the security goal is only to ensure that the RTSP signalling signaling client is
   the same as the one receiving the SRTP security context.

C.1.5.  SAVPF/UDP

   The RTP profile "Extended Secure RTP Profile for RTCP-based Feedback
   (RTP/SAVPF)" [RFC5124] is an RTP profile (SAVPF) that MAY be used in
   RTSP sessions using RTP.  All that is defined for AVP MUST also apply
   for SAVPF.

   The usage of SRTP requires that a cryptographic context is
   established.  The default mechanism for establishing that security
   association is to use MIKEY[RFC3830] with RTSP as defined in
   Appendix C.1.4.1.

C.1.6.  RTCP usage with RTSP

   RTCP has several usages when RTP is used for media transport as
   explained below.  Due to that RTCP MUST be supported if an RTSP agent
   handles RTP.

C.1.6.1.  Media synchronization

   RTCP provides media synchronization and clock drift compensation.
   The initial media synchronization is available from RTP-Info header.
   However, to be able to handle any clock drift between the media
   streams, RTCP is needed.

C.1.6.2.  RTSP Session keep-alive

   RTCP traffic from the RTSP client to the RTSP server MUST function as
   keep-alive.  This requires an RTSP server supporting RTP to use the
   received RTCP packets as indications that the client desires the
   related RTSP session to be kept alive.

C.1.6.3.  Bit-rate adaption

   RTCP Receiver reports and any additional feedback from the client
   MUST be used to adapt the bit-rate used over the transport for all
   cases when RTP is sent over UDP.  An RTP sender without reserved
   resources MUST NOT use more than its fair share of the available
   resources.  This can be determined by comparing on short to medium
   term (some seconds) the used bit-rate and adapt it so that the RTP
   sender sends at a bit-rate comparable to what a TCP sender would
   achieve on average over the same path.

C.1.6.4.  RTP and RTCP Multiplexing

   RTSP can be used to negotiate the usage of RTP and RTCP multiplexing
   as described in [RFC5761].  This allows servers and client to reduce
   the amount of resources required for the session by only requiring
   one underlying transport stream per media stream instead of two when
   using RTP and RTCP.  This lessens the server port consumption and
   also the necessary state and keep-alive work when operating across
   Network and Address Translators [RFC2663].

   Content must be prepared with some consideration for RTP and RTCP
   multiplexing, mainly ensuring that the RTP payload types used do not
   collide with the ones used for RTCP packet types.  This option likely
   needs explicit support from the content unless the RTP payload types
   can be remapped by the server and that is correctly reflected in the
   session description.  Beyond that support of this feature should come
   at little cost and much gain.

   It is recommended that if the content and server support RTP and RTCP
   multiplexing that this is indicated in the session description, for
   example using the SDP attribute "a=rtcp-mux".  If the SDP message
   contains the a=rtcp-mux attribute for a media stream, the server MUST
   support RTP and RTCP multiplexing.  If indicated or otherwise desired
   by the client it can include the Transport parameter "RTCP-mux" in
   any transport specification where it desires to use RTCP-mux.  The
   server will indicate if it supports RTCP-mux.  Servers and Clients
   SHOULD support RTP and RTCP multiplexing.

   For capability exchange, an RTSP feature tag for RTP and RTCP
   multiplexing is defined: "setup.rtp.rtcp.mux".

C.2.  RTP over TCP

   Transport of RTP over TCP can be done in two ways: over independent
   TCP connections using RFC 4571 [RFC4571] or interleaved in the RTSP
   control connection.  In both cases the protocol MUST be "rtp" and the
   lower layer MUST be TCP.  The profile may be any of the above
   specified ones; AVP, AVPF, SAVP or SAVPF.

C.2.1.  Interleaved RTP over TCP

   The use of embedded (interleaved) binary data transported on the RTSP
   connection is possible as specified in Section 14.  When using this
   declared combination of interleaved binary data the RTSP messages
   MUST be transported over TCP.  TLS may or may not be used.

   One should, however, consider that this will result in all media
   streams go through any proxy.  Using independent TCP connections can
   avoid that issue.

C.2.2.  RTP over independent TCP

   In this Appendix, we describe the sending of RTP [RFC3550] over lower
   transport layer TCP [RFC0793] according to "Framing Real-time
   Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over
   Connection-Oriented Transport" [RFC4571].  This Appendix adapts the
   guidelines for using RTP over TCP within SIP/SDP [RFC4145] to work
   with RTSP.

   A client codes the support of RTP over independent TCP by specifying
   an RTP/AVP/TCP transport option without an interleaved parameter in
   the Transport line of a SETUP request.  This transport option MUST
   include the "unicast" parameter.

   If the client wishes to use RTP with RTCP, two ports (or two address/
   port pairs) are specified by the dest_addr parameter.  If the client
   wishes to use RTP without RTCP, one port (or one address/port pair)
   is specified by the dest_addr parameter.  If the client wishes to
   multiplex RTP and RTCP on a single port (see Section
   Appendix C.1.6.4, one port (or one address/port pair) is specified by
   the dest_addr parameter.  Ordering rules of dest_addr ports follow
   the rules for RTP/AVP/UDP.

   If the client wishes to play the active role in initiating the TCP
   connection, it MAY set the "setup" parameter (See Section 16.52) 18.52) on
   the Transport line to be "active", or it MAY omit the setup
   parameter, as active is the default.  If the client signals the
   active role, the ports for all dest_addr values MUST be set to 9 (the
   discard port).

   If the client wishes to play the passive role in TCP connection
   initiation, it MUST set the "setup" parameter on the Transport line
   to be "passive".  If the client is able to assume the active or the
   passive role, it MUST set the "setup" parameter on the Transport line
   to be "actpass".  In either case, the dest_addr port value for RTP
   MUST be set to the TCP port number on which the client is expecting
   to receive the RTP stream connection, and the dest_addr port value
   for RTCP MUST be set to the TCP port number on which the client is
   expecting to receive the RTCP stream connection.

   If upon receipt of a non-interleaved RTP/AVP/TCP SETUP request, a
   server decides to accept this requested option, the 2xx reply MUST
   contain a Transport option that specifies RTP/AVP/TCP (without using
   the interleaved parameter, and with using the unicast parameter).
   The dest_addr parameter value MUST be echoed from the parameter value
   in the client request unless the destination address (only port) was
   not provided in which case the server MAY include the source address
   of the RTSP TCP connection with the port number unchanged.

   In addition, the server reply MUST set the setup parameter on the
   Transport line, to indicate the role the server will play in the
   connection setup.  Permissible values are "active" (if a client set
   "setup" to "passive" or "actpass") and "passive" (if a client set
   "setup" to "active" or "actpass").

   If a server sets "setup" to "passive", the "src_addr" in the reply
   MUST indicate the ports the server is willing to receive an RTP
   connection and (if the client requested an RTCP connection by
   specifying two dest_addr ports or address/port pairs) and RTCP
   connection.  If a server sets "setup" to "active", the ports
   specified in "src_addr" MUST be set to 9.  The server MAY use the
   "ssrc" parameter, following the guidance in Section 16.52. 18.52.  Port
   ordering for src_addr follows the rules for RTP/AVP/UDP.

   Servers MUST support taking the passive role and MAY support taking
   the active role.  Servers with a public IP address take the passive
   role, thus enabling clients behind NATs and Firewalls a better chance
   of successful connect to the server by actively connecting outwards.
   Therefore the clients are RECOMMENDED to take the active role.

   After sending (receiving) a 2xx reply for a SETUP method for a non-
   interleaved RTP/AVP/TCP media stream, the active party SHOULD
   initiate the TCP connection as soon as possible.  The client MUST NOT
   send a PLAY request prior to the establishment of all the TCP
   connections negotiated using SETUP for the session.  In case the
   server receives a PLAY request in a session that has not yet
   established all the TCP connections, it MUST respond using the 464
   "Data Transport Not Ready Yet" (Section 15.4.29) 17.4.29) error code.

   Once the PLAY request for a media resource transported over non-
   interleaved RTP/AVP/TCP occurs, media begins to flow from server to
   client over the RTP TCP connection, and RTCP packets flow
   bidirectionally over the RTCP TCP connection.  As in the RTP/UDP
   case, client to server traffic on the TCP port is unspecified by this
   memo.  The packets that travel on these connections MUST be framed
   using the protocol defined in [RFC4571], not by the framing defined
   for interleaving RTP over the RTSP control connection defined in
   Section 14.

   A successful PAUSE request for a media being transported over RTP/
   AVP/TCP pauses the flow of packets over the connections, without
   closing the connections.  A successful TEARDOWN request signals that
   the TCP connections for RTP and RTCP are to be closed as soon as
   possible.

   Subsequent SETUP requests on an already-SETUP