--- 1/draft-ietf-mmusic-media-loopback-04.txt 2006-09-25 17:12:12.000000000 +0200 +++ 2/draft-ietf-mmusic-media-loopback-05.txt 2006-09-25 17:12:12.000000000 +0200 @@ -1,26 +1,26 @@ K. Hedayat Internet Draft Brix Networks - Expires: February 2007 P. Jones + Expires: April 2007 P. Jones Cisco Systems, Inc. A. Roychowdhury Hughes C. SivaChelvan Cisco Systems, Inc. N. Stratton August 2006 An Extension to the Session Description Protocol (SDP) for Media Loopback - draft-ietf-mmusic-media-loopback-04 + draft-ietf-mmusic-media-loopback-05 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -69,40 +69,39 @@ 1. Introduction..................................................3 2. Terminology...................................................4 3. Offering Entity Behavior......................................4 4. Answering Entity Behavior.....................................4 5. SDP Constructs Syntax.........................................4 5.1 Loopback Type Attribute...................................4 5.2 Loopback Mode Attribute...................................6 5.3 Generating the Offer for Loopback Session.................7 5.4 Generating the Answer for Loopback Session................8 5.5 Offerer Processing of the Answer..........................9 - 5.6 Modifying the Session.....................................9 + 5.6 Modifying the Session....................................10 6. RTP Requirements.............................................10 - 7. Payload format for encapsulated RTP Streams..................10 - 7.1 Usage of RTP Header fields...............................10 - 7.2 RTP Payload Structure....................................11 - 7.3 Usage of SDP.............................................12 - 8. RTCP Requirements............................................13 - 9. Congestion Control...........................................13 - 10. Examples....................................................13 - 10.1 Offer for specific media loopback type..................13 - 10.2 Offer for choice of media loopback type.................14 + 7. Payload formats for Packet loopback..........................10 + 7.1 Encapsulated Payload format..............................11 + 7.2 Direct loopback RTP payload format.......................13 + 8. RTCP Requirements............................................14 + 9. Congestion Control...........................................15 + 10. Examples....................................................15 + 10.1 Offer for specific media loopback type..................15 + 10.2 Offer for choice of media loopback type.................16 10.3 Offer for choice of media loopback type with - rtp-start-loopback...........................................15 - 10.4 Response to INVITE request rejecting loopback media.....16 + rtp-start-loopback...........................................17 + 10.4 Response to INVITE request rejecting loopback media.....18 10.5 Response to INVITE request rejecting loopback media with - rtp-start-loopback...........................................16 - 11. Security Considerations.....................................17 - 12. IANA Considerations.........................................18 - 13. Acknowledgements............................................18 - 14. References..................................................18 + rtp-start-loopback...........................................18 + 11. Security Considerations.....................................19 + 12. IANA Considerations.........................................20 + 13. Acknowledgements............................................20 + 14. References..................................................20 1. Introduction The overall quality, reliability, and performance of VoIP, Real-time Text and Video over IP services rely on the performance and quality of the media path. In order to assure the quality of the delivered media there is a need to monitor the performance of the media transport. One method of monitoring and managing the overall quality of VoIP, Real-time Text and Video over IP Services is through monitoring the quality of the media in an active @@ -124,24 +123,23 @@ The extension defined in this memo introduces new SDP media attributes that enable establishment of media sessions where the media is looped back to the transmitter. The offer/answer model [RFC3264] is used to establish a loopback connection. Furthermore, this extension provides guidelines on handling RTP [RFC3550], as well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] for reporting media related measurements. 2. Terminology - In this document, the key words "MUST", "MUST NOT", "REQUIRED", - "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", - and "OPTIONAL" are to be interpreted as described in RFC 2119 and - indicate requirement levels for compliant implementations. + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in + this document are to be interpreted as described in RFC 2119. 3. Offering Entity Behavior An offering entity compliant to this memo and attempting to establish a media session with media loopback MUST include "loopback" media attributes for each individual media description in the offer message. The offering entity MUST look for the "loopback" media attributes in the media description(s) of the response from the answering entity for confirmation that the request is accepted. @@ -160,77 +158,79 @@ which receives an offer with the "loopback" media attributes MAY ignore the attribute and treat the incoming offer as a normal request. 5. SDP Constructs Syntax Two new media attributes are defined: one indicates the type of loopback and one indicates the mode of the loopback. 5.1 Loopback Type Attribute + The loopback type is a property media attribute with the following syntax: a=loopback: Following is the Augmented BNF [RFC2234] for loopback-type: loopback-type = loopback-type-1 | loopback-type-2 - loopback-type-1 = loopback-type-choice-1 [space loopback-type- - choice-1] - loopback-type-choice-1 = “rtp-pkt-loopback” | “rtp-media-loopback” + loopback-type-1 = loopback-type-choice-1 [space + loopback-type-choice-1] + loopback-type-choice-1 = "rtp-pkt-loopback" | "rtp-media-loopback" loopback-type-2 = loopback-type-choice-2 - loopback-type-choice-2 = “rtp-start-loopback” + loopback-type-choice-2 = "rtp-start-loopback" The loopback type is used to indicate the type of loopback. The loopback-type values are rtp-pkt-loopback, rtp-media-loopback, and rtp-start-loopback. rtp-pkt-loopback: In this mode, the RTP packets are looped back to the sender at a point before the encoder/decoder function in the receive direction to a point after the encoder/decoder function in the send direction. This effectively re-encapsulates the RTP payload with the RTP/UDP/IP overheads appropriate for sending it in - the reverse direction. Any type of encoding related functions, such - as packet loss concealment, MUST NOT be part of this type of - loopback path. Section 7 describes the encapsulated payload format - that MUST be used for this type of loopback. + the reverse direction. Any type of encoding related functions, + such as packet loss concealment, MUST NOT be part of this type of + loopback path. In this mode the RTP packets are looped back with a + new payload type and format. Section 7 describes the payload + formats that MUST be used for this type of loopback. rtp-media-loopback: This loopback is activated as close as possible to the analog interface and after the decoder so that the RTP packets are subsequently re-encoded prior to transmission back to the sender. rtp-start-loopback: In certain scenarios it is possible that the media transmitted by the loopback-source is blocked by a network element until the loopback-mirror starts transmitting packets. Loopback-source and loopback-mirror are loopback modes defined in - section 5.2. One example of this scenario is the presence of an RTP - relay in the path of the media. RTP relays exist in VoIP networks - for purpose of NAT and Firewall traversal. If an RTP relay is - present, the loopback-source’s packets are dropped by the RTP relay - until the loopback-mirror has started transmitting media and the - media state within the RTP relay is established. This loopback - attribute is used to specify the media type for transmitting media - packets by the loopback-mirror prior to the loopback process for - the purpose of setting media state within the network. In the - presence of this loopback attribute the loopback-mirror will - transmit media, according to the description that contains this - attribute, until it receives media from the loopback-source. The - loopback-mirror MAY include this attribute in the answer if it is - not present in the offer. This may be necessary if the loopback- - mirror is aware of NAT’s, firewalls, or RTP relays on the path of - the call. In this case the loopback-source MUST accept media - according to rtp-start-loopback attribute. After the first media - packet is received from the loopback-source, the loopback-mirror - MUST terminate the transmission of rtp-start-loopback media and - MUST start looping back media as defined by the other loopback + section 5.2. One example of this scenario is the presence of an + RTP relay in the path of the media. RTP relays exist in VoIP + networks for purpose of NAT and Firewall traversal. If an RTP + relay is present, the loopback-source's packets are dropped by the + RTP relay until the loopback-mirror has started transmitting media + and the media state within the RTP relay is established. This + loopback attribute is used to specify the media type for + transmitting media packets by the loopback-mirror prior to the + loopback process for the purpose of setting media state within the + network. In the presence of this loopback attribute the loopback- + mirror will transmit media, according to the description that + contains this attribute, until it receives media from the loopback- + source. The loopback-mirror MAY include this attribute in the + answer if it is not present in the offer. This may be necessary if + the loopback-mirror is aware of NAT's, firewalls, or RTP relays on + the path of the call. In this case the loopback-source MUST accept + media according to rtp-start-loopback attribute. After the first + media packet is received from the loopback-source, the loopback- + mirror MUST terminate the transmission of rtp-start-loopback media + and MUST start looping back media as defined by the other loopback attributes present in the offer. If an offer includes the rtp-start-loopback attribute it MUST also include at least one other attribute as defined in this section. The loopback-source is able to filter rtp-start-loopback packets from other types of loopback with the payload type of the packet. The media port number for rtp-start-loopback MUST be the same as the corresponding loopback attribute that will take over after the reception of first media packet from the offering entity. It is recommended that an offering entity specifying media with @@ -299,27 +298,33 @@ like to receive the media stream. The payload type numbers indicate the value of the payload the offerer expects to receive. The RTP payload types indicated in the a=loopback-source line are the payload types for the codecs the offerer is willing to send. However, the answer might indicate a different payload type number for the same codec. In that case, the offerer MUST send the payload type received in the answer. If loopback-type is rtp-pkt-loopback, the loopback-mirror MUST send and the loopback-source MUST receive the looped back packets - encoded in an encapsulated RTP payload as defined in section 7. + encoded in one of the two payload formats (encapsulated RTP or + payload loopback) as defined in section 7. Example: m=audio 41352 RTP/AVP 112 a=loopback:rtp-pkt-loopback a=loopback-source:0 8 a=rtpmap:112 encaprtp/8000 + Example: m=audio 41352 RTP/AVP 112 + a=loopback:rtp-pkt-loopback + a=loopback-source:0 8 + a=rtpmap:112 rtploopback/8000 + Note: NAT devices may change the actual port number that is used for transmission and the expected receive port. 5.4 Generating the Answer for Loopback Session If an answerer wishes to accept the loopback request it MUST include both the loopback mode and loopback type attribute in the answer. If a stream is offered with loopback-source or loopback-mirror attributes, the corresponding stream MUST be loopback-mirror or loopback-source respectively, provided that @@ -348,37 +353,45 @@ a=loopback-source:0 8 The answer that is capable of supporting the offer and chooses to loopback the media using the rtp-media-loopback type MUST contain: m=audio 41352 RTP/AVP 0 8 a=loopback:rtp-media-loopback a=loopback-mirror:0 8 As specified in section 7, if the loopback-type is - rtp-pkt-loopback, the encapsulated RTP payload format MUST be used - for looped back packets. + rtp-pkt-loopback, either the encapsulated RTP payload format or + direct loopback RTP payload format MUST be used for looped back + packets. For example, if the offer contains: - m=audio 41352 RTP/AVP 112 + m=audio 41352 RTP/AVP 112 113 a=loopback:rtp-pkt-loopback a=loopback-source:0 8 a=rtpmap:112 encaprtp/8000 + a=rtpmap:113 rtploopback/8000 - The answer that is capable of supporting the offer MUST contain: + The answer that is capable of supporting the offer MUST contain one + of the following: m=audio 41352 RTP/AVP 112 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 8 a=rtpmap:112 encaprtp/8000 + m=audio 41352 RTP/AVP 113 + a=loopback:rtp-pkt-loopback + a=loopback-mirror:0 8 + a=rtpmap:113 rtploopback/8000 + 5.4.1 Rejecting the Loopback Offer An offered stream with loopback-source MAY be rejected if the loopback-type is not specified, the specified loopback-type is not supported, or the endpoint cannot honor the offer for any other reason. The Loopback request may be rejected by setting the media port number to zero in the answer as per RFC 3264 [RFC3264]. 5.5 Offerer Processing of the Answer @@ -400,47 +413,61 @@ At any point during the loopback session, either participant may issue a new offer to modify the characteristics of the previous session. In case of SIP this is defined in section 8 of RFC 3264 [RFC3264]. This also includes transitioning from a normal media processing mode to loopback mode, and vice a versa. 6. RTP Requirements An answering entity that is compliant to this specification and accepting a media with rtp-pkt-loopback loopback-type MUST loopback - the incoming RTP packets using the encapsulated RTP payload format - as defined in section 7 of this specification. + the incoming RTP packets using either the encapsulated RTP payload + format or the direct loopback RTP payload format as defined in + section 7 of this specification. An answering entity that is compliant to this specification and accepting a media with rtp-media-loopback loopback-type MUST transmit all received media back to the sender. The incoming media MUST be treated as if it were to be played (e.g. the media stream MAY receive treatment from PLC algorithms). The answering entity MUST re-generate all the RTP header fields as it would when transmitting media. The answering entity MAY choose to encode the loopback media according to any of the media descriptions supported by the offering entity. Furthermore, in cases where the same media type is looped back, the answering entity MAY choose to preserve number of frames/packet and bitrate of the encoded media according to the received media. - 7. Payload format for encapsulated RTP Streams + 7. Payload formats for Packet loopback - The payload format described in this section MUST be used by a + The payload formats described in this section MUST be used by a loopback-mirror when rtp-pkt-loopback is the specified - loopback-type. A received RTP packet is encapsulated in the payload - section of the RTP packet generated by a loopback-mirror.Each - received packet MUST be encapsulated in a different packet, the - encapsulated packet MAY be fragmented only if required (for - example: due to MTU limitations). + loopback-type. Two different formats are specified here - an + encapsulated RTP payload format and a direct loopback RTP payload + format. The encapsulated RTP payload format should be used when + the incoming RTP header information needs to be preserved during + the loopback operation. This is useful in cases where loopback + source needs to measure performance metrics in both directions. + However, this comes at the expense of increased packet size as + described in section 7.1. The direct loopback RTP payload format + should be used when bandwidth requirement prevent the use of + encapsulated RTP payload format. - 7.1 Usage of RTP Header fields + 7.1 Encapsulated Payload format + + A received RTP packet is encapsulated in the payload section of the + RTP packet generated by a loopback-mirror. Each received packet + MUST be encapsulated in a different packet, the encapsulated packet + MAY be fragmented only if required (for example: due to MTU + limitations). + + 7.1.1 Usage of RTP Header fields Payload Type (PT): The assignment of an RTP payload type for this packet format is outside the scope of this document; it is either specified by the RTP profile under which this payload format is used or more likely signaled dynamically out-of-band (e.g., using SDP; section 7.3 defines the name binding). Marker (M) bit: If the received RTP packet is looped back in multiple RTP packets, the M bit is set to 1 in the last packet, otherwise it is set to 0. @@ -454,21 +481,21 @@ the loopback-mirror is transmitting this packet to the loopback- source. The RTP timestamp MUST based on the same clock used by the loopback-source. The initial value of the timestamp SHOULD be random for security reasons (see Section 5.1 of RFC 3550 [RFC3550]). SSRC: set as described in RFC 3550 [RFC3550]. CC and CSRC fields are used as described in RFC 3550 [RFC3550]. - 7.2 RTP Payload Structure + 7.1.2 RTP Payload Structure The RTP header in the encapsulated packet MUST be followed by the payload header defined in this section. If the received RTP packet has to be looped back in multiple packets due to fragmentation, the RTP header in each packet MUST be followed by the payload header defined in this section. The header is devised so that the loopback-source can usefully decode looped back packets in the presence of moderate packet loss [RFC3550]. 0 1 2 3 @@ -496,47 +524,102 @@ loopback-mirror is received from the loopback-source. The Receive timestamp MUST be based on the same clock used by the loopback- source. The initial value of the timestamp SHOULD be random for security reasons (see Section 5.1 of RFC 3550 [RFC3550]). Fragmentation (F): 2 bits First Fragment (00) /Last Fragment (01) /No Fragmentation(10)/ Intermediate Fragment (11). This field identifies how much of the received packet is encapsulated in this packet by the loopback- - mirror. If the received packet is not fragmented, this field is set - to 10; otherwise the packet that contains the first fragments sets - this field to 00, the packet that contains the last fragment sets - this field to 01, all other packets set this field to 11. + mirror. If the received packet is not fragmented, this field is + set to 10; otherwise the packet that contains the first fragments + sets this field to 00, the packet that contains the last fragment + sets this field to 01, all other packets set this field to 11. Reserved: 2 bits This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and MUST be ignored by the receiver. Any padding octets in the original packet MUST not be included in - the loopback packet generated by a loopback-mirror. The loopback- - mirror MAY add padding octets if required. + the loopback packet generated by a loopback-mirror. The + loopback-mirror MAY add padding octets if required. - 7.3 Usage of SDP + 7.1.3Usage of SDP The payload type number for the encapsulated stream can be negotiated using a mechanism like SDP. There is no static payload - type assignment for the encapsulate stream, so dynamic payload type - numbers MUST be used. The binding to the name is indicated by an - rtpmap attribute. The name used in this binding is “encaprtp”. + type assignment for the encapsulated stream, so dynamic payload + type numbers MUST be used. The binding to the name is indicated by + an rtpmap attribute. The name used in this binding is "encaprtp". The following is an example SDP fragment for encapsulated RTP. m=audio 41352 RTP/AVP 112 a=rtpmap:112 encaprtp/8000 + + 7.2 Direct loopback RTP payload format + + The direct loopback RTP payload format can be used in scenarios + where the 16 byte overhead of the encapsulated payload format is + significant. It MUST not be used in cases where the MTU on the + loopback path is less than the MTU on the transmit path. When + using this payload format, the receiver MUST loop back each + received packet in a separate RTP packet. + + 7.2.1 Usage of RTP Header fields + + Payload Type (PT): The assignment of an RTP payload type for this + packet format is outside the scope of this document; it is either + specified by the RTP profile under which this payload format is + used or more likely signaled dynamically out-of-band (e.g., using + SDP; section 7.3 defines the name binding). + + Marker (M) bit: Set to the value in the received packet. + + Extension (X) bit: Defined by the RTP Profile used. + + Sequence Number: The RTP sequence number SHOULD be generated by the + loopback-mirror in the usual manner with a constant random offset. + + Timestamp: The RTP timestamp denotes the sampling instant for when + the loopback-mirror is transmitting this packet to the loopback- + source. The RTP timestamp MUST based on the same clock used by the + loopback-source. The initial value of the timestamp SHOULD be + random for security reasons (see Section 5.1 of RFC 3550 + [RFC3550]). + + SSRC: set as described in RFC 3550 [RFC3550]. + + CC and CSRC fields are used as described in RFC 3550 [RFC3550]. + + 7.2.2 RTP Payload Structure + + This payload format does not define any payload specific headers. + The loopback-mirror simply copies the payload data from the payload + portion of the packet received from the loopback-source. + + 7.2.3 Usage of SDP + + The payload type number for the payload loopback stream can be + negotiated using a mechanism like SDP. There is no static payload + type assignment for the stream, so dynamic payload type numbers + MUST be used. The binding to the name is indicated by an rtpmap + attribute. The name used in this binding is "rtploopback". + + The following is an example SDP fragment for encapsulated RTP. + + m=audio 41352 RTP/AVP 112 + a=rtpmap:112 rtploopback/8000 + 8. RTCP Requirements The use of the loopback attribute is intended for monitoring of media quality of the session. Consequently the media performance information should be exchanged between the offering and the answering entities. An offering or answering entity that is compliant to this specification SHOULD support RTCP per [RFC3550] and RTCP-XR per RFC 3611 [RFC3611]. Furthermore, if the client or the server choose to support RTCP-XR, they SHOULD support RTCP-XR Loss RLE report block, Duplicate RLE report block, Statistics @@ -598,24 +681,25 @@ A client sends an INVITE request with SDP which looks like: v=0 o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session e=user@example.com c=IN IP4 192.168.0.12/127 t=0 0 - m=audio 49170 RTP/AVP 0 112 + m=audio 49170 RTP/AVP 0 112 113 a=loopback:rtp-media-loopback rtp-pkt-loopback a=loopback-source:0 a=rtpmap:112 encaprtp/8000 + a=rtpmap:113 rtploopback/8000 The client is offering to source the media and expects the server to mirror the RTP stream at either the media or rtp level. A server sends a response with SDP which looks like: v=0 o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session @@ -619,68 +703,69 @@ o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session e=user@example.com c=IN IP4 192.168.0.12/127 t=0 0 m=audio 49170 RTP/AVP 112 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 a=rtpmap:112 encaprtp/8000 - The server is accepting to mirror the media from the client at the - packet level. + packet level using the encapsulated RTP payload format. 10.3 Offer for choice of media loopback type with rtp-start-loopback A client sends an INVITE request with SDP which looks like: v=0 o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session e=user@example.com c=IN IP4 192.168.0.12/127 t=0 0 - m=audio 49170 RTP/AVP 0 112 + m=audio 49170 RTP/AVP 0 112 113 a=loopback:rtp-media-loopback rtp-pkt-loopback a=loopback-source:0 a=rtpmap:112 encaprtp/8000 + a=rtpmap:113 rtploopback/8000 m=audio 49170 RTP/AVP 100 a=loopback:rtp-start-loopback The client is offering to source the media and expects the server to mirror the RTP stream at either the media or rtp level. The client also expects the server to source media until it receives packets from the server per media described with the rtp-start-loopback attribute. A server sends a response with SDP which looks like: v=0 o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session e=user@example.com c=IN IP4 192.168.0.12/127 t=0 0 - m=audio 49170 RTP/AVP 112 + m=audio 49170 RTP/AVP 113 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 - a=rtpmap:112 encaprtp/8000 + a=rtpmap:113 rtploopback/8000 m=audio 49170 RTP/AVP 100 a=rtpmap:100 pcmu/8000 a=loopback:rtp-start-loopback The server is accepting to mirror the media from the client at the - packet level. The server is also accepting to source media until - it receives media packets from the client. + packet level using the direct loopback RTP payload format. The + server is also accepting to source media until it receives media + packets from the client. 10.4 Response to INVITE request rejecting loopback media A client sends an INVITE request with SDP which looks like: v=0 o=user1 2890844526 2890842807 IN IP4 126.16.64.4 s=Example i=An example session e=user@example.com @@ -786,35 +872,35 @@ [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3611] Almeroth, K., Caceres, R., Clark, A., Cole, R., Duffield, N., Friedman, T., Hedayat, K., Sarac, K. and M. Westerlund, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [RFC2234] Crocker, P. Overell, "Augmented ABNF for Syntax - Specification: ABNF”, RFC 2234, November 1997. + Specification: ABNF", RFC 2234, November 1997. [RFC2119] Bradner, S.,"Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2736] Handley, M., Perkins, C., "Guidelines for Writers of - RTP Payload Format Specifications”, RFC 2736, BCP + RTP Payload Format Specifications", RFC 2736, BCP 0036, December 1999. [RFC3551] Schulzrinne, H., Casner, S., "RTP Profile for Audio - and Video Conferences with Minimial Control”, STD 65, + and Video Conferences with Minimial Control", STD 65, RFC 3551, July 2003. [RFC4566] Handley, M., Jacobson, V., Perkins, C., "SDP: Session - Description Protocol”, RFC 4566, July 2006. + Description Protocol", RFC 4566, July 2006. Authors' Addresses Kaynam Hedayat Brix Networks 285 Mill Road Chelmsford, MA 01824 US Phone: +1 978 367 5611