[Docs] [txt|pdf] [draft-ietf-fecfra...] [Diff1] [Diff2]

INFORMATIONAL

Internet Engineering Task Force (IETF)                          R. Asati
Request for Comments: 6695                                 Cisco Systems
Category: Informational                                      August 2012
ISSN: 2070-1721


            Methods to Convey Forward Error Correction (FEC)
                  Framework Configuration Information

Abstract

   The Forward Error Correction (FEC) Framework document (RFC 6363)
   defines the FEC Framework Configuration Information necessary for the
   FEC Framework operation.  This document describes how to use
   signaling protocols such as the Session Announcement Protocol (SAP),
   the Session Initiation Protocol (SIP), the Real Time Streaming
   Protocol (RTSP), etc. for determining and communicating the
   configuration information between sender(s) and receiver(s).

   This document doesn't define any new signaling protocol.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6695.















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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Specification Language ..........................................3
   3. Terminology/Abbreviations .......................................3
   4. FEC Framework Configuration Information .........................4
      4.1. Encoding Format ............................................5
   5. Signaling Protocol Usage ........................................6
      5.1. Signaling Protocol for Multicasting ........................7
           5.1.1. Sender Procedure ....................................9
           5.1.2. Receiver Procedure .................................11
      5.2. Signaling Protocol for Unicasting .........................12
           5.2.1. SIP ................................................12
           5.2.2. RTSP ...............................................13
   6. Security Considerations ........................................14
   7. IANA Considerations ............................................14
   8. Acknowledgments ................................................14
   9. References .....................................................14
      9.1. Normative References ......................................14
      9.2. Informative References ....................................15

1.  Introduction

   The FEC Framework document [RFC6363] defines the FEC Framework
   Configuration Information that governs the overall FEC Framework
   operation common to any FEC scheme.  This information must be
   available at both the sender and receiver(s).

   This document describes how various signaling protocols such as the
   Session Announcement Protocol (SAP) [RFC2974], the Session Initiation
   Protocol (SIP) [RFC3261], the Real Time Streaming Protocol (RTSP)
   [RFC2326], etc. could be used by the FEC scheme (and/or the Content
   Delivery Protocol (CDP)) to communicate the configuration information



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   between the sender and receiver(s).  The configuration information
   may be encoded in any compatible format, such as the Session
   Description Protocol (SDP) [RFC4566], XML, etc., though this document
   refers to SDP encoding usage quite extensively.

      Note that this document doesn't define any new signaling protocol;
      rather, it just provides examples of how existing protocols should
      be used.  Also, the list of signaling protocols for unicast is not
      intended to be a complete list.

   This document doesn't describe any FEC-Scheme-Specific Information
   (FSSI) (for example, how source blocks are constructed) or any
   sender- or receiver-side operation for a particular FEC scheme (for
   example, whether the receiver makes use of one or more repair flows
   that are received).  Such FEC scheme specifics should be covered in
   separate document(s).  This document doesn't mandate a particular
   encoding format for the configuration information either.

   This document is structured as follows: Section 3 describes the terms
   used in this document, Section 4 describes the FEC Framework
   Configuration Information, Section 5 describes how to use signaling
   protocols for multicast and unicast applications, and Section 6
   discusses security considerations.

2.  Specification Language

   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 [RFC2119].

3.  Terminology/Abbreviations

   This document makes use of the terms/abbreviations defined in the FEC
   Framework document [RFC6363] and defines the following additional
   terms:

   o  Media Sender - Node providing original media flow(s) to the 'FEC
      Sender'

   o  Media Receiver - Node performing the media decoding

   o  FEC Sender - Node performing the FEC encoding on the original
      media flow(s) to produce the FEC repair flow(s)

   o  FEC Receiver - Node performing the FEC decoding, as needed, and
      providing the original media flow(s) to the Media Receiver

   o  Sender - Same as FEC Sender



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   o  Receiver - Same as FEC Receiver

   o  (Media) Flow - A single media instance, i.e., an audio stream or a
      video stream

   This document deliberately refers to the 'FEC Sender' and 'FEC
   Receiver' as the 'Sender' and 'Receiver', respectively.

4.  FEC Framework Configuration Information

   The FEC Framework [RFC6363] defines a minimum set of information that
   is communicated between the sender and receiver(s) for a proper
   operation of an FEC scheme.  This information is referred to as "FEC
   Framework Configuration Information".  This is the information that
   the FEC Framework needs in order to apply FEC protection to the
   transport flows.

   A single instance of the FEC Framework provides FEC protection for
   all packets of a specified set of source packet flows, by means of
   one or more packet flows consisting of repair packets.  As per
   Section 5.5 of the FEC Framework document [RFC6363], the FEC
   Framework Configuration Information includes the following for each
   FEC Framework instance:

   1. Identification of the repair flow(s)

   2. Identification of source flow(s)

   3. Identification of FEC scheme

   4. Length of Explicit Source FEC Payload ID

   5. FSSI

   FSSI basically provides an opaque container to encode FEC-scheme-
   specific configuration information such as buffer size, decoding
   wait-time, etc.  Please refer to the FEC Framework document [RFC6363]
   for more details.

   The usage of signaling protocols described in this document requires
   that the application layer responsible for the FEC Framework instance
   provide the value for each of the configuration information
   parameters (listed above) encoded as per the chosen encoding format.
   In case of failure to receive the complete information, the signaling
   protocol module must return an error for Operations, Administration,
   and Maintenance (OAM) purposes and optionally convey this error to
   the application layer.  Please refer to Figure 1 of the FEC Framework
   document [RFC6363] for further illustration.



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   This document does not make any assumption that the 'FEC Sender' and
   'Media Sender' functionalities are implemented on the same device,
   though that may be the case.  Similarly, this document does not make
   any assumption that 'FEC Receiver' and 'Media Receiver'
   functionalities are implemented on the same device, though that may
   be the case.  There may also be more than one Media Sender.

4.1.  Encoding Format

   The FEC Framework Configuration Information (listed above in
   Section 4) may be encoded in any format, such as SDP, XML, etc., as
   chosen or preferred by a particular FEC Framework instance.  The
   selection of such encoding formats or syntax is independent of the
   signaling protocol and beyond the scope of this document.

   Any encoding format that is selected for a particular FEC Framework
   instance must be known to the signaling protocol.  This is to provide
   a means (e.g., a field such as Payload Type) in the signaling
   protocol message(s) to convey the chosen encoding format for the
   configuration information so that the payload (i.e., configuration
   information) can be correctly parsed as per the semantics of the
   chosen encoding format at the receiver.  Please note that the
   encoding format is not a negotiated parameter, but rather a property
   of a particular FEC Framework instance and/or its implementation.

   Additionally, the encoding format for each FEC Framework
   configuration parameter must be defined in terms of a sequence of
   octets that can be embedded within the payload of the signaling
   protocol message(s).  The length of the encoding format must either
   be fixed or be derived by examining the encoded octets themselves.
   For example, the initial octets may include some kind of length
   indication.

   Independent of the encoding formats supported by an FEC scheme, each
   instance of the FEC Framework must use a single encoding format to
   describe all of the configuration information associated with that
   instance.  The signaling protocol specified in this document should
   not validate the encoded information, though it may validate the
   syntax or length of the encoded information.

   The reader may refer to the SDP elements document [RFC6364], which
   describes the usage of the 'SDP' encoding format as an example
   encoding format for the FEC Framework Configuration Information.








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5.  Signaling Protocol Usage

   The FEC Framework [RFC6363] requires that certain FEC Framework
   Configuration Information be available to both the sender and
   receiver(s).  This configuration information is almost always
   formulated at the sender (or on behalf of the sender) and somehow
   made available at the receiver(s).  While one may envision a static
   method to populate the configuration information at both the sender
   and receiver(s), it would not be optimal, since it would (a) require
   the knowledge of every receiver in advance, (b) require the time and
   means to configure each receiver and sender, and (c) increase the
   possibility of misconfiguration.  Hence, there is a benefit in using
   a dynamic method (i.e., signaling protocol) to convey the
   configuration information between the sender and one or more
   receivers.

   Since the configuration information may be needed at a particular
   receiver versus many receivers (depending on the multimedia stream
   being unicast (e.g., Video on Demand (VoD); or multicast, e.g.,
   broadcast or IPTV), we need two types of signaling protocols -- one
   to deliver the configuration information to many receivers via
   multicasting (as described in Section 5.1), and the other to deliver
   the configuration information to one and only one receiver via
   unicasting (as described in Section 5.2).

   Figure 1 below illustrates a sample topology showing the FEC Sender
   and FEC Receiver (which may or may not be the Media Sender and Media
   Receiver, respectively) such that FEC_Sender1 is serving
   FEC_Receiver11, FEC_Receiver12, and FEC_Receiver13 via the multicast
   signaling protocol, whereas FEC_Sender2 is serving only FEC_Receiver2
   via the unicast signaling protocol.

          FEC_Sender2---------|         |--------FEC_Receiver2
                              |         |
          FEC_Sender1-------IP/MPLS network
                                  |-----------FEC_Receiver11
                                  |-----------FEC_Receiver12
                                  |-----------FEC_Receiver13

               Figure 1.  Topology Using Sender and Receiver

   The rest of the document continues to use the terms 'Sender' and
   'Receiver' to refer to the 'FEC Sender' and 'FEC Receiver',
   respectively.







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5.1.  Signaling Protocol for Multicasting

   This specification describes using SAP version 2 [RFC2974] as the
   signaling protocol to multicast the configuration information from
   one sender to many receivers.  The apparent advantage is that the
   server doesn't need to maintain any state for any receiver using SAP.

      SAP messages are carried over UDP over IP with destination UDP
      port 9875, as described in [RFC2974], and a source UDP port of any
      available number.  The SAP message(s) MUST contain an
      authentication header using Pretty Good Privacy (PGP)
      authentication.

   At the high level, a sender, acting as the SAP announcer, signals the
   FEC Framework Configuration Information for each FEC Framework
   instance available at the sender, using the SAP message(s).  The
   configuration information, encoded in a suitable format as per
   Section 4.1, is carried in the payload of the SAP message(s).  A
   receiver, acting as the SAP listener, listens on a well-known UDP
   port and at least one well-known multicast group IP address (as
   explained in Section 5.1.1).  This enables the receiver to receive
   the SAP message(s) and obtain the FEC Framework Configuration
   Information for each FEC Framework instance.

   Using the configuration information, the receiver becomes aware of
   available FEC protection options, corresponding multicast trees (S,G
   or *,G addresses), etc.  The receiver may subsequently subscribe to
   one or more multicast trees to receive the FEC streams using out-of-
   band multicasting techniques such as PIM [RFC4601].  This, however,
   is outside the scope of this document.





















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   Figure 2 below (reprinted from [RFC2974]) illustrates the SAP packet
   format.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | V=1 |A|R|T|E|C|   auth len    |         msg id hash           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                originating source (32 or 128 bits)            :
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    optional authentication data               |
     :                              ....                             :
     *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
     |                      optional payload type                    |
     +                                         +-+- - - - - - - - - -+
     |                                         |0|                   |
     + - - - - - - - - - - - - - - - - - - - - +-+                   |
     |                                                               |
     :                            payload                            :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2.  SAP Message Format

   While [RFC2974] includes explanations for each field, it is worth
   discussing the 'Payload' and 'Payload Type' fields.  The 'Payload'
   field is used to carry the FEC Framework Configuration Information.
   Subsequently, the optional 'Payload Type' field, which is a MIME
   content type specifier, is used to describe the encoding format used
   to encode the payload.

      For example, the 'Payload Type' field may be application/sdp if
      the FEC Framework Configuration Information is encoded in SDP
      format and carried in the SAP payload.  Similarly, it would be
      application/xml if the FEC Framework Configuration Information
      were encoded in XML format.

   Section 5.1.1 describes the sender procedure, whereas Section 5.1.2
   describes the receiver procedure in the context of config signaling
   using [RFC2974].









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5.1.1.  Sender Procedure

   The sender signals the FEC Framework Configuration Information for
   each FEC Framework instance in a periodic SAP announcement message
   [RFC2974].  The SAP announcement message is sent to a well-known
   multicast IP address and UDP port, as specified in [RFC2974].  The
   announcement is multicast with the same scope as the session being
   announced.

   The SAP module at the sender obtains the FEC Framework Configuration
   Information per instance from the 'FEC Framework' module and places
   that in the SAP payload accordingly.  A single SAP (announcement)
   message must carry the FEC Framework Configuration Information for a
   single FEC Framework instance.  The SAP message is then sent over UDP
   over IP.

      While it is possible to aggregate multiple SAP (announcement)
      messages in a single UDP datagram as long as the resulting UDP
      datagram length is less than the IP MTU of the outgoing interface,
      this specification does not recommend it, since there is no length
      field in the SAP header to identify a SAP message boundary.
      Hence, this specification recommends that a single SAP
      announcement message be sent in a UDP datagram.

   The IP packet carrying the SAP message must be sent to a destination
   IP address of one of the following, depending on the selected scope:

   - 224.2.127.254 (if IPv4 global scope 224.0.1.0-238.255.255.255 is
     selected for the FEC stream), or

   - ff0x:0:0:0:0:0:2:7ffe (if IPv6 multicasting is selected for the FEC
     stream, where x is the 4-bit scope value), or

   - the highest multicast address (239.255.255.255, for example) in the
     relevant administrative scope zone (if IPv4 administrative scope
     239.0.0.0-239.255.255.255 is selected for the FEC stream)

   As defined in [RFC2974], the IP packet carrying a SAP message must
   use destination UDP port 9875 and a source UDP port of any available
   number.  The default IP Time to Live (TTL) value (or Hop Limit value)
   should be 255 at the sender, though the sender implementation may
   allow it to be any other value to implicitly create the multicast
   boundary for SAP announcements.  The IP Differentiated Services Code
   Point (DSCP) field may be set to any value that indicates a desired
   QoS treatment in the IP network.






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   The IP packet carrying the SAP message must be sent with a source IP
   address that is reachable by the receiver.  The sender may assign the
   same IP address in the 'originating source' field of the SAP message
   as that used in the source IP address of the IP packet.

   Furthermore, the FEC Framework Configuration Information must not
   include any of the reserved multicast group IP addresses for the FEC
   streams (i.e., source or repair flows), though it may use the same IP
   address as the 'originating source' address to identify the FEC
   streams (i.e., source or repair flows).  Please refer to IANA
   assignments for multicast addresses.

   The sender must periodically send the 'SAP announcement' message to
   ensure that the receiver doesn't purge the cached entry or entries
   from the database and doesn't trigger the deletion of the FEC
   Framework Configuration Information.

   While the time interval between repetitions of an announcement can be
   calculated as per the very sophisticated but complex method explained
   in [RFC2974], this document recommends a simpler method in which the
   user specifies the time interval in the range of 1-200 seconds, with
   a suggested default value of 60 seconds.  In this method, the 'time
   interval' may be signaled in the SAP message payload, e.g., within
   the FEC Framework Configuration Information.

      Note that SAP doesn't allow the time interval to be signaled in
      the SAP header.  Hence, the usage of a simpler method requires
      that the time interval be included in the FEC Framework
      Configuration Information if the default time interval (60
      seconds) for SAP message repetitions is not used.  For example,
      the usage of the 'r=' (repeat time) field in SDP may convey the
      time interval value if the SDP encoding format is used.

   The time interval must be chosen to ensure that SAP announcement
   messages are sent out before the corresponding multicast routing
   entry, e.g., (S,G) or (*,G) (corresponding to the SAP multicast
   tree(s)) on the router(s) times out.  (It is worth noting that the
   default timeout period for the multicast routing entry is
   210 seconds, per the PIM specification [RFC4601], though the timeout
   period may be set to another value as allowed by the router
   implementation.)

      A SAP implementation may also support the complex method for
      determining the SAP announcement time interval and provide the
      option to select it.






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   The sender may choose to delete the announced FEC Framework
   Configuration Information, as defined in Section 4 of [RFC2974].  The
   explicit deletion is useful if the sender no longer desires to send
   any more FEC streams.

   If the sender needs to modify the announced FEC Framework
   Configuration Information for one or more FEC instances, then the
   sender must send a new announcement message with a different 'Message
   Identifier Hash' value as per the rules described in Section 5 of
   RFC 2974 [RFC2974].  Such an announcement message should be sent
   immediately (without having to wait for the time interval) to ensure
   that the modifications are received by the receiver as soon as
   possible.  The sender must also send the SAP deletion message to
   delete the previous SAP announcement message (i.e., with the previous
   'Message Identifier Hash' value).

5.1.2.  Receiver Procedure

   The receiver must listen on UDP port 9875 for packets arriving with
   an IP destination address of either 224.2.127.254 (if an IPv4 global
   scope session is used for the FEC stream), ff0x:0:0:0:0:0:2:7ffe (if
   IPv6 is selected, where x is the 4-bit scope value), or the highest
   IP address (239.255.255.255, for example) in the relevant
   administrative scope zone (if IPv4 administrative scope 239.0.0.0-
   239.255.255.255 is selected for the FEC stream).  These IP addresses
   are mandated for SAP usage by RFC 2974 [RFC2974].

   The receiver, upon receiving a SAP announcement message, creates an
   entry, if it doesn't already exist, in a local database and passes
   the FEC Framework Configuration Information from the SAP Payload
   field to the 'FEC Framework' module.  Each entry also maintains a
   timeout value, which is (re)set to five times the time interval
   value, which in turn is either the default of 60 seconds or the value
   signaled by the sender.

      Note that SAP doesn't allow the time interval to be signaled in
      the SAP header.  Hence, the time interval should be included in
      the FEC Framework Configuration Information -- for example, the
      usage of the 'r=' (repeat time) field in SDP to convey the time
      interval value if the SDP encoding format is used.

   The timeout value associated with each entry is reset when the
   corresponding announcement (please see Section 5 of [RFC2974]) is
   received.  If the timeout value for any entry reaches zero, then that
   entry must be deleted from the database, as described in Section 4 of
   [RFC2974].  The receiver, upon receiving a SAP delete message, must
   delete the matching SAP entry in its database, as described in
   Section 4 of [RFC2974].



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   The deletion of a SAP entry must result in the receiver no longer
   using the relevant FEC Framework Configuration Information for the
   corresponding instance and no longer subscribing to any related FEC
   streams.

5.2.  Signaling Protocol for Unicasting

   This document describes leveraging any signaling protocol that is
   already used by the unicast application, for exchanging the FEC
   Framework Configuration Information between two nodes.

   For example, a multimedia (VoD) client may send a request via
   unicasting for a particular content to the multimedia (VoD) server,
   which may offer various options such as encodings, bitrates,
   transport, etc. for the content.  The client selects the suitable
   options and answers the server, paving the way for the content to be
   unicast on the chosen transport from the server to the client.  This
   offer/answer signaling, described in [RFC3264], is commonly utilized
   by many application protocols, such as SIP, RTSP, etc.

   The fact that two nodes desiring unicast communication almost always
   rely on an application to first exchange the application-related
   parameters via the signaling protocol makes it logical to enhance
   such signaling protocol(s) to (a) convey the desire for the FEC
   protection and (b) subsequently also exchange FEC parameters, i.e.,
   the FEC Framework Configuration Information.  This enables the node
   acting as the offerer to offer 'FEC Framework Configuration
   Information' for each available FEC instance and the node acting as
   the answerer to convey the chosen FEC Framework instance(s) to the
   offerer.  The usage of the FEC Framework instance is explained in the
   FEC Framework document [RFC6363].

   While enhancing an application's signaling protocol to exchange FEC
   parameters is one method (briefly explained above), an alternative
   method would be to have a unicast-based generic protocol that could
   be used by two nodes, independent of the application's signaling
   protocol.  The latter is not covered by this document, of course.

   The remainder of this section provides example signaling protocols
   and explains how they can be used to exchange the FEC Framework
   Configuration Information.

5.2.1.  SIP

   SIP [RFC3261] is an application-level signaling protocol to create,
   modify, and terminate multimedia sessions with one or more
   participants.  SIP also enables the participants to discover one
   another and to agree on a characterization of a multimedia session



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   they would like to share.  SIP runs on either TCP, UDP, or Stream
   Control Transmission Protocol (SCTP) transport and uses SDP as the
   encoding format to describe multimedia session attributes.

   SIP already uses an offer/answer model with SDP as described in
   [RFC3264] to exchange information between two nodes to establish
   unicast sessions between them.  This document extends the usage of
   this model for exchanging the FEC Framework Configuration Information
   (described in Section 4).  Any SDP-specific enhancements to
   accommodate the FEC Framework are covered in the SDP elements
   specification [RFC6364].

5.2.2.  RTSP

   RTSP [RFC2326] is an application-level signaling protocol for control
   over 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.  RTSP runs on either TCP or
   UDP transports.

   RTSP already provides an ability to extend the existing method with
   new parameters.  This specification defines the
   'FEC-protection-needed' option tag (please see Section 7 for IANA
   Considerations) and prescribes including it in the Require (or
   Proxy-Require) header of SETUP (method) request messages, so as to
   request FEC protection for the data.

   The node receiving such a request either responds with a '200 OK'
   message that includes offers, i.e., available FEC options (e.g., FEC
   Framework Configuration Information for each instance) or a '551
   Option not supported' message.  A sample of a related message
   exchange is shown below.

      Node1->Node2:  SETUP < ... > RTSP/1.0
                     CSeq: 1
                     Transport: <omitted for simplicity>
                     Require: FEC-protection-needed

      Node2->Node1:  RTSP/1.0 200 OK
                     CSeq: 1
                     Transport: <omitted for simplicity>

   The requesting node (Node1) may then send a new SETUP message to
   convey the selected FEC protection to Node2 and proceed with regular
   RTSP messaging.






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   Suffice it to say that if the requesting node (Node1) received a '551
   Option not supported' response from Node2, then the requesting node
   (Node1) may send the SETUP message without using the Require header.

6.  Security Considerations

   This document recommends that SAP message(s) be authenticated to
   ensure sender authentication, as described in Section 5.1.

   There are no additional security considerations other than those
   already covered in [RFC2974] for SAP, [RFC2326] for RTSP, and
   [RFC3261] for SIP.

7.  IANA Considerations

   IANA has registered a new RTSP option tag (option-tag), listed below,
   in the RTSP/1.0 Option Tags table of the "Real Time Streaming
   Protocol (RTSP)/1.0 Parameters" registry available from
   http://www.iana.org/, and it provides the following information in
   compliance with Section 3.8.1 of [RFC2326]:

      o  Name of option-tag:  FEC-protection-needed

      o  Description:         See Section 5.2.2

      o  Change Control:      IETF

8.  Acknowledgments

   Thanks to Colin Perkins for pointing out the issue with the time
   interval for the SAP messages.  Additionally, thanks to Vincent Roca,
   Ali Begen, Mark Watson, Ulas Kozat, and David Harrington for greatly
   improving this document.

9.  References

9.1.  Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2974]   Handley, M., Perkins, C., and E. Whelan, "Session
               Announcement Protocol", RFC 2974, October 2000.








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RFC 6695             FEC Framework Config Signaling          August 2012


   [RFC6363]   Watson, M., Begen, A., and V. Roca, "Forward Error
               Correction (FEC) Framework", RFC 6363, October 2011.

   [RFC6364]   Begen, A., "Session Description Protocol Elements for the
               Forward Error Correction (FEC) Framework", RFC 6364,
               October 2011.

9.2.  Informative References

   [RFC2326]   Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
               Streaming Protocol (RTSP)", RFC 2326, April 1998.

   [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.

   [RFC3264]   Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
               with Session Description Protocol (SDP)", RFC 3264,
               June 2002.

   [RFC4566]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
               Description Protocol", RFC 4566, July 2006.

   [RFC4601]   Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
               "Protocol Independent Multicast - Sparse Mode (PIM-SM):
               Protocol Specification (Revised)", RFC 4601, August 2006.

Author's Address

   Rajiv Asati
   Cisco Systems
   7025-6 Kit Creek Rd.
   RTP, NC  27709-4987

   EMail: rajiva@cisco.com















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