GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6695

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.

Asati Informational [Page 1] RFC 6695 FEC Framework Config Signaling August 2012

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

Asati Informational [Page 2] RFC 6695 FEC Framework Config Signaling August 2012

 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

Asati Informational [Page 3] RFC 6695 FEC Framework Config Signaling August 2012

 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.

Asati Informational [Page 4] RFC 6695 FEC Framework Config Signaling August 2012

 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.

Asati Informational [Page 5] RFC 6695 FEC Framework Config Signaling August 2012

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.

Asati Informational [Page 6] RFC 6695 FEC Framework Config Signaling August 2012

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.

Asati Informational [Page 7] RFC 6695 FEC Framework Config Signaling August 2012

 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].

Asati Informational [Page 8] RFC 6695 FEC Framework Config Signaling August 2012

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:
  1. 224.2.127.254 (if IPv4 global scope 224.0.1.0-238.255.255.255 is

selected for the FEC stream), or

  1. 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

  1. 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.

Asati Informational [Page 9] RFC 6695 FEC Framework Config Signaling August 2012

 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.

Asati Informational [Page 10] RFC 6695 FEC Framework Config Signaling August 2012

 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].

Asati Informational [Page 11] RFC 6695 FEC Framework Config Signaling August 2012

 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

Asati Informational [Page 12] RFC 6695 FEC Framework Config Signaling August 2012

 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.

Asati Informational [Page 13] RFC 6695 FEC Framework Config Signaling August 2012

 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.

Asati Informational [Page 14] 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

Asati Informational [Page 15]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6695.txt · Last modified: 2012/08/02 18:27 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki