[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-watson-fecframe-rtp-raptor) 00 01 02 03 04 05 06 07 RFC 6682

FEC Framework Working Group                                    M. Watson
Internet-Draft                                                   Netflix
Intended status: Standards Track                          T. Stockhammer
Expires: May 29, 2011                                     Nomor Research
                                                       November 25, 2010


                   RTP Payload Format for Raptor FEC
                   draft-ietf-fecframe-rtp-raptor-04

Abstract

   This document specifies an RTP payload format for Forward Error
   Correction /(FEC) repair data produced by the Raptor FEC schemes.
   Raptor FEC schemes are specified for use with the IETF FEC Framework
   which supports transport of repair data over both UDP and RTP.  This
   document specifies the payload format which is required for the use
   of RTP to carry Raptor repair flows.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 29, 2011.

Copyright Notice

   Copyright (c) 2010 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



Watson & Stockhammer      Expires May 29, 2011                  [Page 1]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions, Definitions and Acronyms  . . . . . . . . . . . .  4
   3.  Media Format Background  . . . . . . . . . . . . . . . . . . .  5
   4.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  RTP Header Usage . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Payload Header . . . . . . . . . . . . . . . . . . . . . .  6
     4.3.  Payload Data . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Media Types  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Registration of the application/raptorfec media type . . .  7
       5.1.1.  Media Type Definition  . . . . . . . . . . . . . . . .  7
     5.2.  Registration of the video/raptorfec media type . . . . . .  8
       5.2.1.  Media Type Definition  . . . . . . . . . . . . . . . .  8
     5.3.  Registration of the audio/raptorfec media type . . . . . . 10
       5.3.1.  Media Type Definition  . . . . . . . . . . . . . . . . 10
     5.4.  Registration of the text/raptorfec media type  . . . . . . 12
       5.4.1.  Media Type Definition  . . . . . . . . . . . . . . . . 12
   6.  Mapping to SDP Parameters  . . . . . . . . . . . . . . . . . . 14
   7.  Offer/Answer considerations  . . . . . . . . . . . . . . . . . 15
   8.  Declarative SDP Considerations . . . . . . . . . . . . . . . . 16
   9.  FEC Generation and Recovery Procedures . . . . . . . . . . . . 17
     9.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.2.  Repair Packet Construction . . . . . . . . . . . . . . . . 17
     9.3.  Source Packet Reconstruction . . . . . . . . . . . . . . . 17
   10. Session Description Protocol (SDP) Example . . . . . . . . . . 18
   11. Congestion Control Considerations  . . . . . . . . . . . . . . 19
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 23
     15.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25













Watson & Stockhammer      Expires May 29, 2011                  [Page 2]

Internet-Draft        RTP Payload Format for Raptor        November 2010


1.  Introduction

   The FEC Framework [I-D.ietf-fecframe-framework] defines a general
   framework for the use of Forward Error Correction (FEC) in
   association with arbitrary packet flows, including flows over UDP and
   RTP [RFC3550].  FECs operates by generating repair data packets
   ("repair data") which are sent separately from the source flow.  At a
   receiver the source flow can be reconstructed provided a sufficient
   set of source and repair data packets are received.

   The FEC Framework provides for independence between application
   protocols and FEC codes.  The use of a particular FEC code within the
   framework is defined by means of an FEC scheme which may then be used
   with any application protocol compliant to the framework.

   Repair data flows may be sent directly over a transport protocol such
   as UDP, or they may be encapsulated within RTP.  In the latter case,
   an RTP payload format must be defined for each FEC scheme.

   This document defines the RTP payload format for the Raptor FEC
   schemes defined in [I-D.ietf-fecframe-raptor].






























Watson & Stockhammer      Expires May 29, 2011                  [Page 3]

Internet-Draft        RTP Payload Format for Raptor        November 2010


2.  Conventions, Definitions and Acronyms

   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].














































Watson & Stockhammer      Expires May 29, 2011                  [Page 4]

Internet-Draft        RTP Payload Format for Raptor        November 2010


3.  Media Format Background

   The Raptor and RaptorQ codes are efficient block-based fountain
   codes, meaning that from any group of source packets (or 'source
   block') an arbitrary number of repair packets may be generated.  The
   Raptor and RaptorQ codes have the property that the original group of
   source symbols can be recovered with very high probability from any
   set of symbols (source and repair) only slightly greater in number
   than the original number of source symbols.  The RaptorQ code
   additionally has the property that the probability that the original
   group of source symbols can be recovered from a set of symbols
   (source and repair) equal in number to the original number of source
   symbols is in many cases also very high.

   [I-D.ietf-fecframe-raptor] defines six FEC schemes for the use of the
   Raptor and RaptorQ codes with arbitary packet flows: the first two
   schemes are fully applicable to arbitary packet flows (using Raptor
   and RaptorQ respectively).  The third and fourth schemes are slightly
   optimised versions of the first two schemes which are applicable in
   applications with relatively small block sizes.  The fifth and sixth
   schemes are variants of the third and fourth schemes which are
   applicable to a single source flow which already has some kind of
   identifiable sequence number.  The presence of a sequence number in
   the source flow allows for backwards compatible operation (the source
   flows do not need to be modified in order to apply FEC).  In this
   case, in the language of the FEC Framework, there is no need for an
   Explicit FEC Source Payload ID and it is therefore not included in
   the packets.

   This document specifcies the payload format for RTP repair flows and
   can be used with any of the FEC schemes defined in
   [I-D.ietf-fecframe-raptor].



















Watson & Stockhammer      Expires May 29, 2011                  [Page 5]

Internet-Draft        RTP Payload Format for Raptor        November 2010


4.  Payload Format

4.1.  RTP Header Usage

   The following rules SHALL be followed for the RTP header used with
   FEC repair packets:

   o  Marker bit: The marker bit SHALL be set 1 for the last protection
      RTP packet sent for each source block, and otherwise set to 0

   o  Timestamp: The timestamp SHALL be set to a time corresponding to
      the packet's transmission time.  The timestamp value has no use in
      the actual FEC protection process.  It may be used for packet
      arrival timing and jitter calculations.  The timestamp rate SHALL
      be specified using the "rate" media type parameter defined below.

   Other header fields SHALL be set according to the rules of [RFC3550].

4.2.  Payload Header

   There is no Payload Header in this payload format.

4.3.  Payload Data

   Procedures and data formats for the use of Raptor FEC in an FECFRAME
   context are fully defined in [I-D.ietf-fecframe-raptor] and are not
   duplicated here.  The procedures of those documents SHALL be followed
   in order to generate repair data streams to be carried by the payload
   formats defined in this document.

   The RTP Payload SHALL contain an FEC Repair Payload as defined in
   [I-D.ietf-fecframe-framework] and [I-D.ietf-fecframe-raptor].



















Watson & Stockhammer      Expires May 29, 2011                  [Page 6]

Internet-Draft        RTP Payload Format for Raptor        November 2010


5.  Media Types

5.1.  Registration of the application/raptorfec media type

   This RTP payload format is identified using the application/raptorfec
   media type which is registered in accordance with [RFC4855] and using
   the template of [RFC4288].

5.1.1.  Media Type Definition

   Type name: application

   Subtype name: raptorfec

   Required parameters:

   o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
      SHALL be larger than 1000 to provide sufficient resolution to RTCP
      operations.  However, it is RECOMMENDED to select the rate that
      matches the rate of the protected source RTP stream.

   o  raptor-scheme-id: The value of this parameter is the FEC scheme Id
      for the specific Raptor FEC scheme that will be used as defined in
      [I-D.ietf-fecframe-raptor].

   o  Kmax: The value of this parameter is the FEC Framework
      Configuration Information element "Maximum Source Block Length" as
      defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
      integer.  For specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  T: The value of this parameter is the FEC Framework Configuration
      Information element "Encoding Symbol Size" as defined in
      [I-D.ietf-fecframe-raptor] encoded as a decimal integer.  For
      specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  repair-window: The maximum time that spans the source packets and
      the corresponding repair packets.  The size of the repair window
      is specified in microseconds.

   Optional parameters:

   o  P: The value of this parameter is the FEC Framework Configuration
      Information element "Payload ID Format" as defined in
      [I-D.ietf-fecframe-raptor].  If this parameter is missing then the
      value "A" shall be assumed.




Watson & Stockhammer      Expires May 29, 2011                  [Page 7]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   Encoding considerations: This media type is framed and binary, see
   section 4.8 in [RFC4288]

   Security considerations: Please see security consideration in
   [I-D.ietf-fecframe-framework]

   Interoperability considerations: None

   Published specification: [I-D.ietf-fecframe-raptor]

   Applications that use this media type:

   Additional information:

   Magic number(s): <none defined>

   File extension(s): <none defined>

   Macintosh file type code(s): <none defined>

   Person & email address to contact for further information: Mark
   Watson, watsonm@netflix.com

   Intended usage: COMMON

   Restrictions on usage: This media type depends on RTP framing, and
   hence is only defined for transfer via RTP [[RFC3550]].  Transport
   within other framing protocols is not defined at this time.

   Author: Mark Watson, Netflix

   Change controller: IETF Audio/Video Transport working group delegated
   from the IESG.

5.2.  Registration of the video/raptorfec media type

   This RTP payload format is identified using the video/raptorfec media
   type which is registered in accordance with [RFC4855] and using the
   template of [RFC4288].

5.2.1.  Media Type Definition

   Type name: video

   Subtype name: raptorfec

   Required parameters:




Watson & Stockhammer      Expires May 29, 2011                  [Page 8]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
      SHALL be larger than 1000 to provide sufficient resolution to RTCP
      operations.  However, it is RECOMMENDED to select the rate that
      matches the rate of the protected source RTP stream.

   o  raptor-scheme-id: The value of this parameter is the FEC scheme Id
      for the specific Raptor FEC scheme that will be used as defined in
      [I-D.ietf-fecframe-raptor].

   o  Kmax: The value of this parameter is the FEC Framework
      Configuration Information element "Maximum Source Block Length" as
      defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
      integer.  For specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  T: The value of this parameter is the FEC Framework Configuration
      Information element "Encoding Symbol Size" as defined in
      [I-D.ietf-fecframe-raptor] encoded as a decimal integer.  For
      specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  repair-window: The maximum time that spans the source packets and
      the corresponding repair packets.  The size of the repair window
      is specified in microseconds.

   Optional parameters:

   o  P: The value of this parameter is the FEC Framework Configuration
      Information element "Payload ID Format" as defined in
      [I-D.ietf-fecframe-raptor].  If this parameter is missing then the
      value "A" shall be assumed.

   Encoding considerations: This media type is framed and binary, see
   section 4.8 in [RFC4288]

   Security considerations: Please see security consideration in
   [I-D.ietf-fecframe-framework]

   Interoperability considerations: None

   Published specification: [I-D.ietf-fecframe-raptor]

   Applications that use this media type:

   Additional information:

   Magic number(s): <none defined>




Watson & Stockhammer      Expires May 29, 2011                  [Page 9]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   File extension(s): <none defined>

   Macintosh file type code(s): <none defined>

   Person & email address to contact for further information: Mark
   Watson, watsonm@netflix.com

   Intended usage: COMMON

   Restrictions on usage: This media type depends on RTP framing, and
   hence is only defined for transfer via RTP [[RFC3550]].  Transport
   within other framing protocols is not defined at this time.

   Author: Mark Watson, Netflix.

   Change controller: IETF Audio/Video Transport working group delegated
   from the IESG.

5.3.  Registration of the audio/raptorfec media type

   This RTP payload format is identified using the audio/raptorfec media
   type which is registered in accordance with [RFC4855] and using the
   template of [RFC4288].

5.3.1.  Media Type Definition

   Type name: audio

   Subtype name: raptorfec

   Required parameters:

   o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
      SHALL be larger than 1000 to provide sufficient resolution to RTCP
      operations.  However, it is RECOMMENDED to select the rate that
      matches the rate of the protected source RTP stream.

   o  raptor-scheme-id: The value of this parameter is the FEC scheme Id
      for the specific Raptor FEC scheme that will be used as defined in
      [I-D.ietf-fecframe-raptor].

   o  Kmax: The value of this parameter is the FEC Framework
      Configuration Information element "Maximum Source Block Length" as
      defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
      integer.  For specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].





Watson & Stockhammer      Expires May 29, 2011                 [Page 10]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   o  T: The value of this parameter is the FEC Framework Configuration
      Information element "Encoding Symbol Size" as defined in
      [I-D.ietf-fecframe-raptor] encoded as a decimal integer.  For
      specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  repair-window: The maximum time that spans the source packets and
      the corresponding repair packets.  The size of the repair window
      is specified in microseconds.

   Optional parameters:

   o  P: The value of this parameter is the FEC Framework Configuration
      Information element "Payload ID Format" as defined in
      [I-D.ietf-fecframe-raptor].  If this parameter is missing then the
      value "A" shall be assumed.

   Encoding considerations: This media type is framed and binary, see
   section 4.8 in [RFC4288]

   Security considerations: Please see security consideration in
   [I-D.ietf-fecframe-framework]

   Interoperability considerations: None

   Published specification: [I-D.ietf-fecframe-raptor]

   Applications that use this media type:

   Additional information:

   Magic number(s): <none defined>

   File extension(s): <none defined>

   Macintosh file type code(s): <none defined>

   Person & email address to contact for further information: Mark
   Watson, watsonm@netflix.com

   Intended usage: COMMON

   Restrictions on usage: This media type depends on RTP framing, and
   hence is only defined for transfer via RTP [[RFC3550]].  Transport
   within other framing protocols is not defined at this time.

   Author: Mark Watson, Netflix.




Watson & Stockhammer      Expires May 29, 2011                 [Page 11]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   Change controller: IETF Audio/Video Transport working group delegated
   from the IESG.

5.4.  Registration of the text/raptorfec media type

   This RTP payload format is identified using the text/raptorfec media
   type which is registered in accordance with [RFC4855] and using the
   template of [RFC4288].

5.4.1.  Media Type Definition

   Type name: text

   Subtype name: raptorfec

   Required parameters:

   o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
      SHALL be larger than 1000 to provide sufficient resolution to RTCP
      operations.  However, it is RECOMMENDED to select the rate that
      matches the rate of the protected source RTP stream.

   o  raptor-scheme-id: The value of this parameter is the FEC scheme Id
      for the specific Raptor FEC scheme that will be used as defined in
      [I-D.ietf-fecframe-raptor].

   o  Kmax: The value of this parameter is the FEC Framework
      Configuration Information element "Maximum Source Block Length" as
      defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
      integer.  For specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  T: The value of this parameter is the FEC Framework Configuration
      Information element "Encoding Symbol Size" as defined in
      [I-D.ietf-fecframe-raptor] encoded as a decimal integer.  For
      specific requirements for this value refer to
      [I-D.ietf-fecframe-raptor].

   o  repair-window: The maximum time that spans the source packets and
      the corresponding repair packets.  The size of the repair window
      is specified in microseconds.

   Optional parameters:

   o  P: The value of this parameter is the FEC Framework Configuration
      Information element "Payload ID Format" as defined in
      [I-D.ietf-fecframe-raptor].  If this parameter is missing then the
      value "A" shall be assumed.



Watson & Stockhammer      Expires May 29, 2011                 [Page 12]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   Encoding considerations: This media type is framed and binary, see
   section 4.8 in [RFC4288]

   Security considerations: Please see security consideration in
   [I-D.ietf-fecframe-framework]

   Interoperability considerations: None

   Published specification: [I-D.ietf-fecframe-raptor]

   Applications that use this media type:

   Additional information:

   Magic number(s): <none defined>

   File extension(s): <none defined>

   Macintosh file type code(s): <none defined>

   Person & email address to contact for further information: Mark
   Watson, watsonm@netflix.com

   Intended usage: COMMON

   Restrictions on usage: This media type depends on RTP framing, and
   hence is only defined for transfer via RTP [[RFC3550]].  Transport
   within other framing protocols is not defined at this time.

   Author: Mark Watson, Netflix.

   Change controller: IETF Audio/Video Transport working group delegated
   from the IESG.


















Watson & Stockhammer      Expires May 29, 2011                 [Page 13]

Internet-Draft        RTP Payload Format for Raptor        November 2010


6.  Mapping to SDP Parameters

   Applications that are using RTP transport commonly use Session
   Description Protocol (SDP) [RFC4566] to describe their RTP sessions.
   The information that is used to specify the media types in an RTP
   session has specific mappings to the fields in an SDP description.
   Note that if an application does not use SDP to describe the RTP
   sessions, an appropriate mapping must be defined and used to specify
   the media types and their parameters for the control/description
   protocol employed by the application.

   The mapping of the media type specification for "raptorfec" and its
   parameters in SDP is as follows:

   o  The media type (e.g., "application") goes into the "m=" line as
      the media name.

   o  The media subtype ("raptorfec") goes into the 'a=rtpmap' line as
      the encoding name.  The RTP clock rate parameter ("rate") also
      goes into the 'a=rtpmap' line as the clock rate.

   o  The remaining required payload-format-specific parameters go into
      the 'a=fmtp' line by copying them directly from the media type
      string as a semicolon-separated list of parameter=value pairs.

   An SDP Example is provided in Section 10.

























Watson & Stockhammer      Expires May 29, 2011                 [Page 14]

Internet-Draft        RTP Payload Format for Raptor        November 2010


7.  Offer/Answer considerations

   When offering Raptor FEC over RTP using SDP in an Offer/Answer model
   [RFC3264], the following considerations apply:

   o  Each combination of the Kmax and T parameters produces different
      FEC data and is not compatible with any other combination.  A
      sender application may desire to offer multiple offers with
      different sets of Kmax and T values as long as the parameter
      values are valid.  The receiver SHOULD normally choose the offer
      with the largest value of the product of Kmax and T that it
      supports.

   o  The size of the repair-window is related to the maximum delay
      between the transmission of a source packet and the associated
      repair packet.  This directly impacts the buffering requirement on
      the receiver side and the receiver must consider this when
      choosing an offer.

   o  When the P parameter is omitted, FEC Payload ID Format A MUST be
      assumed.  In an answer which selects an offer in which the P
      parameter was omitted, the P parameter MUST either be omitted, or
      included with value "A".




























Watson & Stockhammer      Expires May 29, 2011                 [Page 15]

Internet-Draft        RTP Payload Format for Raptor        November 2010


8.  Declarative SDP Considerations

   In declarative usage, like SDP in the Real-time Streaming Protocol
   (RTSP) [RFC2326] or the Session Announcement Protocol (SAP)
   [RFC2947], the following considerations apply:

   o  The payload format configuration parameters are all declarative
      and a participant MUST use the configuration that is provided for
      the session.

   o  More than one configuration may be provided (if desired) by
      declaring multiple RTP payload types.  In that case, the receivers
      should choose the repair flow that is best for them.






































Watson & Stockhammer      Expires May 29, 2011                 [Page 16]

Internet-Draft        RTP Payload Format for Raptor        November 2010


9.  FEC Generation and Recovery Procedures

9.1.  Overview

   This document only specifies the repair packet construction when the
   repair packets are delivered with RTP.  Source packet construction is
   covered in [I-D.ietf-fecframe-raptor].  This section provides an
   overview on how to generate repair packets and on how to reconstruct
   missing source packets from a set of available source and repair
   packets.  Detailed algorithms for the generation of Raptor and
   RaptorQ symbols are provided in [RFC5053] and
   [I-D.ietf-rmt-bb-fec-raptorq], respectively.

9.2.  Repair Packet Construction

   The construction of the repair packet is fully specified in
   Section 4.  A repair packet is constructed by the concatenation of

   o  an RTP header as specified in Section 4.1, and

   o  payload data as defined in Section 4.

   Repair Packet Construction may make use of the Sender Operation for
   RTP repair flows as specified in see [I-D.ietf-fecframe-framework],
   section 4.2.

9.3.  Source Packet Reconstruction

   Source Packet Reconstruction may make use of the Receiver Operation
   for the case of RTP repair flows as specified in see
   [I-D.ietf-fecframe-framework], section 4.3.  Depending on the FEC
   scheme in use of the ones defined in [I-D.ietf-fecframe-raptor], the
   appropriate source blocks are formed.  If enough data for decoding of
   any or all of the missing source payloads in the source block has
   been received, the respective FEC decoding procedures are applied.

   In case the FEC scheme uses Raptor codes as defined in [RFC5053],
   then the Example FEC decoder as specifed in [RFC5053], section 5.5,
   may be used.

   In case the FEC scheme uses RaptorQ codes as defined in
   [I-D.ietf-rmt-bb-fec-raptorq], then the Example FEC decoder as
   specifed in [I-D.ietf-rmt-bb-fec-raptorq], section 5.4, may be used.








Watson & Stockhammer      Expires May 29, 2011                 [Page 17]

Internet-Draft        RTP Payload Format for Raptor        November 2010


10.  Session Description Protocol (SDP) Example

   This section provides an SDP [RFC4566] example.  Assume we have one
   source video stream (mid:S1) and one FEC repair stream (mid:R1).  We
   form one FEC group with the "a=group:FEC S1 R1" line.  The source and
   repair streams are sent to the same port on different multicast
   groups.  The repair window is set to 200 ms.  An Explicit Source FEC
   Payload ID is used for the source flow.

     v=0
     o=ali 1122334455 1122334466 IN IP4 fec.example.com
     s=Raptor RTP FEC Example
     t=0 0
     a=group:FEC-FR S1 R1
     m=video 30000 RTP/AVP 100
     c=IN IP4 233.252.0.1/127
     a=rtpmap:100 MP2T/90000
     a=fec-source-flow: id=0; tag-len=4
     a=mid:S1
     m=application 30000 RTP/AVT
     c=IN IP4 233.252.0.2/127
     a=rtpmap:110 raptorfec/90000
     a=fmtp:110 raptor-scheme-id=1; Kmax=8192; T=128; P=A; repair-window=200000
     a=mid:R1



























Watson & Stockhammer      Expires May 29, 2011                 [Page 18]

Internet-Draft        RTP Payload Format for Raptor        November 2010


11.  Congestion Control Considerations

   FEC is an effective approach to provide applications resiliency
   against packet losses.  However, in networks where the congestion is
   a major contributor to the packet loss, the potential impacts of
   using FEC SHOULD be considered carefully before injecting the repair
   flows into the network.  In particular, in bandwidth-limited
   networks, FEC repair flows may consume most or all of the available
   bandwidth and consequently may congest the network.  In such cases,
   the applications MUST NOT arbitrarily increase the amount of FEC
   protection since doing so may lead to a congestion collapse.  If
   desired, stronger FEC protection MAY be applied only after the source
   rate has been reduced.  In a network-friendly implementation, an
   application SHOULD NOT send/ receive FEC repair flows if it knows
   that sending/receiving those FEC repair flows would not help at all
   in recovering the missing packets.  Such a practice helps reduce the
   amount of wasted bandwidth.  It is RECOMMENDED that the amount of FEC
   protection is adjusted dynamically based on the packet loss rate
   observed by the applications.  In multicast scenarios, it may be
   difficult to optimize the FEC protection per receiver.  If there is a
   large variation among the levels of FEC protection needed by
   different receivers, it is RECOMMENDED that the sender offers
   multiple repair flows with different levels of FEC protection and the
   receivers join the corresponding multicast sessions to receive the
   repair flow(s) that is best for them.

   For more background and normative requirements, see
   [I-D.ietf-fecframe-framework], section 8.























Watson & Stockhammer      Expires May 29, 2011                 [Page 19]

Internet-Draft        RTP Payload Format for Raptor        November 2010


12.  Security Considerations

   Security Considerations related to the use of the FEC Framework are
   addressed in [I-D.ietf-fecframe-framework], section 9.  These
   consideration apply in full to users of the RTP payload formats
   defined in this document, since these are defined in terms of the FEC
   Framework.

   No further security considerations related specifically to the Raptor
   FEC schemes defined in [I-D.ietf-fecframe-raptor] have been
   identified.

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550] and in any applicable RTP profile.  The main
   security considerations for the RTP packet carrying the RTP payload
   format defined within this memo are confidentiality, integrity and
   source authenticity.  Confidentiality is achieved by encrypting the
   RTP payload.  Integrity of the RTP packets is achieved through a
   suitable cryptographic integrity protection mechanism.  Such a
   cryptographic system may also allow the authentication of the source
   of the payload.  A suitable security mechanism for this RTP payload
   format should provide confidentiality, integrity protection, and at
   least source authentication capable of determining if an RTP packet
   is from a member of the RTP session.  Note that the appropriate
   mechanism to provide security to RTP and payloads following this memo
   may vary.  It is dependent on the application, transport and
   signaling protocol employed.  Therefore, a single mechanism is not
   sufficient, although if suitable, using the Secure Real-time
   Transport Protocol (SRTP) [RFC3711] is recommended.  Other mechanisms
   that may be used are IPsec [RFC4301] and Transport Layer Security
   (TLS) [RFC5246] (RTP over TCP); other alternatives may exist.



















Watson & Stockhammer      Expires May 29, 2011                 [Page 20]

Internet-Draft        RTP Payload Format for Raptor        November 2010


13.  IANA Considerations

   New media subtypes are subject to IANA registration.  For the
   registration of the payload format and its parameters introduced in
   this document, refer to Section 5.














































Watson & Stockhammer      Expires May 29, 2011                 [Page 21]

Internet-Draft        RTP Payload Format for Raptor        November 2010


14.  Acknowledgements

   Thanks are due to Ali C. Begen and Colin Perkins for thorough review
   of earlier draft versions of this document.















































Watson & Stockhammer      Expires May 29, 2011                 [Page 22]

Internet-Draft        RTP Payload Format for Raptor        November 2010


15.  References

15.1.  Normative References

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

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4855]  Casner, S., "Media Type Registration of RTP payload
              formats", RFC 4855, February 2007.

   [I-D.ietf-fecframe-framework]
              Watson, M., "Forward Error Correction (FEC) Framework",
              draft-ietf-fecframe-framework-10 (work in progress),
              September 2010.

   [I-D.ietf-fecframe-raptor]
              Watson, M., "Raptor FEC Schemes for FECFRAME",
              draft-ietf-fecframe-raptor-02 (work in progress),
              March 2010.

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

   [RFC5053]  Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer,
              "Raptor Forward Error Correction Scheme for Object
              Delivery", RFC 5053, October 2007.

   [I-D.ietf-rmt-bb-fec-raptorq]
              Luby, M., Shokrollahi, A., Watson, M., Stockhammer, T.,
              and L. Minder, "RaptorQ Forward Error Correction Scheme
              for Object Delivery", draft-ietf-rmt-bb-fec-raptorq-04
              (work in progress), August 2010.

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

15.2.  Informative References

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



Watson & Stockhammer      Expires May 29, 2011                 [Page 23]

Internet-Draft        RTP Payload Format for Raptor        November 2010


   [RFC2947]  Altman, J., "Telnet Encryption: DES3 64 bit Cipher
              Feedback", RFC 2947, September 2000.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.







































Watson & Stockhammer      Expires May 29, 2011                 [Page 24]

Internet-Draft        RTP Payload Format for Raptor        November 2010


Authors' Addresses

   Mark Watson
   Netflix
   100 Winchester Circle
   Los Gatos, CA  95032
   U.S.A.

   Email: watsonm@netflix.com


   Thomas Stockhammer
   Nomor Research
   Brecherspitzstrasse 8
   Munich  81541
   Germany.

   Email: stockhammer@nomor.de

































Watson & Stockhammer      Expires May 29, 2011                 [Page 25]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/