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

FEC Framework Working Group                                    M. Watson
Internet-Draft                                             Qualcomm Inc.
Intended status: Standards Track                           March 5, 2010
Expires: September 6, 2010


                   RTP Payload Format for Raptor FEC
                   draft-ietf-fecframe-rtp-raptor-03

Abstract

   This document specifies an RTP Payload Format for Forward Error
   Correction 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 to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   This Internet-Draft will expire on September 6, 2010.

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



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   (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 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.  Congestion Control Considerations  . . . . . . . . . . . . . .  7
   6.  Media Types  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Registration of the application/raptorfec media type . . .  8
       6.1.1.  Media Type Definition  . . . . . . . . . . . . . . . .  8
     6.2.  Registration of the video/raptorfec media type . . . . . .  9
       6.2.1.  Media Type Definition  . . . . . . . . . . . . . . . .  9
     6.3.  Registration of the audio/raptorfec media type . . . . . . 11
       6.3.1.  Media Type Definition  . . . . . . . . . . . . . . . . 11
     6.4.  Registration of the text/raptorfec media type  . . . . . . 12
       6.4.1.  Media Type Definition  . . . . . . . . . . . . . . . . 13
   7.  Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Offer/Answer considerations  . . . . . . . . . . . . . . . . . 16
   9.  Declarative SDP Considerations . . . . . . . . . . . . . . . . 17
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
















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1.  Introduction

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





























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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].














































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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.























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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 Forward Error
   Correction in an FECFRAME context are fully defined in
   [I-D.ietf-fecframe-framework] and [I-D.ietf-fecframe-framework] 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].


















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5.  Congestion Control Considerations

   See [I-D.ietf-fecframe-framework].
















































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6.  Media Types

6.1.  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].

6.1.1.  Media Type Definition

   Type name: application

   Subtype name: raptorfec

   Required parameters:

      rate: The RTP timestamp (clock) rate.  The rate SHALL be larger
      than 1000 Hz 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.

      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].

      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.

      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.

      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:

      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 that the
      value "A" shall be assumed.

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




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

   Interoperability considerations:

   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, watson@qualcomm.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, Qualcomm Inc.

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

6.2.  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].

6.2.1.  Media Type Definition

   Type name: video

   Subtype name: raptorfec

   Required parameters:

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



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      rate of the protected source RTP stream.

      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].

      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.

      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.

      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:

      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 that 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:

   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, watson@qualcomm.com



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   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, Qualcomm Inc.

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

6.3.  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].

6.3.1.  Media Type Definition

   Type name: audio

   Subtype name: raptorfec

   Required parameters:

      rate: The RTP timestamp (clock) rate.  The rate SHALL be larger
      than 1000 Hz 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.

      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].

      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.

      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.

      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:



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      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 that 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:

   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, watson@qualcomm.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, Qualcomm Inc.

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

6.4.  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].







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6.4.1.  Media Type Definition

   Type name: text

   Subtype name: raptorfec

   Required parameters:

      rate: The RTP timestamp (clock) rate.  The rate SHALL be larger
      than 1000 Hz 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.

      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].

      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.

      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.

      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:

      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 that 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:

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

   Applications that use this media type:



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   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, watson@qualcomm.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, Qualcomm Inc.

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






























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7.  Mapping to SDP

   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 above defined payload format media type and its
   parameters SHALL be done according to Section 3 of [RFC4855]
   following the suggestion therein regarding the mapping of payload-
   format-specific paraeters into the ""a=fmtp"" field.

   When the RTP Payload Formats defined in this document are used, the
   Media Type Parameters defined above SHALL be used to specify the FEC
   Framework Configuration Information in preference to the SDP
   attributes specified in [I-D.ietf-fecframe-sdp-elements]































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8.  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".




























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9.  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.






































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10.  IANA Considerations

   This memo requests that IANA registers application/raptorfec as
   specified in Section 6.1.1, video/raptorfec as specified in
   Section 6.2.1, audio/raptorfec as specified in Section 6.3.1 and
   text/raptorfec as specified in Section 6.4.1.  The media type is also
   requested to be added to the IANA registry for "RTP Payload Format
   MIME types" (http://www.iana.org/assignments/rtp-parameters).











































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11.  Security Considerations

   Security Considerations related to the use of the FEC Framework are
   addressed in [I-D.ietf-fecframe-framework].  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.

   Users of RTP should consider the Security Considerations of
   [RFC3550].






































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12.  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-06 (work in progress),
              March 2010.

   [I-D.ietf-fecframe-sdp-elements]
              Begen, A., "SDP Elements for FEC Framework",
              draft-ietf-fecframe-sdp-elements-04 (work in progress),
              August 2009.

   [I-D.ietf-fecframe-raptor]
              Watson, M., "Raptor FEC Schemes for FECFRAME",
              draft-ietf-fecframe-raptor-01 (work in progress),
              July 2009.

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

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

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

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









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Author's Address

   Mark Watson
   Qualcomm Inc.
   3165 Kifer Rd.
   Santa Clara, CA  95051
   U.S.A.

   Email: watson@qualcomm.com










































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