Signaling Media Decoding Dependency in the Session Description Protocol (SDP)
RFC 5583

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Network Working Group                                         T. Schierl
Request for Comments: 5583                                Fraunhofer HHI
Category: Standards Track                                      S. Wenger
                                                             Independent
                                                               July 2009

                Signaling Media Decoding Dependency in
                 the Session Description Protocol (SDP)

Abstract

   This memo defines semantics that allow for signaling the decoding
   dependency of different media descriptions with the same media type
   in the Session Description Protocol (SDP).  This is required, for
   example, if media data is separated and transported in different
   network streams as a result of the use of a layered or multiple
   descriptive media coding process.

   A new grouping type "DDP" -- decoding dependency -- is defined, to be
   used in conjunction with RFC 3388 entitled "Grouping of Media Lines
   in the Session Description Protocol".  In addition, an attribute is
   specified describing the relationship of the media streams in a "DDP"
   group indicated by media identification attribute(s) and media format
   description(s).

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this

Schierl & Wenger            Standards Track                     [Page 1]
RFC 5583       Signaling Media Decoding Dependency in SDP      July 2009

   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Definitions .....................................................4
   4. Motivation, Use Cases, and Architecture .........................5
      4.1. Motivation .................................................5
      4.2. Use Cases ..................................................7
   5. Signaling Media Dependencies ....................................7
      5.1. Design Principles ..........................................7
      5.2. Semantics ..................................................8
           5.2.1. SDP Grouping Semantics for Decoding Dependency ......8
           5.2.2. "depend" Attribute for Dependency Signaling
                  per Media-Stream ....................................8
   6. Usage of New Semantics in SDP ..................................10
      6.1. Usage with the SDP Offer/Answer Model .....................10
      6.2. Declarative usage .........................................12
      6.3. Usage with AVP and SAVP RTP Profiles ......................12
      6.4. Usage with Capability Negotiation .........................12
      6.5. Examples ..................................................12
   7. Security Considerations ........................................15
   8. IANA Considerations ............................................15
   9. Informative Note on "The SDP (Session Description Protocol)
      Grouping Framework" ............................................16
   10. References ....................................................16
      10.1. Normative References .....................................16
      10.2. Informative References ...................................17
   Appendix A.  Acknowledgements .....................................18

Schierl & Wenger            Standards Track                     [Page 2]
RFC 5583       Signaling Media Decoding Dependency in SDP      July 2009