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Source-Specific Media Attributes in the Session Description Protocol (SDP)
RFC 5576

Network Working Group                                          J. Lennox
Request for Comments: 5576                                         Vidyo
Category: Standards Track                                         J. Ott
                                       Helsinki University of Technology
                                                              T. Schierl
                                                          Fraunhofer HHI
                                                               June 2009

                Source-Specific Media Attributes in the
                   Session Description Protocol (SDP)

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.

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Lennox, et al.              Standards Track                     [Page 1]
RFC 5576             Source-Specific SDP Attributes            June 2009

Abstract

   The Session Description Protocol (SDP) provides mechanisms to
   describe attributes of multimedia sessions and of individual media
   streams (e.g., Real-time Transport Protocol (RTP) sessions) within a
   multimedia session, but does not provide any mechanism to describe
   individual media sources within a media stream.  This document
   defines a mechanism to describe RTP media sources, which are
   identified by their synchronization source (SSRC) identifiers, in
   SDP, to associate attributes with these sources, and to express
   relationships among sources.  It also defines several source-level
   attributes that can be used to describe properties of media sources.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. Overview ........................................................3
   4. Media Attributes ................................................4
      4.1. The "ssrc" Media Attribute .................................5
      4.2. The "ssrc-group" Media Attribute ...........................6
   5. Usage of Identified Source Identifiers in RTP ...................7
   6. Source Attributes ...............................................8
      6.1. The "cname" Source Attribute ...............................8
      6.2. The "previous-ssrc" Source Attribute .......................9
      6.3. The "fmtp" Source Attribute ................................9
      6.4. Other Source Attributes ...................................10
   7. Examples .......................................................10
   8. Usage With the Offer/Answer Model ..............................11
   9. Backward Compatibility .........................................11
   10. Formal Grammar ................................................12
   11. Security Considerations .......................................13
   12. IANA Considerations ...........................................14
      12.1. New SDP Media-Level Attributes ...........................14
      12.2. Registry for Source-Level Attributes .....................14
      12.3. Registry for Source Grouping Semantics ...................15
   13. References ....................................................16
      13.1. Normative References .....................................16
      13.2. Informative References ...................................16

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