The Session Description Protocol (SDP) Grouping Framework
RFC 5888

Internet Engineering Task Force (IETF)                      G. Camarillo
Request for Comments: 5888                                      Ericsson
Obsoletes: 3388                                           H. Schulzrinne
Category: Standards Track                            Columbia University
ISSN: 2070-1721                                                June 2010

       The Session Description Protocol (SDP) Grouping Framework

Abstract

   In this specification, we define a framework to group "m" lines in
   the Session Description Protocol (SDP) for different purposes.  This
   framework uses the "group" and "mid" SDP attributes, both of which
   are defined in this specification.  Additionally, we specify how to
   use the framework for two different purposes: for lip synchronization
   and for receiving a media flow consisting of several media streams on
   different transport addresses.  This document obsoletes RFC 3388.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc5888.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Camarillo & Schulzrinne      Standards Track                    [Page 1]
RFC 5888                 SDP Grouping Framework                June 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  3
   4.  Media Stream Identification Attribute  . . . . . . . . . . . .  4
   5.  Group Attribute  . . . . . . . . . . . . . . . . . . . . . . .  4
   6.  Use of "group" and "mid" . . . . . . . . . . . . . . . . . . .  4
   7.  Lip Synchronization (LS) . . . . . . . . . . . . . . . . . . .  5
     7.1.  Example of LS  . . . . . . . . . . . . . . . . . . . . . .  5
   8.  Flow Identification (FID)  . . . . . . . . . . . . . . . . . .  6
     8.1.  SIP and Cellular Access  . . . . . . . . . . . . . . . . .  6
     8.2.  DTMF Tones . . . . . . . . . . . . . . . . . . . . . . . .  7
     8.3.  Media Flow Definition  . . . . . . . . . . . . . . . . . .  7
     8.4.  FID Semantics  . . . . . . . . . . . . . . . . . . . . . .  7
       8.4.1.  Examples of FID  . . . . . . . . . . . . . . . . . . .  8
     8.5.  Scenarios That FID Does Not Cover  . . . . . . . . . . . . 11
       8.5.1.  Parallel Encoding Using Different Codecs . . . . . . . 11
       8.5.2.  Layered Encoding . . . . . . . . . . . . . . . . . . . 12
       8.5.3.  Same IP Address and Port Number  . . . . . . . . . . . 12
   9.  Usage of the "group" Attribute in SIP  . . . . . . . . . . . . 13
     9.1.  Mid Value in Answers . . . . . . . . . . . . . . . . . . . 13
       9.1.1.  Example  . . . . . . . . . . . . . . . . . . . . . . . 14
     9.2.  Group Value in Answers . . . . . . . . . . . . . . . . . . 15
       9.2.1.  Example  . . . . . . . . . . . . . . . . . . . . . . . 15
     9.3.  Capability Negotiation . . . . . . . . . . . . . . . . . . 16
       9.3.1.  Example  . . . . . . . . . . . . . . . . . . . . . . . 16
     9.4.  Backward Compatibility . . . . . . . . . . . . . . . . . . 17
       9.4.1.  Offerer Does Not Support "group" . . . . . . . . . . . 17
       9.4.2.  Answerer Does Not Support "group"  . . . . . . . . . . 17
   10. Changes from RFC 3388  . . . . . . . . . . . . . . . . . . . . 18
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   13. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20