datatracker.ietf.org
Sign in
Version 5.3.0, 2014-04-12
Report a bug

Grouping of Media Lines in the Session Description Protocol (SDP)
RFC 3388

Document type: RFC - Proposed Standard (December 2002)
Obsoleted by RFC 5888
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: WG Document
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 3388 (Proposed Standard)
Responsible AD: Allison Mankin
IESG Note: Responsible: RFC Editor
Send notices to: <jo@acm.org>, <csp@csperkins.org>

Network Working Group                                       G. Camarillo
Request for Comments: 3388                                   G. Eriksson
Category: Standards Track                                      J. Holler
                                                                Ericsson
                                                          H. Schulzrinne
                                                     Columbia University
                                                           December 2002

   Grouping of Media Lines 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.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document defines two Session Description Protocol (SDP)
   attributes: "group" and "mid".  They allow to group together several
   "m" lines for two different purposes: for lip synchronization and for
   receiving media from a single flow (several media streams) that are
   encoded in different formats during a particular session, on
   different ports and host interfaces.

Table of Contents

   1. Introduction..................................................  2
   2. Terminology...................................................  2
   3. Media Stream Identification Attribute.........................  3
   4. Group Attribute...............................................  3
   5. Use of "group" and "mid"......................................  3
   6. Lip Synchronization (LS)......................................  4
      6.1 Example of LS.............................................  5
   7. Flow Identification (FID).....................................  5
      7.1 SIP and Cellular Access...................................  6
      7.2 DTMF Tones................................................  6
      7.3 Media Flow Definition.....................................  6
      7.4 FID Semantics.............................................  7
          7.4.1 Examples of FID.....................................  8
      7.5 Scenarios that FID does not Cover........................  11

Camarillo et. al.           Standards Track                     [Page 1]
RFC 3388             Grouping of Media Lines in SDP        December 2002

          7.5.1 Parallel Encoding Using Different Codecs...........  11
          7.5.2 Layered Encoding...................................  12
          7.5.3 Same IP Address and Port Number....................  12
   8. Usage of the "group" Attribute in SIP........................  13
      8.1 Mid Value in Answers.....................................  13
          8.1.1 Example............................................  14
      8.2 Group Value in Answers...................................  15
          8.2.1 Example............................................  15
      8.3 Capability Negotiation...................................  16
          8.3.1 Example............................................  17
      8.4 Backward Compatibility...................................  17
          8.4.1 Offerer does not Support "group"...................  17
          8.4.2 Answerer does not Support "group"..................  17
   9.    Security Considerations...................................  18
   10.   IANA Considerations.......................................  18
   11.   Acknowledgements..........................................  19
   12.   References................................................  19
   13.   Authors' Addresses........................................  20
   14.   Full Copyright Statement..................................  21

1. Introduction

   An SDP session description typically contains one or more media lines
   - they are commonly known as "m" lines.  When a session description
   contains more than one "m" line, SDP does not provide any means to
   express a particular relationship between two or more of them.  When
   an application receives an SDP session description with more than one
   "m" line, it is up to the application what to do with them.  SDP does
   not carry any information about grouping media streams.

   While in some environments this information can be carried out of
   band, it would be desirable to have extensions to SDP that allow the
   expression of how different media streams within a session
   description relate to each other.  This document defines such

[include full document text]