RFC 3388 (rfc3388) - Page 2 of 21

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

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
   extensions.

2. Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
   [1] and indicate requirement levels for compliant implementations.









Camarillo et. al.           Standards Track