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Versions: 00

Network Working Group                                        A. B. Roach
Internet-Draft                                                M. Thomson
Updates: 5888 (if approved)                                      Mozilla
Intended status: Standards Track                       December 02, 2013
Expires: June 05, 2014


  An Extension for Identification of Groups in the Session Description
                            Protocol (SDP).
                     draft-roach-mmusic-groupid-00

Abstract

   RFC 5888 defines a mechanism for semantically grouping media sections
   in the Session Description Protocol (SDP).  One difficulty that has
   arisen in several applications of SDP is the need to uniquely
   identify these groups either in other protocols or elsewhere in the
   SDP itself.

   This document proposes a simple, backwards-compatible mechanism that
   provides unambiguous identifiers for RFC 5888 groups.

   This document updates RFC 5888.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 05, 2014.

Copyright Notice

   Copyright (c) 2013 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
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Mechanism Description . . . . . . . . . . . . . . . . . . . .   2
   4.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [RFC5888] defines a mechanism for semantically grouping media
   sections in the Session Description Protocol (SDP) [RFC4566] for
   purposes such as lip sync and flow identification.  That mechanism,
   however, defines anonymous groupings, which makes it impossible to
   reliably and unambiguously refer to such groups at a later time (e.g.
   elsewhere in the SDP, or in an application-layer protocol).  This
   document defines a new attribute, "group-id", that can be used to
   attach identifiers to SDP groups.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Mechanism Description

   The mechanism used to assign identifiers to group is very simple and
   straightforward: implementations that wish to assign an identifier to
   groups include a single "group-id" attribute immediately before each
   "group" attribute in the session.  Importantly, it retains backwards-
   compatible with existing [RFC5888] implementations.  This "group-id"
   attribute contains a single token, unique within the session, that
   unambiguously identifies the group defined on the following line.
   Each media section included in that group additionally MUST contain
   an "in-group" attribute that includes the [RFC5888] semantic
   identifier and group-id.  This "in-group" identifier is intended to



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   allow media sections to be self-describing when they appear outside
   the context of a full session.

   For clarity: if an implementation includes a group-id for any groups
   in a session, that implementation MUST include a group-id for every
   group in that session.  Implementations MUST NOT include any
   attributes between a "group-id" attribute and the "group" attribute
   it identifies.  Recipients of such SDP in which a "group-id" appears
   followed by anything other than the "group" attribute MUST ignore the
   errant "group-id" line.

   A simple example of the new group-id syntax follows.  This example
   defines a single lip-sync group, and identifies it with the group
   identifier "abc."

          v=0
          o=Laura 289083124 289083124 IN IP4 eight.example.com
          c=IN IP4 192.0.2.1
          t=0 0
          a=group-id:abc
          a=group:LS 1 2
          m=audio 30000 RTP/AVP 0
          a=mid:1
          a=in-group:LS abc
          m=audio 30000 RTP/AVP 8
          a=mid:2
          a=in-group:LS abc


4.  Syntax

   The new attributes introduced by this mechanism are defined by the
   following ABNF [RFC5234]:

              groupid-attribute = "a=group-id:" group-id

              group-id          = token ; token is defined in RFC 4566

              in-group-attr     = "a=in-group:" semantics SP group-id
                                  ; semantics is defined in RFC 5888


5.  Security Considerations

   This mechanism does not introduce any security issues beyond those
   discussed in [RFC5888].





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6.  IANA Considerations

   This document defines two SDP attributes: "group-id" and "in-group".
   They are to be registered by IANA in the "SDP Parameters" registry as
   follows:

      SDP Attribute ("att-field"):

        Attribute name:     group-id
        Long form:          Group ID
        Type of name:       att-field
        Type of attribute:  session level
        Subject to charset: no
        Purpose:            Identification of SDP groups
        Reference:          this document
        Values:             any token


      SDP Attribute ("att-field"):

        Attribute name:     in-group
        Long form:          Add media section to group
        Type of name:       att-field
        Type of attribute:  media level
        Subject to charset: no
        Purpose:            Associating media sections with groups
        Reference:          this document
        Values:             semantic type followed by group identifier


7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description
              Protocol (SDP) Grouping Framework", RFC 5888, June 2010.

Authors' Addresses






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   Adam Roach
   Mozilla
   Dallas, TX
   US

   Phone: +1 650 903 0800 x863
   Email: adam@nostrum.com


   Martin Thomson
   Mozilla
   650 Castro St. Suite 300
   Mountain View, CA  94041-2021
   US

   Phone: +1 650 903 0800
   Email: mt@moilla.com

































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