Internet DRAFT - draft-roach-mmusic-groupid
draft-roach-mmusic-groupid
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.
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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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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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