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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 Roach & Thomson Expires June 05, 2014 [Page 1] Internet-Draft Group Identifiers December 2013 (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 Roach & Thomson Expires June 05, 2014 [Page 2] Internet-Draft Group Identifiers December 2013 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]. Roach & Thomson Expires June 05, 2014 [Page 3] Internet-Draft Group Identifiers December 2013 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 Roach & Thomson Expires June 05, 2014 [Page 4] Internet-Draft Group Identifiers December 2013 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 Roach & Thomson Expires June 05, 2014 [Page 5]