The Session Description Protocol (SDP) Content Attribute
RFC 4796
Document | Type | RFC - Proposed Standard (February 2007; No errata) | |
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Authors | Jani Hautakorpi , Gonzalo Camarillo | ||
Last updated | 2015-10-14 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4796 (Proposed Standard) | |
Action Holders |
(None)
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||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Cullen Jennings | ||
Send notices to | gunnar.hellstrom@omnitor.se |
Network Working Group J. Hautakorpi Request for Comments: 4796 G. Camarillo Category: Standards Track Ericsson February 2007 The Session Description Protocol (SDP) Content Attribute 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 IETF Trust (2007). Abstract This document defines a new Session Description Protocol (SDP) media- level attribute, 'content'. The 'content' attribute defines the content of the media stream to a more detailed level than the media description line. The sender of an SDP session description can attach the 'content' attribute to one or more media streams. The receiving application can then treat each media stream differently (e.g., show it on a big or small screen) based on its content. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Related Techniques . . . . . . . . . . . . . . . . . . . . . . 2 4. Motivation for the New Content Attribute . . . . . . . . . . . 3 5. The Content Attribute . . . . . . . . . . . . . . . . . . . . 4 6. The Content Attribute in the Offer/Answer Model . . . . . . . 5 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.2. Informational References . . . . . . . . . . . . . . . . 9 Hautakorpi & Camarillo Standards Track [Page 1] RFC 4796 Content Attribute February 2007 1. Introduction The Session Description Protocol (SDP) [1] is a protocol that is intended to describe multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. One of the most typical use cases of SDP is where it is used with the Session Initiation Protocol (SIP) [5]. There are situations where one application receives several similar media streams, which are described in an SDP session description. The media streams can be similar in the sense that their content cannot be distinguished just by examining their media description lines (e.g., two video streams). The 'content' attribute is needed so that the receiving application can treat each media stream appropriately based on its content. This specification defines the SDP 'content' media-level attribute, which provides more information about the media stream than the 'm' line in an SDP session description. The main purpose of this specification is to allow applications to take automated actions based on the 'content' attributes. However, this specification does not define those actions. Consequently, two implementations can behave completely differently when receiving the same 'content' attribute. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [3], and indicate requirement levels for compliant implementations. 3. Related Techniques The 'label' attribute [10] enables a sender to attach a pointer to a particular media stream. The namespace of the 'label' attribute itself is unrestricted; so, in principle, it could also be used to convey information about the content of a media stream. However, in practice, this is not possible because of the need for backward compatibility. Existing implementations of the 'label' attribute already use values from that unrestricted namespace in an application-specific way. So, it is not possible to reserve portions of the 'label' attribute's namespace without possible conflict with already used application-specific labels. Hautakorpi & Camarillo Standards Track [Page 2] RFC 4796 Content Attribute February 2007 It is possible to assign semantics to a media stream with an externalShow full document text