Multiple Synchronization Sources (SSRC) in SDP Media Descriptions
draft-westerlund-mmusic-max-ssrc-01
Network Working Group C.H. Holmberg
Internet-Draft M.W. Westerlund
Intended status: Standards Track B.B. Burman
Expires: September 28, 2013 F.J. Jansson
Ericsson
March 27, 2013
Multiple Synchronization Sources (SSRC) in SDP Media Descriptions
draft-westerlund-mmusic-max-ssrc-01.txt
Abstract
This document describes use-cases where endpoints, for a given media
type, use multiple media sources. It also describes how endpoints
normally support media sources, and limitations associated with the
support of multiple sources.
This document also defines two new SDP attributes, "max-send-ssrc"
and "max-recv-ssrc". The attributes allows an entity to, for a given
media description, indicate sending and receiving capabilities of
multiple media sources, based on codec usage .
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Multiple Media Stream Support . . . . . . . . . . . . . . . . 3
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Multiple Source Support Limitations . . . . . . . . . . . 4
4. SDP max-send-ssrc And max-recv-ssrc Attributes . . . . . . . 4
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Use in Offer/Answer . . . . . . . . . . . . . . . . . . . 6
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
An RTP session [RFC3550] contains a Synchronization Sources (SSRC)
space. This space can encompass a number of endpoints and network
entities, and associated media streams, within the RTP session. As
defined in RFC 3550, within an RTP session, each entity may use zero,
one or multiple SSRCs to indicate a physical media source (e.g. a
camera or a microphone), a conceptual source (e.g. the most active
speaker, selected by an RTP mixer, within a conference), or to
identify a receiver that provides feedback and reports on reception.
A given SSRC value is associated with a physical media source.
Multiple SSRC values can be associated with the same source.
The Session Description Protocol (SDP) [RFC4566] describes media
streams using media descriptions (m- lines). Each m- line is
normally associated with a given media type (e.g. audio or video).
Multiple media streams and media sources might be associated with a
single SDP media description. Each media stream will share the
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