Subject: I-D Action:draft-ietf-avt-rapid-rtp-sync-01.txt

From: [email-masked]
Date: Thu, 7 May 2009 08:45:02 -0700 (PDT)

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Audio/Video Transport Working Group of the IETF.

	Title           : Rapid Synchronisation of RTP Flows
	Author(s)       : C. Perkins, T. Schierl
	Filename        : draft-ietf-avt-rapid-rtp-sync-01.txt
	Pages           : 20
	Date            : 2009-05-07

This memo outlines how RTP multimedia sessions are synchronised, and
discusses how rapidly such synchronisation can occur.  We show that
most RTP sessions can be synchronised immediately, but that the use
of video switching multipoint conference units (MCUs) or large source
specific multicast (SSM) groups can greatly increase the initial
synchronisation delay.  This increase in delay can be unacceptable to
some applications that use layered and/or multi-description codecs.

This memo introduces several mechanisms to reduce the initial
synchronisation delay for multimedia sessions.  It updates the RTP
Control Protocol (RTCP) timing rules to reduce the initial
synchronisation delay for SSM sessions.  A new feedback packet is
defined for use with the Extended RTP Profile for RTCP-based Feedback
(RTP/AVPF), allowing video switching MCUs to rapidly request
resynchronisation.  Two new RTP header extensions are defined to
allow rapid synchronisation of late joiners, and guarantee correct
timestamp based decoding order recovery for layered codecs in the
presence of clock skew.  Therefore, a synchronized insertion of RTP
header extensions is recommended.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-avt-rapid-rtp-sync-01.txt

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