Rapid Synchronisation of RTP Flows

Approval announcement
Draft of message to be sent after approval:

From: The IESG <iesg-secretary@ietf.org>
To: IETF-Announce <ietf-announce@ietf.org>
Cc: Internet Architecture Board <iab@iab.org>,
    RFC Editor <rfc-editor@rfc-editor.org>, 
    avt mailing list <avt@ietf.org>, 
    avt chair <avt-chairs@tools.ietf.org>
Subject: Protocol Action: 'Rapid Synchronisation of RTP Flows' to Proposed Standard

The IESG has approved the following document:

- 'Rapid Synchronisation of RTP Flows '
   <draft-ietf-avt-rapid-rtp-sync-12.txt> as a Proposed Standard

This document is the product of the Audio/Video Transport Working Group. 

The IESG contact persons are Robert Sparks and Gonzalo Camarillo.

A URL of this Internet-Draft is:

Technical Summary
This memo outlines how RTP 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 synchronization delay.  This
increase in delay can be unacceptable to some applications that use
layered and/or multi-description codecs.

This memo introduces three mechanisms to reduce the synchronisation delay
for such sessions.  First, it updates the RTP Control Protocol (RTCP)
timing rules to reduce the initial synchronisation delay for SSM sessions.

  Second, 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.  Finally, 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.

Working Group Summary
There is nothing specific to note.
Document Quality
This document explains and updates the timing consideration for RTCP in
RFC 3550. It also defines new protocol that is referenced by other
documents like payload specification for H.264 SVC


Roni Even is the document shepherd.
The responsible area director is Robert Sparks.