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-04.txt
Pages : 22
Date : 2009-07-03
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 synchronisation
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.
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