Subject: I-D Action:draft-versteeg-avt-rapid-synchronization-for-rtp-02.txt

From: [email-masked]
Date: Mon, 9 Mar 2009 13:45:01 -0700 (PDT)

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title           : Unicast-Based Rapid Synchronization with RTP Multicast Sessions
	Author(s)       : B. Steeg, et al.
	Filename        : draft-versteeg-avt-rapid-synchronization-for-rtp-02.txt
	Pages           : 32
	Date            : 2009-03-09

When a receiver joins a multicast session, it may need to acquire and
parse certain Reference Information before it can process any data
sent in the multicast session.  Depending on the join time, length of
the Reference Information repetition interval, size of the Reference
Information as well as the application and transport properties, the
time lag before a receiver can usefully consume the multicast data,
which we refer to as the synchronization delay, varies and may be
large.  This is an undesirable phenomenon for receivers that
frequently switch among different multicast sessions, such as video
broadcasts.  In this document, we describe a method using the
existing RTP and RTCP protocol machinery that reduces the
synchronization delay.  In this method, an auxiliary unicast RTP
session carrying the Reference Information to the receiver precedes/
accompanies the multicast flow.  This unicast flow may be transmitted
at a faster than natural rate to further accelerate the
synchronization.  The motivating use case for this capability is
multicast applications that carry real-time compressed audio and
video.  However, the proposed method can also be used in other types
of multicast applications where the synchronization delay is long
enough to be a problem.

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