Subject: I-D Action:draft-ietf-avt-rapid-acquisition-for-rtp-02.txt

From: [email-masked]
Date: Tue, 25 Aug 2009 01:15:01 -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           : Unicast-Based Rapid Acquisition of Multicast RTP Sessions
	Author(s)       : B. Ver Steeg, et al.
	Filename        : draft-ietf-avt-rapid-acquisition-for-rtp-02.txt
	Pages           : 45
	Date            : 2009-08-25

When an RTP receiver joins a primary 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 an RTP receiver can
usefully consume the multicast data, which we refer to as the
Acquisition 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 acquisition delay.  In this
method, an auxiliary unicast RTP session carrying the Reference
Information to the receiver precedes/accompanies the primary
multicast stream.  This unicast RTP flow may be transmitted at a
faster than natural rate to further accelerate the acquisition.  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 acquisition delay is long enough to be a
problem.

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