Unicast-Based Rapid Acquisition of Multicast RTP Sessions
RFC 6285
Internet Engineering Task Force (IETF) B. Ver Steeg
Request for Comments: 6285 A. Begen
Category: Standards Track Cisco
ISSN: 2070-1721 T. Van Caenegem
Alcatel-Lucent
Z. Vax
Magnum Semiconductor
June 2011
Unicast-Based Rapid Acquisition of Multicast RTP Sessions
Abstract
When an RTP 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 (or appearance)
interval, size of the Reference Information, and 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 can 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 RTP
Control Protocol (RTCP) machinery that reduces the acquisition delay.
In this method, an auxiliary unicast RTP session carrying the
Reference Information to the receiver precedes or accompanies the
multicast stream. This unicast RTP flow can be transmitted at a
faster than natural bitrate to further accelerate the acquisition.
The motivating use case for this capability is multicast applications
that carry real-time compressed audio and video. However, this
method can also be used in other types of multicast applications
where the acquisition delay is long enough to be a problem.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Ver Steeg, et al. Standards Track [Page 1]
RFC 6285 RAMS June 2011
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6285.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Acquisition of RTP Streams vs. RTP Sessions . . . . . . . 6
1.2. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 7
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Elements of Delay in Multicast Applications . . . . . . . . . 8
5. Protocol Design Considerations and Their Effect on
Resource Management for Rapid Acquisition . . . . . . . . . . 10
6. Rapid Acquisition of Multicast RTP Sessions (RAMS) . . . . . . 12
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 12
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