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