RFC 2762 (rfc2762) - Page 1 of 12

Sampling of the Group Membership in RTP

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Network Working Group                                      J. Rosenberg
Request for Comments: 2762                                  dynamicsoft
Category: Experimental                                   H. Schulzrinne
                                                            Columbia U.
                                                          February 2000


                Sampling of the Group Membership in RTP

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   In large multicast groups, the size of the group membership table
   maintained by RTP (Real Time Transport Protocol) participants may
   become unwieldy, particularly for embedded devices with limited
   memory and processing power. This document discusses mechanisms for
   sampling of this group membership table in order to reduce the memory
   requirements. Several mechanisms are proposed, and the performance of
   each is considered.

1 Introduction

   RTP, the Real Time Transport Protocol [1], mandates that RTCP packets
   be transmitted from each participant with a period roughly
   proportional to the group size. The group size is obtained by storing
   a table, containing an entry for each unique SSRC seen in RTP and
   RTCP packets. As members leave or time out, entries are deleted, and
   as new members join, entries are added. The table is thus highly
   dynamic.

   For large multicast sessions, such as an mbone broadcast or IP-based
   TV distribution, group sizes can be extremely large, on the order of
   hundreds of thousands to millions of participants. In these
   environments, RTCP may not always be used, and thus the group
   membership table isn't needed. However, it is highly desirable for
   RTP to scale well for groups with one member to groups with one
   million members, without human intervention to "turn off" RTCP when
   it's no longer appropriate. This means that the same tools and



Rosenberg & Schulzrinne       Experimental
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