RFC 2762 (rfc2762) - Page 1 of 12
Sampling of the Group Membership in RTP
Alternative Format: Original Text Document
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