Internet Engineering Task Force Audio/video Transport Wg Internet-draft New Results in Rtp Scalability

Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as \work in progress". To learn the current status of any Internet-Draft, please check the \1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 1 Abstract Recently, a number of problems related to RTP scalability to large multicast groups have been identiied. The main problem, congestion of RTCP packets due to near-simultaneous joins, has been resolved in previous work. In this document, we present some additional problems and describe the solutions. In particular, we discuss the problem of BYE oods and premature timeouts. To resolve the BYE ood problem, we propose a BYE reconsideration mechanism. To help alleviate premature timeouts, we propose a reverse timer reconsideration algorithm. Both algorithms are simple, and require minimal state and computation. 2 Introduction Recently, a number of problems related to RTP 1] scalability to large multicast groups have been identiied 2]. The most serious of these problems is RTCP congestion in simultaneous joins. In this scenario, a large number of users join a session at nearly the same time. This can happen if the join is an automatic response to an announced session on the mbone 3], or if RTP is being used for broadcast applications, and a popular show comes on. When this happens, each user joins the group believing that they are the only user. They then send their initial RTCP packets within a short period of time, causing a ood of RTCP reports. This can result in network and/or access link congestion. For modem dial-in users, the slow access links can cause congestion even with moderate simultaneous joins. To combat this problem, an algorithm called reconsideration has been proposed 4] 5]. This algorithm causes backoo in the transmission of RTCP packets as group sizes increase. However, several new problems have recently been discovered relating to RTCP scalability. These diiculties are similar to the step-join congestion problem, but diierent in that they require additional algorithms to resolve. This document describes the two …