RFC 2121 (rfc2121) - Page 1 of 12

Issues affecting MARS Cluster Size

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Network Working Group                                      G. Armitage
Request for Comments: 2121                                    Bellcore
Category: Informational                                     March 1997


                   Issues affecting MARS Cluster Size

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   IP multicast over ATM currently uses the MARS model [1] to manage the
   use of ATM pt-mpt SVCs for IP multicast packet forwarding. The scope
   of any given MARS services is the MARS Cluster - typically the same
   as an IPv4 Logical IP Subnet (LIS). Current IP/ATM networks are
   usually architected with unicast routing and forwarding issues
   dictating the sizes of individual LISes. However, as IP multicast is
   deployed as a service, the size of a LIS will only be as big as a
   MARS Cluster can be. This document provides a qualitative look at the
   issues constraining a MARS Cluster's size, including the impact of VC
   limits in switches and NICs, geographical distribution of cluster
   members, and the use of VC Mesh or MCS modes to support multicast
   groups.

1. Introduction

   A MARS Cluster is the set of IP/ATM interfaces that are willing to
   engage in direct, ATM level pt-mpt SVCs to perform IP multicast
   packet forwarding [1]. Each IP/ATM interface (a MARS Client) must
   keep state information regarding the ATM addresses of each leaf node
   (recipient) of each  pt-mpt SVC it has open. In  addition, each MARS
   Client receives MARS_JOIN and MARS_LEAVE messages from the MARS
   whenever there is a requirement that Clients around the Cluster need
   to update their pt-mpt SVCs for a given IP multicast group.

   The definition of Cluster 'size' can mean two things - the number of
   MARS Clients using a given MARS, and the geographic distribution of
   MARS Clients. The number of MARS Clients in a Cluster impacts on the
   amount of state information any given client may need to store while
   managing  outgoing  pt- mpt SVCs. It also impacts on the average rate
   of JOIN/LEAVE traffic that is propagated by the MARS on
   ClusterControlVC, and the number of pt-mpt VCs that may need
   modification each time a MARS_JOIN or MARS_LEAVE appears on
   ClusterControlVC.



Armitage                     Informational
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