RFC 2121 (rfc2121) - Page 1 of 12
Issues affecting MARS Cluster Size
Alternative Format: Original Text Document
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