RFC 2191 (rfc2191) - Page 1 of 12

VENUS - Very Extensive Non-Unicast Service

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Network Working Group                                      G. Armitage
Request for Comments: 2191                         Lucent Technologies
Category: Informational                                 September 1997


               VENUS - Very Extensive Non-Unicast Service

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

   The MARS model (RFC 2022) provides a solution to intra-LIS IP
   multicasting over ATM, establishing and managing the use of ATM pt-
   mpt SVCs for IP multicast packet forwarding. Inter-LIS multicast
   forwarding is achieved using Mrouters, in a similar manner to which
   the "Classical IP over ATM" model uses Routers to inter-connect LISes
   for unicast traffic. The development of unicast IP shortcut
   mechanisms (e.g.  NHRP) has led some people to request the
   development of a Multicast equivalent. There are a number of
   different approaches. This document focuses exclusively on the
   problems associated with extending the MARS model to cover multiple
   clusters or clusters spanning more than one subnet. It describes a
   hypothetical solution, dubbed "Very Extensive NonUnicast Service"
   (VENUS), and shows how complex such a service would be. It is also
   noted that VENUS ultimately has the look and feel of a single, large
   cluster using a distributed MARS.  This document is being issued to
   help focus ION efforts towards alternative solutions for establishing
   ATM level multicast connections between LISes.

1. Introduction

   The classical model of the Internet running over an ATM cloud
   consists of multiple Logical IP Subnets (LISs) interconnected by IP
   Routers [1].  The evolving IP Multicast over ATM solution (the "MARS
   model" [2]) retains the classical model. The LIS becomes a "MARS
   Cluster", and Clusters are interconnected by conventional IP
   Multicast routers (Mrouters).

   The development of NHRP [3], a protocol for discovering and managing
   unicast forwarding paths that bypass IP routers, has led to some
   calls for an IP multicast equivalent.  Unfortunately, the IP
   multicast service is a rather different beast to the IP unicast
   service. This document aims to explain how much of what has been
   learned during the development of NHRP must be carefully scrutinized



Armitage                     Informational
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