VENUS - Very Extensive Non-Unicast Service (RFC2191)
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2019-Feb-15
Internet Society Requests For Comment (RFCs)
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. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.
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.
The MARS model (RFC2022) 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.
The classical model of the Internet running over an ATM cloud consists of multiple Logical IP Subnets (LISs) interconnected by IP Routers . The evolving IP Multicast over ATM solution (the "MARS model" ) retains the classical model. The LIS becomes a "MARS Cluster", and Clusters are interconnected by conventional IP Multicast routers (Mrouters).
The development of NHRP , 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 [Page 1]
RFC 2191 VENUS September 1997
before being re-applied to the multicast scenario. Indeed, the service provided by the MARS and MARS Clients in  are almost orthogonal to the IP unicast service over ATM.
For the sake of discussion, let’s call this hypothetical multicast shortcut discovery protocol the "Very Extensive Non-Unicast Service" (VENUS). A "VENUS Domain" is defined as the set of hosts from two or more participating Logical IP Subnets (LISs). A multicast shortcut connection is a point to multipoint SVC whose leaf nodes are scattered around the VENUS Domain. (It will be noted in section 2 that a VENUS Domain might consist of a single MARS Cluster spanning multiple LISs, or multiple MARS Clusters.)
VENUS faces a number of fundamental probl...