DMRP: a distributed multicast routing protocol for ATM networks

In this paper, we present a distributed multicast routing protocol (DMRP) for dynamic computation of multicast trees. This protocol is a distributed version of a centralized heuristic for dynamic Steiner tree computation. The protocol is deadlock-free and is a correct implementation of the centralized heuristic. It can be easily extended to the hierarchical framework supported by ATM Forum's PNNI protocols. This makes the protocol very scalable. Our motivation is to make this protocol a standard for multicasting under the PNNI framework. Our protocol draws a lot of inspiration from PIM, which has been proposed as the standard for multicasting in the Internet domain. We would like to emphasize that unlike PIM which caters to maintaining only soft-states, DMRP maintains hard states. The hard states are required under the ATM framework and make the DMRP protocol compatible with the philosophy of PNNI. The sharing of the multicast tree among multiple senders makes effective use of the network resources. This reduces the overall cost of the multicast tree. The protocol relies on participant initiated join, where the participant who wants to establish connection with the multicast group computes the path to the already existing multicast tree. Using simulations, we show that the number of messages generated before a participant can join the multicast tree is small. Further, the join latency is also small. The simplicity of the protocol lends itself to easy implementation for the support of multipoint connections under the PNNI framework.