Exploiting the Bandwidth-Memory Tradeoff in Multicast State Aggregation

Multicast data distribution is achieved through three mechanisms: rendezvous of senders with receivers, distribution tree building protocols, and multicast data forwarding. While the first two mechanisms have been extensively studied, scaling multicast forwarding state has not been addressed. The lack of efficient strategies for multicast forwarding state aggregation could seriously inhibit the deployment of inter-domain multicast, because there is no “natural” limit to the number of concurrent multicast groups, especially given the possible proliferation of lowbandwidth multicast groups. In this paper, we describe leaky aggregation, which carefully trades off gratuitous data distribution for reduced forwarding state. Our simulations show that the leaky strategy, under expected operating conditions, scales forwarding state as the number of “highbandwidth” groups. This is desirable scaling behavior, given that network capacity limits the number of such groups. Keywords— Multicast, Multicast Forwarding, State Aggregation