An Evaluation of Shared Multicast Trees with Multiple Active Cores

Native multicast routing protocols have been built and deployed using two basic types of trees: singlesource, shortest-path trees and shared, core-based trees. Core-based multicast trees use less routing state compared to shortest-path trees, but generally have higher end-to-end delay and poor fault tolerance. In this paper we consider a new type of shared multicast structure that uses multiple, independent, simultaneously-active cores. Our design provides for low end-to-end delay, improved fault tolerance, and low source discovery delay, while balancing bandwidth cost and routing state. These results indicate that shared trees with multiple active cores are a viable alternative to shortest-path trees. The Internet’s multicast routing structure is still evolving [1]. Since its inception in 1992, the Multicast Backbone [7] — the multicast-capable subset of the Internet — has primarily consisted of DVMRP [9, 26], PIM [10], and MOSPF [21] routers, tied together with a complex set of interoperability rules and utilizing a flat routing topology. In recent years, network operators have introduced native multicast support, policy, and a hierarchical structure. The current near-term solution consists of domains running PIM-SM [13] internally, connected by MSDP [15] for interdomain reachability. Eventually, MSDP will be replaced by BGMP [20], although some engineers advocate using the single-source architecture proposed by Express [8]