Issue No. 04 - April (2008 vol. 19)
In this paper, we propose a scalable and adaptive multicast forwarding mechanism based on Explicit Multicast (Xcast). This mechanism optimizes the allocation of forwarding states in routers and can be used to improve the scalability of traditional IP multicast and Source-Specific Multicast. Two optimization problems are formulated in this paper. The first one, MINSTATE, is to minimize the total number of routers storing forwarding states in a multicast tree. We design a distributed algorithm that obtains the optimal solution of the problem. The second one, BALANCESTATE, is to minimize the maximum number of forwarding states stored in a router for all multicast groups. We prove that the second problem is NP-hard and propose an approximation algorithm and a distributed algorithm for the problem. We prove that this allocation is a special case of our mechanism. From the simulation results, we show that the forwarding state allocation provided by previous work is concentrated on the backbone routers in the Internet, which may cause the scalability problem. In contrast, our mechanism can balance the forwarding states stored among routers, and also reduce the number of routers storing the forwarding states of a multicast tree. Therefore, our mechanism can improve the scalability of Source-Specific Multicast and traditional IP multicast.
W. Liao and D. Yang, "Optimal State Allocation for Multicast Communications With Explicit Multicast Forwarding," in IEEE Transactions on Parallel & Distributed Systems, vol. 19, no. , pp. 476-488, 2007.