Forwarding state reduction for delay-constrained multicasting in IP networks

The multicast forwarding state scalability issue is one of the critical issues that delay the deployment of IP multicast in the global Internet. With traditional protocols, each router is required to maintain a forwarding entry locally for each group whose distribution tree passes through the router itself. Consequently, the number of forwarding entries at routers increases linearly with the number of concurrent ongoing multicast sessions. This can pose the forwarding state scalability issue when the number of multicast sessions is very large. The paper addresses this scalability issue in providing efficient delay-constrained multicasting in IP networks. We propose a scalable multicast routing heuristic. Its computational complexity is deduced to be O(m|V|²), where m is the size of the multicast group and |V| is the size of the network. In particular, if the heuristic is executed online, its computational complexity can be further reduced to O(m²). This property makes the heuristic scale well with the number of concurrent sessions since multicasting subject to a delay constraint is typically executed on a per-session basis. Simulation results show that the proposed heuristic can achieve high performance in reducing the forwarding state at routers and in utilizing network resources efficiently.