Multicast tree construction in directed networks

Significant interest exists within the military in moving towards an integrated services environment where traditional network services such as ftp, telnet, and e-mail can co-exist with real-time services such as voice, video, and satellite imagery. Multicast routing is an effective means of providing the efficient utilization of network resources required to realize such an environment. Traditional multicast routing algorithms assume a symmetric network topology. Many military communication assets are either asymmetric in their load or asymmetric in capacity (a good example is the direct broadcast satellite). In addition, many military communication assets are bandwidth constrained, and routing symmetrically may further contribute to congestion. Therefore, a multicast tree construction which tolerates network asymmetry is desirable for many military communication environments. This paper proposes an algorithm for constructing shared multicast distribution trees in networks with asymmetric link capacities or loads. The algorithm tolerates asymmetry by building distinct, loop-free, sender and receiver paths onto a shared delivery tree. Additionally, the algorithm exhibits desirable security properties. Simulation results are presented that demonstrate the lower tree cost and better load balancing characteristics of the resultant trees over shortest path trees, with only a modest increase in path length.