Delay constrained multicast routing: What can we learn from an exact approach?

Delay constrained multicast routing is a typical problem in many emerging applications such as voice over IP, video on demand and teleconferencing etc. Equivalently referred to as the delay constrained minimum Steiner tree (DCMST), this problem requires to find a tree spanning a source and a set of destination nodes such that the total cost is minimized while the delay from the source to each destination node is no more than a preset upper bound. Due to its NP-complete nature, all previous work focused on developing efficient heuristics. In this paper, we study this problem from a completely different perspective by using an exact approach, which has never been done before. Preliminary experimental results demonstrate that the exact algorithm described in this paper works surprisingly well, and in certain cases it outperforms some fast heuristics. Even though the exact algorithm is not expected to be used in practice, its relative high efficiency makes it possible of creating a set of benchmark instances for evaluating the performance of a heuristic most accurately. In addition, with the help of this algorithm, we are able to gain insight into some interesting properties of this problem, which in turn may help us to design more efficient heuristics.