Multicast scheduling in WDM switching networks

Optical WDM networks are attracting more and more attention because of its huge bandwidth to meet ever increasing demand of modern networking applications. In this paper we study supporting multicast in WDM switching networks. Multicast is the operation to send information from one source to multiple destinations. In WDM switching networks, contention occurs when one output fiber is the destination of more than k inputs, where k is the number of wavelengths on each fiber. In this paper, we study scheduling algorithms which can select a group of multicast connection requests that are contention-free. We first prove that the problem of scheduling the maximum number of such connection requests through the network simultaneously is NP-hard. On the other hand, lack of optical buffers in WDM switching networks requires a very fast scheduling algorithm. We then turn to develop approximation scheduling algorithms that can provide sub-optimal solutions. We present four polynomial approximation scheduling algorithms and study their performance through simulations. We also discuss their performance ratio to the optimal algorithm. Our results demonstrate that one of the simple algorithms (the fastest one) yields throughput close to other three more complex algorithms, thus could be a good candidate for multicast scheduling in WDM switching networks.