An Interval-Based Scheduling Algorithm for Optical WDM Star Networks

Abstract

This paper considers scheduling algorithms for multiple access protocols associated with wavelength division multiplexed (WDM) multi-channel optical networks based on the star topology. To share the available channels among nodes, several demand assignment multiple access protocols based on reservation schemes have been proposed. The core of such reservation-based protocols is the scheduling algorithm, which allocates channels and time slots to the nodes based on traffic demand. The key objectives of the scheduling algorithm design are maximization of network utilization and minimization of packet delay. There is a trade-off between these two requirements: it takes more computation time to achieve a better utilization, which in turn will increase packet delay. This trade-off directly affects the overall network performance. Another important requirement is the consideration of transceiver tuning latencies. In this paper, we propose an on-line scheduling algorithm called OIS (On-line Interval-based Scheduling) to balance these requirements and increase network throughput. We also require that the scheduling algorithms be simple so that hardware implementation is feasible to reduce overall delay. We compare our scheduling algorithm to the Transmission Assignment Algorithm (TAA) studied by Borella and Mukherjee (1996); and to a matrix decomposition algorithm studied by Sivalingam and Wang (1996). We show that our algorithm, although suffering from small utilization loss, requires significantly less computation time and results in higher network throughput. In particular, for higher network speeds such as 2.4 Gbps per channel, the potential improvement using our algorithm is substantial. We also provide conditions when either protocol performs better compared to the other.