Optimal FDL Design for Time-Wavelength Crossconnects and Optical Packet Switches

Time-Wavelength-Switched Networks (TWSNs) provide a finer bandwidth granularity than traditional wavelength routing networks. In TWSNs, time on every wavelength is slotted and the crossconnects are configured to switch slots within a frame, and connections are assigned one or more slots per frame. Fiber Delay Line (FDL) banks within the crossconnects can reduce the probability of connection blocking due to output slot contention. In this paper, we consider the optimal construction of an FDL bank with a limited number of recirculations through the FDLs. Specifically, given a frame consisting of M slots, an FDL bank of D FDLs per output link, we develop a method to find a set of delay values D = {d(1), d(2), d(D)} such that the set of achievable delays using no more than K recirculations through the bank is maximized. Maximizing the number of achievable delays provides more flexibility in slot provisioning for connections, and is expected to decrease the blocking probability. We investigate the impact of the FDL configuration on a crossconnect's performance. Our results show that the optimal FDL bank construction presented here achieves better blocking than previously considered FDL bank configurations. We also present a solution to the FDL bank design problem for an optical packet switch, and show through simulations that packet drop probability is considerably reduced for the optimal configuration.