Efficient routing and wavelength assignment for reconfigurable WDM networks with wavelength converters

We consider the problem of wavelength assignment in a reconfigurable bi-directional ring network with wavelength converters. We show that for N-node P-port bidirectional rings, a minimum number of [PN/4] wavelengths are required to support all possible virtual topologies in a rearrangeably non-blocking fashion, and provide an algorithm that meets this bound for connected topologies using no more than [PN/2] wavelength converters. This improves over the tight lower bound of [PN/3] wavelengths required for such rings given in [1] if no wavelength conversion is available. We also provide another algorithm that uses more wavelengths yet requires significantly fewer converters. Both algorithms are then extended to the case of unconnected topologies using at most one additional wavelength. Finally, we develop a method that allows the wavelength converters to be arbitrarily located at any node in the ring. This gives significant flexibility in the design of the networks. For example, all [PN/2] converters can be collocated at a single hub node, or distributed evenly among the N nodes with [P/2] converters at each node.