Effects of wavelength routing and selection algorithms on wavelength conversion gain in WDM optical networks

Wavelength division multiplexing technology is emerging as the transmission mechanism for future optical networks. In these networks, it is desired that a wavelength can be routed without electrical conversions. Two technologies are possible for this purpose: wavelength selective cross-connects (WSXC), and wavelength interchanging cross-connects (WIXC) which involve wavelength conversion. It is believed that wavelength converters may improve the blocking performance, but there is a mix of results in the literature. We use two metrics to quantify this gain: reduction in blocking probability and increase in maximum utilization, compared to a network without converters. We study the effects of wavelength routing and selection algorithms on these measures for mesh networks. We propose two k shortest path algorithms for selecting the route-wavelength pair: one selecting the pair that maximizes conversion gain (called the MHLR algorithm), and another selecting the least loaded pair (called the LLR algorithm). The LLR algorithm achieves much better blocking performance compared to the MHLR algorithm while conversion gains for both algorithms are comparable. We also conclude that conversion gains can be orders of magnitude larger with these algorithms compared to the shortest path routing. However, these large gains are not realized in a sufficiently wide utilization region, and are diminished with an increased number of fibers. Therefore, the overall usefulness of wavelength conversion in long-distance networks emerges as questionable.