Quantifying the benefit of configurability in circuit-switched WDM ring networks

We attempt to characterize the gain in traffic capacity that a reconfigurable network offers over a fixed topology network. We define the gain as the ratio of the maximum offered loads that the two systems can support for a given blocking probability. We develop a system model to analytically predict the blocking probability for both the fixed and reconfigurable systems. This model is different from previous models developed to analyze the blocking probability in WDM networks in that it accounts for a port limitation at the nodes. We study high-bandwidth calls, where each call requires an entire wavelength. We find that reconfigurability offers a substantial performance improvement, particularly when the number of available wavelengths significantly exceeds the number of ports per node. In this case, we find that the gain approaches a factor of N/2 over a fixed topology unidirectional ring, and N/4 over a fixed topology bi-directional ring (where N is the number of nodes in the ring). We validate our model via simulation, and we find that it agrees strongly with the simulation results, particularly for a large number of ports per node. We also obtain upper and lower bounds on capacity for various ring topologies that give additional insight into the benefits of configurability