Quantifying the benefit of configurability in circuit-switched WDM ring networks with limited ports per node

In a reconfigurable network, lightpath connections can be dynamically changed to reflect changes in traffic conditions. This paper characterizes the gain in traffic capacity that a reconfigurable wavelength division multiplexed (WDM) network offers over a fixed topology network where lightpath connections are fixed and cannot be changed. 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 approximate 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 validate our model via simulation and find that it agrees strongly with simulation results. We study high-bandwidth calls, where each call requires an entire wavelength and 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, in a ring with N nodes, the gain approaches a factor of N/2 over a fixed topology unidirectional ring, and N/4 over a fixed topology bidirectional ring. Hence, a reconfigurable unidirectional (bidirectional) ring can support N/2(N/4) times the load of a fixed topology unidirectional (bidirectional) ring. We also show that for a given traffic load, a configurable system requires far fewer ports per node than a fixed topology system. These port savings can potentially result in a significant reduction in overall system costs.