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 chang ed to reflect changes in traffic conditions. This paper characterizes the g ain in traffic capacity that a reconfigurable wavelength division multiplez ed (WDM) network offers over a fixed topology network where lightpath conne ctions 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 bloc king probability, We develop a system model to approximate the blocking pro bability for both the fixed and reconfigurable systems. This model is diffe rent from previous models developed to analyze the blocking probability in WDM networks in that it accounts for a port limitation at the nodes. We val idate our model via simulation and find that it agrees strongly with simula tion results, We study high-bandwidth calls, where each call requires an en tire wavelength and find that reconfigurability offers a substantial perfor mance improvement, particularly when the number of available wavelengths si gnificantly exceeds the number of ports per node. In this case, in a ring w ith N nodes, the gain approaches a factor of N/2 over a fixed topology unid irectional ring, and N/4 over a fixed topology bidirectional ring. Hence, a reconfigurable unidirectional (bidirectional) ring can support N/2(N/4) ti mes the load of a fixed topology unidirectional (bidirectional) ring. We al so show that for a given traffic load, a configurable system requires far f ewer ports per node than a fixed topology system. These port savings can po tentially result in a significant reduction in overall system costs.