This paper proposes a new fixed-alternate routing algorithm for all-optical WDM networks without wavelength conversion in order to reduce the connection blocking probability. The key idea in the proposed fixed-alternate routing algorithm is to try to route the traffics in approximately the optimal way. The multiple routing paths between each source-destination pair are arranged and used in descending order according to the traffic intensities obtained by solving a nonlinear multicommodity flow optimization problem. It is well known that finding the connection blocking probability is a very difficult task. Therefore, an objective function closely related to the connection probability is devised and used to formulate a nonlinear multicommodity flow optimization problem. Simulations are performed to study the performance of the proposed fixed-alternate routing algorithm. Our simulation results show that sorting the routing paths according to the optimally assigned traffic intensities in the proposed fixed-alternate routing algorithm can effectively reduce the connection blocking probability compared with sorting the routing paths according to hop counts in a typical fixed-alternate routing algorithm. In general, in all-optical WDM networks, a connection request that goes through a longer path experiences higher connection blocking probability than a connection request that goes through a shorter path. This is known as the fairness problem. Our simulation results show that the proposed algorithm yields better fairness than a typical fixed-alternate routing algorithm.
