Two New Algorithms for Static Virtual Topology Design in Optical WDM Networks

In this paper, we present two improved algorithms to establish lightpaths in a physical topology for the formation of a static WDM virtual topology. One of the major design issues in these networks is the volume of traffic in the intermediate nodes and the number of optical hops between network nodes so that the delay is less and at the same time greater capacity can be achieved. We first present an algorithm that is based on average weighted hop count as objective function to generate connection requests for connecting physical nodes optically. The second algorithm is a lookahead version of our first algorithm. We study the performances of the algorithms with regard to the performance metrics such as number of requests blocked, maximum hops required from a source to destination, maximum traffic to be handled in a node, average intermediate traffic and average spare wavelengths remaining after the completion of the virtual topologies. We find that on the average the lookahead scheme optimizes the objective function better, but at the cost of maximum load in any node. To improve the wavelength utilization we also discuss a wavelength assignment algorithm which uses the best alternate physical path while establishing lightpaths. We have simulated about six thousand random graphs of various sizes and densities to show how our algorithm behaves in comparison to a widely used existing algorithm.