Effectiveness of optimal node assignments in wavelength division multiplexing networks with fixed regular virtual topologies

In this paper, we consider the optimal node assignment problem in wavelength division multiplexing lightwave networks, which is to optimally assign network nodes to the locations in a regular virtual topology through wavelength assignments. Unlike previous work, which concentrated on a single virtual topology, we consider this problem as a class of problems by formulating it as a quadratic assignment problem. As a result, our objective is of a wider scope: identify the factors responsible for effective (or ineffective) node assignments. Optimal node assignments are considered effective if they could significantly improve the performance given by a random node assignment. The performance metric considered here is the average weighted hop distance. Based on a set of carefully designed experiments and analyses, we have concluded that variability in virtual topologies' hop-distance distributions, variability in network traffic distributions, and pattern matching between distance and traffic matrices are major factors in determining the effectiveness of optimal node assignments. In particular, optimal node assignments are most effective for linear virtual topologies and clustered traffic patterns.