Solving very large RWA data instances

While the Routing and Wavelength Assignment (RWA) has been widely studied, few studies attempt to solve realistic size instances, namely, with 150 wavelengths per fiber and a few hundred nodes. Indeed, state of the art is closer to around 20 nodes and 30 wavelengths, regardless of what the authors consider, heuristics or exact methods with very few exceptions. In this paper, we are interested in reducing the gap between realistic data sets and testbed instances that are often used, using exact methods. Even if exact methods may fail to solve in reasonable time very large instances, they however output bounds on the accuracy of the heuristic solutions. The novelty of our work is to exploit the observations that optimal solutions contain a very large number of lightpaths associated with shortest paths or k shortest paths with a small k. We propose different RWA algorithms that lead to solve exactly or near exactly much larger instances than in the literature with up to 150 wavelengths and 50 nodes.