Capacitated Multi-Layer Network Design with Unsplittable Demands: Polyhedra

We consider the Capacitated Multi-Layer Network Design with Unsplittable demands (CMLND-U) problem. Given a two-layer network and a set of traffic demands, this problem consists in installing minimum cost capacities on the upper layer so that each demand is routed along a unique ”virtual” path (even using a unique capacity on each link) in this layer, and each installed capacity is in turn associated a ”physical” path in the lower layer. This particular hierarchical and unsplittable requirement for routing arises in the design of optical networks, including optical OFDM based networks. In this paper, we give an ILP formulation to the CMLND-U problem and we take advantage of its sub-problems to provide a partial characterization of the CMLND-U polytope including several families of facets. Based on this polyhedral study, we develop a branch-and-cut algorithm for the problem and show its effectiveness though a set of experiments, conducted on random, realistic and real instances.