Exact ILP solution for the grooming problem in WDM ring networks

We consider the problem of traffic grooming in second generation SONET/WDM rings with low-rate traffic circuits associated with a set of heterogeneous rate granularities. While networks are no longer limited by transmission bandwidth, the key issue in WDM network design has evolved towards the processing capabilities of electronic switches, routers and multiplexers. Therefore, we focus here on traffic grooming with minimum interconnecting equipment cost. We first formulate the problem as a generic integer linear programming (ILP) or a mixed integer linear programming (MILP) problem that encompasses several design specifications: UPSR vs. BLSR, non bifurcated vs. bifurcated flows, wavelength continuity constrained or free signal regeneration. Within the context of second generation SONET/WDM rings, we define the cost by a function of the number of transport blades, taking into account that the number of transport blades makes up a significant portion of the overall network cost. Using the CPLEX mixed ILP package, we next compare the optimal solutions of the ILP or MILP programs for different design assumptions, including the classical assumptions with a single hub where the lightpaths directly connect the hub to all other nodes.