Traffic grooming in WDM networks with multi-layer switches

We develop traffic grooming algorithms for WDM networks with multi-layer switches. We consider a node as an N-layer switch, in which a given layer k is an aggregated set of elements of layer k-1. Typical examples of layers are wavelengths, bands and fibers. The cost of a given node depends on the number of input and output ports of each layer. Assuming this model and a traffic matrix - with unity elements in layer 0 - minimizing the cost of the network consists of grooming traffic in such a way that as much traffic as possible is switched in the highest possible layer (fibers in our example). When some traffic is switched along a path in the network within the same layer, we represent it with a pipe. Each pipe has an associated linear cost depending on the current layer and on the number of nodes crossed in that pipe. In the case of a two layers model the problem was considered in Gerstel et al. (2000) for rings or in Cinker et al. (2000) for general topologies. We present an integer linear programming formulation for this model that aims to minimize the overall cost of the network for a given input traffic matrix. We ran experiments using the CPLEX optimization package on various topologies such as actual networks like the Pan-European all optical network (Batchelor et al. (1999)) as well as rings and meshes of various sizes.