Improved Approaches for Cost-Effective Traffic Grooming in WDM Ring Networks: ILP Formulations, Single-Hop and Multihop Connections *

Traffic grooming is the term used to describe how different traffic streams are packed into higher-speed streams. In a WDM SONET/ring network, each wavelength can carry several lower-rate traffic streams in TDM fashion. The traffic demand, which is an integer multiple of the timeslot capacity, between any two nodes is established on several TDM virtual connections. A virtual connection needs to be added and dropped only at the two end nodes of the connection; as a result, the electronic Add/Drop Multiplexors (ADMs) at intermediate nodes (if there are any) will electronically bypass this timeslot. Instead of having an ADM on every wavelength at every node, it may be possible to have some nodes on some wavelength where no add/drop is needed on any time slot; thus, the total number of ADMs in the networks (and hence the network cost) can be reduced. Under the static traffic pattern, the savings can be maximized by carefully packing the virtual connections into wavelengths. In this work, we allow arbitrary (non-uniform) traffic and we first present a formal mathematical definition of the problem, which turns out to be an integer linear program (ILP). Then, we propose a simulated-annealing-based heuristic algorithm for the case where all the traffic are carried on directly connected virtual connections (referred to as the “single-hop” case). Then, we study the case where a hub node is used to bridge traffic from different wavelengths (referred to as the multihop case). We find the following main results. The simulated-annealing-based approach has been found to achieve the best results so far in most cases relative to other comparable approaches proposed in the literature. In general, a multihop approach can achieve better equipment savings when the grooming ratio is large, but it consumes more bandwidth. *This work has been supported in part by Intelligent Fiber Optic Systems (IFOS) and the State of California UC MICRO Program Grant No. 99-086.