Interconnected WDM Ring Networks: Strategies for Interconnection and Traffic Grooming*

In telecommunication networks, SONET self -healing rings are widely deployed as transport infrastructure. Typically, multiple rings are interconnected together to provide a large geographical coverage. A typical network-planning problem of traffic grooming deals with packing several TDM sub-channels into high-speed wavelength channels in a WDM ring with the goal of saving SONET equipment usage. The two problems of how to interconnect WDM ring networks as well as how to groom the traffic in interconnected rings are addressed. We compare four interconnection strategies rangin g from using traditional Digital Crossconnects to using innovative Optical Crossconnects. We present both formal mathematical formulations and detailed heuristic approaches for solving the traffic -grooming problems in interconnected rings. Our quantitative results show that TDM-level switching is useful when the number of sub-channels in a wavelength is neither too small nor too large, while pure optical switching may be a better choice for other cases. A mixed switching architecture can achieve maximum ben efit by adopting a winning strategy from the above two approaches.