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A heuristic methodology is proposed for the setting up of a stack of wavelength-division-multiplexing (WDM) rings with wavelength reuse when the design traffic exceeds the capacity of a single ring and no wavelength conversion is employed. A ring stack consists of an overlay of rings routed over the same physical route, and it can be setup and dimensioned in a myriad of ways. The design traffic comprises of a set of bidirectional lightpaths or wavelength connections. There exists a tradeoff between the number of nodes and the number of rings required to carry this traffic, and it is demonstrated that both cannot be minimized simultaneously. For certain traffic patterns, we identify stacks requiring the minimum number of nodes or WADM's, which is desirable from a cost point of view, and stacks requiring the minimum number of rings. An algorithm is presented that manipulates the tradeoff phenomenon to produce a spectrum of designs with deterministic composition. We finally conclude by identifying factors that may influence the choice of design.
Date of Publication: April 2000