A New Model for Optimal Routing and Wavelength Assignment in Wavelength Division Multiplexed Optical Networks

We consider the problem of routing and assignment of wavelength (RAW) in optical networks. Given a set of re-quests for all-optical connections (or lightpaths), the problem is to [a)find routes from the source nodes to their respective destination nodes, and [ b) assign wavelengths to these routes. Since the number of wavelengths is limit-ed, lightpaths cannot be established between every pair of access nodes. In this paper, we first consider the dynamic RAW problem where lightpath requests arrive randomly with exponentially distributed call holding times. Then, the static RAW problem is considered which assumes that all the lightpaths that are to be set-up in the network are known initially. Several heuristic algorithms have already been proposed for establishing a maximum number of lightpaths out of a given set of requests. Howevel; most of these algorithms are based on the traditional model of cir-cuit-switched networks where routing and wavelength as-signment steps are decoupled. In this paper a new graph-theoretic formulation of the RAW problem, dubbed as lay-ered-graph, has been proposed which provides an effi-cient tool for solving dynamic as well as static RAWprob-lems. The layered-graph model also provides a framework for obtaining exact optimal solution for the number of re-quested lightpaths as well as for the throughput that a giv-en network can support. A dynamic and two static RAW schemes are proposed which are based on the layered-graph model. Layered-graph-based RAW schemes are shown to peg?orm better than the existing ones. 1