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 requests 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 limited, 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. However most of these algorithms are based an the traditional model of circuit-switched networks where routing and wavelength assignment steps are decoupled. In this paper a new graph-theoretic formulation of the RAW problem, dubbed as layered-graph, has been proposed which provides an efficient tool for solving dynamic as well as static RAW problems. The layered-graph model also provides a framework for obtaining exact optimal solution for the number of requested lightpaths as well as far the throughput that a given 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 perform better than the existing ones