An efficient and general graph-theoretic model (the wavelength-graph (WG)) has been proposed which enables solution of the static routing and wavelength assignment (RWA) problems in multihop wavelength routing (WR) wavelength division multiplexing (WDM) networks simultaneously, and-as a unique feature-it optimises the optical layer jointly with the electrical one. Based on the proposed WG model the problem has been formulated as an integer linear program (ILP), solved by stochastic algorithms improved by simple heuristics. The topology of the physical layer, the type of each node (e.g., OADM, OXC or EXC), the number of available wavelengths per link and the capacity of each wavelength-channel are assumed given with the aggregated traffic demand of each node-pair. The output of the optimisation is the system of wavelength paths, light paths and semi-light paths. The objective of the optimisation is to reduce resource usage at upper (electrical) layers, subject to the constrained amount of capacity of each wavelength and a limited number of wavelengths. Although the problem to be solved is NP-hard, all methods proposed give a result in a very short time.
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