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Routing, Wavelength Assignment in Optical Networks Using an Efficient and Fair EDP Algorithm Pallavi Manohar and V. Sridhar ? Applied Research Group, Satyam Computer Services Ltd., 14 Langford Avenue, Lalbagh Road, Bangalore 560 025 INDIA. { pallavi mm, sridhar } @satyam.com Abstract. Routing and wavelength assignment (RWA) problem in wavelength routed optical networks is typically solved using a combi- nation of integer programming and graph coloring. Such techniques are complex and make extensive use of heuristics. RWA with maximum edge disjoint path (EDP) using simple bounded greedy algorithm is shown to be as good as previously known solution method. In this paper, we present shortest path Frst greedy algorithm for maximum EDP with construction of path conflict graph which gives fair and efficient solution to the RWA problem in optical networks. Keywords: Optical Networks, Routing and Wavelength Assignment, Edge Disjoint Path Algorithms. 1 Introduction Routing and wavelength assignment (RWA) for the lightpaths of the virtual topology in wavelength routed optical networks is typically solved in two parts – lightpath routing, to determine the route of the lightpaths on the physical topol- ogy, and wavelength assignment, to assign the wavelengths to each lightpath in the virtual topology such that wavelength constraints are satisFed for each phys- ical link. The RWA problem for a given physical network and virtual topology is known to be NP-complete. ±urther, routing and wavelength assignment prob- lems are each known to be NP-complete [3] and many heuristic solutions have been proposed [7,8]. See [3,10,11] for a survey of the various solutions to the RWA problem. Lightpath routing is done by Frst selecting the lightpaths and then assigning routes to them. The order in which the lightpaths are assigned can be selected by di²erent heuristic schemes such as random, Fxed, longest- Frst, or shortest-Frst. Routes can be found by techniques such as shortest path algorithm, weighted shortest path, or K shortest path algorithms. The route is selected from the available candidates using di²erent schemes such as random, Frst-Ft, or probability. The RWA problem is also solved by formulating it as an ? Member, IEEE M. Bubak et al. (Eds.): ICCS 2004, LNCS 3038, pp. 1178–1184, 2004. c ± Springer-Verlag Berlin Heidelberg 2004
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Routing, Wavelength Assignment in Optical Networks 1179 integer linear program (ILP) optimization problem [9] with one of two objective functions – minimize the required number of wavelengths to establish the given set of lightpaths and maximize the number of established lightpaths with a Fxed number of wavelengths. A hard version of the problem is when no wavelength conversion is used at the routing nodes of the physical network and this requires that the wavelength continuity constraint be satisFed, i.e., a lightpath should use the same wavelength on all the links in its path. Extensive and complex heuris- tics are used to solve the ILP. One solution considers a fractional relaxation with
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