Improved Construction Heuristics and Iterated Local Search for the Routing and Wavelength Assignment Problem Kerstin Bauer 1 , Thomas Fischer 1 , Sven O. Krumke 2 , Katharina Gerhardt 2 , Stephan Westphal 2 , and Peter Merz 1 1 Department of Computer Science University of Kaiserslautern, Germany {k_bauer,fischer,pmerz}@informatik.uni-kl.de 2 Department of Mathematics University of Kaiserslautern, Germany {krumke,gerhardt,westphal}@mathematik.uni-kl.de Abstract. This paper deals with the design of improved construction heuristics and iterated local search for the Routing and Wavelength As- signment problem (RWA). Given a physical network and a set of com- munication requests, the static RWA deals with the problem of assigning suitable paths and wavelengths to the requests. We introduce bench- mark instances from the SND library to the RWA and argue that these instances are more challenging than previously used random instances. We analyze the properties of several instances in detail and propose an improved construction heuristic to handle ‘problematic’ instances. Our iterated local search finds the optimum for most instances. 1 Introduction The Routing and Wavelength Assignment problem (RWA) deals with Wavelength Division Multiplexed (WDM) optical networks, where communication requests between nodes in a network have to be fulfilled by routing them on optical fiber links with a given capacity. Chlamtac et al . [1] showedthe static RWA in general networks to be NP-complete since it contains the graph-coloring problem. The problem is defined as follows: Given is a graph G(V,E,W ) with nodes V , arcs E and wavelengths W . An arc e ∈ E is an optical fiber link in the physical network, where each wavelength λ ∈ W is eligible. A request r i =(v s i ,v t i ,d i ) connects nodes v s i and v t i having a demand of d i ∈ N + . For each unit of demand a lightpath between the request’s endpoints has to be established. A lightpath is an optical path between two nodes created by the allocation of the same wave- length throughout the path of optical fiber links providing a ‘circuit-switched’ interconnection. Lightpaths have to fulfill two constraints: The wavelength con- flict constraint defines that each wavelength on a physical link is used by at most one lightpath at the same time. The wavelength continuity constraint requires a lightpath to use the same wavelength on each link. There are problem variants J. van Hemert and C. Cotta (Eds.): EvoCOP 2008, LNCS 4972, pp. 158–169, 2008. c  Springer-Verlag Berlin Heidelberg 2008