Photon Netw Commun (2009) 17:21–33 DOI 10.1007/s11107-008-0140-3 Genetic algorithm to design logical topologies in reconfigurable WDM networks Ramón J. Durán · Ignacio de Miguel · Noemí Merayo · Patricia Fernández · Juan Carlos Aguado · Rubén M. Lorenzo · Evaristo J. Abril Received: 22 December 2006 / Accepted: 23 July 2007 / Published online: 11 August 2008 © Springer Science+Business Media, LLC 2008 Abstract A new method to design logical topologies based on genetic algorithms is presented. Not only does the algo- rithm determine which nodes should be connected by means of lightpaths with the aim of minimizing congestion, but it also solves the routing and wavelength assignment problem. In this way, the algorithm guarantees that the logical topol- ogy obtained can be embedded in the optical network subject to the available set of resources. The algorithm is effective in terms of both congestion and fairness. For instance, when compared with other work, the congestion is significantly reduced (from 20% to 75% depending on the matrix of traf- fic considered), and the fairness, when evaluated in terms of the Jain index, is generally higher than 0.94. Moreover, the algorithm brings advantages when employed in dynamic sce- narios where the logical topology is frequently reconfigured, as it is fast and, in contrast to other algorithms previously proposed, the calculation process can be stopped at any time (if required) in order to give the best virtual topology found up to the moment. Keywords Logical topology design · Genetic algorithms · Congestion · Wavelength routing · Optical networks 1 Introduction Communication networks are facing not only significant increases in data traffic but also frequent variations of traffic patterns. Wavelength-routed optical networks are a solution for that scenario as they offer the possibility of R. J. Durán (B ) · I. de Miguel · N. Merayo · P. Fernández · J. C. Aguado · R. M. Lorenzo · E. J. Abril Department of Signal Theory, Communications and Telematic Engineering, University of Valladolid, Campus “Miguel Delibes”, 47011 Valladolid, Spain e-mail: rduran@tel.uva.es dynamically adapting to traffic conditions by means of rec- onfiguring the virtual (or logical) topology, that is, the set of lightpaths embedded in it. A lightpath is an all-optical connection between two net- work nodes, which are not necessarily adjacent in the phys- ical topology [1]. Establishing one lightpath (or even more) between each source-destination pair could lead to signifi- cant costs when implementing the network. Hence, a more cost-effective solution is to establish only a subset of those lightpaths. In this way, a lower number of transceivers per node and a lower number of wavelengths are required. The drawback is that not all the traffic can be transmitted directly from the source node to the destination node through an opti- cal circuit (single-hop communication), but traffic between pairs of nodes which are not directly connected by a light- path must traverse one or more intermediate nodes where conversion to the electronic domain and electronic process- ing is necessary (multi-hop scenario). One benefit of this architecture is that the set of lightpaths established—that is, the virtual topology—can be reconfigured by deleting and adding new ones, in order to adapt to traffic changes or to react to network failures. Since traffic demand changes constantly, there has been considerable interest in the area of reconfiguration of the log- ical topology in recent years (see [2] and references therein). There are three important issues involved in the reconfigura- tion of the logical topology. The first one is to determine a virtual topology that can efficiently transport the new traffic demand, subject to the available set of resources and optimiz- ing parameters such as network congestion (i.e., the traffic carried by the most loaded lightpath) or end-to-end delay. The second issue is to decide when to trigger the reconfiguration process, and the third issue is to choose a reconfiguration transition sequence for smoothly shifting from the current virtual topology to the new one. 123