1 A TABU SEARCH ALGORITHM FOR DYNAMIC ROUTING IN ATM CELL-SWITCHING NETWORKS P Cortes 1† , J Muñuzuri 1 and J. Fernández 1 1 Seville University Grupo Ingeniería Organización. Escuela Superior Ingenieros, Camino de los Descubrimientos s/n. Sevilla 41092. SPAIN † E-mail: pca@esi.us.es † URL: http://io.us.es/P.Cortes/ Abstract This paper deals with the dynamic routing problem in ATM cell-switching networks. We present a mathematical programming model based on cell loss and a Tabu Search algorithm with short-term memory that is reinforced with a long-term memory procedure. The estimation of the quality of the solutions is fast, due to the specific encoding of the feasible solutions. The Tabu Search algorithm reaches good quality solutions, outperforming other approaches such as Genetic Algorithms and the Minimum Switching Path heuristic, regarding both cell loss and the CPU time consumption. The best results were found for the more complex networks with a high number of switches and links. Keywords: Tabu Search, dynamic routing, ATM 1. Introduction The general problem of real time operation in telecommunication networks involves a collection of different complex problems. Consequently, optimisation in real time operation in telecommunication networks arises when communications have to be routed across the network from the origin point to the destination. In this context soft computing can offer additional capabilities with respect to other traditional approaches. The basic and more traditional problem of real time operation is known as routing and can be undertaken in either a static or dynamic way. Static routing makes use of the routing tables that are constructed by means of the capacity assignment and multicommodity flow problem. In this case the network is analysed offline using deterministic and static demands of traffic. Dynamic routing arises when the messages are routed in real time trying to minimise the losses or to minimise the delays experienced by the messages. Several specific problems following on from the basic problem have been tackled. Medhi et al. (2000) have considered solution approaches to a multi-hour combined capacity design and routing problem, which arises in the design of dynamically reconfigurable broadband communication networks that use the virtual path concept. They compared a genetic algorithm, a Lagrangian relaxation based subgradient optimisation method, a generalised proximal point algorithm with subgradient optimisation, and a hybrid approach where the subgradient based method is combined with a genetic algorithm. Also, Xu et al. (1997) presented a tabu search approach that optimises the link capacities in a dynamic routing telecommunications network. The traffic between any pair of nodes in the network is routed over a one-link direct path or, if no direct capacity is available, over a two- link alternate path. Later, Shyur et al. (2001) presented a non-time dependent model to solve the problem of optimising the system of virtual paths using a tabu search approach. Although these two papers make use of tabu search approaches, as ours does, they cannot be directly compared to our paper because they do not use a time horizon with different time scales, as is considered here. More recently, Cortes et al. (2002) have presented a genetic algorithm for dynamic routing in ATM networks. The model objective was to minimise cell loss subject to strict delay conditions. Alternatively, Wille et al. (2006) showed models and algorithms considering at the same time the dynamics of packet network and the grade of service (GoS) user-layer requirements.