Call Routing by Simulated Annealing 1

Simulated Annealing (SA) is a powerful stochastic search algorithm applicable to a wide range of problems. This paper presents some experiments of applying SA to an NP-hard problem, i.e., call routing in circuit-switched telecommunications networks. The call routing problem considered here can be described as assigning calls to paths in a network so that the number of calls blocked can be minimised. Previously, the problem has been approached by linear programming and some heuristic algorithms. However, none of these algorithms has solved the problem satisfactorily due to the nonlinear nature of the problem. Linear programming can only nd a rough approximation to the actual global optimal solution. This paper applies SA to the call routing problem in circuit-switched telecommunication networks. We have carried out two sets of experiments. The rst set investigates random selection of paths in SA with uniform distribution. The second set studies non-uniform probabilistic selection of paths in SA according to whether a path is a direct one or not and the path capacity available. These two results are also compared with the result generated by a simple heuristic algorithm. Our experiments show that non-uniform probabilistic selection of paths in SA can lead to the least number of calls blocked among the three methods we investigated. We will also examine the impact of di erent probability distributions on the result of routing in this paper. X. Yao: Call Routing by Simulated Annealing 1