The hop-limit approach for spare-capacity assignment in survivable networks

This paper presents a new approach for spare-capacity assignment in mesh-type self-healing networks which use reconfigurable network elements as transmission hubs. Under this approach the process of reducing total weighted cost of spare capacity is obtained by taking into account all network's eligible restoration routes which do not violate a predetermined hop-limit value. The process derived considers a given set of possible failure scenarios, which include single-link, multi-link and node failures, and is adaptive to accommodate several practical considerations such as integrality of spare channels and modularity of transmission systems. This process is generally composed of two parts: part 1 relies on a linear-programming formulation (min-max) from which a lower bound solution of spare cost is found; part 2 rounds-up the solution of part 1 to a feasible solution and uses a series of max-flow tests aimed at tightening the rounded-up assignment to a practical optimum. For small and moderate size networks a mixed-integer-programming formulation of part 1 can be used to obtain optimal results. A network, which has already been studied in the literature, is analyzed to illustrate the approach developed and to demonstrate, for cases where hop limits can feasibly be kept low, its superiority over other algorithms published in this area.