Topological optimization for spare-sharing-based wavelength-routed all-optical networks

In this paper, we propose a two-level fault tolerance strategy for wavelength-routed all-optical networks. The first-level strategy is applied to handle the large-scale disaster induced failures while the second-level strategy protects the network against regular single-link failures. The first-level fault tolerance is achieved by solving a topological optimization problem to re-regulate the traffic away from the disaster-affected area with minimum resource cost. Shared lightpath protection is applied in the second-level fault tolerance design to reduce resource allocation. First, by comparing with a simple greedy approach that we develop, we show that the traditional Routing and Wavelength Assignment (RWA) method, in which the routing and wavelength assignment are considered in a separate fashion, cannot lead to satisfying performance. Next, in order to obtain better performance, based on drawback analysis of the greedy approach, we propose a two-phase heuristic algorithm, in which the first phase is designed to generate an initial feasible solution and the second phase iteratively perfects the initial solution until no improvement can be made. For the design of the first phase, two variations are proposed featuring different types of initial solution generation. The numerical results show that, combined with perfection phase, both design variations can lead to considerable performance improvement over the greedy solutions. Finally, we propose a Performance Indicator (PI) that provides insight into the reason for performance difference among algorithms.