Near-optimal FIPP p-cycle network designs using general path-protecting p-cycles and combined GA-ILP methods

Recent work on failure independent path-protecting p-cycles (FIPP) has revealed some new, relatively simple and possibly cost-effective approaches for FIPP p-cycle network design. The first step of the proposed strategy consists of solving a more general path-protecting p-cycle (GPP) problem in which the constraint of failure independence is relaxed. The second step consists of imposing the failure independence constraint onto the GPP solution and identifying the working paths that become unprotected as a result. A FIPP p-cycle solution is extracted by capacitating additional cycles to protect these paths, the number of which the results revealed to never exceed three. Another contribution of this work is the adaptation of the novel combination of genetic algorithms with integer linear programming (GA-ILP) to the GPP concept, which allowed us to solve large GPP problem instances. GA-ILP solutions were typically within 1% of optimality for smaller networks for which the exact solutions were known. The GPP and FIPP solutions obtained with the assistance of GA-ILP were considerably better (by as much as 23%) than those obtained by the FIPP disjoint route set (DRS) method. Furthermore, the results obtained in this paper also showed that relaxing the disjoint route set constraint in FIPP p-cycle networks can result in as much as 9% decrease in spare capacity cost. Also in this paper, we ventured to provide a true comparison of span-protecting p-cycles with FIPP p-cycles, from the capacity efficiency perspective.