In this paper we consider the problem of provisioning spare capacity in two-layer backbone networks using shared backup path protection. First, two spare capacity allocation (SCA) optimization problems are formulated as integer linear programming (ILP) models for the cases of protection at the top layer against failures at the bottom layer. The first model captures failure propagation using overlay information between two layers for backup paths to meet diversity requirements. The second model improves bandwidth efficiency by moving spare capacity sharing from the top layer to the bottom layer. This exposes a tradeoff between bandwidth efficiency and extra cross-layer operation. Next, the SCA model for common pool protection is developed to allow spare capacity sharing between two layers. Our previous SCA heuristic technique, successive survivable routing (SSR) is extended for these optimization problems. Numerical results for a variety of networks indicate that the common pool protection is attractive to enhance bandwidth efficiency without loss of survivability and that the SSR heuristic quickly results in near optimal solutions

This paper presents an investment strategy to reduce the risk associated with failures in wavelength division multiplexing (WDM) optical networks. The investment strategy determines how to allocate a fixed budget for implementing survivability techniques in different parts of the network such that the expected loss of traffic (ELT) is minimized. Two survivability schemes are considered in this paper: dedicated link protection and dedicated path protection. Two analytical techniques for evaluating network unavailability and ELT are presented in this paper: a fault tree analysis and an event tree. Based on the event tree approach, we propose a novel mixed integer linear programming (MILP) formulation for the investment strategy problem. Numerical results illustrating the investment strategy for both link and path protection are presented and discussed