Scalable Design of p-Cycles for Node Protection without Candidate Pre-Enumeration

The problem of the design of p-cycles in WDM mesh networks under single link failure scenario has been extensively investigated; however, there are very fewer studies upon the design of p-cycles for protecting against a single node failure. In this paper, we develop a new scalable design approach for calculating p-cycles with node protection capability. Conventional design methods formulate the problem as an Integer Linear Program (ILP). To solve the ILP, the prerequisite is the enumeration of all possible cycle candidates in a network. As the number of cycles increases exponentially with the increase of the network size, these methods suffer from the scalability issue. We propose a new design and solution method based on large scale optimization tools, namely Column Generation (CG), where p-cycles are generated on the fly when needed and embedded in the optimization process. The main advantage of our CG-based method is that no p-cycles are a-priori off-line enumerated; the generation of the promising set of p-cycles is embedded in the optimization process. We have carried out intensive experiments on several network instances for comparing our method with an existing method in the literature. Numerical results show that our CG-based method outperforms the previous method in terms of scalability. As it is important for Internet service providers, we also compare the spare capacity requirement of p-cycles for link and node protection with that for link protection.