Dynamic lightpath protection in WDM mesh networks under wavelength-continuity and risk-disjoint constraints

Path protection requires finding a working path and a protection path that are link disjoint. In this paper, we consider two fundamental problems on dynamic lightpath protection in WDM mesh networks. In the first problem, we consider a network without wavelength converters; thus both the working lightpath and protection lightpath are subject to the wavelength continuity constraint. Existing polynomial time algorithms can be applied to find a pair of link-disjoint lightpaths on a single wavelength; however, such algorithms fail if the working and protection lightpaths are on two different wavelengths. In the second problem, we consider a network with full wavelength conversion; thus the wavelength continuity constraint does not apply. Yet a single factor can cause multiple fiber links to fail simultaneously. The problem becomes finding link-disjoint lightpaths that are also risk disjoint. We prove that both of the two problems are NP-complete. We develop ILP formulations and heuristic algorithms for the two NP-complete problems. Practical constraints such as service level agreement (SLA) and priority are also considered. Computer simulations are conducted to evaluate the performance of the heuristic algorithms.