Survivable impairment-aware traffic grooming in WDM rings

Wavelength Division Multiplexing (WDM) optical networks offer a large amount of bandwidth using multiple, but independent wavelength channels (or lightpaths), each operating at several Gb/s. Since the traffic between users is usually only a fraction of the capacity offered by a wavelength, several independent traffic streams can be groomed together. In addition, in order to reverse the effect of noise and signal degradations (physical impairments), optical signals need to be regenerated after a certain impairment threshold is reached. We consider survivable impairment-aware traffic grooming in WDM rings, which are among the most widely deployed optical network topologies. We first show that the survivable impairment-aware traffic grooming problem, where the objective is to minimize the total cost of grooming and regeneration, is NP-hard. We then provide approximation algorithms (for uniform traffic), and efficient heuristic algorithms whose performance is shown to be close to the lower-bounds (for non-uniform traffic) both when (1) the impairment threshold can be ignored, and (2) the impairment threshold should be considered.