Dynamic Lightpath Allocation in Translucent WDM Optical Networks

The optical reach (the distance an optical signal can travel before the signal quality degrades to a level that necessitates regeneration) ranges from 500 to 2000 miles. To establish a lightpath of length greater than the optical reach, it is necessary to regenerate optical signals. In a translucent optical network, there are regeneration points, where the signal undergoes Optical-Electronic-Optical (O-E-O) conversion. In this paper we have proposed routing algorithms for translucent networks in a dynamic lightpath allocation environment in which requests for communication arrive continuously. In response to each request for communication, the objective is to establish, if possible, a path, from the source to the destination of the request for communication, so that a lightpath may be established, using the path that requires the fewest stages of regeneration. In practical transparent networks, a lightpath must satisfy the wavelength continuity constraint. However, in a translucent network, this constraint can be relaxed at the regeneration points. We have proposed an Integer Linear Program, to give the optimum results for small networks, as well as an efficient heuristic for this problem that works for larger networks. We have evaluated the heuristic through extensive simulations to establish that the heuristic produces close-to-optimal solutions in a fraction of the time needed for the optimal solutions. Our extensive evaluations demonstrate the relative impact of a set of network resources, such as (i) the number of regenerators, (ii) the optical reach of the regenerators and (iii) the number of wavelengths, on the network performance, measured in terms of the call blocking probability. To the best of our knowledge this is the first study that undertakes such an evaluation for translucent networks.