A GRASP-based network re-optimization strategy for improving RWA in multi-constrained optical transport infrastructures

In wavelength-routed optical networks, end-to-end connection demands are dynamically routed according to the current network status. Naive path selection schemes, the wavelength continuity constraint and the limited or inaccurate information available can cause the virtual topology resulting from the currently allocated lightpaths to become sub-optimal. We propose an efficient re-optimization technique based on a GRASP meta-heuristic. Our work is focused on a hybrid online-offline scenario: connections are ordinarily routed dynamically using one of the available algorithms for online routing, but occasionally, when reorganization of the current virtual topology is desirable, existing paths are re-routed in order to improve load balancing and hence the ability to efficiently accept further connections. Because global changes of the logical topology and/or routing scheme can be disruptive for the provided connection services, we used iterative stepwise approaches based on a sequence of small actions (i.e., single connection re-routing and on local search from a given configuration). Simulation results demonstrate that several network performance metrics - including connection blocking ratios and bandwidth gains - are significantly improved by such approach. In particular, we achieved to accept more connection requests in our re-optimized networks with respect to the same networks without re-optimization, thus lowering the blocking ratio. Besides, in all tests we measured a notable gain in the number of freed bandwidth OC-units thanks to our re-optimization approach.