Impairment Aware RWA in Optical Networks: Over-provisioning or Cross Optimization?

In transparent and translucent wavelength routed optical networks the signal quality degrades due to physical layer impairments while the interference among lightpaths implies that routing decisions for one lightpath affect and are affected by the decisions made for other lightpaths. To establish a lightpath for a new connection two main approaches can be used. The most common approach is to select a lightpath that has acceptable transmission quality under a worst case interference assumption, ensuring that the selected lightpath will not become infeasible due to the possible establishment of future interfering connections. This approach sacrifices candidate path space for a quick and stable lightpath selection, which is appealing from a complexity viewpoint. The second approach is to consider the current network utilization and account for the actual interference among lightpaths, performing a cross layer optimization between the network and physical layers. In this case, however, the algorithm has to check whether the establishment of the new lightpath turns infeasible some of the already established connections. The question that arises is whether the performance benefits that can be achieved through the second approach are worth the added complexity introduced by the cross-layer optimization applied.