Survivable Routing of Logical Topologies in WDM Networks

Network restoration is often done at the electronic layer by rerouting traffic along a redundant path. With Wavelength Division Multiplexing (WDM) as the underlying physical layer, it is possible that both the primary and backup paths traverse the same physical links and would fail simultaneously in the event of a link failure. It is therefore critical that lightpaths are routed in such a way that a single link failure would not disconnect the network. We call such a routing survivable and develop algorithms for survivable routing of a logical topology. We prove necessary and sufficient conditions for a routing to be survivable and use this condition to formulate the problem as an Integer Linear Program. We use our new formulation to route various logical topologies over a number of different physical topologies and show that this new approach offers a much greater degree of protection than alternative routing schemes such as shortest path routing and a greedy routing algorithm.