The cost of loop free alternates in IP over WDM

In IP networks, the failure recovery time of IP restoration is sufficient for most applications. But some services require very short recovery times (50 ms) that can be achieved only by protection switching. Loop-free alternates (LFAs) is a protection switching mechanism that is in the IP layer. We consider IP over WDM networks where IP routing eventually restores all traffic, while LFAs protect the fraction of the traffic that has high priority. Simulations show that if 50% of the traffic has high priority then the additional cost to protect the high priority traffic using LFAs is just a few percent, e.g., 1% on average. Thus, with very little additional network cost, LFAs can guarantee that a large fraction of traffic will be protected between all source-destination pairs. In addition, a network design algorithm is presented that, given a traffic matrix and physical network topology, will find a low cost network design that includes determining the IP network topology, IP link capacities, lightpath routing, and LFAs.