Cost of Loop-Free Alternates in IP-Over-WDM Networks

In Internet protocol (IP) networks, the failure recovery time of IP restoration, of several hundreds of milliseconds or up to seconds, is sufficient for most applications. But protection switching is needed for services that require very short recovery times of at most 50 ms. Loop-free alternates (LFAs) is a protection switching mechanism that is in the IP layer. We consider IP-over-WDM (wavelength division multiplexed) 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 percent on average, under a particular cost model. 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 a physical network topology, will find a low-cost network design that includes determining the IP network topology, IP-link capacities, lightpath routing, and LFAs.