Protection of traffic in IP-over-WDM networks using loop-free alternates

Abstract

Core IP-over-WDM (Internet Protocol, Wavelength Division Multiplexing) networks often suffer failures, potentially causing costly service interruptions. The IP network layer can recover from these failures in a few hundreds of milliseconds, but some applications require that some of the traffic be recovered in 50 ms or less. The WDM layer can protect such high priority traffic by duplicating the optical signal, but this requires additional wavelengths and power. Multiprotocol Label Switching Fast Reroute (MPLS FRR) can also provide protection, but it involves installing and maintaining an additional network layer on top of IP. A simple and commercially available mechanism to protect high priority traffic in the IP layer is Loop-free Alternates (LFA). However, a network equipped with LFA may have an additional cost. In this dissertation, using LFA as the primary protection mechanism, we minimize the costs of our model networks while protecting a high priority fraction of the traffic. To gain insight into the problem, we first use a completely connected IP topology over a WDM ring as a model network, and assume the traffic between the network nodes is uniform. Such a simplified network allows for analytical as well as algorithmic results. The resulting costs show that networks using LFA are cost-effective compared to MPLS FRR and networks using only WDM optical protection, but care must be taken to route the WDM lightpaths. Then, we use less constrained IP and WDM network topologies, and more realistic assumptions about the traffic. For such a generalized network model we present algorithms to design IP network topologies, determine the lightpath capacities, route the lightpaths, and find the LFA backup routes to minimize the network cost. The resulting costs show that a network with LFA has, on the average, a cost of less than 1% more than a network without. The dissertation thus shows that, in many cases, LFAs are a feasible protection mechanism in IP-over-WDM networks.