On Survivable Routing of Mesh Topologies in IP-Over-WDM Networks
Generally, there are two approaches for providing survivability of IP-over-WDM networks: protection and restoration. Protection uses pre-computed backup paths applied in the case of a failure. Restoration finds dynamically a new path, once a failure has occurred. Protection is less resource efficient (the resources are committed without prior knowledge of the next failure) but fast, whereas restoration is more resource efficient and slower. Protection and restoration mechanisms can be provided at different layers. IP layer (or logical layer) survivability mechanisms can handle failures that occur at both layers, contrary to WDM layer (or physical layer) mechanisms that are transparent to the IP topology. It is not obvious which combination (mechanism/layer) is the best; each has pros and cons.