 general also capa- ble to manage a lower number of failures, the overall resilience factor RF is sometimes defined as RF ER (8.40) where F is the maximum number of contemporary failures that can be partially recovered and for our assumptions R1 = 1. From the earlier discussion, it results that a key point in evaluating the survivability of a network is the analysis of the time that various elements of the recovery process, either protocols of hardware mechanisms, take to do their work. Thus a detailed analysis of the recovery process is needed. When a failure occurs the network goes into the recovery state. The network in this state performs a series of opera- tions aimed to perform recovery of the lost connections and return of the network to the normal state after the failure has been repaired. These phases can be described as follows: Phase 1: Fault detection Phase 2: Fault localization and isolation Phase 3: Fault notification Phase 4: Recovery (protection/restoration) Phase 5: Reversion (normalization) Fault detection, localization, and notification phases are often joined together and called fault management. Reversion, also known as normalization process, is the mechanism bringing back the network from the recovery state, where the failed connections are rees- tablished using spare capacity, to the normal state. This process can be performed only after the physical repair of the failure and, among other elements, comprise the switch back of the connections affected by the failure to a working path. It is to note that not always the working path after reversion is the same of those before reversion: as a matter of fact some restoration mechanisms reroute the connections in the reversion phase without any knowledge of their route before the failure occurs. In order to perform failure recovery, alternative backup paths are required. These backup paths can be either set-up prior the failure or a posteriori. Given such possibilities, a range of different subphases in an a priori or a posteriori manner exists w