rocess time dynamic. In the simulation, the network is loaded as foreseen by the ILP design and no further connection request arrives during the simulation period. Telecommunication Networks TABLE 8.7 Normalized Cost Parameters for the Network Design and Performance Evaluation Examples Presented in This Section (per Span of 75 km) The process of failure events is considered a Poisson process with average interarrival time equal to 1000 days. In every failure instant, the program extracts one of three possible failure scenarios, each one with its own probability: 1. Single link failure (88%) 2. Double link failure (11%) 3. Triple link failure (1%) Once the failure scenario is fixed, a group of failed links is randomly individuated and the failure and successive recovery simulated in the time domain. Besides the solution we have chosen in this section, it is also possible to develop analytical models for the surviv- ability strategy performance evaluation. A detailed comparison among the results of ana- lytical models and time domain simulations is carried out in Ref. [25] and we recommend the interested reader to start from this quite complete work to study this subject. 8.5.1 Survivability Techniques Performance Evaluation The first parameter related to the effectiveness of a survivability strategy is the resulting network availability. In Section 8.4.1, we have introduced a concept somehow similar to network availability in an operative manner as the probability that no service disruption happens during a given time and we have called it survivability degree. It was useful at that time not to complicate further an example, but now we have to use more complete standard definitions. ITU-T Rec. E.800 defines the so-called instantaneous availability A(t) of a system as the ratio between the up time Tup (that is, the time in which the system worked correctly) and the total system working time. Since the complement of the up time is the down time (that is, the time Tdw in which the system was out of work) it can be wr