extracting the failure starting instants ti with j = 1 to N The simulation, in correspondence of each failure event, evaluates the duration of the different phases of protection or restoration and recovery for each individual GLSP and for each individual failure event. Let us consider the k-th GLSP; in correspondence of the generic h-th simulated failure it can be in one of three states: 1. Not involved in the failure 2. Restored after the failure via the network survivability mechanism 3. Impossible to restore via the survivability mechanism, restored when the network return in the working state that is when the failure is fully repaired Let us assume a multiple survivability mechanism: for example, shared protection at the optical layer and Type 1 restoration at the MPLS layer coordinated through a hold-off time SO as to avoid interlayer problems. Simulating NF failure scenarios, let us assume that No,k simulated failure events do not involve the k-th GLSP, in N1,k events, corresponding to the initial instants thi, it is recovered in a time Tkih via the first survivability mechanism (in our example also the faster) while in N2,k events, corresponding to the initial instants th2, it is recovered in a time Tkin via the second survivability mechanism (in our example also the slower). Finally, in N3,k = NF - No.k-N1x-N2, failure events, the k-th GLSP is not recovered SO that it turns up again only when the failure is completely repaired after a time Tk.h. Telecommunication Networks Thus the steady-state availability of the k-th GLSP can be evaluated as (8.36) where TT is the total simulated time that is the time elapsing from the simulation MPLS layer n start t = 0 to the instant in which, after the last failure event, the network is again in the working state. Considering the average availability with respect to the Np GLSPs that are routed at the considered layer through the network it is finally obtained: (8.37) In cases in which both the recovery time and the failure repair time do not depend on the particular 