res (days) Dedicated protection switching time (ms) Shared protection switching time (ms) Average type 1 restoration recovery time (ms) Standard deviation of type 1 restoration recovery time (ms) Average type 2 restoration recovery time (ms) Standard deviation of type 2 restoration recovery time (ms) Average type 3 restoration recovery time (ms) Standard deviation of type 3 restoration recovery time (ms) Hold off time (ms) Maximum OXC wavelength ports Maximum LSR optical ports Maximum LSR output LSP Telecommunication Networks TABLE 8.10 Main Results of the Performance Evaluation of Different Survivability Strategies 1 A (x10-5) 1 + 1 Protection 1:1 Protection Shared protection Type 3 restoration Type 2 restoration Type 1 restoration paths to be frequently quite longer with respect of working path and sharing the protec- tion capacity helps only partially. The result is that even when using shared protection a bit more that 50% of the network CAPEX is used to set up protection capacity. The situation is completely different considering restoration at the MPLS layer. As a mat- ter of fact, while optical channel protection is constrained to maintain the optical channel in its wholeness protecting it as a single entity, MPLS restoration does not have this constraint. What happens is that when restoration is in place and a link fails, layers 1 and 2 com- municate through the common control plane and the GLSPs are individually restored not only by opening other optical paths exploiting free resources in layer 1, but also filling free spaces in already created optical paths and exploiting grooming to better distribute the traffic to be restored. This causes a negligible increase of the cost of layer 2 (less than 2%) but the effect is strong and the final efficiency of restoration is near 70% if only the optical layer is consid- ered or about 65% if all the network is taken into account. The first type of restoration, without any preassignment of resources is slightly better due to the stub reuse and stub release procedu