amplifiers, DCFs, and SO on and moreover we have to add the protection switch card with all the related monitor- ing), but the network design remains the same. The failure probability of such a protection mechanism adopted is such that within the repair time both the working and the protec- tion links fail. The probability of two failures on two specific links is, in a first approximation, Pf2 = Thus the survivability degree can be approximately expressed as D=1-P(fail) - (8.6) where P(fail) is given by (8.7) If the network has 100 links and Pf in the network, repair time is 2 X 10-4; the result of is D 22 0.999996, a value compliant with values required for D in real networks. 8.4.1.2.2 Optical Channel: 1+1 Dedicated Protection In this case, every GLSP is routed two times in the transport layer on two optical paths such that the links of the working path are never in the same SRLG with any link of the protection path. In our example, we have to connect the following node couples: (2,3), (1,3), (3,4). For each couple of node, two completely disjoined paths are to be found following the desired design criterion. From the topology, it is quite clear that a design with the hub is impossible in this case due to lack of sufficient topology connectivity. Considering the minimum node cost design, suitable couples of paths are listed in Table 8.5. TABLE 8.5 List of Working and Protection Paths for the Minimum Node Cost Design GLSP Ends Working Route Protection Route (2,3) 2-4-3 (1,3) 1-4-3 1-2-3 (3,4) 3-2-4 Convergent Network Management and Control Plane If dedicated protection is to be implemented, the signal has to be doubled by a splitter after the OXC and sent simultaneously on the working and protection paths. Thus, looking at Table 8.5, two links have to be equipped for protection only (links 1-2 and 2-4) and six more wavelengths are needed. In a certain number of real situations, the protection paths can be identified as follows: The working path is routed following the chosen routing criterion. A new topology is 