thms, the cost does not change more that 20% from the value obtained from ILP. The reason essentially has to be found in two characteristics of the considered networks: Telecommunication Networks Normalized network cost Pure OSPF ILP optimization= 100 Modified Cost constrained routing Number of network nodes FIGURE 8.26 Comparison among routing based design based on a set of 10 random network for all the considered values of the number of nodes. All the considered networks have a connectivity around 2.2 and the design do not include any survivability mechanism. All costs are normalized with respect to the optimized cost obtained with the ILP. connectivity and geographic extension. The connectivity is low, generally two paths between any couple of node with a few exceptions, thus a smart optimization algo- rithm cannot do much better than a simple OSPF having a little number of alternatives. Moreover the number of nodes is also low, SO that any advantage achieved in node dimensioning has little impact. The transmission systems are not SO long, SO that the platform cost (proportional to the system length) has less impact with respect to a continental network like the North American one. This also explains why the performance of the M-OSPF is SO near to the simple OSPF. It is interesting to note that the situation depicted in the figure is common to a significant part of the national networks in Europe and Asia, but for connectivity that is generally slightly higher, while a completely different problem is the design of a U.S. or a Chinese network due to the greater extension and number of nodes. 8.5 GMPLS Network Design for Survivability Since core network equipment processes a huge amount of traffic, survivability against failures is a key characteristic of carrier networks. Transport networks based on SDH/ SONET or on OTN assures a high degree of reliability by using protection mechanisms, like self-healing rings, to recover the traffic affected by a cable cut or by a node failure in a SO short time not to influe