Davide Cherubini - PhD Thesis - UniCA Eprints

7.4 The Real ISP’s Italian Backbone NetworkSurvivability optimizationSimulation of a single edge failure has shown to TINet’s network operators analarming situation. In fact, two congestion scenarios arose if the original IS-ISmetrics configuration is held, and Figure 7.13 displays such conditions when edges10 and 12 fail.The optimization of IS-IS metrics, considering the failure scenarios alreadyproduces good results, avoiding the congestion when the aforementioned edgesfail as shown in Figure 7.14.In the other hand, introducing the survivability constraints within the LPmodel, it is possible to reach a much better configuration, reducing the congestionby 29.1% with respect to the ISP’s configuration and implementing only 86 LSPs,as shown in Table 7.8 and in Figure 7.15.Phase u max % Gain (Default) % Gain (Tinet) # LSPDefault u max = 128% – – 0Tiscali u max = 117% 8.6% – 0IS-IS opt. u max = 85% 33.6% 27.3% 0MPLS opt. u max = 83% 35.2% 29.1% 86Table 7.8: Survivability scenarios comparison for the Tinet network79