Davide Cherubini - PhD Thesis - UniCA Eprints

7.2 The highly meshed networkA unit link metrics value has been assigned to all arcs (default configurationsuggested by the major router vendors). Note that in that case, the shortestpaths are those with the minimum number of hops.The obtained results have been also compared with those of the IS-IS metricsoptimization performed using a metaheuristics algorithm (in particular a TabuSearch algorithm implemented by the research group of University of Cagliari[60]), which considers the failure scenarios in the search process.The LP model have been applied starting from the conditions above describedand, as shown in Table 7.2, the objective function value has been evaluatedand compared in both “normal condition” (solution of the GRP) and in “failurecondition” (adding the survivability constraint).The last column of Table 7.2 shows the number of explicit LSPs determined bythe model.Phase Normal Condition Failure Condition # LSPIS-IS Default Routing u max = 34% u max = 70% 0IS-IS optimization u max = 29% u max = 47% 0MPLS optimization u max = 23% u max = 35% 55Joint IS-IS/MPLS opt. u max = 23% u max = 35% 48Table 7.2: Comparing results for the synthetic networkResults discussionThe obtained results show that the application of the model starting either fromthe “default” configuration or the “IS-IS optimal configuration”, produces thesame maximum link utilization. Only the number of LSPs needed changes andthis may depend on the fact that (likely) the IS-IS optimization already identifiessome best paths.It is important to note that, in case of failure, the maximum link occupation hasbeen halved with respect to the “default” configuration.67