An heuristic for maximally SRLG-disjoint path pairs calculation

Most network operators seek to offer reliable connections. The use of Shared Risk Link Groups allows an upper layer to select adequate protection paths. When path protection is used, routing algorithms seek to obtain SRLG-disjoint path pairs (or set of paths). When no totally SRLG-disjoint paths can be found one may try to obtain the SRLG least coupled (or maximally disjoint) path pair. An heuristic for maximally SRLG-disjoint path pairs calculation, considering a min-min formulation, designated TA-max, is proposed, which is a modification of the Trap Avoidance (TA) algorithm. Expressions are derived for estimating sufficient shared backup bandwidth (BBW) and for minimal BBW allocation and deallocation for partially SRLG-disjoint path pairs. The heuristic performance is evaluated using a virtual topology built over the NSFNET network and is compared with another heuristic (Modified-CoSE). Several network performance measures were considered, with and without backup bandwidth sharing, considering dynamic traffic. Results show TA-max is adequate for on-line routing and that it has better performance than Modified-CoSE regarding CPU time.