Evaluating dual-failure restorability in mesh-restorable WDM optical networks

Double link failure models, in which any two links in the network fail in an arbitrary order, are becoming critical in survivable optical network design. A significant finding is that designs offering complete dual-failure restorability require almost triple the amount of spare capacity. In this paper, networks are designed to achieve 100% restorability under single link failures, while maximizing coverage against any second link failure in the network. In the event of a single link failure, the restoration model attempts to dynamically find a second alternate link-disjoint end-to-end path to provide coverage against a sequential overlapping link failure. Sub-graph routing [1] is extended to provide dual-failure restorability for a network provisioned to tolerate all single-link failures. This strategy is compared with shared-mesh protection. The results indicate that sub-graph routing can achieve overlapping second link failure restorability for 95-99% of connections. It is also observed that sub-graph routing can inherently provide complete dual-failure coverage for similar to 72-81% of the connections.