Mesh-restorable networks with complete dual failure restorability and with selectively enhanced dual-failure restorability properties

We consider extensions of the most common mesh-restorable network capacity design formulation that enhance the dual-failure restorability of the designs. A significant finding is that while design for complete dual-failure restorability can require triple the spare capacity, dual failure restorability can be provided for a fairly large set of priority paths with little or no more spare capacity than required for single-failure restorability. As a reference case we first study the capacity needs under complete dual-failure restorability. This shows extremely high capacity penalties to support 100% dual-failure restorability. A second design model allows a user to specify a total capacity budget limit and obtain the highest average dual-failure restorability possible for that investment limit. This formulation can also be used to traceout the capacity-versus-availability trade-off curve for a mesh network. A third design strategy supports multiplerestorability service class definitions at minimum total cost. Restorability can range from best-efforts-only on any failure to an assurance of complete single and dual-failure restorability, on a per-demand basis. Prior work has only considered multiple service classes ranging from assured single-failure restorability and downwards in quality. This work shows how to economically support an added service class in the upward quality direction: assured dual failure survivability. This lets a network operator tailor the investment in capacity to provide ultra-high availability on a selective basis, while avoiding the very high investment required for complete dual-failure restorability for all.