Maintenance-immune Design of Span-restorable Mesh Networks

In contemplating mesh-based networking, some operators have expressed concern about the possible effects of span maintenance actions on network restorability, and hence availability. We consider this problem for span-restorable networks and provide two main advances. One is a bi-criteria optimization method that allows a controlled trade-off between the cost of spare capacity and the reduction of restorability risk, through enhancement of the ability to roll to protection on the same span without exporting any working flow onto other spare channels of the network as a whole. The second approach directly designs the spare capacity of a span-restorable network so that it is 100% immune to risk of restorability loss due to maintenance actions. This approach is mathematically similar to the problem of designing for 100% restorability for dual-failure scenarios but requires significantly less additional capacity. The maintenance immune design concept can easily be adapted to provide maintenance immunity for priority service paths only. Other desirable side-effects of the spare capacity additions for maintenance immunity are further enhancement of the actual dual-failure restorability levels and further expansion of the protected working capacity envelope provided for dynamic service path provisioning.