Preprovisioning networks to support fast restoration with minimum over-build

Supporting fast restoration for general mesh topologies with minimal network over build is a technically challenging problem. Traditionally, ring based SONET networks have offered 50 ms restoration at the cost of requiring 100% over-build. Recently, fast (local) reroute has gained momentum in the context of MPLS networks. Fast reroute, when combined with preprovisioning of protection capacities and bypass tunnels, comes close to providing fast restoration for mesh networks. Preprovisioning has the additional advantage of greatly simplifying network routing and signaling. Thus even for protected connections, online routing can now be oblivious to the offered protection, and may only involve single shortest path computations. In this paper we are interested in the problem of reserving the least amount of the network capacity for protection, while guaranteeing fast restoration to all the supported connections. We show that the problem is NP-complete, and we present efficient approximation algorithms for the problem. These guarantees are provided even when the protection is for multiple link failures. In addition, the total amount of protection capacity reserved by these algorithms is just a small fraction of the amount reserved by existing ring-based schemes (e.g. SONET), especially on dense networks. The presented algorithms are computationally efficient, and can even be implemented on the network elements. Our simulation on some standard core networks, show that our algorithms work well in practice as well.