Resilient routing of variable traffic with performance guarantees

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Pre-configuring the network in a traffic independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through shared backup path restoration. We view this as important progress towards adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet service provider (ISP) networks. In shared backup path restoration, each connection consists of a link-disjoint primary and backup path pair - two backup paths can share bandwidth on their common links if their primary paths are link disjoint. We show that the optimization problem for maximum throughput two-phase routing with shared backup path restoration is NP-hard. Assuming an approximation oracle for a certain disjoint paths problem (called SBPR-DISJOINT-PATHS, which is also NP-hard) involving the dual variables of a path indexed linear programming formulation for the problem, we design a combinatorial algorithm with provable guarantees. We also provide heuristics for finding approximating solutions to the SBPR-DISJOINT-PATHS problem. We evaluate the throughput performance and number of intermediate nodes in two-phase routing for the above and other restoration mechanisms for two-phase routing on actual ISP topologies collected for the Rocketfuel project.