Designing Low-Capacity Backup Networks for Fast Restoration

There are two basic approaches to allocate protection resources for fast restoration. The first allocates resources upon the arrival of each connection request; yet, it incurs significant set-up time and is often capacity-inefficient. The second approach allocates protection resources during the network configuration phase; therefore, it needs to accommodate any possible arrival pattern of connection requests, hence calling for substantial over-provisioning of resources. In this study we establish a novel protection approach that overcomes all the above drawbacks. During the network configuration phase, we construct an (additional) low-capacity backup network. Upon a failure, traffic is rerouted through a bypass in the backup network. We establish that, with proper design, backup networks induce minor capacity overhead. We further impose several design requirements (e.g., hop-count limits) on backup networks and their induced bypasses, and prove that, commonly, they also incur minor overhead. Our approach offers additional benefits, most notably: traffic demands can be routed in an unprotected fashion, using standard routing schemes; moreover, upon a failure, control effort and congestion on the (primary) network are small and localized since affected traffic is immediately rerouted through the backup network. Motivated by these findings, we design efficient algorithms for the construction of backup networks.