A Geographic Multi-Topology Routing approach and its benefits during large-scale geographically correlated failures

Large-scale geographical events can significantly disrupt network services. In particular, the routing churn that occurs during such large-scale events has been shown to cause significant impact in route stability and transient behavior. We take a Geographic Multi-Topology Routing (gMTR) approach for pre-planning of geographically correlated failures. Thus, in the event of a failure, the gMTR approach switches to a virtual topology that reduces the impact of routing changes that can result in dropped connections until new paths can be established. Two algorithms are proposed to generate virtual topologies, Geographic Coverage MTR (gcMTR) and Geographic Targeted MTR (gtMTR). The first method, gcMTR, is to create virtual topologies taking a network wide coverage approach for which we consider taking both a circular coverage approach and a hexagonal coverage approach. gtMTR, on the other hand, is a targeted approach that can be used in anticipation of a specific event where the knowledge of the impending event is available. We propose another algorithm that specifies a way to detect a geographic event and select a topology to use. We evaluated our approach on two network topologies and observed that the number of connections that are dropped during a geographic event can be reduced significantly using our gMTR approach, thereby reducing the impact to the non-affected part of the network. We performed an analysis of the topology size versus the disaster size, topology location versus disaster location, and general density of the topology. Finally, a simulation model of the larger topology is used to study the effects of geographically correlated failures both with gcMTR and using default topologies. This provides a way to assess the gains from using gMTR to mitigate the impact of large scale geographic impacts.