Benefits of Multi-Topology Routing during Geographically Correlated Failures

During large geographic events in networks, the routing churn that occurs has been shown to cause significant impacts in routing stabilization following the event. This work is an extension of earlier work that proposed a set of algorithms that is based on MultiTopology Routing (MTR) for pre-planning for geographically correlated failures. Thus, in the event of a failure, our approach, Geographic MTR, switches to virtual topologies that reduce the impact of routing changes that can result in dropped connections until new link state and shortest path trees can be established. Two algorithms are used 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. In addition to the circular coverage approach presented earlier, we offer a hexagonal approach that provides significantly better coverage. gtMTR is a targeted approach that can be used in anticipation of a specific event where knowledge of that event exists. The third algorithm described in this work specifies a way to detect a geographic event and select a topology to use. We also explore other methods of detecting and predicting geographic events for the purpose of topology selection, recognizing that additional information like weather forecasts or political events may lead to future geographic events. 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, thereby reducing the impact to the non-affected part of the network. Analysis of topology size versus disaster size, topology location versus disaster location, and general density of the topology is performed. Finally, a simulation model of a large network 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 of using MTR to mitigate the impacts of large scale geographic impacts.