A k-Cover Model for Reliability-Aware Controller Placement in Software-Defined Networks

The main characteristics of Software-Defined Networks are the separation of the control and data planes, as well as a logically centralized control plane. This emerging network architecture simplifies the data forwarding and allows managing the network in a flexible way. Controllers play a key role in SDNs since they manage the whole network. It is crucial to determine the minimum number of controllers and where they should be placed to provide low latencies between switches and their assigned controller. It is worth to underline that, if there are long propagation delays between controllers and switches, their ability of reacting to network events quickly is affected, degrading reliability. Thus, the Reliability-Aware Controller Placement (RCP) problem in Software-Defined Networks (SDNs) is a critical issue. In this work we propose a k-cover based model for the RCP problem in SDNs. It simultaneously optimizes the number and placement of controllers, as well as latencies of primary and backup paths between switches and controllers, providing reliable networks against link, switch and controller failures. Although RCP problem is NP-hard, the simulation results show that reliabilities greater than 97%, satisfying low latencies, were obtained and the model can be used to find the optimum solution for different network topologies, in negligible time.