Optimal Model for Failure Foresight Capacitated Controller Placement in Software-Defined Networks

Controller placement is an important problem in software-defined networks. If a controller fails, there may be no controller with enough spare capacity to serve switches of the failed controller, which leads to switches being disconnected from the controller. Even if there are controllers with enough spare capacity, reassigning switches of the failed controller may drastically increase the worst case latency. In this letter, we propose a mathematical model for the capacitated controller placement that plans ahead for the failures to avoid a drastic increase in the worst case latency and disconnections. The objective of our model is to minimize the worst case latency between the switches and their Kth reference controllers. We also introduce a variant of the proposed model that minimizes the worst case latencies with and without failures together. Our simulation results show that the controller placements that plan ahead for the failures result in much lower latency compared with the placement without planning ahead.