A Cross Entropy-Based Approach to Controller Placement Problem with Link Failures in SDN

The Controller Placement Problem (CPP) is a key research topic in Software Defined Network (SDN), as the communication delay is influenced by the position of controllers and switches. On that basis, the network failures may happen occasionally, which can cause the increase of propagation latency and the reduction of network performance. As a result, it is essential to research the Controller Placement problem for Link Failures (CPLF). In this paper, authors propose a method based on the cross entropy to solve CPP after link failures, and adopt the Halton sequence to reduce the computation overhead of simulating link failures while guaranteeing the accuracy. In the experiments, we measure and compare the worst-case delay among three methods: our proposed cross entropy-based controller placement algorithm, the optimized controller placement algorithm and a greedy-based controller placement algorithm, and conduct experiments on six real network topologies. The experimental results verify that our proposed method can reduce the worst-case delay by 27% in comparison with GPA. Moreover, the proposed method can always find optimized controller placement schemes no matter how the network scale or the number of controller varies, with a less than 0.6% error when compared with the optimal solution.