Minimizing Controller Response Time Through Flow Redirecting in SDNs

Software defined networking (SDN) is becoming increasingly prevalent for its programmability that enables centralized network configuration and management. With the growth of SDNs, a cluster of controllers cooperatively manages more and more switches/flows in a network to avoid the single-controller congestion/failure and improve the control-plane robustness. Under the architecture with multiple controllers, it is expected to minimize the maximum response time on these controllers to provide better QoS for users. To achieve this target, two previous methods are mainly used, the static scheme and the dynamic scheme. However, these methods may lead to an increase of the control-plane communication overhead/delay. In this paper, we propose to minimize the maximum response time on controllers through flow redirecting, which is implemented by installing wildcard rules on switches. We formulate the minimum controller response time problem, which takes the flow-table size and link capacity constraints into account, as an integer linear program, and prove its NP-Hardness. Two algorithms with bounded approximation factors are designed to solve this problem. We implement the proposed methods on our SDN testbed. The testing results and extensive simulation results show that our proposed algorithm can reduce the maximum controller response time by about 50%-80% compared with the static/dynamic methods under the same controller cost, or reduce the number of controllers by 30% compared with the dynamic method while preserving almost the same controller response time.