An Effective Load Balanced Controller Placement Approach in Software-Defined WANs

Wide Area Networks (WANs) are widely used in various fields such as business, education, government and military. The traditional network management of WANs has been difficult to meet the requirements of network development. Software-Defined Networking (SDN), a new network architecture with the concept of the separation between control and forwarding and centralized management, provides a practical solution for the efficient management of WANs. A Software-Defined WAN (SD-WAN) is usually deployed with multiple controllers due to the requirements of delay, scalability and reliability. The controller placement is a significant issue in a SD-WAN. In the literature, many approaches focus on reducing the delay between switches and controllers. However, these approaches may lead to load imbalance among controllers, which would have a negative impact on the performance and reliability of the network. In this paper, we define the load balanced controller placement problem, whose objective is to reduce the average delay between switches and controllers while maintaining load balance among controllers. And we propose an effective controller placement approach based on topological potential and minimum-cost flow to solve this problem. Extensive simulations on various real WAN topologies verify that our controller placement approach can effectively reduce the delay between switches and controllers and maintain good load balance among controllers. Our approach can also reduce the number of required controllers to avoid overload.