The distributed Software-Defined Networking (SDN) approach has been adopted to address the scalability issue linked to the use of a single SDN controller, particularly in large-scale networks. However, this method gives rise to a new challenge of uneven load balance on the distributed SDN controller. Several studies tried to solve this issue but they have focused only on balancing the load when an overload occurs and have not achieved the load balance continuously. In this paper, we propose the multiple threshold load balance (MTLB) switch migration scheme to achieve continuous load balancing among the controllers. This approach classifies the load into several gradual levels that represents the basis for the switch migration when the load of a controller differs from others, which lead the threshold value to be dynamically adjusted. Moreover, our scheme reduces the overhead of unwanted update operations among the controllers by adopting the controller load status as an indicator for disseminating the load information. We implement our scheme using the Floodlight controller and Mininet emulator. The experimental results show that our scheme has better comprehensive performance than the other schemes in terms of response time, control overhead, and throughput rate.

分布式软件定义网络 (SDN) 方法已被用来解决与使用单个 SDN 控制器相关的可扩展性问题，尤其是在大型网络中。然而，这种方法给分布式SDN控制器带来了负载均衡不均衡的新挑战。一些研究试图解决这个问题，但他们只关注发生过载时的负载平衡，并没有持续实现负载平衡。在本文中，我们提出了多阈值负载平衡（MTLB）交换机迁移方案，以实现控制器之间的连续负载平衡。这种方法将负载分为几个渐变级别，代表了当控制器的负载与其他控制器的负载不同时交换机迁移的基础，从而导致阈值动态调整。而且，我们的方案通过采用控制器负载状态作为传播负载信息的指标来减少控制器之间不需要的更新操作的开销。我们使用 Floodlight 控制器和 Mininet 模拟器来实现我们的方案。实验结果表明，我们的方案在响应时间、控制开销和吞吐率方面比其他方案具有更好的综合性能。