Link backup is an important factor in the fault tolerance of SDN. The current research directions are proactive schemes and reactive schemes. The proactive schemes deploy the backup flow rules in the switches in advance and reserve the backup bandwidth. In reactive schemes, the controller calculates the backup path when a failure occurs. The proactive scheme easily causes the switch and link bandwidth resources to be exhausted, while the recovery time of the reactive scheme is too long. Moreover, none of the current methods considers the flow interruption rate. This article designs a set of efficient and low interruption rate link backup scheme. Our objective is to reduce the number of interrupted flows due to link failures. With this objective, we formalize the selection of the backup paths as an integer programming problem, and prove that it is NP-hard. Then we design a heuristic algorithm to solve it. We propose two algorithms to further optimize the calculated backup paths to reduce the need for backup flow rules and backup bandwidth. Simulations show that our method can effectively reduce the flow interruption rate after link failure recovery, and only needs less network resources.

链路备份是SDN容错的重要因素。目前的研究方向是主动式方案和反应式方案。主动方案预先在交换机中部署备份流规则并预留备份带宽。在反应式方案中，控制器在发生故障时计算备用路径。主动方案容易导致交换机和链路带宽资源耗尽，而被动方案的恢复时间过长。此外，目前的方法都没有考虑流动中断率。本文设计了一套高效、低中断率的链路备份方案。我们的目标是减少由于链路故障而中断的流的数量。为了这个目标，我们将备份路径的选择形式化为整数规划问题，并证明它是NP-hard的。然后我们设计了一个启发式算法来解决它。我们提出了两种算法来进一步优化计算的备份路径，以减少对备份流规则和备份带宽的需求。仿真表明，我们的方法可以有效降低链路故障恢复后的流中断率，并且只需要较少的网络资源。