Software-defined networking (SDN) is a revolutionary network architecture that separates the network control layer from the underlying equipment. Multiple controllers form a logically centralized control layer in large-scale networks, which raises the controller placement problem. Most of the research on latency-oriented controller placement optimized the delay between switches and controllers assuming the network is reliable. However, the network is subject to link failures. In this paper, we formulate a novel multi-objective SDN controller placement problem with the aim to minimize the switch-to-controller communication delay for both the cases without link failure and with single-link-failure. We propose an efficient metaheuristic-based Reliability-Aware and Latency-Oriented controller placement algorithm (RALO) for multi-objective multiple controller placements. The algorithm constructs an initial feasible solution by a greedy method with network partition, then repeatedly generates new solutions with variable neighborhood search. Once a new solution is generated, the algorithm decides whether to accept the new solution as a non-dominated solution to the problem and performs update operation on the Pareto optimal solution set. Meanwhile, to avoid falling into the local optimum, the algorithm also performs perturbation and destruction operations on the current solution. We finally conduct experiments through simulations on 8 real network topologies and two kinds of generated networks conforming to ER (Erdos–Renyi) random model and small-world model. Experimental results demonstrate that the proposed algorithm can achieve a competitive performance of switch-to-controller latencies in both the cases without link failure and with single-link failure, and the accumulated delay of primary and backup paths between the controllers and the switches. The Pareto optimal solution set provided by algorithm RALO allows network administrators with flexible choices to strike a trade-off between the switch-to-controller delay of primary and backup paths.

软件定义网络（SDN）是一种革命性的网络体系结构，它将网络控制层与底层设备分开。多个控制器在大型网络中形成逻辑上集中的控制层，这引起了控制器放置问题。假设网络是可靠的，有关延迟的控制器放置的大多数研究都优化了交换机和控制器之间的延迟。但是，网络容易出现链路故障。在本文中，我们提出了一个新颖的多目标SDN控制器放置问题，目的是在没有链路故障和单链路故障的情况下，最小化开关到控制器的通信延迟。我们为多目标多控制器布置提出了一种有效的基于元启发式的可靠性感知和面向延迟的控制器布置算法（RALO）。该算法通过网络分区的贪婪方法构造了一个初始可行解，然后通过可变邻域搜索反复生成新的解。生成新解决方案后，算法将决定是否接受新解决方案作为对该问题的非支配解决方案，并对Pareto最优解决方案集执行更新操作。同时，为了避免落入局部最优，该算法还对当前解执行扰动和破坏操作。最后，我们通过仿真对8种真实网络拓扑以及两种符合ER（Erdos–Renyi）随机模型和小世界模型的生成网络进行了实验。实验结果表明，该算法在无链路故障和单链路故障的情况下，以及控制器与交换机之间的主路径和备用路径的累积时延都能达到交换机到控制器延迟的竞争性能。算法RALO提供的帕累托最优解决方案集使网络管理员可以灵活选择，在主要路径和备用路径的切换到控制器延迟之间进行权衡。实验结果表明，该算法在无链路故障和单链路故障的情况下，以及控制器与交换机之间的主路径和备用路径的累积时延都能达到交换机到控制器延迟的竞争性能。算法RALO提供的帕累托最优解决方案集使网络管理员可以灵活选择，在主要路径和备用路径的切换到控制器延迟之间进行权衡。实验结果表明，该算法在无链路故障和单链路故障的情况下，以及控制器与交换机之间的主，备用路径的累积延迟情况下，都能达到交换机到控制器延迟的竞争性能。算法RALO提供的帕累托最优解决方案集使网络管理员可以灵活选择，在主要路径和备用路径的切换到控制器延迟之间进行权衡。