Quest: Quality of Service-Centric Resilient Routing for Software-Defined Wide Area Networks

Emerging network applications pose diverse Quality of Service (QoS) demands, prompting the adoption of Software-Defined Networking (SDN) in Wide Area Networks (WANs), known as Software-Defined Wide Area Networks (SD-WANs). SDN introduces path programmability, allowing controllers to dynamically adjust flow forwarding paths at their switches to accommodate varying traffic conditions and differentiated QoS requirements. However, controller failures can lead to the offline state of controlled switches, causing flows traversing these switches to lose path programmability and degrade QoS. Existing solutions typically focus on indirect metrics such as path programmability or coarse-grained load balancing, which often neglect the individual QoS demands of each flow and the control plane performance. To fill this research gap, we propose Quest, a QoS-aware resilient routing framework designed to preserve QoS in both data and control planes during controller failures. Compared to existing solutions, Quest explicitly addresses the critical limitations by jointly optimizing fine-grained QoS-aware flow routing and control plane latency. We formulate an optimization problem that jointly ensures QoS-aware flow routing and minimizes control plane delays. Due to the complexity of this problem, we utilize a linearization approach and further develop a heuristic QoS-centric resilient routing algorithm. Extensive simulations using real-world topologies and traffic traces demonstrate that Quest substantially improves network performance, achieving a 1.71% increase in average throughput ratio, a 46.65% reduction in average latency, and a 62.74% decrease in average control latency compared to baseline approaches.