Fault-Resilient Real-Time Communication Using Software-Defined Networking

The development of complex cyber-physical systems necessitates real-time networking with timing guarantees even in the presence of a link fault. Targeting firm real-time flows with the maximum allowable number of continuous deadline misses, this paper introduces FR-SDN, a fault-resilient SDN (Software-Defined Networking) framework that satisfies the timing requirements of firm real-time flows. To this end, we first investigate individual steps for path restoration: fault recognition, path recalculation, and path reassignment. We then design novel system architecture that reduces the delay of the fault recognition and path reassignment steps to potentially assign more time budget to the path recalculation step. Based on the calculation of tight upper-bounds on the delays in individual steps under the proposed system design, we derive a necessary feasibility condition that guarantees the timing requirements of firm real-time flows, and we calculate a time budget for the path recalculation step. Finally, we develop a multi-constrained path finding algorithm that can dynamically adjust the scope of flows to reroute according to the time budget. To the best of our knowledge, FR-SDN is the first study on adaptive path restoration for real-time flows, taking into account path restoration delay and fault tolerance constraints in case of link fault. We have implemented and evaluated FR-SDN on top of Open vSwitch to demonstrate its effectiveness, achieving an order of magnitude reduction in path restoration delay. In addition, we have deployed FR-SDN into a 1/10 scale autonomous vehicle and have shown, via an in-depth case study of adaptive cruise control, that FR-SDN is able to meet all fault tolerance requirements so that it can behave similarly as if there were no link failure.

I. Introduction

Recent advances in embedded processors and software technologies have fostered the development of complex cyber-physical systems (CPS) such as autonomous driving vehicles. CPS typically integrate sensors, actuators, and computing units to continuously interact with the physical world in realtime. Thus, it is important to develop network techniques that meet CPS requirements. In this paper, we focus on two key requirements on CPS networking, which are deterministic and fault-tolerant communications.