Time-based Coordination in Geo-Distributed Cyber-Physical Systems

Emerging Cyber-Physical Systems (CPS) such as connected vehicles and smart cities span large geographical areas. These systems are increasingly distributed and interconnected. Hence, a hierarchy of cloudlet and cloud deployments will be key to enable scaling, while simultaneously hosting the intelligence behind these systems. Given that CPS applications are often safety-critical, existing techniques focus on reducing latency to provide real-time performance. While low latency is useful, a shared and precise notion of time is key to enabling coordinated action in distributed CPS. In this position paper, we argue for a global Quality of Time (QoT)-based architecture, centered around a shared virtualized notion of time, based on the timeline abstraction [1]. Our architecture allows applications to specify their QoT requirements, while exposing timing uncertainty to the application. The timeline abstraction with the associated knowledge of QoT enables scalable geo-distributed coordination in CPS, while providing avenues for fault tolerance and graceful degradation in the face of adversity.