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. 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.