Distributing Deterministic, Accurate Time for Tightly Coordinated Network and Software Applications: IEEE 802.1AS, the TSN profile of PTP

Abstract

Real-time cooperation among agents requires sharing of certain temporal information. That information might take the form of "take action X right now!" or it might better be achieved in some cases by establishing an a priori agreement by which each action should be taken and when, together with a shared understanding of what time it is. Distributed applications increasingly rely on this latter synchronized time approach rather than explicit "right now!" communication for cooperative sense and control tasks. Such a capability is foundational to the field of cyber physical systems (CPS) where computation and communication interact with the physical world in real time. While multiple historical approaches exist for time-synchronized (and timely) communication among sensing, computing, and actuating devices, the addition of robust temporal performance characteristics to standard Ethernet through the work of the Time Sensitive Networking (TSN) Task Group of IEEE 802.1 is bringing together the benefits of standard IT networking with excellent worst case latency and synchronization performance that was previously available only to these specialized and sometimes proprietary networks. Such advances will be important in next-generation applications as diverse as CPS/real-time distributed control, smart factories, sensor fusion, autonomous vehicles, and even cloud applications [1]. As we show, precision network time synchronization can dramatically enhance the operation of these applications and is a requirement of certain new network latency enhancements as well.