Time Signals Converging within Cyber-Physical Systems

Time is central to predicting, measuring and controlling properties of the physical world, and is one of the most important constraints distinguishing Cyber-Physical Systems (CPS) from distributed computing in general. However, mixing the cyber and the physical presents a fundamental challenge, since computers and communications systems have abstracted away the physical layer and timing is fundamentally a physical signal. While such abstractions have yielded significant benefits, time has been a casualty. CPS used in industry today achieve time-awareness by making use of time-aware fieldbuses and devices with specialized proprietary software. However, this approach has proved restrictive in both the topologies achievable and the scalability of networks beyond a certain size. The new era of the Internet-of-Things and the Industrial Internet is paving the way for convergence, where time needs to be an integral part of the cyber, making integration of cyber and physical seamless. However, this requires successful research in a number of different areas. The National Institute of Standards and Technology (NIST) has formed a CPS Public Working Group (PWG), with members from global industry, academia and government. This CPS PWG is tasked with creating a set of frameworks and reference architectures for CPS, to promote proper function and interoperability. Public documents from this effort will soon be available. We discuss the timing section of the CPS PWG document and focus on the status of challenges and efforts to integrate time-sensitive with best-effort processes in CPS nodes and the networks that connect them.