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Industrial control systems have strict requirements for time-sensitive applications and clock synchronization services. Performance of such applications is adversely impacted by packet delays and jitters. The impact is especially critical in process industries due to harsh environmental conditions. In this paper, we analyze delays and jitters to assess the performance of time-sensitive applications. To this end, we captured and analyzed round trip delay data retrieved from a paper factory. Analysis shows that a sub-millisecond level average delays and the jitters derived from the observed data are sufficient to meet the minimum 10ms update frequency required for most critical control applications. Moreover, the filtered delay variations at the end devices are less than the recommended 150us, which guarantees an adequate time synchronization accuracy in the factory network. Besides, this analysis can provide significant insights into performance bottlenecks for factory applications.

Recent advances in industrial internet of things~(IIoT) and cyber-physical systems drive Industry 4.0 and lead to advanced applications. The adequate performance of time-critical automation applications depends on a clock synchronization scheme used by control systems. Network packet delay variations adversely impact the clock synchronization performance. The impact is significant in industrial sites, where software and hardware resources heavily contribute to delay variations, and where harsh environmental conditions interfere with communication network dynamics. While existing time synchronization methods for IIoT devices, e.g., Simple Network Time Protocol~(SNTP), provide adequate synchronization in good operating conditions, their performance degrades significantly with deteriorating network conditions. To overcome this issue, we propose a scalable, software-based, lightweight clock synchronization method, called CoSiNeT, for IIoT devices that maintains precise synchronization performance in a wide range of operating conditions. We have conducted measurements in local network deployments such as home and a university campus in order to evaluate the proposed algorithm performance. The results show that CoSiNeT matches well with SNTP and state-of-the-art method in good network conditions in terms of accuracy and precision; however, it outperforms them in degrading network scenarios. In our measurements, in fair network conditions, CoSiNeT improves synchronization performance by 23% and 25% compared to SNTP and state-of-the-art method. In the case of poor network conditions, it improves performance by 43% and 26%, respectively.

Time synchronization is essential for the correct and consistent operation of automation systems. An inaccurate analysis being a consequence of improper synchronization, can affect automation functions, e.g., by producing false commands and warnings. Industrial systems are evolving from the rigid automation pyramid to a flexible and reconfigurable architecture due to market evolution. The new trends in Cyber-Physical-Systems (CPS), Industry 4.0, and Internet of Things (IoT) are enabling this evolution. Citing a need to understand the future synchronization requirements, this paper envisions the architecture, communication network, and applications of future automation systems. Built on this vision, the paper derives the future needs of synchronization and analyzes them with state-of-art synchronization means. Based on the analysis, we envision the future of synchronization systems for automation systems.

Synchronization is essential for correct and consistent operation of automation systems. Synchronized devices accurately time-stamp the events and enable timely communication of messages over a communication network. In absence of a common time base, critical functions of automation systems cannot be carried out in a safe fashion. Unsynchronized systems may lead to malfunctions such as false alarms, wrong decisions and erroneous outcomes resulting into serious showstopper for plant operations. Despite technical advances in synchronization, industrial automation systems have lagged compared to telecommunication and financial services in utilization of latest synchronization technology. Thus, there is a need to investigate the adoption of synchronization in industrial networks, its current state and implementation problems. We carried out an extensive literature search in a structured way to study the evolution of synchronization in automation systems. We also investigated today's industrial automation systems and their network topologies to get insight into the synchronization techniques and mechanisms being used. As an outcome of study, the paper highlights the challenges related to synchronization in existing automation networks that need to be addressed in the immediate and short-term future.