Abstract
Recent advances in the industrial internet of things (IIoT) and cyber–physical systems drive Industry 4.0 and have led to remote monitoring and control applications that require factories to be connected to remote sites over wide area networks (WAN). The adequate performance of remote applications depends on the use of a clock synchronization scheme. Packet delay variations adversely impact the clock synchronization performance. This impact is significant in WAN as it comprises wired and wireless segments belonging to public and private networks, and such heterogeneity results in inconsistent delays. Highly accurate, hardware–based time synchronization solutions, global positioning system (GPS), and precision time protocol (PTP) are not preferred in WAN due to cost, environmental effects, hardware failure modes, and reliability issues. As a software–based network time protocol (NTP) overcomes these challenges but lacks accuracy, the authors propose a software–based clock synchronization method, called CoSiWiNeT, based on the random sample consensus (RANSAC) algorithm that uses an iterative technique to estimate a correct offset from observed noisy data. To evaluate the algorithm’s performance, measurements captured in a WAN deployed within two cities were used in the simulation. The results show that the performance of the new algorithm matches well with NTP and state–of–the–art methods in good network conditions; however, it outperforms them in degrading network scenarios.
Highlights
Due to the market and business evolution, industrial automation systems are evolving from the rigid automation pyramid to a flexible and reconfigurable architecture
In order to address these challenges, this paper proposes a software–based, scalable, yet accurate and precise clock synchronization algorithm for wide area networks (WAN) called CoSiWiNeT based on Random sample consensus (RANSAC) algorithm to effectively deal with outliers in noisy offset data and predict correct clock offsets
The results of traces 3 and 4 reveal that the performance of CoSiWiNeT is almost comparable with state–of–the–art Kalman filter (KF) algorithm, least square (LS) algorithm, and state–of–the–practice network time protocol (NTP) protocol on the first three parameters
Summary
Due to the market and business evolution, industrial automation systems are evolving from the rigid automation pyramid to a flexible and reconfigurable architecture. Numerous applications based on remote monitoring and control such as remotely controlling a valve in a factory, predicting or preventing maintenance of factory assets based on periodic collection and analysis of factory sensor data by third–party vendors, controlling the production schedules in a factory based on the current inventory status of another raw material–producing factory, are grabbing the attention of plant owners, industries, and research institutes Network packet delay variation or jitter adversely affects the clock synchronization accuracy This effect is prominent in WAN as the different network segments contribute differently to end–to–end packet delays, e.g., the jitter of a fiber optics link is much less than the wireless links, resulting in variable end–to–end packet delays over time.
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