Black-Box Analysis of the Publish-Subscribe Notification Latency in Real OPC UA Servers

Among the many enabling technologies Industry 4.0 relies on, the Industrial Internet of Things is a relevant one that enables both horizontal and vertical integration in modern enterprises, to accomplish complex functions that exploit either cloud or edge processing. In particular, the OPC UA protocol is knowing an ever increasing attention for interconnecting devices, equipment, and facilities in next-generation plants. This work focuses on the characterization of the notification latency in distributed systems that rely on the OPC UA publish-subscribe paradigm for interactions. In particular, starting from a black-box experimental evaluation carried out on real setups, we tried to explain the seemingly peculiar behavior of some popular solutions by means of theoretical models complemented with code inspection.