Improving OPC UA Publish-Subscribe Mechanism over UDP with Synchronization Algorithm and Multithreading Broker Application

Abstract

Communication protocols are evolving continuously as the interfacing and interoperability requirements are the foundation of Industry 4.0 and Industrial Internet of Things (IIoT), and the Open Platform Communication Unified Architecture (OPC UA) protocol is a major enabling technology. OPC UA was adopted by the industry, and research is continuously carried out to extend and to improve its capabilities, to fulfil the growing requirements of specific industries and hierarchical levels. Consistent issues that have to be approached are related to the latest specifications and the real-time context that could extend the applicability of the protocol and bring significant benefits in terms of speed, data volumes, footprint, security. The real-time context is essential in the automotive sector and it is highly developed within some specific protocols. The current work approaches first the conceptual analysis to improve the OPC UA interfacing using the Publish-Subscribe mechanism, focusing on real-time constraints and role distribution between entities, and considering some well-founded interfacing strategies from the automotive sector. The conceptual analysis is materialized into a solution that takes OPC UA Publish-Subscribe over User Datagram Protocol (UDP) mechanism to the next level by developing a synchronization algorithm and a multithreading broker application to obtain real time responsiveness and increased efficiency by lowering the publisher and the subscriber footprint and computational effort, reducing the difficulty of sending larger volumes of data for various subscribers and the charge on the network and services in terms of polling and filtering. The proof of concept is evaluated and the results prove the efficiency of the approach and the solution.

Approaching OPC UA Publish–Subscribe in the Context of UDP-Based Multi-Channel Communication and Image Transmission

“…The authors in [ 7 ] presented research that analyzed the real-time requirements from different perspectives in the context of the OPC UA publish–subscribe mechanism, and the concept that is targeting different domains has been implemented. Other studies have targeted the exploration of the OPC UA publish–subscribe mechanism in comparison with similar paradigms from different communication protocols used in other domains, and architectural insights and improvements have been suggested for specific use-cases from the industry [ 8 ].…”

“…In [ 19 ], for the exchange of information, the OPC UA entities were implemented on Raspberry PI Model 3B+, from different open-source stacks, and with efficiency measurements being performed. In [ 8 ], the authors implemented and tested multiple OPC UA publishers and subscribers on devices with high resources and also on embedded devices with the objective of performing synchronization regarding the information exchange among devices.…”

“…However, OPC UA would have to assure also the real-time, speed, and volume requirements. Based on researches of [ 7 ] and [ 8 ], the bitwise/tag-based communication would assure the real-time constraints and the publish–subscribe mechanism. The purpose is to elevate the OPC UA publish–subscribe mechanism from the previous researches to fit longer-term, higher volumes, and faster data movement, which are necessary requirements for image transmissions in the context of complete integration with the process flow.…”

“…For the implementation of the OPC UA entities, the authors have taken into consideration multiple OPC UA open-source stacks implemented in different programming languages for the current study. Based on the implementation reliability that was present in various research projects [ 7 , 8 , 29 ], and on studies regarding the capabilities and the efficiency of the OPC UA stacks [ 19 ], the open62541 SDK [ 30 ] was selected for the implementation of the OPC UA publisher and the OPC UA subscriber on both devices.…”

“…This way the capabilities of the protocol can be extended, and better performances are reachable regarding volumes, speed, availability, footprint, and security. The OPC UA publish–subscribe mechanism is developed successfully in [ 7 , 8 ], allowing the expansion of the protocol applicability. However, the research has to evolve and provide a solution for OPC UA publish–subscribe based image transmission that would allow complete integration of the protocol in the industry.…”