Mühlbauer, NikolasKirdan, ErkinPahl, Marc-OliverWaedt, KarlReussner, Ralf H.Koziolek, AnneHeinrich, Robert2021-01-272021-01-272021978-3-88579-701-2https://dl.gi.de/handle/20.500.12116/34742OPC UA is an industry-standard architecture for automation, process controlling and monitoring. It is a detailed and complex machine-to-machine communication protocol which makes it challenging to implement. The complexity of the protocol leads to heterogeneity among implementations. Today, there are several open-source implementations without a compliance certificate accredited by the OPC Foundation. Certified implementations undergo various tests to fulfil interoperability. Every implementation fits different use-cases and requirements as each of them comes with its own features. In this paper, we make a feature-based comparison of the most common open-source OPC UA implementations. We investigate their support for the essential features and functionalities. Furthermore, we evaluate their interoperability. Overall, our study shows that open-source implementations have good coverage of features and functionalities, especially open62541 and UA-.NETStandard. Furthermore, our tests show that they do not have any significant interoperability issue.enopc uaopen-sourceinteroperability10.18420/inf2020_341617-5468