OPC UA PubSub and ClientServer models are complementary and can be combined and used synergistically. The OPC UA Information Model is the foundation for both. A typical scenario involves using ClientServer interactions for configuration, control, and on-demand data access, while PubSub is used for efficient, high-speed dissemination of real-time data. For instance, a Client application might use ClientServer to configure a Server and set up PubSub connections. Subsequently, the Server/Publisher publishes real-time data updates using PubSub, and the Client/Subscriber subscribes to this data stream for continuous monitoring.

OPC PubSub can easily be integrated into Servers and Clients. Quite typically, a Publisher will be a Server (the owner of information) and a Subscriber is often a Client. Above all, the PubSub Information Model for configuration promotes the configuration of Publishers and Subscribers using the OPC UA ClientServer model.

Figure 7 depicts a single OPC UA Application that acts as both a Server and a Publisher.

Figure 7 – Integrated ClientServer and PubSub models

Nevertheless, the PubSub communication does not require such a role dependency. I.e., Clients can be Publishers and Servers can be Subscribers. In fact, there is no necessity for Publishers or Subscribers to be either a Server or a Client to participate in PubSub communications.