PubSub and Client Server are both based on the OPC UA Information Model. PubSub therefore can easily be integrated into Servers and Clients. Quite typically, a Publisher will be an 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 Client Server model. Figure 8 depicts a single OPC UA Application that acts as both a Server and a Publisher.
Figure 8 – Integrated Client Server 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.