PubSuband Client Serverare both based on the OPC UA Information Model. PubSubtherefore can easily be integrated into Serversand Clients. Quite typically, a Publisherwill be a Server(the owner of information) and a Subscriberis often a Client. Above all, the PubSub Information Modelfor configuration promotes the configuration of Publishersand Subscribersusing the OPC UA Client Servermodel.
Nevertheless, the PubSubcommunication does not require such a role dependency. I.e., Clientscan be Publishersand Serverscan be Subscribers. In fact, there is no necessity for Publishersor Subscribersto be either a Serveror a Clientto participate in PubSubcommunications.