With PubSub, OPC UA Applicationsdo not directly exchange requests and responses. Instead, Publisherssend messages to a Message Oriented Middleware, without knowledge of what, if any, Subscribersthere may be. Similarly, Subscribersexpress interest in specific types of data, and process messages that contain this data, without knowledge of what Publishersthere are.
PubSubis used to communicate messages between different system components without these components having to know each other’s identity.
The identity of the Subscribers and the forwarding of published data to the Subscribersis the responsibility of the Message Oriented Middleware. The Publisherdoes not know or even care if there is one or many Subscribers. Effort and resource requirements for the Publisherare predictable and do not depend on the number of Subscribers.