An OPC UA Application can be pre-configured to send messages as a Publisher but commonly it is required to configure the information to be included into messages and also the frequency the messages are sent.
Subscribers can use discovery mechanisms to find Publishers and to get the DataSetMetaData necessary to understand the messages. One example are HMI applications where the configuration can be done inside the Subscriber. But if the Subscriber is a device, it is expected that a configuration tool is required to configure the Subscriber functionality in the device.
The PubSubConfigurationDataType and the other configuration Structures defined in Clause 6 can be used to prepare an offline PubSub configuration that can be stored in a binary file using the UABinaryFileDataType. Such a configuration can be used to configure Publishers and Suscribers if they do not have a online configuration interface or are configured through product-specific configuration tools.
If Publishers and Suscribers are also OPC UA Servers, they can provide the PubSub configuration Information Model defined in Clause 9. This model can be used by generic PubSub configuration tools.
A typical use case is controller to controller or machine to machine communication where both communication partners have a pre-configured list of input and output data Variables and a generic configuration tool establishes the communication by selecting the Variables to be published in the Publisher and then configures the Subscriber to receive the messages from the Publisher and to select the target Variables in the Subscriber.