UA Part 14: PubSub Main Technology Features
In general speaking the following two distinct patterns are used to transfer data between communicating parties:
- connection-oriented: requires a session that has to be established before any data can be sent between sender and receiver
- connectionless-oriented: the sender may start sending messages (called packets or datagrams) to the destination without any preceding handshake procedure
Each has its own advantages and disadvantages. In general, the OPC UA is a session centric communication. The session is established by the OPC UA Client that must connect to the OPC UA Server before any data can be exchanged between them. In this Client/Server scenario defined by the Services in Part 4, the data flow is bidirectional over the session. The session entities communicate over a secure channel that is created in the underlying communication layer and relies upon it for secure communication. It enables to log-in using user authentication and operations authorization. More details you can find in the section: