This is one model, used by ROS nodes. The ROS nodes continuously communicate which each other.
Another model is Call-and-Response.
This is really high level. I don’t know how this fits into the picture of the whole Communication Protocols.
The Pub-Sub pattern is one in which a publisher sends a message to a topic on a message broker. A subscriber binds to the topic and receives messages from the topic in an asynchronous manner.
Since the Pub-Sub pattern is asynchronous, there is no blocking lock between sender and receiver. The sender sends the message to the broker and then moves onto other tasks. The receiver accepts a message at its convenience. Messages in the Pub-Sub pattern tend to be discrete, containing all the information that a process needs to act upon the data provided.