Message Oriented Middleware as used in this document is any infrastructure supporting sending and receiving NetworkMessages between distributed applications. OPC UA does not define a Message Oriented Middleware, rather it uses protocols that allow connecting, sending and receiving data. The transport protocol mappings for PubSub are described in 7.3.
This document describes two general types of Message Oriented Middleware to cover a large number of use cases. The two types, broker-less and broker-based middleware, are described in 22.214.171.124 and 126.96.36.199.