Message Oriented Middleware as used in this specification 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 part 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 and