Tom Jenkins - I work with MQTT every day, and there are device's that have this feature built-in. I realize it's not the only part of IOT/IIOT but it does/will play a BIG part in this new world.
I also don't work in the "PLANT" environment, I work in the oilfields, where we use this protocol to communicate all of our data from the REMOTE units(which are in 7 states) back to the SCADA server(Ignition).
Now if you really what to understand MQTT you can talk with Mr. Arlen Nippers from Cirrus Link (He is the Co-Inventor) of MQTT. About 2 years ago he helped me to understand this new protocol, and that's why I am where I'm at today.
As always this is just my 2 cents worth.
Everyone have a GREAT day!!