title: What is the difference between MQTT and OPC-UA (pub/sub)
body: <p>So MQTT is the light weight messaging protocol based on publish/subscribe model.</p>
  <p>Originally OPC-UA was based on a request/response model, but I have read that it now also supports pub/sub extension.</p>
  <p>I also understand that OPC-UA is a not really a protocol but a system architecture. Other than this fact, from the view point of protocol features (considering pub/sub only) what is the difference between MQTT and OPC-UA?</p>