MQTT is often used to obtain high resolution data from field devices. With this in mind, we ran some very simple tests to see how quickly we could publish data from a SCADAPack RTU to CloudMQTT.
Actual publishing performance will be highly dependent on RTU loading and communications network latency and throughput.
Publishing in Tags format requires one network transaction per tag. Publishing in JSON format requires one transaction for all tags. JSON publishing is faster than Tags because network latency and throughput can cause 10s to 100s of milliseconds of delay for each publishing attempt.
The screen grab below shows that the RTU can publish 48 values per second over a TLS connection to CloudMQTT's free plan, which is throttled at 10 kbit/s. This is 4 reporting groups with 16 values each. The RTU is on a hardwired ethernet connection in an office, and as such has a very low latency, high speed connection.
