NODE-RED flow to measure and chart end-to-end latency to/from a MQTT broker.
Each broker section is a publisher and subscriber pair to measure the end-to-end latency.
The local broker is there just to verify stability and compare to intranet.
Just import the .json into your copy of NODE-RED with dashboard installed.
For details see https://gambitcomm.blogspot.com/2018/08/video-monitor-end-to-end-latency-of.html