I'm working on an IoT project that involves thousands of MQTT clients that are connected to a broker (mosquitto) via 4G/WiFi router/modem. Less than 10 clients are connected to the same router, and the routers come from different places (different cities).
Right now we have very few clients and they are always-connected to the broker. I know from this discussion that there will be no problems even when they will grow up to 1000+ units.
My question is about the traffic load on the 4G connection. The end-user is afraid about data consumption with all those "channels" opened and not used. As far as I understand when there is no activity only the keep-alive packets are sent, though I cannot find this information for sure in the MQTT documentation.
Can I assume the traffic when no packets are published is negligible?