MQTT

MQTT is hard to understand not because of its packet types, but because it builds message distribution on a broker in the middle, topic-based routing, and the reality of weak or unstable connections. Many devices already have network access and a TCP connection, yet the subscriber still does not receive the status update. Or a device comes back online after being disconnected for a few minutes, and the application expects the message to be recovered, only to get part of it back. The difficult part is not the message format itself. It is the fact that MQTT treats distribution as a broker-centered problem.