Thank you for your explanation. I think I understand it at a basic level.
The gateway serves as the Wi-Fi connected intermediary between the IoT device and the MQTT broker. Rather than have a device connected directly to the network (typically via Wi-Fi), the IoT device connects to the MQTT gateway via whatever the interface is (RF, IR, BLE, GPIO, etc.). The gateway then interchanges data with the IoT device directly.
The MQTT gateway is connected to the MQTT broker via Wi-Fi. It subscribes to MQTT topics associated with its connected devices and “acts” on those topics to send the information to the associated device (e.g., transmit an RF or IR sequence to the device) or to respond to requests for information about a particular device (e.g., an MQTT request for the current temperature reading from a connected sensor). It also takes data or actions from its connected devices and publishes that information via MQTT.
So, If I have a device which does not have Wi-Fi or I don’t want to continue to load down my Wi-Fi with individual Wi-Fi connected IoT devices, I can deploy a gateway with several connected devices and have it be the “intermediary”. This means that I can place the gateway within good range of a strong Wi-Fi signal yet still reach end-point devices which may be further away or in areas where the Wi-Fi signal may not be “stable”.
Yes? Sort of?
One additional question - your architecture diagram shows the home automation hub interfacing with the gateway. In my experience, the hub is subscribed to MQTT topics. Thus the broker is the orchestrator. Granted, the broker might be embedded in the automation hub. But it might be a standalone broker (e.g., mosquitto). So, in the diagram, there is an implicit MQTT broker; yes?