Fetching data from different data sources present a number of challenges. Given the numerous different standards for dataset formats it is preferred to generalize the data before it is sent to Thingsboard. Since Thingsboard have integrated possibilities for subscribing to a MQTT-broker to fetch data for it's dashboards a Mosquitto-broker was created on the Azure VM to act as a relay to Thingsboard. MQTT is a lightweight communication protocol that is used frequently in IoT-applications. There are a few key features that make it ideal for those kind of appliications. First of all, the protocol being lightweight means it is easy to implement, and with minimized data packets which results in low network usage. Furthermore, this leads to low power usage which saves battery time. Naturally this is very important for battery-restricted devices, for example a sensor node that is only running on battery. Lastly, the protocol provides real-time data which means immediatly after the sensor has published you can subscribe to the broker and get instant update no matter where you are in the world, as long as you're connected to the internet.
Implementations of MQTT contains clients and a broker. The clients either publish or subscribe to the broker, which stores the latest sensor-values in topics. The protocol has two commands, publish, and subscribe which is self-explanatory. An example on how the MQTT communication flow is provided below where a sensor-node which publishes temperature-data to a broker. With to clients subscribing to that data.