{"id":1398,"date":"2016-12-20T00:01:05","date_gmt":"2016-12-19T23:01:05","guid":{"rendered":"http:\/\/iot.fkainka.de\/?p=1398"},"modified":"2018-10-24T16:05:10","modified_gmt":"2018-10-24T15:05:10","slug":"day-20-mqtt-message-queue-telemetry-transport","status":"publish","type":"post","link":"https:\/\/iot.fkainka.de\/en\/day-20-mqtt-message-queue-telemetry-transport","title":{"rendered":"Day 20: MQTT (Message Queue Telemetry Transport)"},"content":{"rendered":"

For the last days of this Advent, you’ll now become familiar with a subject that plays a large role in the realm of the IoT. We’re dealing with the messaging protocol MQTT, which was specially developed for the communication from machine to machine (M2M). The protocol is thus so brilliant because e.g. control data, measurement data or texts can be exchanged very easily and compactly. The overhead (data that’s transferred alongside the actual user data) is much lower than with HTTP and can be processed readily even by embedded devices, meaning microcontrollers like our NanoESP. At the same time, the controller doesn’t constantly have to establish a connection and query whether there’s been a change; instead, the connection is continually maintained and the client automatically gives information about changes.<\/p>\n

A so-called broker forms the basis for the communication. A broker is a server application that processes all data. A device can now connect to the broker and “publish” messages, i.e. send them to the broker. Another device can “subscribe” to specific topics and then immediately receives a new message published to this topic delivered by the broker. So that you don’t have to set up your own broker, a public broker has been set up for you at the address broker.fkainka.de<\/strong>.<\/p>\n

\"Der<\/a>

The MQTT broker delivers the messages<\/p><\/div>\n

The topics are structured hierarchically, where subtopics are each separated with a slash. There are also so-called wild cards. With a “+” or “#” you can subscribe to multiple topics at the same time. Publishing with the wild cards “#” or “+” isn’t possible, however. For example, the topics<\/p>\n

MyHome\/Kitchen\/Temperature<\/strong><\/p>\n

MyHome\/Bathroom\/Temperature<\/strong><\/p>\n

can thus be received at the same time by subscribing to the topic<\/p>\n

MyHome\/+\/Temperature<\/strong><\/p>\n

– The plus thereby always replaces only one topic level. The # replaces all at once. With the topic<\/p>\n

MyHome\/#<\/strong><\/p>\n

you thus receive all messages that are published in all subtopics of MyHome. The data that are published to a topic can be virtually anything, from pure texts to measurement values or simple 1\/0 commands for switching a light.
\n