MQTT Client Message Queueing and Delivery

In this tutorial I want to talk about the pros and cons of queueing or buffering messages on an MQTT network. I want to start by discussing points of connection failure and the affects of failure  by using the reference diagram below:

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Using the Mosquitto_ctrl Tool

The Mosquitto_ctrl tool was introduced with mosquitto v2 and is used for dynamically making user and ACL changes on a mosquitto broker. To use it the target broker needs to have the dynamic security plugin enabled. The tool is effectively a modified mosquitto publish client and if you subscribe to the $CONTROL topic you can see the messages that it publishes (example shown below).

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Sparkplug Payloads and Messages

In a Sparkplug MQTT network there is no direct link between end nodes and the primary application (control node). All communication between nodes is via a central MQTT server. In this tutorial we will look at the message payloads and  how the various components establish a session with the MQTT broker and what they publish.

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Arduino -Sending and Receiving JSON Data over MQTT

To send an receive JSON data with Arduino you can use the ArduinoJson library. The online documentation contains several usage examples, and there is even a book that supports the project. In this example we are going to send a JSON object using MQTT, receive that object and decode it.

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MQTT-SN Topic Names and Identifiers

MQTT Topics are UTF-8 strings structured in a hierarchy similar to folders and files in a file system using the forward slash ( / )as a delimiter. To be valid a topic must be at least 1 character long and generally in real world applications they 10s of characters in length. The topic is sent with every message published, and so in order to reduce the length of published messages MQTT-SN uses shorter topic names. it does this by using a variety of topic identifiers in place of standard topic name used in MQTT.

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