Category: MQTTv5

Previous Tutorial Connecting to a Broker Using MQTTv5 and python. Again this tutorial assumes you are already familiar with the basics after using MQTTv3.1.1. This is covered in these tutorials: MQTT Publish and Subscribe for Beginners Subscribing using The Paho Python Client publishing messages using the Python client

In this tutorial we will look at how you connect to a broker using MQTTv5. The tutorial assumes you are already familiar with the basics after using MQTTv3.1.1. This is covered in this tutorial: Python MQTT Client Connections- Working with Connections The main changes to take into account when moving your code to MQTT v5 are the properties object and increased reason codes.

The Last Will message in MQTT v5 functions the same way as that of last will v3.1.1 ,however the last Will messages has been expanded considerably from version 3.1.1.

In MQTT v3.1.1 we have the concept of clean sessions or non persistent/persistent connections. On connect the client indicates to the server using the clean session flag if the session state should be kept by the server when the client disconnects. Session state includes any client subscriptions and also messages depending on the QOS used and is covered in detail in the Understanding clean sessions tutorial , I recommend you read before proceeding if you are unfamiliar with clean sessions.

The Paho Python client version 1.5.1 included support for MQTTv5. Because of the new capabilities of MQTTv5 there have been changes to many of the common functions like connect,subscribe and publish etc. The aim of this tutorial is to point out the main changes, and what you need to do in your code to use the new features.

Properties (MQTTv5) are probably one of the most important additions to the MQTT protocol, and are available in most MQTT message types including acknowledgement messages. The property fields are dependent upon message type, so a CONNECT message will have different property fields than a PUBLISH message. I have listed the property fields for each message type with links to the online documentation describing the filed and its use.

Shared subscriptions provide for client load balancing. With normal subscriptions(non shared subscriptions) if,for example, 4 clients were subscribed to a topic and a client published a message on that topic then that message is sent to all 4 subscribing clients. With a shared subscription then the message would only be sent to one of the subscribing clients.

MQTTv5 Topics are essentially the same as those in v3.1.1 (See Understanding MQTT topics) ,but two new features have been introduced in v5. They are: Topic aliases Shared Topics In this tutorial we will be covering topic aliases.

User properties allow you to add your own meta data to MQTT messages. User properties consist of an array of user defined UTF-8 key/value pairs and are carried in the message property field.

The MQTT protocol allows messages with a maximum size of 268435455 bytes approx 256MB. This is obviously a very large message size and one that most brokers,especially public brokers, will restrict.