Understanding MQTT Topics

MQTT Topics are structured in a hierarchy similar to folders and files in a file system using the forward slash ( / )as a delimiter. Using this system you can create a user friendly and self descriptive naming structures of you own choosing. Topic names are: Case sensitive use UTF-8 strings. Must consist of at least one character to be valid. Except for the $SYS topic there is no default or standard topic structure. That is there are no topics created on a broker by default, except for the $SYS topic. All topics are created by a subscribing or publishing

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Paho Python MQTT Client Subscribe With Examples

To receive messages on a topic you will need to subscribe to the topic or topics. To subscribe to a topic you use the subscribe method of the Paho MQTT Class object. In this tutorial we will look at some examples of using the subscribe method. The diagram below illustrates the subscribe message flow.

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Introduction to MQTT Security Mechanisms

In this tutorial we look at how you can restrict access to a broker, and how you can protect your data using various security mechanisms. It is important to note that these security mechanisms are initiated by the broker, and it s up to the client to comply with the mechanisms in place.

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MQTT Retained Messages Explained

Normally if a publisher publishes a message to a topic, and no one is subscribed to that topic the message is simply discarded by the broker. However the publisher can tell the broker to keep the last message on that topic by setting the retained message flag. This can be very useful, as for example, if you have sensor publishing its status only when changed e.g. Door sensor. What happens if a new subscriber subscribes to this status?

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MQTT Last Will and Testament Examples

The last will and testament message is used to notify subscribers of an unexpected shut down of the publisher. The basic process is. The publisher tells the broker to notify all subscribers to a topic, using the last will message , in the event that the connection breaks If the broker detects a connection break it sends the last will message to all subscribers of that topic. Again you will find more detail in this MQTT essentials article here

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MQTT Clean Sessions and QOS Examples

When a client connects to a broker it can connect using either a non persistent connection (clean session) or a persistent connection.. With a non persistent connection the broker doesn’t store any subscription information or undelivered messages for the client. This mode is ideal when the client only publishes messages. It can also connect as a durable client using a persistent connection.

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