What is MQTT?

MQTT, which stands for Message Queuing Telemetry Transport, is a lightweight and efficient publish-subscribe messaging protocol designed for constrained devices and low-bandwidth, high-latency, or unreliable networks. MQTT is particularly popular in the Internet of Things (IoT) and machine-to-machine (M2M) communication scenarios. Here are some key characteristics and concepts related to MQTT:

1. Publish-Subscribe Model: MQTT follows a publish-subscribe messaging pattern. In this model, devices or applications called "publishers" send messages to specific "topics." Other devices or applications, known as "subscribers," express interest in receiving messages on specific topics. When a message is published on a topic, the broker ensures that it is delivered to all subscribers interested in that topic.

2. Quality of Service (QoS): MQTT supports different levels of QoS to ensure the reliability of message delivery. There are three levels:

   • QoS 0 (At most once): Messages are delivered at most once. There is no acknowledgment of receipt, and some messages may be lost.

   • QoS 1 (At least once): Messages are guaranteed to be delivered at least once. Duplicates may occur.

   • QoS 2 (Exactly once): Messages are guaranteed to be delivered exactly once, with no duplicates.

3. Lightweight: MQTT is designed to be lightweight and efficient, making it suitable for devices with limited processing power and memory. The protocol minimizes overhead and is efficient in terms of both message size and bandwidth usage.

4. Retained Messages: MQTT supports the concept of retained messages. When a message is sent with the "retain" flag, the broker stores the last message sent on that topic. Any new subscribers to that topic will immediately receive the retained message.

5. Last Will and Testament (LWT): MQTT allows clients to specify a "last will" message. If a client unexpectedly disconnects, the broker will send the last will message to a specified topic. This feature is often used for indicating the client's status.

6. Session Persistence: MQTT brokers can be configured to maintain client sessions, remembering which topics a client has subscribed to. This ensures that clients receive messages they missed while disconnected.

7. Security: MQTT can be used with various security mechanisms, including Transport Layer Security (TLS) for encrypted connections and username/password authentication. Security is crucial when dealing with sensitive data in IoT applications.

8. Wildcards: MQTT supports wildcards in topic subscriptions, allowing subscribers to receive messages from multiple topics with a common pattern.

Popular MQTT brokers and client libraries are available for various programming languages, making it easy to implement MQTT in a wide range of applications.

In summary, MQTT is a messaging protocol designed for efficient, lightweight, and reliable communication, especially in IoT and M2M applications. Its publish-subscribe model, support for different QoS levels, and lightweight nature make it well-suited for constrained devices and unreliable networks.

Configuration

• Broker Url: The url for the mqtt broker to connect to.

• Username: The user name to use if the broker does NOT allow for anonymous connections.

• Password: The password to use to use if the broker does NOT allow for anonymous connections.

• Last Will and Testament: The last will and testament is a message that will be sent out to subscribers if this client disconnects ungracefully.

  • Topic: The topic to published data to. Can and include wildcards (+, #).

  • Payload: The data to published to a topic.

  • Retain: Whether or not the message should be retained by the broker and sent to clients as soon as they subscribe rather then having to wait for the next update the topic.

  • Quality of Service: The qos to use when sending the the message. The broker will use this field when sending the message to a subscribed client.

Functions

Publish

Publish data to an mqtt topic

Takes an array of object with the fields

• Topic: The topic to publish data to.

• Payload: A string representing the data to publish

• Encoding: The way to encode the data from the payload

Testing 

MQTT Explorer - 

MQTT Explorer

MQTT Explorer can be used to connect to Mosquitto or any other broker to publish values and make changes to topics that can be picked up by other clients