MQTT (Message Queuing Telemetry Transport) Protocol

MQTT is a lightweight, publish-subscribe network protocol that transports messages between devices. It is designed for connections with remote locations where a "small code footprint" is required or the network bandwidth is limited.

Protocol Overview

• Architecture: Based on a Client/Broker model.
• Transport: Typically runs over TCP/IP, but variants like MQTT-SN (for Sensor Networks) can run over UDP/Bluetooth.
• Port: Default is 1883, while encrypted (TLS/SSL) is 8883.
• Payload: Can carry up to 256MB of data; control headers can be as small as 2 bytes.
• QoS (Quality of Service):
  • Level 0: At most once (Fire and forget).
  • Level 1: At least once (Acknowledged).
  • Level 2: Exactly once (Four-step handshake).

Features & Security

• Topic System: Uses a hierarchical structure (e.g., home/living-room/temperature).
• Retained Messages: The broker stores the last message on a topic for new subscribers.
• Last Will and Testament (LWT): Notifies other clients when a client unexpectedly disconnects.
• Security: Basic authentication uses plain-text usernames and passwords. TLS/SSL is highly recommended to protect against interception and tempering.

Recommended Implementations

Brokers

• Eclipse Mosquitto: a popular lightweight open-source MQTT broker.
  • Mosquitto Official Site
  • Eclipse IoT Projects
• EMQX: Scalable, distributed MQTT broker for IoT.

Client Libraries

• Eclipse Paho: A collection of high-quality MQTT client libraries.
  • Eclipse Paho Project Site
• • eclipse/paho.mqtt.golang
    • Go, EPL-2.0 / EDL-1.0
    • The standard MQTT client library for Go. Supports MQTT 3.1, 3.1.1, and V5. Supports TCP, TLS, and WebSockets.

Resources

• MQTT Official Site
• MQTT Specifications
• Comparison of MQTT Implementations (Wikipedia)