MQTT: IoT Device Communication Protocol Stack

Around us, more and more smart devices are quietly changing our lives. Have you ever wondered what happens behind the scenes when you use a mobile app to turn on the smart bulb at home? Today, let’s explore the “delivery guy” of communication between IoT devices – the MQTT protocol.

What is MQTT?

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol. To put it simply, it is like “WeChat” in the IoT world, responsible for delivering messages between different devices.

Core Features

1. Lightweight: Small data transmission, suitable for low bandwidth environments
2. Publish/Subscribe Model: More flexible communication between devices
3. Reliability Guarantee: Supports three levels of message QoS
4. Strong Real-time Performance: Low latency, quick response

How MQTT Works

Publish/Subscribe Model

Imagine a smart home system:

• The smart bulb is the publisher, regularly publishing its status
• The mobile app is the subscriber, receiving the status information from the bulb
• The MQTT server is the broker, responsible for forwarding messages

Python code example for publisher

# MQTT Publisher Example
import paho.mqtt.client as mqtt

# Create MQTT client
client = mqtt.Client()
client.connect("localhost", 1883)

# Publish message
client.publish("home/light", "on")

Topics

MQTT uses topics to categorize messages. For example:

• home/light/status
• home/temperature
• home/humidity

Python code example for subscriber

# MQTT Subscriber Example
import paho.mqtt.client as mqtt

def on_message(client, userdata, message):
    print(f"Received message: {message.payload.decode()}")

client = mqtt.Client()
client.on_message = on_message
client.connect("localhost", 1883)
client.subscribe("home/light/#")
client.loop_forever()

QoS Levels

MQTT provides three levels of Quality of Service:

1. QoS 0: At most once delivery, like a lost package
2. QoS 1: At least once delivery, may be duplicated
3. QoS 2: Exactly once delivery, the most reliable but the slowest

Practical Case: Smart Temperature Monitoring

Let’s implement a simple temperature monitoring system.

Python code example

import paho.mqtt.client as mqtt
import random
import time

# Simulate temperature sensor
def publish_temperature():
    client = mqtt.Client()
    client.connect("localhost", 1883)
    
    while True:
        temperature = round(random.uniform(20, 30), 2)
        client.publish("sensor/temperature", str(temperature))
        time.sleep(5)

# Temperature monitoring client
def monitor_temperature():
    def on_message(client, userdata, message):
        temp = float(message.payload.decode())
        if temp > 28:
            print(f"Warning: High temperature ({temp}°C)! ")
        else:
            print(f"Current temperature: {temp}°C")

    client = mqtt.Client()
    client.on_message = on_message
    client.connect("localhost", 1883)
    client.subscribe("sensor/temperature")
    client.loop_forever()

Exercises

1. How to implement a simple MQTT chat room?
2. Use MQTT protocol to control the smart bulb switch
3. How to handle MQTT reconnection issues?

⚠️ Precautions

• Ensure the security of the MQTT server
• Design the topic structure reasonably
• Choose the appropriate QoS level
• Handle reconnection mechanisms properly

Tips

1. It is recommended to use Mosquitto as the MQTT broker
2. You can use the MQTT Explorer tool to debug messages
3. Set an appropriate heartbeat interval to maintain the connection

Friends, today’s programming lesson ends here! Remember to practice hands-on, and feel free to ask me questions in the comments. I wish you a pleasant learning experience and smooth sailing on your programming journey! See you next time!