MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol widely used in IoT, home automation, and real-time applications. It operates on a publish-subscribe model, making it highly efficient for low-bandwidth and high-latency networks.
Why MQTT?
Lightweight & Efficient
Works on low-power devices
Reliable with QoS levels
Supports bi-directional communication
1. Understanding MQTT
MQTT works with three main components:
1️⃣ Broker – Central server managing message distribution. (e.g., Mosquitto, HiveMQ)
2️⃣ Publisher – Sends messages to a topic.
3️⃣ Subscriber – Listens for messages from a topic.
1.1 MQTT Communication Flow
🔹 Publisher sends messages to a topic
🔹 Broker receives and forwards messages
🔹 Subscriber listens for topic updates
2. Setting Up MQTT in Python
We use the paho-mqtt library to implement MQTT in Python.
2.1 Install the Paho-MQTT Library
pip install paho-mqtt
3. Running an MQTT Broker
For testing, install Mosquitto MQTT broker:
On Linux/macOS:
sudo apt install mosquitto mosquitto-clients
sudo systemctl start mosquitto
On Windows: Download from Mosquitto
4. Implementing MQTT in Python
4.1 Writing an MQTT Publisher
import paho.mqtt.client as mqtt
broker = "localhost" # Change to broker IP if remote
port = 1883
topic = "home/temperature"
client = mqtt.Client()
client.connect(broker, port)
for i in range(5):
message = f"Temperature: {20 + i}°C"
client.publish(topic, message)
print(f"Published: {message}")
client.disconnect()
This script sends temperature updates to the broker.
4.2 Writing an MQTT Subscriber
import paho.mqtt.client as mqtt
broker = "localhost"
topic = "home/temperature"
def on_message(client, userdata, message):
print(f"Received: {message.payload.decode()}")
client = mqtt.Client()
client.connect(broker)
client.subscribe(topic)
client.on_message = on_message
client.loop_forever()
This listens for temperature updates.
5. QoS (Quality of Service) Levels
MQTT supports three QoS levels:
| QoS Level | Description |
|---|---|
| 0 (At most once) | Message sent without acknowledgment (Fastest, but may be lost). |
| 1 (At least once) | Message delivered at least once (May receive duplicates). |
| 2 (Exactly once) | Ensures one-time delivery (Most reliable but slowest). |
Modify QoS in publish/subscribe:
client.publish(topic, message, qos=1)
client.subscribe(topic, qos=2)
6. Securing MQTT Communication
🔹 Enable Authentication: Username & Password
🔹 Use TLS Encryption for secure transmission
🔹 Restrict Topics for better security
6.1 Setting Up Authentication
Modify Mosquitto config file (mosquitto.conf):
allow_anonymous false
password_file /etc/mosquitto/passwd
Create a password file:
mosquitto_passwd -c /etc/mosquitto/passwd username
6.2 Connecting with Authentication in Python
client.username_pw_set("username", "password")
client.connect(broker, port)
7. IoT Project: Sending Sensor Data with MQTT
7.1 Simulating a Temperature Sensor
import paho.mqtt.client as mqtt
import random
import time
broker = "localhost"
topic = "sensor/temp"
client = mqtt.Client()
client.connect(broker)
while True:
temp = round(random.uniform(20.0, 30.0), 2)
client.publish(topic, f"Temperature: {temp}°C")
print(f"Sent: {temp}°C")
time.sleep(2)
This script sends random temperature values every 2 seconds.
8. Cloud-Based MQTT Brokers
🔹 HiveMQ – Free public broker: broker.hivemq.com
🔹 EMQX – Scalable MQTT cloud broker
🔹 Adafruit IO – MQTT for IoT projects
Connecting to a Cloud MQTT Broker:
broker = "broker.hivemq.com"
client.connect(broker, 1883)