Protocol Comparison MQTT vs. WebSocket: A Detailed Comparison

Protocol Overviews

Architecture Comparison

MQTT: Publish-Subscribe Model

MQTT implements a publish-subscribe (pub/sub) architecture which decouples senders (publishers) from receivers (subscribers):

• Central Broker: Acts as an intermediary that routes messages
• Publishers: Send messages to specific topics without knowing who will receive them
• Subscribers: Receive messages from topics they're interested in without knowing who published them
• Topics: Hierarchical addressing scheme used for message filtering
• Many-to-Many: Multiple publishers can publish to the same topic and multiple subscribers can receive from it

WebSocket: Direct Client-Server Model

WebSocket implements a direct communication channel between clients and servers:

• No Intermediary: Direct connection between client and server
• Bidirectional: Both client and server can initiate sending messages at any time
• Event-Based: Often implemented with event-driven programming models
• Application-Specific Routing: Requires custom implementation for message routing
• Typically One-to-One: Each connection is between a specific client and server

MQTT over WebSocket

One important point to understand is that MQTT can run over WebSocket as a transport protocol. This approach combines the benefits of both technologies:

Detailed Feature Comparison

Performance Considerations

Overhead and Efficiency

MQTT is designed to be extremely lightweight:

• The minimum MQTT header can be as small as 2 bytes
• Fixed header size ranges from 2 to 5 bytes
• Optimized for minimizing bandwidth usage

WebSocket has some additional overhead:

• Initial connection requires an HTTP handshake
• Minimum frame header is 2 bytes, but typically 4-8 bytes
• Client-to-server messages require masking, adding overhead

Scalability

Both protocols have different scalability characteristics:

• MQTT:
  • Broker architecture can become a bottleneck
  • Clustering and federation can improve scalability
  • Well-suited for many-to-many communications
• WebSocket:
  • Direct connections can scale linearly with server resources
  • May require load balancing for very high connection counts
  • Better suited for one-to-one or few-to-few communications

When to Use Each Protocol

Implementation Examples

MQTT Example (Python)

import paho.mqtt.client as mqtt

# Callback when connected
def on_connect(client, userdata, flags, rc):
    print(f"Connected with result code {rc}")
    # Subscribe to topic
    client.subscribe("sensors/temperature")

# Callback when message is received
def on_message(client, userdata, msg):
    print(f"Received message on {msg.topic}: {msg.payload.decode()}")

# Create client
client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

# Connect to broker
client.connect("mqtt.example.com", 1883, 60)

# Publish a message
client.publish("sensors/status", "online", qos=1, retain=True)

# Start network loop
client.loop_forever()

WebSocket Example (JavaScript)

// Create WebSocket connection
const socket = new WebSocket('wss://example.com/socket');

// Connection opened
socket.addEventListener('open', (event) => {
    console.log('Connected to WebSocket server');
    
    // Send a message
    socket.send(JSON.stringify({
        type: 'status',
        data: 'online'
    }));
});

// Listen for messages
socket.addEventListener('message', (event) => {
    const message = JSON.parse(event.data);
    console.log('Received message:', message);
});

// Connection closed
socket.addEventListener('close', (event) => {
    console.log('Disconnected from WebSocket server');
});

// Error handling
socket.addEventListener('error', (event) => {
    console.error('WebSocket error:', event);
});

MQTT over WebSocket Example (JavaScript)

// Using the MQTT.js library
const client = mqtt.connect('wss://mqtt.example.com:8884/mqtt', {
    clientId: 'browser_client_' + Math.random().toString(16).substr(2, 8),
    username: 'username',
    password: 'password'
});

// Handle connection
client.on('connect', function () {
    console.log('Connected to MQTT broker over WebSocket');
    
    // Subscribe to topics
    client.subscribe('sensors/temperature');
    
    // Publish a message
    client.publish('sensors/status', 'online from browser', {
        qos: 1,
        retain: true
    });
});

// Handle incoming messages
client.on('message', function (topic, message) {
    console.log(`Received message on ${topic}: ${message.toString()}`);
});

// Handle errors
client.on('error', function (error) {
    console.error('MQTT error:', error);
});

Real-World Applications

Conclusion

MQTT and WebSocket serve different purposes but can also work together:

• MQTT is an application layer protocol that provides a publish-subscribe messaging pattern with built-in features like QoS levels, retained messages, and last will and testament, making it ideal for IoT and machine-to-machine communications.
• WebSocket is a transport layer protocol that provides full-duplex communication channels, primarily designed for direct bidirectional communication between web browsers and servers.
• MQTT over WebSocket combines both worlds, allowing MQTT's rich messaging features to work in web browsers and other environments where traditional MQTT connections might be restricted.

When choosing between these technologies, consider your specific requirements for message routing, delivery guarantees, client platforms, and network constraints. In many cases, you may even use both protocols in different parts of your architecture.

With MQTT.pro's serverless MQTT broker service, you can leverage the power of MQTT with both traditional connections and WebSocket support, providing flexibility for various client types while maintaining the reliability and efficiency benefits of MQTT.