Advantages of MQTT Over HTTP

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Source | Embedded Miscellaneous

In the past decade, the Internet of Things (IoT) has been developing rapidly, and in many scenarios, networking is essential. Both MQTT and HTTP are used in IoT applications, but their application scenarios differ.

In IoT applications, MQTT (Message Queuing Telemetry Transport) is often preferred over HTTP (Hypertext Transfer Protocol) due to the following advantages:

Advantages of MQTT

1. Saves Network Bandwidth

Packet Size: MQTT uses a lightweight protocol, resulting in smaller packet sizes compared to HTTP. The message header of MQTT requires only 2 bytes, while the HTTP protocol’s header is much more complex, with even the simplest HTTP request having a header of at least several hundred bytes.
Transmission Efficiency: The publish-subscribe mechanism of MQTT means that data is sent only once per cycle, whereas HTTP sends header information with every request, making MQTT more bandwidth-efficient when transmitting large amounts of data.

2. Better Latency

Connection Mechanism: The client-server model of HTTP requires establishing a connection for each request, leading to higher latency. In contrast, MQTT allows the client to establish a connection with the server only once, and subsequent requests only need to send a small data packet to update the status, enabling faster device status updates.

3. Higher Reliability

Publish-Subscribe Model: MQTT employs a publish-subscribe model that ensures reliable data transmission even in unstable network conditions. When a device goes offline, MQTT stores the data in a queue until the device comes back online to send it.
Automatic Reconnection Mechanism: MQTT features an automatic reconnection mechanism that can restore the connection even if the network is disconnected, ensuring reliable message transmission.

4. Better Security

Encryption Protocol: MQTT supports TLS/SSL encryption protocols, ensuring data security during transmission. In contrast, HTTP requires more complex security measures, such as HTTPS.

5. Better Scalability

Many-to-Many Communication: MQTT supports a many-to-many communication model, making it easy to scale to large systems.
Low-Cost Implementation: The lightweight nature of MQTT makes the cost of implementing MQTT libraries low and easy to port to different platforms.

6. Suitable for Resource-Constrained Devices

Low Power Consumption: The MQTT protocol can maintain long connections while keeping low power consumption during idle times, saving device energy.
Data Handling: MQTT is data-centric, transmitting data as byte arrays, making it very suitable for resource-constrained devices and helping to save battery life.

7. Efficient Message Distribution

Publish-Subscribe Model: The publish/subscribe model used by MQTT is very suitable for message distribution between devices in IoT applications. This model allows a single device to send messages to multiple subscribers simultaneously, making information transfer both efficient and flexible.

Application Code Comparison

MQTT Pseudocode Example

// MQTT client connects to the MQTT server
mqttClient.connect("mqtt://broker.example.com:1883", clientId)

// Subscribe to a specific topic
mqttClient.subscribe("sensor/data", qos=1)

// Publish a message to the topic
mqttClient.publish("sensor/data", "temperature=25.5C", qos=1)

// Receive and process messages
onMessageReceived(message) {
    if (message.topic == "sensor/data") {
        processSensorData(message.payload)
    }
}

HTTP Pseudocode Example

// HTTP client sends a GET request
response = httpClient.get("http://api.example.com/sensor/data")

// Process response data
if (response.statusCode == 200) {
    sensorData = parseSensorDataFromResponse(response.body)
    processSensorData(sensorData)
}

// Send a POST request to update sensor data (usually not used for real-time data transmission)
requestBody = "temperature=25.5C"
response = httpClient.post("http://api.example.com/update/sensor/data", requestBody)

Practical Example Comparison Analysis

Assuming there is a smart home system that includes multiple smart bulbs and temperature sensors.

Using MQTT: Each bulb and sensor connects to the MQTT server (broker) as an MQTT client. The temperature sensor periodically publishes messages containing temperature data to the “sensor/temperature” topic. The bulbs subscribe to this topic and automatically adjust brightness or color upon receiving new temperature data. This method allows real-time communication between bulbs and sensors, maintaining high reliability even in unstable network conditions.
Using HTTP: Each bulb and sensor needs to periodically send HTTP requests to a central server to retrieve or update data. For example, the temperature sensor needs to send an HTTP POST request to upload temperature data, while the bulbs need to send HTTP GET requests to obtain the latest temperature data to adjust brightness. In this method, each request must wait for the server’s response, which can lead to issues in unstable or high-latency networks. Additionally, since HTTP is stateless, bulbs may need to retrieve temperature data each time they need to adjust brightness.

MQTT is more suitable than HTTP for IoT applications because it offers better bandwidth utilization, lower latency, higher reliability, better security, better scalability, and is more suitable for resource-constrained devices. These advantages make MQTT the preferred protocol for IoT applications.

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Advantages of MQTT Over HTTP

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