MQTT vs. HTTP: When to Use Which Protocol?

In the world of data communication, there are many protocols, but two of the most well-known are MQTT and HTTP . Both have their strengths and weaknesses, and choosing the right protocol depends heavily on the requirements of your application. This article compares MQTT and HTTP and shows when to use each protocol.

Fundamental Differences

HTTP: Request-Response Model

HTTP (Hypertext Transfer Protocol) is the standard protocol for communication on the World Wide Web. It operates on the request-response principle:

• A client (e.g., a browser or app) sends a request to a server.
• The server processes the request and sends a response back.
• The connection is usually closed after the response.

HTTP is stateless, meaning each request is treated independently of previous requests. For websites and REST APIs, HTTP is ideal because it is simple to implement and widely used.

MQTT: Publish-Subscribe Model

MQTT (Message Queuing Telemetry Transport), on the other hand, is based on the publish-subscribe model:

• Publishers send messages to a topic via a central broker.
• Subscribers subscribe to these topics and receive all messages published to them.
• The broker manages the topics and forwards the messages to the appropriate subscribers.

MQTT is event-driven and particularly efficient for real-time communication, as messages are transmitted immediately as soon as they are available.

When to Use HTTP?

HTTP is particularly suitable for applications where:

• Data is retrieved on demand, such as loading a webpage or querying an API.
• Real-time communication is not required.
• Simple implementation and compatibility with existing web technologies are important.
• Large amounts of data are transferred, such as file downloads or streaming.

Examples:

• Websites and web apps
• REST APIs for data queries
• File uploads and downloads

When to Use MQTT?

MQTT is the better choice when:

• Real-time data transmission is crucial, such as for sensor values or control commands.
• Devices with limited resources (e.g., microcontrollers, sensors) need to communicate.
• Low bandwidth is available, as MQTT handles data very efficiently.
• Scalability is important, such as in IoT networks with thousands of devices.

Examples:

• Smart Home: Controlling lights, thermostats, or security cameras.
• Industrial IoT: Monitoring machines and production processes.
• Environmental Monitoring: Real-time data from sensors measuring air quality or temperature.

Protocol Comparison

Criteria	MQTT	HTTP
Communication Model	Publish-Subscribe	Request-Response
Real-Time Capability	Yes, event-driven	No, only on request
Resource Consumption	Very low	Higher (overhead due to headers)
Stateful	Optional (depends on QoS)	No (stateless)
Scalability	Very good (ideal for IoT)	Good, but less efficient
Typical Application	IoT, real-time data, M2M	Websites, APIs, file transfer

Combined Use of MQTT and HTTP

In many modern applications, MQTT and HTTP are combined to leverage the advantages of both protocols:

• HTTP for configuration and retrieving data on demand.
• MQTT for real-time communication and data streaming.

Example: A smart home app could use HTTP to load the user interface and configure devices. At the same time, MQTT could be used for real-time control of devices and receiving sensor values.

Conclusion

The choice between MQTT and HTTP depends on the requirements of your application:

• HTTP is ideal for classic web applications where data is retrieved on demand.
• MQTT is the better choice for IoT applications where real-time data transmission, resource efficiency, and scalability are paramount.

If you are planning an IoT project or need to control devices in real time, you should consider MQTT. For web applications or retrieving data, HTTP remains the first choice. In many cases, a combination of both protocols can be the optimal solution.

Official Resources and Further Reading

If you want to dive deeper into the technical details of MQTT and HTTP, here are the official specifications and useful resources:

• MQTT 5.0 Specification (OASIS): The complete documentation of the MQTT 5.0 protocol, including all features such as Shared Subscriptions and QoS levels.
• MQTT 3.1.1 Specification (OASIS): The official documentation of the previous version for comparison.
• HTTP/1.1 Specification (RFC 7230): The technical foundation of the HTTP protocol, defined by the IETF.
• HTTP/2 Specification (RFC 7540): Information on the modern HTTP/2 protocol with improved performance characteristics.
• MQTT.org: The official website with additional resources, implementations, and community links.
• IETF HTTP Working Group: Current developments and standards related to HTTP.

These resources will help you better understand the technical differences between MQTT and HTTP and make the right decision for your project.