MQTT vs HTTP for IoT: Detailed Protocol Comparison

As the IoT explodes with connected devices, selecting the right communication protocol is all-important to building efficient and scalable IoT solutions. MQTT vs. HTTP are frequently discussed protocols in this regard. Both have their own advantages and ideal applications.

Consider a manufacturing plant that uses a real-time asset monitoring solution based on MQTT. On the other hand, a smart home setup might use HTTP for periodic data uploads from smart devices. However, HTTP is not limited to periodic data transfers, nor is MQTT reserved only for real-time asset tracking.

Let's review each protocol’s features and how it works in different IoT settings to determine the best uses for each protocol. This article compares MQTT vs. HTTP for IoT applications based on benchmarks. Here, we'll explore the pros and cons of each protocol and discuss their ideal applications.

What is MQTT?

MQTT is an application-level communication protocol widely adopted in IoT environments. Although it originally stood for MQ Telemetry Transport, it has been a standalone term since 2013.

Other popular IoT networking protocols at the application level include HTTP, CoAP, and AMQP. MQTT stands out due to its design for constrained environments with low bandwidth, high latency, and unreliable connections.

MQTT operates on a publish-subscribe (pub-sub) messaging model, which is particularly suitable for minimizing resource consumption. In the pub-sub model, clients publish messages on specific topics. Subscribers to these topics receive the messages, which makes for a flexible, many-to-many communication pattern. Separating publishers and subscribers makes IoT systems more scalable and adaptable.

History of MQTT

In 1999, Arlen Nipper of Eurotech and Andy Stanford-Clark of IBM developed MQTT. The goal was to create a protocol that minimizes battery and bandwidth usage when connecting oil pipelines via satellite.

The protocol was designed with several key requirements, which you can see below:

• Simple implementation
  
• Reliable data delivery
  
• Efficient data transmission
  
• Minimal bandwidth usage
  
• Ability to handle various data types
  
• Persistent connection

While initially intended for proprietary embedded systems, MQTT has become a cornerstone of open IoT communication.

Main Uses of MQTT

MQTT is widely used in various industries to enable seamless communication between devices. Its lightweight nature and efficient data transmission make it particularly suitable for IoT applications where HTTP might be too resource-intensive.

MQTT’s ability to facilitate seamless device communication has led to widespread adoption across various industries. Let’s go through some key use cases for MQTT in IoT.

Industrial automation: MQTT can link machines and sensors in factories to allow real-time monitoring, process control, and improved efficiency.

Transportation: Connected car systems and other transportation networks utilize MQTT for real-time tracking and monitoring of vehicles, improving safety and traffic flow.

Agriculture: Farmers use MQTT to monitor soil moisture, weather conditions, and crop growth, optimizing irrigation and management practices.

Healthcare: Medical devices like glucose meters and heart rate monitors connect via MQTT to enable remote patient monitoring.

Smart homes and buildings: MQTT connects thermostats, light bulbs, and other supported appliances. Thus, it enables real-time remote control and management for connected IoT devices.

Main Components of MQTT

MQTT broker: This server is a central message hub that receives messages from publishers and forwards them to subscribed clients.

MQTT client: Any device or application interacting with the broker can be a client. Clients can publish (send) or subscribe (receive) messages.

MQTT topic: The topic is a hierarchical string the broker uses to filter messages for each client. Publishers send messages to specific topics, and subscribers receive messages only from topics they are subscribed to. Also, MQTT clients can subscribe to any subject that matches a specified pattern using wildcards.

MQTT message: The message is actual data transmitted over the network. These messages are typically small and use a binary format.

MQTT session: The session is a persistent connection between a client and a broker. Sessions enable message buffering and automatic reconnection, thus ensuring reliable communication even with temporary disconnections.

The pub-sub architecture allows MQTT to function efficiently in resource-constrained environments, supporting reliable and scalable communication across diverse IoT applications.

What is HTTP?

HTTP, or Hypertext Transfer Protocol, is a fundamental application layer protocol that underpins the World Wide Web. It supports the transfer of information between networked devices, mostly using a client-server model. In a typical HTTP interaction, a client device sends a request to a server, which then responds with the requested information.

History of HTTP

HTTP's development began in 1989 with Tim Berners-Lee at CERN, who outlined its first version, HTTP/0.9. It was further developed and officially documented as HTTP/1.0 in 1996. The evolution continued with HTTP/1.1 in 1997. Over 85% of websites now use HTTPS, the secure variant of HTTP.

In 2015, HTTP/2 was introduced to enhance the efficiency of HTTP communications, reduce latency, and improve resource utilization. As of January 2024, nearly all web browsers support HTTP/2, and 36% of websites use it.

HTTP/3, published in 2022, further optimized the protocol using QUIC instead of TCP for transport. This version is designed to reduce latency and improve performance, especially in environments with high packet loss. As of February 2024, most web browsers support HTTP/3, and 29% of websites use it.

Main Use of HTTP in IoT

The HTTP protocol is effective but has limitations in IoT, such as slower data transmission, resource-intensive usage, and complicated message formats. Despite not being the most efficient protocol for IoT due to its high overhead, HTTP finds its applications in scenarios where occasional data retrieval and standard web communication patterns are adequate.

IoT devices that support the HTTP protocol typically fall into the following categories:

Consumer electronics: Smart home devices like smart TVs, thermostats, smart speakers, and home security systems often use HTTP for communication.

Industrial IoT: Devices used in manufacturing and automation, such as sensors and actuators in industrial environments, sometimes use HTTP for data exchange and control.

Healthcare: Medical monitoring devices, such as glucose and heart rate monitors, often use HTTP to transmit data to healthcare providers.

Automotive IoT: Connected car systems, including infotainment and telematics units, often use HTTP for updates and data transmission.

These categories leverage HTTP due to its widespread adoption, ease of use, and compatibility with existing web infrastructure. However, it’s worth noting that for certain IoT applications protocols optimized for low power consumption and low latency, such as MQTT and CoAP, are also commonly used.

Fundamentals of HTTP

HTTP communication is based on several key concepts. Let’s discuss them below.

Methods: HTTP defines several methods (GET, POST, PUT, DELETE, etc.) that specify the desired action to be performed on the identified resource.

Requests: Clients send requests to servers, including a method, URL, headers, and sometimes a body containing data.

Responses: Servers reply with responses containing a status code, headers, and often a body with the requested content.

Stateless protocol: Each HTTP request is independent, requiring any necessary state information to be included in each request.

Headers: Both requests and responses include headers that provide additional information about the message or the requested resource.

These fundamentals make HTTP a versatile protocol, but its request-response model and stateless nature can pose challenges in IoT applications requiring real-time or continuous data flow.

HTTP's versatility and widespread adoption make it suitable for many IoT applications, particularly those that benefit from its established infrastructure and ease of integration with web technologies. However, its higher overhead and stateless design can have limitations in more resource-constrained and continuous data flow environments.

MQTT vs HTTP for IoT: Protocols Comparison

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Performance

When it comes to bandwidth efficiency, MQTT has a clear advantage due to its lower protocol overhead. When a connection is established, an MQTT packet contains a minimum of two bytes, whereas an HTTP packet typically contains more than eight bytes. This difference becomes particularly significant when many small data packets are transferred.

According to the 2016 study, the overhead in HTTP leads to performance degradation, especially with a high volume of small data blocks. However, if the number of devices is 10, the payload size is zero, and if the length of topics is more than 680 bytes, HTTP’s overhead is smaller than that of MQTT.

Google’s study on MQTT vs. HTTP comparison points out that the initial connection setup for MQTT sends approximately 6300 bytes per message, which is more than the 5600 bytes sent by HTTP. However, when reusing the same MQTT connection for multiple messages, the data amount per message reduces to around 400 bytes, showcasing MQTT's efficiency in sustained communication.

Latency is another critical performance metric. The initial connection setup time in MQTT can increase response times to match those of HTTP for single message transmissions, approximately 120 ms per message. However, the MQTT protocol shines when the same connection is reused for multiple messages, reducing the average response time to around 40 ms per message. HTTP does not offer similar reductions in latency with the increasing number of messages shared.

The HTTP protocol benefits from using the existing Internet infrastructure, but this comes with a cost. The protocol requires computing power and is not efficient for most IoT devices.

MQTT is more efficient at power consumption, particularly when maintaining a persistent connection. The overhead in setting up and tearing down connections frequently makes MQTT less efficient if not managed properly. Reusing the same MQTT connection for multiple messages optimizes power usage, making it more suitable for IoT devices vs. HTTP.

Reliability

The protocol offers different levels of Quality of Service (MQTT QoS) for message delivery: at most once (QoS 0), at least once (QoS 1), and exactly once (QoS 2). These options provide flexibility and reliability, depending on the application's requirements. While reliable for web communication, HTTP does not offer these granular delivery guarantees.

MQTT supports persistent connections, allowing for continuous communication without frequently re-establishing connections. This persistence is beneficial for applications requiring consistent and ongoing data exchange. HTTP treats each request independently, which can be inefficient for continuous data flow scenarios.

Scalability

MQTT is designed to handle many concurrent connections with a smaller RAM footprint, making it suitable for large-scale IoT deployments. HTTP can also manage many connections but may require more resources, impacting scalability.

MQTT's lower overhead and persistent connection model enable higher message throughput than HTTP. This makes MQTT more efficient when frequent and rapid message exchanges are necessary.

Security

Both protocols support various authentication mechanisms. MQTT typically uses username and password authentication and can also integrate with more advanced methods such as OAuth. HTTP supports similar mechanisms, including OAuth, API keys, and others, offering robust authentication options.

Encryption is crucial for securing IoT communications. MQTT often employs TLS to encrypt messages and ensure data integrity and confidentiality. Similarly, HTTP can use HTTPS to provide a secure communication channel.

Use Cases

MQTT excels in machine-to-machine (M2M) communication, event-driven sensor/actuator applications, and scenarios with constrained resources. It is particularly well-suited for applications where bandwidth and power are limited, such as remote monitoring, telemetry, and smart agriculture.

HTTP is preferred for web-driven applications, periodic data retrieval, and integration with existing web infrastructure. It works well for RESTful APIs, data reporting, cloud integration, and web interfaces. HTTP is also a practical choice for connecting existing HTTP-enabled devices to an IoT platform without adding a new protocol stack.

Summary

When choosing between MQTT vs. HTTP for IoT, pay the most attention to your application's specific needs. MQTT is tailored for reliable low-latency communication in resource-constrained IoT environments. In contrast, HTTP offers broader compatibility and ease of integration with existing web technologies, making it suitable for web-based applications and APIs.

Understanding each protocol’s strengths and limitations helps make an informed decision for optimal performance and scalability in IoT deployments. And, of course, stay up to date with the latest developments in IoT messaging protocols and IoT technology overall.