What is MQTT?

What is MQTT, and how does it work?

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol for efficient real-time communication between devices. It follows a publish-subscribe pattern, where one or more publishers send messages to a central broker, and subscribers receive those messages from the broker.

At its core, MQTT operates based on the concept of topics. Topics are channels or categories to which messages can be published or subscribed. When a message is published on a specific topic, the broker distributes it to all subscribers who have expressed interest in it.

The workflow of MQTT involves three key components: publishers, subscribers, and brokers. Publishers are responsible for creating and sending messages to the broker, specifying the desired topic. Subscribers, on the other hand, register their interest in specific topics with the broker. When a message is published on a topic, the broker forwards it to all relevant subscribers.

MQTT utilizes a lightweight protocol that requires minimal network bandwidth and computational resources to ensure efficient communication. It is designed to be reliable, even in scenarios with limited connectivity or low bandwidth. MQTT also supports various quality of service (QoS) levels, allowing publishers to specify the assurance required for message delivery.

MQTT can work over various network protocols, including TCP/IP, WebSocket, etc. It is highly scalable, enabling communication between many devices and brokers. The MQTT protocol is also extensible, allowing additional features and functionalities to be added as needed.

What features does MQTT offer?

MQTT offers a range of features that make it a popular choice for developers building realtime chat and messaging applications. Here are some of the key features:

  • Lightweight and efficient: MQTT is designed to be lightweight, making it suitable for use in constrained environments with limited bandwidth and processing power.

  • Publish/subscribe messaging model: MQTT uses a publish/subscribe messaging pattern, where a publisher sends messages to specific topics, and subscribers receive messages from those topics. This decoupled model allows for efficient and scalable communication between multiple clients. It also reduces network traffic and minimizes data overhead.

  • Quality of Service (QoS) levels: MQTT supports three levels of QoS, which define the message delivery guarantee.

    • QoS 0 provides at most once delivery

    • QoS 1 provides at least once delivery

    • QoS 2 provides exactly once delivery

This flexibility allows developers to choose the appropriate level of reliability for their application.

  • Retained messages: MQTT allows for the retention of the last message published on a topic. This means that a new subscriber can receive the last known state of a topic immediately upon connection, ensuring that no important data is missed.

  • Persistent sessions: MQTT supports persistent sessions, which enable clients to maintain their subscriptions and queued messages even when disconnected. This feature ensures that clients can resume communication seamlessly upon reconnection.

  • Lightweight footprint: MQTT has a small code footprint, making it efficient in memory and processing power usage. This is especially important for devices with limited resources, as it allows them to efficiently implement MQTT communication without sacrificing performance.

  • Security: MQTT supports TLS/SSL encryption, ensuring data is securely transmitted over the network. It also provides authentication mechanisms, such as username/password or client certificates, to verify the identity of clients and ensure that only authorized clients can access the MQTT broker.

  • Scalability: MQTT is designed to be highly scalable, allowing for seamless communication between thousands or even millions of devices. It uses a lightweight protocol and efficient publish/subscribe model, reducing network traffic and enabling efficient message distribution across many clients.

  • Wide support: MQTT is widely supported by various programming languages and platforms, making it easy for developers to integrate it into their applications. Numerous MQTT client libraries and tutorials are also available, providing developers with various options for implementing MQTT communication.

What are the disadvantages of using MQTT?

Limited message size: MQTT has a limitation on the size of messages it can handle, typically ranging from 256KB to 256MB, depending on the implementation. This can be a drawback for applications that require transmitting large data payloads.

Lack of built-in security: While MQTT itself doesn’t provide built-in security mechanisms, it can be used securely over a TLS/SSL connection. However, implementing security features such as authentication and encryption requires additional configuration and setup.

Complexity: MQTT can be complex to set up and configure, especially for developers new to the protocol. It requires understanding topics, message queues, and subscribing and publishing to topics. This learning curve may add complexity to the development process.

Lack of built-in persistence: MQTT does not provide built-in persistence, meaning messages are not stored in the broker if a client is offline. This can be a limitation for applications that require message persistence or delivery to offline clients.

Limited support for complex scenarios: MQTT is primarily designed for lightweight and simple messaging scenarios. It may not be the best choice for complex scenarios that require advanced features such as request/response communication or complex message routing.

MQTT vs. Web Sockets

MQTT and Web Sockets are widely used communication protocols for building real-time chat and messaging applications. However, there are several key differences between the two:

  1. Protocol: MQTT is a publish/subscribe messaging protocol, whereas Web Sockets is a bidirectional communication protocol. MQTT is primarily designed to efficiently distribute messages to multiple recipients, while Web Sockets allow for full-duplex communication between a client and a server.

  2. Messaging Patterns: MQTT follows a publish/subscribe model, where clients can subscribe to specific topics and receive messages published to those topics. On the other hand, Web Sockets enable real-time, full-duplex communication by establishing a persistent connection between the client and the server.

  3. Overhead: MQTT is a lightweight protocol that uses a binary format for message transmission, resulting in lower network overhead than WebSockets, which uses a text-based protocol (HTTP) for communication. This makes MQTT more efficient in terms of bandwidth and processing power usage.

  4. Scalability: MQTT is designed to be highly scalable, allowing for low-latency communication between millions of devices. It uses a lightweight protocol and efficient publish/subscribe model, reducing network traffic and enabling efficient message distribution across many clients. Web Sockets, although capable of handling many connections, may require more server resources to maintain the bidirectional communication.

  5. Compatibility: MQTT is widely supported by various programming languages and platforms, making it easy for developers to integrate it into their applications. Numerous MQTT client libraries are also available, providing developers with several options for implementing MQTT communication. Web Sockets has limited support in some programming languages and platforms, making it more challenging for developers to integrate into their applications.

  6. Security: MQTT and Web Sockets support secure communication by allowing encryption protocols such as SSL/TLS. However, MQTT also provides built-in authentication and access control support, allowing developers to implement secure messaging applications easily. Web Sockets may require additional implementation of security measures.

  7. Reliability: MQTT supports QoS levels, ensuring reliable message delivery even in unreliable network conditions. Web Sockets don’t have built-in support for QoS and rely on the underlying transport layer (usually TCP) for reliable message delivery.

  8. Use cases: MQTT is often used in applications where low latency and efficient distribution of messages to multiple recipients are critical, such as IoT (Internet of Things) applications, real-time monitoring systems, and chat applications with many connected clients. Web Sockets are commonly used in applications requiring realtime, bidirectional communication between a client and a server, such as collaboration tools, stock trading platforms, and multiplayer online games.


MQTT and HTTP are different protocols used to communicate between devices and servers. Here are the key differences between the two:

Messaging Pattern

  • MQTT (Message Queuing Telemetry Transport) is a lightweight publish-subscribe messaging protocol. It follows a publish-subscribe pattern, where clients can publish messages to a topic, and others can subscribe to it to receive those messages.

  • HTTP (Hypertext Transfer Protocol) is a request-response protocol. Clients send HTTP requests to a server, and the server responds with the requested data.

Overhead and Efficiency

  • MQTT is designed to be lightweight and efficient, making it ideal for resource-constrained devices and networks with low bandwidth or high latency. It uses a binary format with a small header size, reducing the network overhead.

  • HTTP has a larger overhead due to its textual, human-readable format. It includes additional metadata and headers, making it less efficient for constrained environments.

Realtime Communication

  • MQTT is optimized for real-time communication and enables instantaneous message delivery to multiple recipients. It is commonly used in applications that require low latency and efficient distribution of messages, such as IoT applications and chat applications.

  • HTTP, while it can support real-time communication through techniques such as long polling or server-sent events, is not inherently designed for real-time communication. It is better suited for request-response interactions, such as retrieving web pages or sending form data.


  • MQTT supports message encryption and authentication through Transport Layer Security (TLS) or Secure Sockets Layer (SSL). It also provides features like access control lists and fine-grained security policies, allowing for secure and controlled communication.

  • HTTP also supports encryption and authentication through protocols like HTTPS (HTTP Secure), which may require additional configuration and setup. It offers features like HTTP headers and cookies for authentication and authorization, but it may not provide the same level of flexibility and control as MQTT regarding security.


  • MQTT is designed to be highly scalable, efficiently distributing messages to many connected clients. It uses a lightweight protocol and a publish-subscribe model, which reduces the server's load and enables horizontal scaling.

  • HTTP can also be scalable but may require additional infrastructure and techniques like load balancing or caching to handle many concurrent requests. It is primarily designed for request-response interactions, which may not be as efficient for scenarios with a high number of connected clients.

How is MQTT used to communicate between different devices?

To understand how MQTT is used to communicate between different devices, let's delve into its key components and workflow:

MQTT Broker: At the core of MQTT communication is the MQTT broker. It serves as a central hub that receives and distributes messages between devices. The broker connects with MQTT clients (devices) and delivers messages to the intended recipients.

MQTT Clients: Devices that utilize MQTT and connect to the broker are called MQTT clients. These clients can be anything from sensors, smartphones, and IoT devices to server applications. MQTT clients can publish (send) and subscribe (receive) to various topics.

Topics: MQTT communication revolves around topics. Topics act as channels or subjects to which clients publish messages or subscribe to receive messages. A topic represents a specific data category or subject of interest. For example, in a realtime chat application, topics could be "chat/room1" or "chat/user1" representing different chat rooms or individual users.

Publish-Subscribe Model: MQTT uses a publish-subscribe messaging pattern. When an MQTT client wishes to send a message, it publishes it to a specific topic. The broker then distributes the message to all subscribed clients interested in that topic. This model allows for efficient one-to-many communication, where a single message can be delivered to multiple recipients without needing individual point-to-point connections.

Quality of Service (QoS): MQTT provides different levels of Quality of Service to ensure reliable message delivery. There are three levels: QoS 0 (At most once), QoS 1 (At least once), and QoS 2 (Exactly once). The choice of QoS level depends on the specific application requirements and the importance of message delivery.

Retained Messages: MQTT supports retained messages, which are stored by the broker and made available to clients who subscribe to a topic, even if they were not connected at the time of message publication. This feature is useful for providing clients with the latest state or data upon connection.

MQTT utilizes these components and features to enable efficient and scalable communication between different devices. It minimizes network overhead, allows for real-time updates, and provides reliability in message delivery. MQTT's lightweight design also makes it suitable for resource-constrained devices and networks.

MQTT, scalability, and secure communication

MQTT provides several features that support scalability and secure communication in real-time chat and messaging applications:

Lightweight Protocol

MQTT is designed to be lightweight, minimizing network overhead and resource usage. This makes it suitable for scaling to many connected devices, including resource-constrained devices such as IoT or mobile devices.

Asynchronous Communication

MQTT supports asynchronous communication, allowing real-time updates without blocking or waiting for responses. This enables efficient and scalable communication in real-time chat and messaging applications, where multiple clients must receive updates simultaneously.

Scalable Architecture

MQTT follows a client-server architecture, where multiple clients connect to a central broker. This architecture allows for horizontal scalability, as additional brokers can be added to handle increased traffic and load. It also supports distributed deployments, where brokers can be deployed across different regions or data centers for improved performance and fault tolerance.

Security Features

MQTT provides security features to ensure secure communication in real-time chat and messaging applications. It supports Transport Layer Security (TLS) encryption for data transmission, ensuring confidentiality and integrity. It also supports authentication mechanisms, such as username/password or client certificates, to verify the identity of clients and prevent unauthorized access.

Access Control

MQTT brokers often support access control mechanisms, allowing administrators to define and enforce fine-grained access policies. This ensures that only authorized clients can publish or subscribe to specific topics, protecting sensitive information and preventing unauthorized access to the messaging system.

Message Filtering

MQTT supports flexible message filtering through topics. Clients can subscribe to specific topics of interest, allowing them to receive relevant messages while filtering out irrelevant ones. This reduces network congestion and improves scalability by minimizing the amount of data that needs to be transmitted and processed.

Setting up an MQTT infrastructure

There are several tools available to help with setting up an MQTT infrastructure. Here are a few popular options:

MQTT Broker: The core component of an MQTT infrastructure is the MQTT broker. Several open-source brokers are available, such as Mosquitto, HiveMQ, and EMQ X. These brokers provide the necessary functionality to manage MQTT connections, handle message routing, and ensure reliable delivery.

MQTT Client Libraries: MQTT client libraries are essential for developers to connect their applications to an MQTT broker. These libraries provide the necessary API to send and receive MQTT messages. Most programming languages have MQTT client libraries, including popular ones like Paho MQTT for Java, MQTT.js for JavaScript, and Eclipse Mosquitto for C/C++.

MQTT Testing Tools: To ensure the reliability and scalability of your MQTT infrastructure, it's important to conduct thorough testing. MQTT testing tools like MQTT.fx, MQTTBox, and HiveMQ's MQTT CLI can help you simulate different scenarios, test message handling, and monitor MQTT traffic.

MQTT Dashboard: A dashboard can provide real-time monitoring and visualization of your MQTT infrastructure. Tools like Grafana, InfluxDB, and Node-RED can help you build interactive dashboards to monitor MQTT topics, track message rates, and analyze performance metrics.

MQTT Cloud Services: If you prefer a managed solution, several cloud providers offer MQTT as a service. These services handle the infrastructure setup, scaling, and management for you. Examples include Amazon IoT Core, Google Cloud IoT Core, and Microsoft Azure IoT Hub.

[Read more on: MQTT in IOT]

What challenges should be considered when deploying an MQTT system?

When deploying an MQTT system, there are several challenges that developers should consider. These challenges can impact the messaging application's scalability, security, and overall performance. Here are some key challenges to keep in mind:

  1. Scalability: One of the main challenges when deploying an MQTT system is ensuring scalability. As the number of connected clients and message traffic increases, the system should be able to handle the increased load without compromising performance. This requires carefully planning and implementing a scalable architecture that can handle many concurrent connections and messages.

  2. Network Connectivity: MQTT relies on a network connection between clients and the broker for communication. However, network connectivity can be unreliable and intermittent, especially in mobile or remote environments. Developers should consider implementing strategies to handle network disruptions and ensure the system can recover gracefully when connectivity is restored.

  3. Security: MQTT communication involves sensitive data, and ensuring its security is crucial. Challenges related to security include authenticating clients, encrypting data transmission, and preventing unauthorized access. Developers should implement secure authentication mechanisms, such as username/password or certificates, and enable encryption using protocols like SSL/TLS to protect the data during transmission.

  4. Quality of Service (QoS): MQTT supports different levels of Quality of Service (QoS) to ensure message delivery reliability. However, choosing the appropriate QoS level can be challenging. Higher QoS levels (e.g., QoS 2) provide stronger message delivery guarantees but come with increased overhead and potential for performance impact. Developers should carefully consider the trade-offs between QoS levels and choose the level that best suits their application's requirements.

  5. Message Persistence: MQTT messages are typically delivered in a "fire and forget" manner, meaning that once a message is published, it is not stored or persisted by the broker. This can be a challenge if message persistence is required, for example, in cases where the message needs to be stored and retrieved later. Developers should consider implementing mechanisms to persist messages, such as storing them in a database or using MQTT brokers that support message persistence.

  6. Error Handling and Monitoring: When deploying an MQTT system, it is important to have robust error handling and monitoring mechanisms in place. This includes handling connection errors and message delivery failures and monitoring the system for performance bottlenecks or security breaches. Developers should implement logging and monitoring tools to track and diagnose issues and define appropriate error-handling strategies to ensure the system remains reliable and performant.

What types of applications can benefit from using MQTT?

MQTT’s simplicity, efficiency, and support for low-power, low-bandwidth networks make it suitable for various applications. Here are some types of MQQT use cases:

  • IoT Applications: MQTT is commonly used in IoT applications to enable communication between devices, sensors, and cloud platforms. It allows for efficient and reliable data exchange in resource-constrained environments where devices may have limited processing power or network bandwidth.

  • Real-time Monitoring and Control Systems: MQTT's publish-subscribe model makes it an ideal choice for real-time monitoring and control systems. It enables devices or sensors to publish data to a central broker, which can then be subscribed to by interested parties to receive real-time updates. This is particularly useful in scenarios like home automation, industrial automation, or remote infrastructure monitoring.

  • Instant Messaging and Chat Applications: MQTT's lightweight nature and support for efficient message delivery make it suitable for real-time chat and messaging applications. It allows for quick and reliable message exchange between clients, providing a seamless user experience.

  • Telemetry and Remote Sensing: MQTT's efficient message transmission and low overhead make it well-suited for telemetry applications. It enables remote sensing and monitoring of various parameters like temperature, pressure, humidity, etc., and facilitates the transmission of this data to a central system for analysis and decision-making.

  • Machine-to-Machine Communication: MQTT's publish-subscribe model enables efficient and scalable machine-to-machine communication. It allows different devices or systems to exchange data and control signals in a decentralized and asynchronous manner, facilitating interoperability and integration between disparate systems.

  • Distributed Systems and Event-Driven Architectures: MQTT's lightweight and event-driven nature makes it suitable for building distributed and event-driven architectures. It enables different components or services to communicate and react to events in a loosely coupled manner, promoting scalability and flexibility.

  • Mobile Apps: Due to its low power consumption, efficient message delivery, and support for intermittent connectivity, MQTT is ideal for mobile applications. It allows mobile devices to exchange data with backend servers or other devices resource-efficiently, minimizing battery usage and network overhead.

  • Gaming and Real-Time Multiplayer Apps: Thanks to its real-time capabilities and support for publish-subscribe messaging, MQTT is a great fit for gaming and real-time multiplayer applications. It enables seamless communication and synchronization between players, facilitating real-time gameplay and interaction.

The Evolution of MQTT

MQTT has several versions developed to enhance its functionality and address various requirements. The different versions of MQTT are as follows:

  • MQTT v3.1: This is the most widely used version of MQTT. It is a lightweight, publish-subscribe-based messaging protocol for resource-constrained devices and unreliable networks. MQTT v3.1 provides Quality of Service (QoS) levels, retained messages, and session management.

  • MQTT v3.1.1: This version is an updated version of MQTT v3.1 and includes some improvements and bug fixes. It clarifies certain protocol aspects and adds enhanced authentication and authorization mechanisms.

  • MQTT-SN (MQTT for Sensor Networks): MQTT-SN is a variation of MQTT designed for sensor networks, where devices may have limited processing power and memory. It provides a lightweight protocol for efficient communication between sensors and gateways.

  • MQTT v5.0: MQTT v5.0 is the latest version of MQTT, released in 2019. It introduces several new features and enhancements to the protocol, including extended authentication mechanisms, support for shared subscriptions, message properties, and improved error handling. MQTT v5.0 offers more flexibility and functionality compared to previous versions.

Developers should consider their applications' specific requirements and capabilities when choosing the MQTT version. MQTT v3.1 and v3.1.1 are widely supported and used, making them a good choice for most applications. However, MQTT-SN may be better if working with resource-constrained devices or sensor networks. For developers who want to take advantage of the latest features and enhancements, MQTT v5.0 is the recommended choice.

PubNub & MQTT

PubNub and MQTT can work together to create a powerful and scalable real-time messaging system. Here's how they can be integrated:

  1. PubNub's Real-Time Network: PubNub provides a global real-time network as a message broker, facilitating client data exchange. It offers features like presence detection, message history, and access control, making it the gold standard platform for real-time communication.

  2. MQTT as a Protocol: MQTT is a lightweight publish-subscribe messaging protocol that allows devices and systems to communicate in a scalable and efficient manner. It uses a broker-based architecture, where clients publish messages to topics, and other clients subscribe to those topics to receive the messages.

  3. PubNub's MQTT Bridge: PubNub provides an MQTT bridge that allows MQTT clients to connect to PubNub's real-time network. This bridge is an intermediary between MQTT clients and the PubNub network, enabling seamless integration between the two technologies.

  4. Data Flow: When an MQTT client publishes a message to a topic, the MQTT bridge receives it and forwards it to the PubNub network. The message is then transmitted to all subscribers who have subscribed to that topic, ensuring real-time delivery. Similarly, messages received from PubNub can be forwarded to MQTT clients through the bridge.

  5. Scalability and Reliability: By combining PubNub's global network infrastructure with MQTT's lightweight and efficient messaging protocol, developers can build highly scalable and reliable realtime messaging systems. PubNub's network spans multiple data centers and provides automatic failover, ensuring high availability and reliability. MQTT's lightweight design minimizes network overhead and allows efficient communication even in resource-constrained environments.

  6. Security: PubNub offers several security features to protect data transmitted over its network, including end-to-end encryption, access control, and authentication mechanisms. MQTT also supports secure communication through Transport Layer Security (TLS) encryption. By leveraging these security features, developers can build secure real-time messaging applications.

  7. Integration with Other Services: PubNub's platform integrates with various other services, such as cloud storage providers, analytics platforms, and third-party APIs, allowing developers to augment their real-time messaging applications with additional functionality. MQTT's flexibility and compatibility make integrating with other systems and services easy.

Integrating PubNub and MQTT gives developers a powerful and scalable solution for building real-time chat and messaging applications. By leveraging PubNub's real-time network and MQTT's efficient messaging protocol, developers can create highly reliable, secure, and efficient applications that facilitate seamless user communication and interaction.

With over 15 points of presence worldwide supporting 800 million monthly active users and 99.999% reliability, you’ll never have to worry about outages, concurrency limits, or any latency issues caused by traffic spikes. PubNub is perfect for any application that requires real-time data.

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