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Introduction to MQTT 5 Protocol - MQTT 5 Essentials Part 1

by Mary Brickenstein-Hofschen
13 min read

MQTT has solidified its footprint by connecting numerous constrained devices across multiple deployments, establishing a vast network of connected systems and standalone devices. From connected cars and manufacturing systems, logistics to enterprise chat applications, and mobile apps, MQTT’s widespread use has spurred demands for its evolution. MQTT 5 answers this call, promising an extensive array of exciting new features and improvements.

IOT Protocols Trend

In this comprehensive 12-part MQTT 5 Essentials series, we provide an in-depth exploration of MQTT 5. The series demystifies topics ranging from foundational changes in the protocol to user properties, shared subscriptions, payload format description, request-response pattern, topic alias, enhanced authentication, and flow control. By the end of this series, you will thoroughly understand MQTT 5’s practical implications for IoT and how it can empower optimized IoT solutions through its strengths. In this article (Part 1), we will provide a high-level overview of MQTT’s origins and subsequent evolution.

Before delving into MQTT 5, we recommend reviewing the MQTT Essentials series if you are new to MQTT or want a refresher. This foundational knowledge of the MQTT 3.1.1 protocol will enhance your comprehension of the improvements and fundamental changes introduced in MQTT 5.

Why Was MQTT Invented and How Has the Protocol Evolved?

The MQTT protocol was ingeniously crafted in the late 1990s by Andy Stanford-Clark from IBM and Arlen Nipper from Cirrus Link, to monitor oil and gas pipelines over satellite networks. They designed MQTT with openness, simplicity, and to easily implement. As a result, MQTT emerged as an ultra-lightweight protocol that saves network bandwidth and device resources, ensuring reliable delivery. Its design allowed thousands of devices to connect with a single MQTT server, making it the perfect fit for constrained environments and low-bandwidth, high-latency networks – precisely the conditions in IoT ecosystems.

MQTT 5 history

Design Goals of MQTT 5

The OASIS Technical Committee (TC), tasked with defining and standardizing MQTT, faced the complex challenge of adding long-desired features without increasing overhead or decreasing ease of use. They sought to improve performance and scalability without inducing unnecessary complexity. After much deliberation, the TC decided on a host of functional objectives for MQTT 5, aimed at enhancing scalability, formalizing common patterns such as capability discovery and request-response, and enabling extensibility mechanisms like user properties.

MQTT 5: Breathing Life into Large-Scale Systems

A key goal for MQTT 5 was to improve its ability to handle large-scale systems. The previous MQTT 3.1.1 showcased MQTT’s unique scalability and statefulness in IoT protocols, with HiveMQ’s enterprise MQTT platform marking a milestone by achieving 200 million concurrent connections. MQTT 5 builds on this legacy, simplifying the process for an MQTT server to scale to an incredible number of concurrently connected clients.

Unveiling the Mystery: Why MQTT 5, Not MQTT 3.1.2?

The move from the nomenclature MQTT 3.1.1 to MQTT 5 might seem strange, but there was a desire to synchronize the version numbering with the major updates in the protocol’s capabilities. Hence, the next significant release after MQTT 3.1.1 was MQTT 5.

Is there MQTT 4? If Not, Why?

You might be curious why the successor to MQTT 3.1.1 is MQTT 5.

The answer is surprisingly simple: The MQTT protocol defines a fixed header in the CONNECT packet. This header contains a single byte value for the protocol version.

If you inspect a few CONNECT packets on the wire, you’ll notice something interesting: MQTT 3.1 has the value "3" as protocol version and MQTT 3.1.1 has the value "4". To synchronize the protocol version value on the wire with the official protocol version name, the new MQTT version gets to use “5” for both the protocol name and value.

Unlocking the Power of IoT with MQTT 5: New Features and Improvements

MQTT 5 introduced enhancements to improve performance, increase reliability, and provide greater control over communication between clients and servers. Some of the key enhancements include better error reporting, enhanced scalability, and improved support for offline message queueing. These improvements ensure that MQTT can handle the ever-increasing demands of modern IoT environments, where the number of connected devices and the amount of data they generate are growing exponentially. One of the significant improvements in MQTT 5 is the introduction of enhanced authentication mechanisms. These provide a more robust security framework critical in today’s world, where the risk of cyber-attacks is always looming. With MQTT 5, users have more options for securing their devices and data, including using more sophisticated encryption algorithms and key management techniques.

In addition, MQTT 5 introduced Shared Subscriptions, a feature that allows load balancing of messages across multiple client instances. This ensures that people can manage many messages effectively without overloading individual clients. The shared subscriptions feature is practical in scenarios where many devices are transmitting data concurrently.

Further, MQTT 5 also introduces the concept of message properties, allowing additional metadata to be included with each message. This is useful for providing context about the transmitted data, such as timestamps, location information, or device status.

As described, the transition from MQTT 3.1.1 to MQTT 5 was not a simple version number update but rather a significant leap in the protocol’s capabilities, addressing several areas of improvement. The result is a more robust, reliable, and scalable protocol better suited to modern IoT applications’ needs.

It’s important to understand these changes and improvements when considering MQTT for IoT applications, as they can significantly affect the performance and reliability of your IoT system. So, whether you’re a developer, a systems integrator, or an end user, the step to MQTT 5 is a key advancement in evolving IoT communication protocols.

While MQTT 5 brings numerous benefits, it also demands careful implementation. Like any technology upgrade, it is critical to evaluate the implications on your specific use case and ensure the transition is controlled and managed. Understanding the benefits and potential challenges of MQTT 5 will help ensure a successful implementation, maximizing the potential benefits of this powerful IoT communication protocol.

As we look to the future, MQTT remains a vital player in IoT. With MQTT 5, developers now have even more flexibility in designing and implementing solutions that can handle the diverse requirements of modern IoT systems.

The evolution of MQTT doesn’t stop at version 5. The MQTT Technical Committee is already working on further enhancements and features that will continue to advance the protocol’s capabilities. This ongoing work demonstrates the strong commitment of the MQTT community to the continued growth and advancement of this technology, ensuring that MQTT will remain a relevant and powerful tool for IoT communication in the foreseeable future.


As technology continues to evolve, and as the needs of IoT systems grow and change, so will MQTT. It’s critical for anyone working in the IoT space to stay abreast of these developments to ensure they are leveraging the full power of MQTT and other related technologies to deliver the most effective, reliable, and secure IoT solutions possible.

In Part 2 of this series, Foundational Changes in the MQTT 5 Protocol, we will explore the crucial enhancements that make MQTT 5 a revolutionary tool for IoT communications. We’ll examine features such as advanced authentication, improved error reporting, and shared subscriptions, showing how they redefine the design and management of MQTT-based systems. Get ready for a deep dive into MQTT 5’s capabilities and how they can elevate your IoT solutions.

Sign up for our newsletter to get regular updates. Subscribe to our RSS feed here to stay updated. We encourage you to visit our MQTT Glossary for an in-depth understanding of the essential MQTT terminologies. It will equip you with the necessary vocabulary to grasp the complexities of MQTT and its various versions. Watch the video below that complements the concepts discussed in this article.

Watch the Video

  • 00:00 - Welcome to the MQTT 5 Essentials series
  • 00:20 - The history of MQTT
  • 01:26 - Principal goals of MQTT
  • 01:50 - What happened to MQTT 4?
  • 02:02 - Announcing part 2 - Foundational changes in the protocol

FAQs on MQTT 5

Mary Brickenstein-Hofschen

Mary is a technical writer at HiveMQ. She enjoys providing precise information that helps HiveMQ users get things done.

  • Contact Mary Brickenstein-Hofschen via e-mail

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