In-Depth Guide to Best IoT Protocol MQTT

Table of Contents

• What is MQTT?

• MQTT Platform Use Cases

• Why is MQTT the Best Protocol for IoT?

• How Does MQTT Work?

• MQTT Workflow

This article will demonstrate how to get started with the MQTT protocol through code examples. IoT and MQTT beginners can understand the concepts related to MQTT and quickly start developing MQTT services and applications through this article.

What is MQTT?

MQTT (Message Queuing Telemetry Transport) is a lightweight, publish-subscribe messaging protocol designed for resource-constrained devices and low-bandwidth, high-latency, or unreliable networks. It is widely used in Internet of Things (IoT) applications, providing efficient communication between sensors, actuators, and other devices.

MQTT Platform Use Cases

The MQTT platform is a key component of IoT. It can be used in various IoT scenarios involving the connection of a large number of devices, such as:

• Internet of Vehicles (IoV): The MQTT platform securely and efficiently connects vehicles to the cloud. It integrates vehicle data with other systems and services. This makes the future of data and services crucial for the IoV possible.

• Electric Vehicle Charging Networks: The MQTT platform creates a cloud system that connects charging networks, vehicle networks, and the internet, with data collection and processing capabilities. It provides optimal solutions for the IoT era, enhancing the performance of charging stations.

• Logistics Asset Management: The MQTT platform collects, transmits, and manages sensor data from vehicles and warehouses in the logistics chain. It offers data-driven solutions for logistics companies to monitor their assets and discover the value of data.

• Industrial Production: Smart factory applications can utilize the MQTT platform for data collection, transmission, and distribution, enabling equipment health management, energy consumption operations, production monitoring and analysis, product quality traceability, supply chain operations, and predictive maintenance.

With advancements in IoT technology, industries such as energy, smart homes, and healthcare are exploring different application scenarios. The MQTT platform continues to play a critical role as a key IoT connectivity infrastructure, enriching its application scenarios across various fields.

Why is MQTT the Best Protocol for IoT?

MQTT has become one of the best IoT protocols due to its unique features and functionalities tailored to the specific needs of IoT systems. Some key reasons include:

• Lightweight: IoT devices are often limited in processing power, memory, and energy consumption. The minimal overhead and smaller packet size of MQTT make it an ideal choice for these devices, as it consumes fewer resources and achieves efficient communication even in resource-constrained scenarios.

• Reliable: IoT networks may encounter high latency or unstable connections. MQTT supports different QoS levels, session awareness, and persistent connections, ensuring reliable message delivery even under challenging conditions, making it highly suitable for IoT applications.

• Secure Communication: Security is crucial in IoT networks as they often transmit sensitive data. MQTT supports Transport Layer Security (TLS) and Secure Sockets Layer (SSL) encryption, ensuring the confidentiality of data during transmission. Additionally, it provides authentication and authorization mechanisms through username/password credentials or client certificates, protecting access to the network and its resources.

• Bidirectionality: The publish-subscribe model of MQTT allows seamless bidirectional communication between devices. Clients can publish messages to topics and subscribe to receive messages on specific topics, enabling effective data exchange across different IoT ecosystems without direct coupling between devices. This model also simplifies the integration of new devices, ensuring easy scalability.

• Continuous, Stateful Sessions: MQTT allows clients to maintain stateful sessions with the broker, enabling the system to remember subscriptions and undelivered messages even after disconnection. Clients can also specify a keep-alive interval during the connection, prompting the broker to check the connection status regularly. If the connection is lost, the broker stores undelivered messages (depending on the QoS level) and attempts to deliver them when the client reconnects. This feature ensures reliable communication and reduces the risk of data loss due to intermittent connections.

• Support for Large Scale IoT Devices: IoT systems often involve a large number of devices, requiring protocols capable of handling large-scale deployments. The lightweight nature, low bandwidth consumption, and efficient resource utilization of MQTT make it highly suitable for large-scale IoT applications. The publish-subscribe model allows MQTT to scale effectively as it decouples senders and receivers, reducing network traffic and resource usage. Furthermore, the protocol supports different QoS levels, allowing message delivery to be customized based on application needs, ensuring optimal performance in various scenarios.

• Language Support: IoT systems typically include devices and applications developed in various programming languages. The extensive language support of MQTT facilitates seamless communication and interoperability across different IoT ecosystems. You can visit our MQTT Client Programming blog series to learn how to use MQTT in PHP, Node.js, Python, Golang, Node.js, and other programming languages.

How Does MQTT Work?

To understand how MQTT works, one must first grasp the concepts of MQTT Client, MQTT Broker, Publish-Subscribe Model, Topic, and QoS:

MQTT Client

Any application or device that runs an MQTT client library is an MQTT client. For example, an instant messaging application using MQTT is a client, various sensors that report data via MQTT are clients, and various MQTT testing tools are also clients.

MQTT Broker

The MQTT Broker handles client connections, disconnections, subscription and unsubscription requests, and message routing. A powerful MQTT broker can support massive connections and millions of messages throughput, helping IoT service providers focus on business and quickly create reliable MQTT applications.

For more details about MQTT brokers, please refer to the blog “Ultimate Guide to MQTT Broker Comparison 2023”.

Publish-Subscribe Model

The publish-subscribe model differs from the client-server model in that it separates the client sending the message (publisher) from the client receiving the message (subscriber). Publishers and subscribers do not need to establish a direct connection; the MQTT Broker is responsible for routing and distributing all messages.

The diagram below shows the MQTT publish/subscribe process. The temperature sensor connects to the MQTT server as a client and publishes temperature data to a topic (e.g., Temperature), and the server receives the message and forwards it to the clients subscribed to the Temperature topic.

Topics

The MQTT protocol routes messages based on topics. Topics are differentiated by slashes to indicate hierarchy/, similar to URL paths, for example:

chat/room/1
sensor/10/temperature
sensor/+/temperature

MQTT topics support the following wildcards:+ and #.

• +: Represents a single-level wildcard, for example, a/+ matches a/x or a/y.

• #: Represents a multi-level wildcard, such as a/# matches a/x, a/b/c/d.

For more details about MQTT topics, please refer to the blog Understanding MQTT Topics & Wildcards by Case.

Quality of Service (QoS)

MQTT provides three levels of Quality of Service to ensure message delivery reliability across different network environments.

• QoS 0: Messages are delivered at most once. If the client is currently unavailable, it will lose this message.

• QoS 1: Messages are delivered at least once.

• QoS 2: Messages are delivered exactly once.

For more details about MQTT QoS, please refer to the blog Introduction to MQTT QoS (Quality of Service).

MQTT Workflow

Now that we understand the basic components of MQTT, let’s look at how the general workflow operates:

1. The client initiates a connection with the broker using TCP/IP and optionally uses TLS/SSL encryption for secure communication. The client provides authentication credentials and specifies clean or persistent sessions.

2. The client can publish messages to specific topics or subscribe to topics to receive messages. The publishing client sends messages to the broker, while the subscribing client expresses interest in receiving messages about specific topics.

3. The broker receives the published messages and forwards them to all clients subscribed to the relevant topics. It ensures reliable message delivery based on the specified Quality of Service (QoS) level and manages the message storage for disconnected clients based on the session type.