MQTT Protocol for IoT Communication

September 26, 2023

MQTT Basics: A Lightweight Communication Protocol for IoT 

Companies in the industrial environment can draw significant benefits from IoT applications. With heterogeneous IoT devices using diverse communication technologies, however, a shared language is needed to interact with one another and external systems, such as cloud services. MQTT Protocol for IoT Communication provides a common framework for IoT device-to-device and device-to-cloud communication, setting rules and standards for data transmission. Due to the variety of existing IoT devices, different IoT protocols have emerged, each targeting specific use cases and applications. Selecting the right one is an essential step in the deployment of an IoT environment. 

What is MQTT and why you should use it 

One protocol that stands out in M2M and IoT applications is MQTT (Message Queuing Telemetry Transport). MQTT Protocol for IoT Communication is a lightweight and highly efficient messaging protocol intended for use in constrained environments – such as IoT devices – or applications with limited bandwidth.  

MQTT's Publish-Subscribe Mechanism

MQTT Protocol for IoT Communication leverages a flexible routing mechanism and asynchronous communication based on the publish-subscribe paradigm. IoT devices – clients – can either publish (transmit) or subscribe to topics to receive messages of interests. Clients do not communicate with each other: the MQTT broker is responsible for receiving client-initiated connections and forwarding messages to subscribers. The publish/subscribe mechanism has capabilities such as one-to-one, many-to-many or one-to-none, also providing bi-directional communication between devices and the cloud.  

MQTT's Efficiency and Resilience

MQTT Protocol for IoT Communication is lightweight in terms of both protocol overhead and resource usage. The data payload avoids carrying excessive protocol-related information, thereby optimizing the usage of limited bandwidth and reducing data transmission costs, which is critical in IoT applications. As an event-driven protocol, clients only publish when they have information to transmit, and a broker only sends out to subscribers when new data arrives. This minimizes unnecessary network traffic and resource consumption.  

Where network connections are unreliable – as is often the case with IoT environments – clients might temporarily disconnect or experience network interruptions. MQTT is resilient to such network challenges. The decoupling of publishers and subscribers means that even if a subscriber disconnects, it won't affect the publishing devices. Also, MQTT brokers can retain session information for clients. This means that even if a client disconnects and reconnects, it can resume its previous session, including subscribed topics and undelivered messages. This session persistence is particularly helpful in maintaining continuity during network disruptions.

Reliable Message Delivery 

The MQTT protocol provides three different Quality of Service (QoS) levels with varying degrees of message delivery assurance. This allows designers to select the option that aligns the most with both the network reliability and the application’s needs. 

  • QoS 0 (At Most Once): Messages are sent with the “fire and forget” approach, with the publisher dispatching the message to the broker without any acknowledgment of its delivery. Since no retransmission mechanism is set up, if the client is not available at that time the message is lost.  
  • QoS 1 (At Least Once): When a message is published, the broker acknowledges its receipt. If a confirmation is not received within a specified time frame, the sender retransmits the message. This ensures that the message will arrive at least once but may result in duplicates if the acknowledgment is lost.  
  • QoS 2 (Exactly Once): The client and broker use a four-way-handshake process to ensure that the message is delivered exactly once to the subscriber, leveraging acknowledgment and deduplication mechanisms.  

MQTT Security Mechanisms 

Security is the cornerstone of any IoT application, and MQTT Protocol for IoT Communication security is crucial in protecting IoT systems from various attacks and threats. The protocol incorporates robust mechanisms for authentication, encryption, and authorization, ensuring that only authorized devices can interact and exchange data. 

Alternative Protocols for IoT Communication

  • Authentication: Client authentication ensures that only authorized clients can connect to the broker. Password authentication is the most common method. When an MQTT client connects to the broker, it sends its username and password in the CONNECT packet. The broker compares them with the previously stored credentials. If there is no match, the broker will reject the client's connection request. Other methods include SCRAM (Salted Challenge Response Authentication Mechanism) authentication, Token Based authentication like JWT, and more. 
  • Encryption: This feature is essential to safeguard data privacy and integrity, especially when MQTT is used over public networks like the internet. MQTT runs over TCP/IP protocol. TCP connections are unencrypted by default. However, encrypted communication can be secured on the transport layer by using TLS (Transport Layer Security) communication between clients and the broker. TLS ensures that exchanged data is secure, making it challenging for intruders to intercept or tamper with the information being sent. 
  • Authorization: MQTT brokers can enforce access control through authorization mechanism. Access control lists (ACLs) or custom authorization rules can determine which authenticated clients can publish or subscribe to certain topics, ensuring that data is shared only with authorized parties. 

Alternative Lightweight Protocols for IoT 

MQTT is a lightweight yet robust communication protocol for IoT, but it’s not the only alternative. 

CoAP (Constrained Application Protocol) is also designed for resource-constrained IoT devices and low-power networks. It uses the same REST model as HTTP, but it depends on UDP (User Datagram Protocol) packets for communication and message passing. Reducing the size of network packages, it decreases bandwidth overload, but also saves battery power and storage space, improving the IoT lifecycle. CoAP is widely adopted in IoT applications that require interoperability with web-based services such as industrial automation, smart homes, and healthcare.  

AMQP (Advanced Message Queuing Protocol) is an open application layer protocol for IoT, excellent in scenarios necessitating intricate routing and queuing. Like MQTT, it supports publish-subscribe and client-server communication and it has similar QoS mechanisms. Compared with MQTT, AMQP is more secure. It integrates TLS to ensure data encryption upon transfer, and SASL (Simple Authentication Security Layer) framework for secure authentication handshake between clients and servers. However, as a heavy and verbose protocol its application is often limited to large-scale IoT deployments where guaranteed message delivery and complex routing are critical. 

IoT devices in IIoT scenario leveraging MQTT for real-time communication, OTA updates, remote monitoring, and predictive maintenance

MQTT-powered IoT Use Cases 

Typically, IoT devices have limited resources. Since MQTT is more lightweight compared to alternative communication protocols, it is often a wise choice for IoT. In the IIoT scenario, MQTT facilitates real-time communication between on-field devices and sensors and the cloud, enabling simultaneous distribution of OTA updates to multiple devices, remote monitoring and configuration, predictive maintenance. Sensors collecting data on machine status, temperature, and production rates, might publish their readings to a central MQTT broker. Operators can subscribe to MQTT topics related to specific machines to receive real-time updates on equipment performance and intercept potential issues.  

MQTT is also widely adopted in home automation systems. Suppose a smart home is set up with smart lights bulbs, motion sensors, and a central hub integrated into a MQTT-based home automation system. When a motion sensor detects a movement, it publishes an MQTT message to the hub. The hub acts as an MQTT broker sending a command to the smart lights’ bulbs subscribed to this topic, which automatically turns on.  

Cities are also increasingly integrating MQTT-based IoT sensors networks to become more efficient and sustainable. For example, environmental sensors throughout the city collect data on air quality, weather conditions, and noise levels and publish this data to a central MQTT broker. Real-time data collection allows authorities to monitor and analyze environmental conditions instantaneously. They can promptly respond to pollution events, weather anomalies, or excessive noise levels, ensuring a healthier urban environment. 

Moving IoT data with MQTT Broker 

As already mentioned, the two main components of the MQTT protocol are the client and the broker. MQTT clients can range from microcontrollers to servers and can function as both publishers and subscribers. The MQTT broker serves as a central hub, receiving messages from publishers and delivering them to subscribers. It manages communication flow, filters messages by subscription topic, maintains session data for connected clients, and handles authentication and authorization. Since brokers may have to handle millions of simultaneously connected clients, they can distribute message processing across multiple broker nodes to better manage heavy workloads, ensuring scalability and fault tolerance. When choosing an MQTT broker, enterprises should assess their scalability, integration into backend systems, failure-resistance, and easy monitoring.  

CLEA's MQTT Implementation

Platforms like Clea, tailored explicitly for the IoT landscape, leverage MQTT Protocol for IoT Communication to facilitate data exchange and orchestration, empowering IoT applications to operate at peak efficiency. These platforms often include MQTT brokers as core components to facilitate device-to-device and device-to-cloud communication. In MQTT terms, Clea relies on a broker providing an MQTT protocol built upon the MQTT v3.1.1 specification, BSON (Binary JSON, version 1.1) serialized payloads and on optional zlib deflate.  The broker is responsible for receiving, processing, and routing MQTT messages between IoT devices and the cloud service. This ensures that field data is appropriately ingested into cloud databases, analytics platforms, or other cloud-based applications for real-time processing and decision-making.  

Why Choose MQTT for Your IoT Project?

In the dynamic IoT landscape, selecting the right communication protocol for a particular deployment is mission-critical. The choice must necessarily align with the needs of the particular application. MQTT, with its bidirectional pub/sub architecture, is flexible and scalable for a wide variety of use cases and IoT system architectures. Reliability, capability to support unlimited devices, fast response time, and a strong developer community simplifying the protocol’s implementation are just some of the reasons that make MQTT a well-suited option for IoT projects. Our IoT platform Clea uses MQTT Protocol for IoT Communication as a part of the tech stack, and this is also among the many reasons why you should consider it for your next IoT project. 

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