The world of the Internet of Things (IoT) is expanding rapidly, and one of the key technologies that enables efficient and reliable communication between IoT devices is MQTT, which stands for Message Queuing Telemetry Transport. In this blog, we’ll explore MQTT, from its history and evolution to its architecture, QoS levels, topics, payloads, and role in IoT applications.

What is MQTT?

MQTT is a lightweight, open-source messaging protocol designed for efficient, real-time communication between devices, particularly in constrained environments. It was created by Dr. Andy Stanford-Clark of IBM and Arlen Nipper of Arcom in the late 1990s. MQTT is characterized by its low overhead and minimal bandwidth and power consumption, making it an ideal choice for many IoT applications.

MQTT has come a long way since its inception in terms of history and evolution. It was originally developed to monitor oil pipelines but has since evolved into one of the IoT communication standards. The protocol addressed the need for reliable, low-bandwidth, and low-latency messaging in remote and unreliable networks.

Why MQTT is Important in the IoT Era

MQTT is crucial in many IoT applications where a few or millions of devices are interconnected. Its lightweight nature and reliability make it perfect for several IoT applications where devices often have limited resources and intermittent connectivity. MQTT ensures data is efficiently and securely transmitted between IoT devices and central systems.

Also, the MQTT's device-agnostic nature ensures that devices from different manufacturers seamlessly communicate, fostering interoperability. The common language provided by MQTT topics and payloads promotes a standardized communication framework, allowing for the integration of diverse IoT devices into a cohesive ecosystem

MQTT Architecture

Client-Server Model

MQTT is based on a client-server model, where clients are the devices or applications that communicate using MQTT, while the server is called a broker. The broker is responsible for receiving, routing, and delivering messages to the appropriate clients. Brokers are the backbone of MQTT communication, acting as intermediaries that manage the message flow. Clients can be publishers and subscribers, sending and receiving messages through the broker.

Many IoT platforms offer an integrated MQTT Broker; an example is TagoIO, where you can integrate your MQTT devices and create scripts to manipulate data, create notifications, and visualize said data.

Publish/Subscribe Communication Model

MQTT employs a publish/subscribe communication model, where publishers send messages on specific topics, and subscribers express interest in specific topics. This decouples the sender and receiver, allowing for more scalable and flexible communication. For example, a weather station could publish temperature data on “weather/temperature,” while a mobile application could subscribe to that topic to receive updates on temperature changes.

What is MQTT Quality of Service 

MQTT offers three Quality of Service (QoS) levels, which determine the message delivery guarantees:

1. QoS 0 - At most once: This level guarantees no delivery. The message is sent once, and the sender does not expect an acknowledgment or guarantee of message delivery. This level is suitable for non-critical data where message loss is acceptable.

2. QoS 1 - At least once: This level provides guaranteed delivery but may result in duplicates. The message is sent at least once, and the sender expects an acknowledgment from the receiver. If the acknowledgment is not received, the sender resends the message. This level is appropriate for critical data where message loss is unacceptable.

3. QoS 2 - Exactly once: This level provides guaranteed delivery with no duplicates. The message is sent exactly once, and the sender expects an acknowledgment from the receiver. If the acknowledgment is not received, the sender resends the message. This level is suitable for critical data with zero tolerance for message loss.

The choice of QoS level depends on the specific requirements of the application. Selecting the appropriate QoS level impacts the message delivery, influencing message duplication and network overhead.

MQTT Topics and Payloads

MQTT Topics and Payloads are two essential components of the MQTT protocol. Topics are like channels that messages are published to and subscribed from. They are hierarchical and help organize messages.

Message payloads contain the actual data to be transmitted. Depending on the application’s requirements, they can be in various formats, such as JSON, XML, or binary. The payload format should be chosen based on the application’s needs and the available resources.

A Look at Real-world Use Cases using MQTT

As we explore the efficiency of MQTT in IoT communication, it's crucial to examine how this protocol seamlessly integrates with devices from various manufacturers such as Dragino, RAK Wireless, Seeed Studio, and Khomp. Let's delve into real-world use cases, showcasing MQTT's versatility across IoT devices.

1.  SCADA MQTT Systems (Supervisory Control and Data Acquisition): MQTT is often integrated into SCADA systems to facilitate real-time data exchange between field devices and the central monitoring system. It helps collect and manage data from various sensors and devices distributed across an industrial environment.
   
   

2. Healthcare Monitoring with Wearable Sensors: Healthcare scenarios involve wearable sensors from different providers, each offering unique monitoring capabilities. Regardless of brand, wearable sensors can publish vital sign data on a standardized topic like "health/patient1/vital-signs." MQTT's interoperability ensures seamless integration, allowing healthcare professionals to monitor patients with diverse sensor types.

3. Environmental Monitoring with Various Sensors: Environmental monitoring combines sensors from multiple manufacturers, offering parameters like air quality, noise levels, or radiation detection. MQTT's topic-based communication allows environmental sensors to publish data on shared topics like "environment/air-quality" or "environment/noise-levels." This interoperability streamlines the integration of diverse environmental sensors into a comprehensive monitoring system.

What does the future bring for MQTT?

MQTT stands out as a highly advantageous communication protocol for IoT solutions, garnering attention as a preferred option. Nevertheless, the expansive realm of IoT protocols presents various alternatives, with CoAP being a notable contender. A distinctive feature of CoAP is its ability to operate over TCP/IP and UDP, setting it apart from MQTT, which is predominantly associated with TCP/IP. The IoT landscape's ongoing evolution adds uncertainty as to which communication protocol will emerge as the most widely adopted. As technological advancements continue to shape the IoT ecosystem, the dynamic interplay between MQTT, CoAP, and other contenders will ultimately determine the protocol that best aligns with the diverse and evolving needs of IoT applications.