What is MQTT?
MQTT (Message Queuing Telemetry Transport) is a lightweight and efficient messaging protocol that follows a publish/subscribe model. It enables reliable data transmission between IoT devices, even over low-bandwidth networks. Originally developed for M2M (Machine-to-Machine) communication, it has now become one of the core protocols in the IoT ecosystem.
MQTT Architecture
MQTT relies on three main components:
- Publisher: The device or application that generates and sends the message.
- Broker: The central server that receives messages from publishers and delivers them to subscribers.
- Subscriber: The device or application that subscribes to a specific topic and receives messages from the broker.
This architecture ensures that devices don’t need direct connections to each other — all communication happens via the broker.
Why is MQTT Used?
- Low data usage: Battery-friendly, ideal for constrained environments.
- Real-time delivery: Sensor data is transmitted instantly.
- Highly scalable: Supports thousands, even millions, of devices communicating through a single broker.
- Security: Offers TLS encryption and authentication for secure communication.
MQTT QoS (Quality of Service) Levels
MQTT defines three QoS levels that determine message delivery reliability:
- QoS 0 – At most once: The message is sent once with no delivery guarantee.
- QoS 1 – At least once: The message is guaranteed to be delivered, but duplicates may occur.
- QoS 2 – Exactly once: The message is delivered exactly one time, ensuring the highest reliability (but also the slowest).
Advantages of MQTT
- Lightweight and efficient: Works with just a few kilobytes of overhead.
- Open standard: Supported across many platforms and programming languages.
- Flexible topic hierarchy: Enables structured and scalable message routing.
- Broad ecosystem support: Widely adopted by IoT platforms, cloud services, and device manufacturers.
Disadvantages of MQTT
- Broker dependency: If the broker fails, all communication stops.
- Network security risks: Misconfiguration may leave the system vulnerable to attacks.
- Not suitable for large data: Limited to small payloads — unsuitable for video or heavy file transfers.
Use Cases
- Collecting and processing sensor data
- Remote device control (e.g., switching lights on/off in a smart home)
- Industrial automation systems
- Smart home and building automation
- Vehicle tracking systems
Example Scenario
A temperature sensor publishes data every 5 seconds to the topic
factory/room1/temperature.
A monitoring application subscribes to this topic, and if the temperature exceeds 50°C, it automatically generates an alert and notifies the maintenance team.