What Is MQTT?

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol designed for efficient communication between devices in a network. It was developed by IBM in the late 1990s and has since become an open standard maintained by the OASIS consortium.


MQTT is designed to be simple and efficient, making it well-suited for resource-constrained devices and networks with limited bandwidth or intermittent connectivity. It follows a publish-subscribe messaging model, where devices communicate by publishing messages to topics and subscribing to topics to receive relevant messages.


Here's a brief overview of how MQTT works:


1. Broker: MQTT uses a central message broker, which acts as an intermediary between publishers and subscribers. The broker receives messages published by devices and routes them to subscribers based on their topic subscriptions.


2. Topics: Messages in MQTT are organized into topics, which are hierarchical and represented by strings. Topics can have multiple levels, separated by forward slashes (e.g., "sensors/temperature/living-room"). Publishers send messages to specific topics, and subscribers receive messages from topics they are interested in.


3. Publishers: Devices that generate data or events are MQTT publishers. They publish messages to specific topics on the broker. Publishers can also include a Quality of Service (QoS) level, which determines the reliability of message delivery.


4. Subscribers: Devices that want to receive data or events from MQTT are subscribers. They subscribe to specific topics on the broker and receive messages published to those topics. Subscribers can filter messages based on topic patterns to receive only relevant information.


5. QoS Levels: MQTT supports three levels of Quality of Service:

   - QoS 0 (At most once): The broker delivers the message once, and no confirmation or acknowledgment is requested. This level has the lowest reliability.

   - QoS 1 (At least once): The broker ensures that the message is delivered at least once to the subscriber. It may result in duplicate messages.

   - QoS 2 (Exactly once): The broker guarantees that the message is delivered exactly once to the subscriber. This level provides the highest reliability but introduces additional overhead.

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