MQTT is an OASIS standard messaging protocol for the Internet of Things (IoT). It is designed as an extremely lightweight publish/subscribe messaging transport that is ideal for connecting remote devices with a small code footprint and minimal network bandwidth. MQTT today is used in a wide variety of industries, such as automotive, manufacturing, telecommunications, oil and gas, etc.
## Concepts
### 1. **Publisher-Subscriber Model:**
MQTT follows a publish-subscribe communication model, where clients (publishers) send messages to topics, and other clients (subscribers) receive messages from those topics.
### 2. **Broker:**
The MQTT broker is a server that receives published messages from clients and delivers them to the appropriate subscribers.
### 3. **Topics:**
Topics act as channels or categories to which messages are published. Subscribers express interest in specific topics to receive relevant messages.
## MQTT Components
### 1. **Publisher:**
- A client that sends messages to a specific topic.
### 2. **Subscriber:**
- A client that expresses interest in a specific topic and receives messages published to that topic.
### 3. **Broker:**
- The server that handles message routing between publishers and subscribers.
## Topics and Subscriptions
Each message is inside a topic allowing for organizing them.
### 1. **Topics:**
- Hierarchical and structured, topics enable flexible message routing.
### 2. **Wildcards:**
- MQTT supports wildcards (`+` and `#`) for subscribing to multiple topics.
## Real-world Use Case
### 1. **IoT (Internet of Things):**
- MQTT is widely used in IoT scenarios for efficient communication between devices.
- Smart homes leverage MQTT for controlling and monitoring devices. For example [zigbee2mqtt](../applications/web/zigbee2mqtt.md) with [Home Assistant](../applications/web/Home%20Assistant.md).
