What is MQTT?
MQTT is a lightweight messaging protocol for connecting devices over internet. Invented by IBM in 1999 for oil pipeline monitoring. Now THE standard for Industrial IoT. Used by Facebook Messenger, AWS IoT, Azure IoT Hub, and millions of smart devices.
WhatsApp Analogy
MQTT Broker is like WhatsApp server — receives and delivers messages. Machines subscribe to topics like joining groups. When a sensor publishes, everyone subscribed receives instantly. No need to know IP addresses — communicate through broker.
Three Concepts
Broker: central server (Mosquitto is free). Publish: device sends message to topic (temperature sensor publishes 72.5 to factory/oven1/temperature). Subscribe: device listens to topic (dashboard subscribes and shows gauge).
Topic Structure
Organized like folders: factory/line1/motor1/speed. Wildcards: factory/line1/# subscribes to all Line 1 data. factory/+/motor1/speed subscribes to Motor 1 from all lines.
Getting Started
Install Mosquitto from mosquitto.org. Open two CMD windows. Window 1: mosquitto_sub -h localhost -t test/greeting. Window 2: mosquitto_pub -h localhost -t test/greeting -m Hello. Message appears instantly. That is MQTT working.
Is MQTT secure?
Basic MQTT has no security. Enable TLS on port 8883 and require authentication for production.
MQTT vs Modbus?
Modbus for direct PLC communication. MQTT for IoT and cloud. Modern systems use both.
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