MQTT (Message Queuing Telemetry Transport)

A lightweight publish/subscribe messaging protocol (ISO/IEC 20922) designed for IoT and constrained networks, running over TCP with minimal overhead. Clients publish messages to a broker on named topics; other clients subscribed to those topics receive the messages. Three QoS levels control delivery guarantees: at-most-once (0), at-least-once (1), and exactly-once (2).