MQTT is a lightweight messaging protocol commonly used in IoT for reliable, low-bandwidth communication between devices. It uses a publish-subscribe model, where devices (clients) publish data to topics, and others subscribe to these topics, allowing for efficient many-to-many communication. In software engineering, MQTT brokers like Mosquitto or EMQX serve as central message routers, managing client connections, topic filtering, and quality of service (QoS) levels. Implementing MQTT involves integrating client libraries (such as Eclipse Paho) into device software, handling message serialization (JSON or binary formats), and maintaining persistent sessions. To ensure secure communication, developers must implement TLS encryption, authentication mechanisms like username/password or certificate-based authentication, and access control lists (ACLs) on the broker. Managing message delivery is also crucial, especially in QoS levels (0, 1, 2) that define delivery guarantees. For large-scale deployments, software engineers may create load balancers and message queues to distribute MQTT broker loads efficiently. Additionally, MQTT can be integrated with microservices via bridge connections to relay messages between brokers and backend services for further processing or visualization.