The MQTT protocol follows the publish-subscribe model. It activates the message broker between the data publisher and subscribers. The MQTT is responsible to gather all the messages from client nodes and sending the messages to the subscribers. The essential concepts of MQTT are topic, subscriber, and broker. A topic denotes a group of similar messages. The subscribers request the messages from the MQTT broker on the basis of topics. The MQTT subscribers are connected to the server to subscribe to the interesting topics and MQTT publishers publish the topic-related messages to the interested subscribers. The MQTT brokers act as intermediate for forwarding the messages to both publishers and subscribers. The MQTT is a simple protocol and it is suitable for IoT tin devices. By default, it has no security schemes. It minimizes the processing complexity during message exchanges and so it may tend to have serious security issues.