Message Queue Telemetry Transport (MQTT) protocol is an application layer protocol. The application layer provides an interface between the end nodes (IOT devices) and the network. In case of computers, laptops and mobile devices, the application layer is usually implemented by the browser. In case of IOT devices, the application layer may be implemented either by the running operating system (if an embedded OS is running on it) or by the firmware.  In computing world, the most common and ubiquitous application layer protocol used is Hypertext Transfer Protocol (HTTP). The HTTP protocol has been designed for communication between a client and a server. The protocol uses request/response method in which when a client needs data from the server then it sends a request message to the server and server sends back a response message.