The IoT is an internetworking of different smart devices and the physical world. The application layer communication is very prominent in the design of application-specific IoT. The application layer protocols offer application-specific services and assure better communication efficiency among the application program in the IoT. Application layer protocols in IoT must consider some major challenges in IoT-s network communications, such as resource restriction and communication reliability. Most Internet-related applications apply HTTP. However, it is inappropriate for small IoT devices.
   Moreover, the HTTP header includes hundreds of bytes, which is difficult to implement over resource-restricted tiny devices. The specifically designed application protocols for IoT are Constrained Application Protocol (CoAP), Message Queue Telemetry Transport (MQTT), Extensible Message and Presence Protocol (EMPP), and Advanced Message Queuing Protocol (AMQP). The first two protocols are widely used due to their simple functions