Internet of Things: Survey and open issues of MQTT protocol

Internet of Things (IoT) is based on a wireless network that connects a huge number of smart objects, products, smart devices, and people. It has another name which is Web of Things (WoT). IoT uses standards and protocols that are proposed by different standardization organizations in message passing within session layer. Most of the IoT applications protocols use TCP or UDP for transport. XMPP, CoAP, DDS, MQTT, and AMQP are grouped of the widely used application protocols. Each one of these protocols have specific functions and are used in specific way to handle some issues. This paper provides an overview for one of the most popular application layer protocols that is MQTT, including its architecture, message format, MQTT scope, and Quality of Service (QoS) for the MQTT levels. MQTT works mainly as a pipe for binary data and provides a flexibility in communication patterns. It is designed to provide a publish-subscribe messaging protocol with most possible minimal bandwidth requirements. MQTT uses Transmission Control Protocol (TCP) for transport. MQTT is an open standard, giving a mechanisms to asynchronous communication, have a range of implementations, and it is working on IP.