• The acronym of MQTT is Message Queuing Telemetry Transport. It is an open-source, lightweight standard that publishes/subscribes messaging transport protocol that is ideal for connecting remote devices.
•  It is an OASIS and ISO standardized messaging protocol for the IoT. 
• MQTT was developed by Dr. Andy Stanford-Clark, IBM, and Arlen Nipper in 1999.
• The MQTT mostly consists of publisher, broker, topic, and single or multiple subscribers.
• The main aim is to send messages from the publisher to the broker and the broker makes data available to the subscriber. MQTT requires the use of a broker as the main mediator as shown below. 

• Here, the publisher is any connected device, the data is made available by a broker to a subscriber with the authority to manage the data. 
• MQTT is created upon TCP/IP (transmission control protocol and internet protocol)
• MQTT transmits messages in packets.
• In 2014, the OASIS released its MQTT 3.1.1 version, the last version of MQTT V5.0 on 7th march 2019.
• It is easily deployable and energy-efficient for millions of devices. 
• MQTT is the client-server based protocol that can be used as a client and broker to communicate between devices and through an application-based web or mobile app. 
• It is a bidirectional protocol.
• It has default encrypted URL port number 1883.

Important terms related to MQTT network

1. Broker: It is the server that sends the data to the targetted client which is connected to the server. 
2. Client: It is the device that is connected to the broker which sends and receives the data.
3. Topic: It is the name that the message is given related to the client, publish or subscribe or both with the topic.
4. Publish: Based on the topic name the client sends the data to the broker later to transmit it to the interested clients. 
5. Subscribe: The client communicates with the broker on the topic which is focused on. When a topic is subscribed, the message is sent to the broker and distributed to subscribers of the particular topic. The client can unsubscribe so that messages can be stopped from being received from the broker for the topic. 
6. QoS(Quality of Services): MQTT uses QoS levels in IoT to ensure confirmed delivery of messages to the receiver side even though connectivity between devices is unstable. It is the key factor that gives the client to choose the different levels of services that suits the reliability of the network and application logic. The value of the level ranges between 0-2, those values are assigned as follows:  0- at most one, 1- at least one, and lastly 2- exact one.

Where is MQTT used? 

• MQTT is used in many industries such as automotive, manufacturing, telecommunication, etc.
•  It is also used in IIoT (Industrial Internet of Things), in the smart home automation systems alongside cloud platforms such as Microsoft Azure, AWS, and IBM Watson. 
• Facebook also uses MQTT as a communication protocol for its messenger and Instagram platform. Even IBM Watson uses MQTT as the main communication protocol.  
• It is used in devices like smartphones, computers, cars, refrigerators, wearables, remote sensors, and other smart devices and machines to talk to each other and exchange information.

In this blog, the overview of the MQTT is described consisting of an introduction, facts, working,terms related to it and the applications. There are many applications and similar other protocols like MQTT in IoT.

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