MQTT Full Form, what is mqtt in iot, mqtt protocol,

MQTT Full Form, (MQ Telemetry Transport) Architecture and Variable Header, MQTT Payload-Topic & FAQs

MQTT Full Form:- MQTT stands for Message Queuing Telemetry Transport. MQTT is a machine-to-machine Internet of Things connectivity protocol. It is an extremely lightweight publish-subscribe messaging transport protocol. This protocol is useful for connections to remote locations where bandwidth is a premium. These characteristics make it useful in a variety of situations, including persistent environments such as machine-to-machine communication and Internet of Things contexts. It is a publish and subscribe system where we as a client can publish and receive messages. This eases communication between multiple devices. It is a simple messaging protocol designed for limited devices and low bandwidth, so it is a perfect solution for Internet of Things applications.

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Symptoms of MQTT

MQTT has some unique features which are rarely found in other protocols. Some of the features of MQTT are given below:

  • It is a machine-to-machine protocol, i.e. it provides communication between devices.
  • Also, It is designed to be a simple and lightweight messaging protocol that uses a publish/subscribe system to exchange information between a client and a server.
  • It is not necessary that both the client and the server establish a connection at the same time.
  • It provides faster data transmission, similar to how WhatsApp/Messenger provides faster delivery. It is a real-time messaging protocol.
  • This allows customers to subscribe to a limited selection of topics so that they can find the information they are looking for.

History of MQTT, MQTT Full Form

MQTT was developed by Dr Andy Stanford-Clark, IBM and Arlen Nipper. Previous versions of protocol 3.1 and 3.1.1 were made available under In 2014, MQTT was officially published by OASIS. So, OASIS has become a new home for MQTT development. Then, OASIS started further development of MQTT. Version 3.1.1 is backwards compatible with 3.1 and brought only minor changes such as changes to the connect message and clarification of the 3.1 version. The most recent version of MQTT is 5.0, which is the successor to version 3.1.1. Version 5.0 is not backward, as comfortable as version 3.1.1. Specifications-wise, version 5.0 has a significant number of features that the code has put in place.

The major functional objectives in version 5.0 are:

  • Increased scalability and large-scale systems to install with thousands or millions of devices.
  • error reporting improvements

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MQTT Full Form
MQTT Full Form

MQTT Architecture

To understand the MQTT architecture, let us first look at the components of MQTT.

  1. Message
  2. Customer
  3. server or broker
  4. Subject


A message is data that is carried by protocols across the network for applications. When the message is transmitted over the network, the message contains the following parameters:

  • payload data
  • Quality of Service (QoS)
  • collection of properties
  • subject name


In MQTT, there are two roles client and publisher client. Clients subscribe to topics to publish and receive messages. In simple words, we can say that if any program or device uses MQTT, then that device is called a client. A device is a client if it opens a network connection to the server, publishes messages that other clients want to see, subscribes to messages it is interested in receiving, unsubscribes to messages it is interested in receiving Not interested in receiving and turns off the device. Network connection to the server.

In MQTT, the client performs two operations:

Publish: When the client sends the data to the server, we call this operation Publish.

Subscribe: When the client receives the data from the server, we call this operation a subscription.

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Device or program that allows a client to publish and subscribe to messages. A server accepts network connections from clients, accepts messages from clients, processes subscribe and unsubscribe requests, forwards application messages to clients, and closes network connections to clients.


The label assigned to the message is checked against the membership known by the server, known as TOPIC.

MQTT Full Form
MQTT Full Form

MQTT architecture

Now we will look at the architecture of MQTT. To understand this more clearly, we will look at an example. Suppose a device has a temperature sensor and wants to send ratings to a server or broker. If a phone or desktop application wants to receive this temperature value on the other side, two things will happen. The publisher first defines the topic; For example, the temperature then publishes the message, ie the value of temperature. After publishing the message, the phone or desktop application on the other hand will subscribe to the topic, i.e. temperature, and then receive the value of the published message, i.e. temperature. The role of the server or broker is to deliver the published message to the phone or desktop application.

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MQTT Message Format

MQTT uses a command and command acknowledgement format, which means that each command has an associated acknowledgement. As shown in the figure above, in MQTT Full Form the connect command has a connect acknowledgement, the subscribe command has a subscribe acknowledgement, and the publish command has a publish acknowledgement. This mechanism is similar to the handshaking mechanism in the TCP protocol.

Now we will look at the packet structure or message format of MQTT.

MQTT Protocol

The MQTT message format consists of a 2-byte fixed header, which is present in all MQTT packets. The second field is a variable header, which is not always present. The third field is a payload. Also, MQTT Full Form is not always present. The payload field basically contains the data that is being sent. We might think that the payload is a mandatory field, but it is not. Some commands do not use the payload field, for example, disconnect messages.

Remaining Length, MQTT Full Form

The remaining Length is a variable-length integer indicating the number of bytes remaining within the current control packet, including the data in the variable header and payload. Therefore, the remaining length variable is equal to the data in the header plus the payload.

  1. Remaining Length = Variable Header Length + Payload Length
  2. For example, if the variable header length is 20 and the payload length is 30, the remaining length is 50.
  3. The remaining length can be used up to 4 bytes, and it starts from 2 bytes and can be used up to 4 bytes.
  4. This field uses 7 bits for the length, and the MSB bit can be used to carry the flag. If the continuation flag is 1, the next byte is also a part of
  5. the remaining length. If the continuation flag is 0, then the one byte remaining is the last of the length.

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MQTT Full Form
MQTT Full Form

Variable Header

Some types of MQTT control packet types also contain an optional field, that is, the variable header component. So, This field is located between the Fixed header and the payload. The contents of the variable header depend on the packet type. The variable header contains a packet identifier field, which is common to many packet types. Also, The variable header component of many MQTT control packet types includes a 2-byte integer, ie the packet identifier field.

The packet identifier field is included in the list below:

  1. published
  2. pub back
  4. Public
  5. pub comp
  6. subscribe
  7. sub back
  8. cancel membership
  9. unstack

Key points related to the packet identifier field:

  • If the QoS (Quality of Service) value is set to zero, then a public packet should not contain the packet identifier field. This means that if the QoS value is greater than zero, only the PUBLISH packet will contain the packet identifier field.
  • When a client publishes a new SUBSCRIBE, UNSUBSCRIBE, or MQTT control packet, it MUST specify a non-zero packet identifier that is currently unused.
  • When a server sends a newly published MQTT control packet, MQTT Full Format SHOULD specify a non-zero packet identifier that is currently unused.
  • PUBACK, PUBREC, PUBUREL, and PUBREC are acknowledgement packets of the PUBLISH command which have the same packet identifier as the PUBLISH packet.
  • SUBACK and UNSUBACK are the acknowledgement packets for SUBSCRIBE and UNSUBSCRIBE, respectively. Both the packets, i.e.

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What is the MQTT Topic?

With MQ Telemetry Transport, resource-constrained IoT devices can send or publish information on a specific topic to a server that acts as an MQTT message broker. The broker then broadcasts the information to clients who have previously subscribed to the client’s topic. To a human, a topic resembles a hierarchical file path. Clients can subscribe to a specific hierarchy level of a topic or use wildcard characters to subscribe to multiple levels.

The MQTT protocol is a good choice for wireless networks that have varying latency due to occasional bandwidth limitations or unreliable connections. If the subscribing client’s connection to the broker is interrupted, the broker buffers the messages and forwards them to the subscriber when the subscriber is back online. If the broker’s connection to the publishing client is disconnected without notification, the broker may disconnect and send a cached message with the publisher’s instructions to the subscriber.

What is the MQTT Payload?

So, Messages are shared with other devices or software through a broker that uses MQTT. Each message has a subject, based on which the message can be further processed by the broker. Additionally, each message contains a message content, the so-called payload. The MQTT payload is not bound to a fixed structure and can be freely designed. However, it is helpful to specify a particular structure for the message content so that it can be read by other devices or software. Possible message structures are JSON, XML or OPC UA. A defined structure enables smooth internal communication as all devices and software communicate with the same structure.

MQTT Full Form
MQTT Full Form

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FAQs on MQTT Full Form

What is MQTT used for?

MQTT is a standards-based messaging protocol, or set of rules, used for machine-to-machine communication. Smart sensors, wearables and other Internet of Things (IoT) devices typically have to transmit and receive data over resource-constrained networks with limited bandwidth.

Why is MQTT used in IoT?

The MQTT protocol is thus energy efficient and easy to deploy for millions of devices. Connecting devices across unreliable networks: MQTT in IoT uses QoS levels to ensure guaranteed delivery of messages to receivers, even when connections between devices are unreliable.

What does MQTT mean in IoT?

Message Queuing Telemetry Transport:

Also, MQTT stands for Message Queuing Telemetry Transport. It is a lightweight messaging protocol for use in cases where clients require a small code footprint and are connected to unreliable networks or networks with limited bandwidth resources.

Is MQTT better than HTTP?

MQTT is better than HTTP if you have devices that communicate regularly. The MQTT protocol can keep a connection open for as long as possible, sending only one data packet.

What is the example of MQTT in real life?

Smart Home and Wearable Devices:

MQTT is used for communication between multiple consumer IoT devices. This can include everything from smart home devices like thermostats, appliances, or security systems, as well as smartwatches, fitness trackers, health monitoring devices, or wearable devices like your smartphone.

Is MQTT a TCP protocol?

So, MQTT is a protocol that runs over TCP/IP and is used to transport lightweight messages between devices. As manufacturing begins to invest deeper and deeper into the Internet of Things (IoT), MQTT will become more prevalent on the factory floor.

Which devices use MQTT?

It enables computers, smartphones, cars, refrigerators, thermostats, wearables, remote sensors and other smart devices and machines to talk to each other and exchange information. MQTT Full Form This technology is called Message Queuing Telemetry Transport (MQTT).

Is MQTT a wifi?

The MQTT NCD WiFi allows the entire line of sensors to communicate via the Internet to any MQTT Broker service using a WiFi connection. It only requires network connection credentials, connection information about the MQTT host broker, and authentication information for the MQTT connection, if applicable.

Does MQTT use JSON?

So, The sensor uses the MQTT protocol with data in JSON format for all data sent over the sensor network. MQTT is a lightweight broker-based publish/subscribe messaging protocol designed for use on low bandwidth networks.

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