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MQTT – IoT Messaging Protocol

Introduction

• MQTT is a standard messaging protocol for IoT( Internet Of Things).
• It follows the OASIS( Organization for the Advancement of Structured Information Standards ) standards.
• It is a very lightweight pub-sub(Publish and Subscribe) messaging transport for IoT devices.
• It provides bidirectional communication.
• Encryption of messages is very easy.
• The message delivery system is very reliable.
• MQTT is used in – Logistics, smart homes, manufacturing, smart cities, and many more.

Client

• An MQTT Client is a device such as a microcontroller.
• Every client has a separate ID or name.
• The client name must be unique.
• Every Client connects to an MQTT broker over a network.
• Publisher and subscriber both are MQTT clients.
• Every client connects to a broker to talk to another client.
• No two clients can communicate without the help of a broker.

Broker

• The broker is the one that manages the communication between publisher and subscriber.
• It can be called the heart of the MQTT.
• A single broker can handle up to millions of active connections.
• It also supports session maintenance and data recovery.
• Authentication and Authorization are also done at the broker’s end.
• Every message that is published passes through a broker.

Topic/Subscription

• The topic is a string that is used for sending messages.
• The broker uses the topic to distinguish between messages, like which message is for which topic.
• Every subscriber subscribes to a topic so as to receive the messages published on that topic.
• The topic is similar to an API path in that is it can be hierarchically separated by /.
• An example of one topic is car/front/ac/temperature.
• A wildcard + symbol is used to define that any value can be fitted there.
• An example of a wildcard – car/+/ac/temperature. here in + sign can have any values like front or back.
• For defining the multi-level hierarchy # symbol is used.
• An example of a multi-level hierarchy is – car/#, it will cover anything that starts with car/.
• Topics are also known as subscriptions.

Quality Of Service (QoS)

• Quality of service means how better the communication will be.
• There are 3 QoS defined in MQTT – 0, 1, 2
• 0 means the message will be delivered without any confirmation.
• 1 means the message will be delivered at least once with confirmation.
• 2 means the message will be delivered exactly once with 4 part hand-shake.
• QoS is the best way of communication with all the security but all the slowest.

References-

• https://mqtt.org/

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