About MQTT Message Queuing Telemetry Transport protocol

MQTT is an open-source protocol Message Queuing Telemetry Transport designed by IBM, Originally this for restricted resources for low bandwidth and high-latency and designed for unreliable networks.

MQTT consists of one broker server and two types of consumers referred to as Publisher (Publish client) and Subscriber (Subscribe client). It sends messages in bytes using setPayloads() and getPayloads() methods. Broker server acts as associate degree intercessor for messages sent between Publish consumer and Subscribe consumer when both having the same topic.

MQTT supports three Levels of Quality of Services (QoS) shows packet exchange measure according to three different QoS levels:

(1) QoS Level zero sends a message just once following the message distribution flow, and doesn't check whether or not the message arrived in its destination,

(2) QoS Level one sends the message at least once, and checks the delivery status of the message by using the status check message, and

(3) QoS Level two passes the message through precisely once utilizing the 4-way shake. MQTT transmits messages through the Broker server to create an association between Publish and Subscribe Consumers. Every consumer transmits and receives the message via Broker server in line with totally different Topics.

MQTT Architecture:-

(i) The sensor is a device, connects to server/broker over TCP.

(ii) This is message-oriented. Each message is discrete garbage of information which is obscure to the broker.

(iii) where the message has published that address is called topic. Clients may subscribe or unsubscribe to multiple topics based on its needs and messages in MQTT are published on topics.

MQTT Features:

1.) Faster response times

2.) Throughput

3.) Lower battery use

4.) Lower bandwidth usage in cases where the connectivity is Intermittent. An enterprise application needs to interact with one or more phone applications or tablet applications need to send data reliably without requiring code we can retry logic.

MQTT Callback Inbuilt Methods:

1. connectionLost (Throwable throwable): whenever connection lost, this method throws an error
2. messageArrived (String topic, MqttMessage): whenever message arrived catch by this method with the topic and message in bytes we can get it by getPayloads().
3. deliveryComplete (): after received message, this sends delivery complete successfully. Only if the QoS value is 2.

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