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This article will explain in detail what the QoS provided by MQTT refers to. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

QoS is identified in CONNECT, PUBLISH, and SUBSCRIBE, so what is the QoS provided by MQTT?

QoS rating in MQTT

As a protocol originally used to transmit data in an environment where the network bandwidth is narrow and the signal is unstable, MQTT designed a set of mechanisms to ensure the stable transmission of messages, including message reply, storage and retransmission. Under this mechanism, three different levels of QoS are provided:

QoS0,At most once, at most once; QoS1,At least once, at least once; QoS2,Exactly once, make sure only once.

What do you mean, QoS is an agreement between the sender (Sender) and the recipient (Receiver) of the message:

On behalf of QoS0, Receiver can receive at most one message sent by Sender, that is, Sender tries its best to send a message to Receiver, but if it fails, forget it; QoS1 representative, Receiver can receive at least one message sent by Sender, that is to say, Sender sends a message to Receiver. If it fails, it will continue to retry until Receiver receives the message, but because of retransmission, Receiver may receive duplicate messages. QoS2 represents a message sent by Sender. Receiver ensures that it can be received and only once, that is, Sender tries its best to send a message to Receiver. If it fails, it will continue to retry until Receiver receives the message, while ensuring that Receiver will not receive duplicate messages because of message retransmission. So much for sharing what the QoS provided by MQTT means. I hope the above content can be of some help to you and learn more knowledge. If you think the article is good, you can share it for more people to see.

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