This article will delve into how to implement the Request / Response pattern under the asynchronous message delivery framework of MQTT, with the new features of MQTT 5.0.

Will Message is an important feature in MQTT, which solves the problem that only the server can know whether clients are offline. It allows us to gracefully take follow-up actions for unexpectedly offline clients.

Shared subscription is a new feature introduced by MQTT 5.0 protocol, which is equivalent to the load balancing function of subscribers.

In this article, we will introduce the session mechanism of MQTT protocol, as well as Clean Start and Session Expiry Interval, two connection parameters used to manage the session lifecycle.

In this article, we will focus on the Payload Format Indicator and Content Type properties of MQTT 5.0, exploring how they make the parsing of messages more transparent and efficient.

MQTT 5.0 is the latest version of the protocol, offering many improvements and new features over its predecessors.

The Message Expiry Interval is a new feature introduced in MQTT 5.0, which allows the publisher to set an expiry interval for time-sensitive messages.

To achieve the Enhanced Authentication, MQTT introduced the AUTH packet to implement any number of authentication data exchanges, to support various types of authentication mechanisms, such as SCRAM, Kerberos authentication, and so on.

In MQTT, both the client and the server can send a DISCONNECT packet to the other party before disconnecting the network connection, indicating the reason for the connection closure.

MQTT has a type of packet used to simulate heartbeats between the client and server to maintain the connection. They are PINGREQ and PINGRESP packets, which we often call heartbeat packets.

In MQTT, the SUBSCRIBE packet is used to initiate a subscription request, while the SUBACK packet is used to return the subscription result. The UNSUBSCRIBE and UNSUBACK packets are used when unsubscribing.

This blog will introduces the PUBLISH packet used to deliver application messages in MQTT, and its response packets.