WillMessage (optional) A client can specify its last will message in the form of a MQTT message and topic.

Username and Password (optional) Client can send a username and password to improve communication security.The client needs to send regular PING messages, within the KeepAlive period, to the broker to maintain the connection alive.

KeepAlive This interval, express in seconds, defines the maximum period of time that broker and client can remain in contact without sending a message.Instead, if the flag is set to true, it means discarding all existing sessions and messages for that client (mandatory if the ClientId is empty). CleanSession If the CleanSession is set to false and the broker has information stored for that client, broker uses the existing session and delivers previously queued messages to the client.An empty ClientID means an “anonymous” connection: therefore, the broker does not memorize any information about the client. ClientID ClientID is an unique ID used by brokers to identify the client and store information (called session) about it.With this message, a client presents itself to a broker providing the following main information: Before starting the message exchange over topics, the client needs to initiate the communication by sending the CONNECT message to the broker.

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