Send a PINGREQ message to the gateway to reset the Keep Alive interval and ensure the gateway's liveliness.
async mqttsn.ping(): Promise<void>
The client must send a PINGREQ message using this method during each KeepAliveInterval period. If the client does not send any message to the gateway during this period, it will be considered lost and will disconnect.
The client also uses this message to supervise the liveliness of the gateway to which they are connected. If a client does not receive a PINGRESP from the gateway even after multiple retransmissions of the PINGREQ message, it should first try to connect to another gateway before trying to re-connect to this gateway.
See KeepAliveInterval for more information.
For more detailed requirements regarding Keep Alive intervals and reconnection, refer to the MQTTSN specification.