当AT+CFM=1(QOS 1),设备会在数据包未收到确认之前重新传输

When AT+CFM=1 (QOS 1), the device will retransmit the data packet before receiving the confirmation, which means that the Sender sends a message to the Receiver. If the sending fails, it will continue to retry until the Receiver receives the message, but Due to retransmission, Receiver may receive duplicate messages;

When at-CFM-1 (QOS 1), the device re-transmits the packet before it receives an acknowledgement, which means that Sender sends a message to Receiver and, if the send fails, continues to try again until receiver receives the message, but for re-transmission reasons, receiver may receive duplicate messages;

When at + CFM = 1 (QoS 1), the device will retransmit the packet before receiving the acknowledgement. In other words, the sender sends a message to the receiver. If the sending fails, it will continue to try again until the receiver receives the message. However, due to retransmission, the receiver may receive a duplicate message;