Step 1-3-1: the second node transmits a configuration message 8 (an optional solution of the first message) to the first node. The function of this message is to provide the first node with a configuration for the retransmission data packet. The message includes at least one of the following information:
Step 1-3-2: the first node starts to cache the data received from the user. This step may be that the first node starts to cache the data packet based on the configuration message 8 of step 1-3-1. Further, this embodiment may also include: the first node transmits a configuration message 9 (an optional solution of the second message) to the second node, the function of the message is to indicate the data packet cached at the first node, and the message includes at least one of the following information: