1) sliding window mechanism, establish a perimeter and received, allowing the sender to know how much has been sent (confirmed), the number of bytes not yet confirmed the number of bytes sent yet; let the recipient know (has confirmed receipt of the number of bytes)
2) retransmission timeout, send a message for each TCP segment, the timer is set once, the retransmission time, but not received acknowledgment, retransmits the segment, the round-trip time is the weighted average time
3) ARQ, sequence for transmission errors to be retransmitted, if the intermediate sequential lost packets, the transmission time of the receiving window acknowledgment number, will send ack number lost before selecting retransmission packet number, select OK