如果在报文段中的数据未确认之前定时器超时，TCP就认为该报文段已经丢失或出现损坏，从而重传这一报文段。

If the timer expires before data in the segment is acknowledged, TCP assumes that the segment has lost or being damaged, and a retransmission is sent.

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采用“停一等”协议、超时重传、错误重传等措施，提高了在应用编程的灵活性、可靠性和稳健性。

Some measures such as "stop-and-wait" protocol, and overtime and error retransmissions are taken. As a result, the flexibility, reliability and robustness of IAP are enhanced.

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