TCP/IP Guide

TCP Adaptive Retransmission and Retransmission Timer Calculations

Whenever a TCP segment is transmitted, a copy of it is also placed on the retransmission queue. When the segment is placed on the queue, a retransmission timer is started for the segment, which starts from a particular value and counts down to zero. This timer controls how long a segment can remain unacknowledged before the sender gives up, concludes that the segment is lost, and sends it again.

The length of time we use for retransmission timer is thus very important. If it is set too low, we might start retransmitting a segment that was actually received, because we didn't wait long enough for the acknowledgment of that segment to arrive. Conversely, if we set the timer too long, ...