Our retransmission strategy is motivated by such evidence as the Internet trace reports by Lin and Kung [12], which show that 85% of TCP timeouts are due to non-trigger. Non-trigger is when a packet is retransmitted by the sender without previous attempts, i.e., TCP's fast retransmission mechanism never happened. For this reason we need to quickly recover losses without necessarily waiting for three duplicate acknowledgments from the receiver.
Given that TCP-Santa Cruz has a much tighter estimate of the RTT time per packet and that the TCP-SC sender receives precise information on each packet correctly received, TCP-Santa Cruz is able to determine when a packet has been dropped and can avoid waiting for TCP's Fast Retransmit algorithm and quickly retransmit and recover a lost packet once any ACK for a subsequently transmitted packet is properly received and a time constraint is met.
Suppose packet i, initially transmitted at time ti, is lost and is marked as a hole in the ACK window. Packet i can be retransmitted as soon as an acknowledgment arrives for any packet transmitted at time tx, such that tx > ti, and tcurrent - ti > RTTe, where tcurrent is the current time and RTTe is the estimated round-trip time of the connection. Any packet which is marked as unreceived in the ACK window can be a candidate for early retransmission.