TCP Retransmit (RXT) Flag
Ericsson Research
Ericsson Research
This document proposes a solution to TCP’s retransmission ambiguity problem. It is based on using a single bit, named the Retransmit (RXT) flag, taken from the Reserved field of the TCP header. The TCP sender sets the RXT flag in segments containing retransmitted data. In response to such a segment, the TCP receiver sends an immediate pure ACK with the RXT flag set. By inspecting the RXT flag of the ACKs that arrive after a retransmit the TCP sender can then resolve the retransmission ambiguity. This protocol feature provides a basis for future TCP enhancements such as schemes to detect and respond to spurious timeouts and packet re-orderings.