NetApp, Inc. NetApp, Inc. The Spurious Retransmission Detection (SRD) algorithm allows a TCP sender to always detect if it has entered loss recovery unnecessarily. It requires that both the TCP Echo option defined in [I-D.zimmermann-tcpm-echo-option], and the SACK option [RFC2018] be enabled for a connection. The SRD algorithm makes use of the fact that the TCP Echo option, used in conjunction with the SACK feedback, can be used to completely eliminate the retransmission ambiguity in TCP. Based on the reflected data contained in the first acceptable ACK that arrives during loss recovery, it decides whether loss recovery was entered unnecessarily. The SRD mechanism further enables improvements in loss recovery. This includes a TCP enhancement to detect and quickly resend lost retransmissions.