New Reno TCP New Reno, defined by (which obsolesces previous definitions in and ), improves retransmission during the fast-recovery phase of TCP Reno. During fast recovery, to keep the transmit window full, for every duplicate ACK that is returned, a new unsent packet from the end of the congestion window is sent. The difference from Reno is that New Reno does not halve ssthresh immediately which may reduce window too much if multiple packet losses occur. It doesn't exit fast-recovery and reset ssthresh until acknowledges all of the data. After retransmission, newly acknowledged data have two cases: Full acknowledgments: The ACK acknowledges all the intermediate segments sent, the ssthresh can be not changed, cwnd can be set to ssthresh Partial acknowledgments: The ACK does not acknowledge all data. It means another loss may occur, retransmit the first unacknowledged segment if permitted It uses a variable called "recover" to record how much data needs to be recovered. After a retransmit timeout, it records the highest sequence number transmitted in the recover variable and exits the fast recovery procedure. If this sequence number is acknowledged, TCP returns to the congestion avoidance state. A problem occurs with New Reno when there are no packet losses but instead, packets are reordered by more than 3 packet sequence numbers. In this case, New Reno mistakenly enters fast recovery. When the reordered packet is delivered, duplicate and needless retransmissions are immediately sent. New Reno performs as well as SACK at low packet error rates, and substantially outperforms Reno at high error rates. TCP Vegas Until the mid-1990s, all of TCP's set timeouts and measured round-trip delays were based upon only the last transmitted packet in the transmit buffer. University of Arizona researchers Larry Peterson and Lawrence Brakmo introduced TCP Vegas in which timeouts were set and round-trip delays were measured for every packet in the transmit buffer. In addition, TCP Vegas uses additive increases in the congestion window. In a comparison study of various TCP s, TCP Vegas appeared to be the smoothest followed by TCP CUBIC. TCP Vegas was not widely deployed outside Peterson's laboratory but was selected as the default congestion control method for DD-WRT firmware v24 SP2. TCP Hybla TCP Hybla aims to eliminate penalties to TCP connections that incorporate a high-latency terrestrial or satellite radio links. Hybla improvements are based on analytical evaluation of the congestion window dynamics. TCP BIC Binary Increase