RTO calculation (1)


TCP monitors the performance of each connection and computes appropriate RTO.
Adapt to various communication media (from analog modem to high-speed LAN..)
Adapt to network condition. (congestion..)

Old algorithm for RTO
TCP uses weighted average of measured RTTs as estimated RTT.
SRTT = α × SRTT + (1 - α) * measured RTT
        0 < α < 1  (usually set to 0.8 or 0.9)
TCP computes timeout from SRTT
RTO = β × SRTT
       β > 1 (usually set to 2)