An Investigation into Transport Protocols and Data Transport ...

4.5. TCP Variants 62
This enables spurious packet delays to be absorbed into the time-out to
facilitate a good estimation of the RT O.
RTT measurements resulting from retransmitted segments are not included
[KP87] to avoid false positive RTO calculations.
Standard TCP implementations (such as TCP Tahoe - See Section 4.5.1)
only time-stamp a single packet per RTT to reduce the CPU load, and thus
only a single RTT measurement can be gathered per RTT which will limit
the robustness of the above algorithm. More accurate RTT samples can be
gathered by using using the TCP Timestamp option (See Section 5.2.1) to
facilitate a more robust RTO calculation.
4.5 TCP Variants
Whilst the basic design of TCP has changed little since its incarnation, various
adaptations to the basic flow recovery mechanism have enabled TCP to
adapt as the Internet has evolved.
The original specification in [Pos81b] implements only the sliding window
and flow control of TCP. Also a very basic RTO estimator was used.
This section describes the major implementations and alterations of the TCP
algorithm to the current state.
4.5.1 TCP Tahoe
Designed in 1988, TCP Tahoe by Van Jacobson [Jac88] extends the original
TCP by Postel [Pos81b] with five new mechanisms that have become de-facto
TCP mechanism: slow start, ack clocking, window dynamic adjustment,
fast retransmit and round-trip time variance estimation. All of these new