An Investigation into Transport Protocols and Data Transport ...

6.1. Survey of New-TCP Algorithms 112
6.1.1 HighSpeed TCP
The HighSpeed TCP for Large Congestion Windows was introduced in [Flo03]
as a modification of TCP’s congestion control mechanism to improve performance
of TCP connections with large congestion windows.
The strategy under HSTCP is to slowly improve the performance of the
TCP flow as a function of the current cwnd such that when the cwnd is
larger, the increase parameter is increased and reduction of cwnd upon loss
detection is decreased. Therefore, as the HSTCP flow deviates from the
expected achievable cwnd of standard TCP, both the reduction in the change
of throughput upon congestion is decreased, and the rate of increase at which
HSTCP probes for extra bandwidth increases.
HSTCP is based on the adaptation of the response function in Equation
5.7 such that the high throughputs are achievable under realistic loss
conditions. The HSTCP response function is defined using three parameters:
W switch , W High and P . They are used to establish a point of transition from
standard TCP behaviour to HighSpeed TCP behaviour.
As such, HighSpeed TCP’s response function is the same as that of the
Standard TCP when the current congestion window, cwnd, is less than or
equal to W Switch . HighSpeed TCP uses an alternative response function when
the current congestion window is greater than W Switch . W High and P are used
to specify the upper end of this response function, where the packet drop rate
P is that needed to achieve an average congestion window of W High under
the HighSpeed TCP regime. Also, 0 < H decr ≤ 0.5 is specified such that
when cwnd = W High and a congestion event occurs, cwnd will be decreased
by a factor of H decr such that cwnd ← cwnd − H decr × cwnd.
The HighSpeed TCP response function is therefore represented by new