An Investigation into Transport Protocols and Data Transport ...

9.3. Internet Transfers 231
Stanford LBL Dublin Rutherford
Standard TCP 220 28 145 168
HSTCP 246 75 151 208
ScalableTCP 249 173 149 172
H-TCP 248 206 143 234
FAST 249 221 65 238
BicTCP 247 135 152 240
Table 9.1: Number of individual New-TCP measurements to each site.
run over the period of 2 months between October and December of 2004 and
were ran over a 24 hour period, 7 days a week.
All traffic was either routed through Dante’s GEANT network if the destination
was European, or through the DataTAG network via its production
link over to the U.S. whereby it was locally routed onto Internet2’s Abilene
network. All network paths are shown in Appendix D.
There are problems associated with the way that Linux accounts for the
number of packets in flight whereby there is no artificial inflation of cwnd
during loss recovery. The result of this is that upon a TCP time-out (when
cwnd is set to 1 segment) it will limit the number of packets that can be
retransmitted each RTT. Because there is no artificial inflation of cwnd,
loss recovery occurs at a rate of 1 packet per RTT after a TCP time-out.
Therefore the loss recovery time is proportional to the number of packets
lost. For large cwnd values where many packets can be lost, this recovery
time can be very long for long distance networks. This is documented in
[HLW + 04].
This effect was especially noticeable during the initial slow-start period of
tests and caused many occurrences whereby the TCP flow spent nearly all of
the test time in loss recovery. As such, the initial slow start was disabled such