UDT Tests
Description
Also the performance of the Itanium hosts using the
UDT special protocol will be investigated
here. One of the available control variables is the maximum value of theso
called flow window (FC) size. It should be equal to
FC = Bandwidth × (RTT + 0.01) / MTU
Please note that a larger value (but not too large) does not hurt, but a smaller
window will limit the speed like the TCP window does. To investigate
this behaviour, corresponding tests as described in the
"TCP Tests" subsection has been
executed: the tests were performed as a function of the flow window size and of
the # parallel flows. Also here the sum of the flow window size, taken over
the # parallel flows, was kept constant. However, in contradiction with the
TCP tests, the parallel flows were generated here by spawning separate
processes: no pthread library has been implemented here.
Results
Below the results of UDT tests have been presented, where the sum bandwidth
values (taken over the # parallel flows) have been plotted as a function od
the sum UDT flow window (also taken over the # parallel flows) and of the
# parallel flows. The test duration was 60 s, while each 4 s a
bandwidth interval report has been printed. A MTU value of 9000 Bytes has
been used. As with the TCP tests the bandwidth
values have been represented by means of the medians. See also the
description of the TCP medians
calculation.
In the following plots results are prented that were obtained at
December 13, 2003. That is before the period when there were some
hardware problems with the Chicago Itanium. Further below analogous results are
presented when these problems had been fixed again. In
the sum UDT bandwidth has been displayed as a function of the sum UDT flow
window and the # parallel flows for the direction
StarLight -> Amsterdam Science Park and in
for the reverse direction. In these tests the under boundary for an UDT flow
window for a single parallel flow was 50. Tests with smaller values had
been skipped. The reason was that older versions of UDT showed instabilities
with very small flow window window sizes.
| . |
|
Sum UDT bandwidth values, taken over the
# parallel flows, as a function of the sum UDT flow window size, also
taken over the # parallel flows, and of the # parallel flows for
the test direction StarLight -> Amsterdam Science
Park. The test date was December 13, 2003. |
| . |
|
Sum UDT bandwidth values, taken over the
# parallel flows, as a function of the sum UDT flow window size, also
taken over the # parallel flows, and of the # parallel flows for
the test direction Amsterdam Science Park ->
StarLight. The test date was
December 13, 2003. |