In Microsoft they use similar test when they calculate link speed for
applying Group Policy.
Here is what they do. I'm sorry I couldn't find a link on Google, so I'm
pasting the text
<quote>
Topic: How to Configure Refresh Rates for Group Policy
Components
Group Policy can detect a slow network links by using an algorithm. The
algorithm that Group Policy uses to determine whether a link should be
considered slow is as follows:
1. The client computer that is attempting to process Group Policy sends a
zero
byte file to the authenticating domain controller, or server, which then
returns the file to the client computer. The client computer measures the
time it takes for the file to complete the round trip, and if it is less
than ten
milliseconds, the client computer assumes a fast link is present and sets
the
fast link flag.
2. If the round trip time in step 1 is more than 10 milliseconds, the
client
computer saves the round trip time. Name this value time_1.
3. The client computer sends a compressed file that is two kilobytes (KB)
in
size to the server, which then returns the file to the client. The client
computer again measures the time it takes the file to complete the round
trip. Name this value time_2.
Note
The file that is sent to the server in step 3 is actually a JPEG file.
JPEG files are compressed by definition. A compressed file is used because
of the fact that data that is sent through a modem is frequently compressed
and compressing the file would make the link appear faster than it really
is.
4. The client computer repeats step 3 two more times. Name these values
time_3 and time_4.
5. The client computer subtracts the value for time_1 from time_2, time_3,
and
finally, from time_4. This subtraction is done to remove the overhead
caused by session setup. Name these values delta_1, delta_2, and delta_3.
Algorithm used by
Group Policy to detect
slow network links
6. The average of the values for delta_1, delta_2, and delta_3 is
calculated.
Name this value avg.
7. The connection speed is calculated as (the units are shown for clarity):
(Connection Speed kilobits/second) = 2*(2 KB)*(8 bits/byte)*(1,000
milliseconds/second)/(avg milliseconds)
Because 2 KB of data move through each modem, Ethernet card, or other
device in the link, once in each direction, there is a total of 4 KB, or 2
times
the 2 KB, processed. This is why a leading factor of 2 is on the right side
of
the equation.
Note
The connection speed calculated is the average of the upload and
download speeds. In most situations, this average is the same as the
download
speed itself. However, in some situations, the upload and download speeds
are
different enough that you should take the speed difference into account. An
example of different speeds is Asymmetric Digital Subscriber Line (ADSL).
Using ADSL, you might have upload speeds of 128 kilobits per second (Kbps)
and download speeds of 768 Kbps.
To specify the threshold value for slow link detection for computer
configuration Group Policy settings, you use the Computer
Configuration\Administrative Templates\System\Group Policy\Group Policy
slow link detection setting. To set this value for user configuration Group
Policy settings, you use the User Configuration\Administrative
Templates\System\Group Policy\ Group Policy slow link detection setting. The
allowed value range is 0 to 4,294,967,200 Kbps. A value of zero indicates
that
all links should be considered fast
</quote>
Dusko Savatovic
