[ntp:questions] wedge scattergram questions

Werner Siedenburg pcween at pcween.de
Mon Jun 4 10:02:06 UTC 2007

Hello! In Mr. Mills' book I saw some interesting "wedge scattergrams".
I have some questions about them:

1. What is the exact use of these scattergrams?
Mr. Mills writes that "the shape of the wedge reveals intimate details about
the network path characteristics". How? The only thing I notice: The further
left the
apex of the scattergram is, the better (because of lower delay). What else
can you see
in them?

2. I understand that "under low traffic conditions, the points are
concentrated about the apex of the wedge and begin to extend rightward along
the limb lines as
network traffic increases".

But why is the most accurate offset measured at the lowest delay?
The only reason I can think of is that the bigger the delay, the bigger the
difference between both clocks. But I doubt this plays a role at "normal"

3. How can I create my own wedge scattergrams? I configured my ntpd to
generate rawstats. Do you just calculate the offset 1/2*[(T2-T1)+(T3-T4)]
and delay
(T4-T1)-(T3-T2) for every line in the rawstats-file? and afterwards plot the
whole thing where delay
is the x-axis and offset the y-axis?
Is there a script (e.g. MATLAB .m-file) that does this automatically?
I suppose, a wedge scattergram only show delay/offset-combinations from ONE
specific server.

Thanks in advance,

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