[ntp:questions] questions Digest, Vol 33, Issue 15

Elio elio.gi at gmail.com
Wed Jul 11 08:13:31 UTC 2007


From: "Jason Rabel" <jason at extremeoverclocking.com> wrote:


>> Is there someone that have tested the delay of variously servers in the
>> world? Is there an official document of the performances of the
>>timeservers ?

>Performance of what exactly? You have the performance of the time server
>itself, which is how accurate that machine keeps time. Then you have the
>performance of the network, will vary greatly just from the usual flow of
>Internet traffic. The further the server physically is you are trying to
>contact, the greater and more erratic the delay will be (over the
Internet).
>Thus it is good practice to contact servers located near you. A traceroute
>will reveal the path your packets take across the Internet, showing how
many
>hops from router to router, how many backbone jumps, and any points of
>congestion... The fewer the better. But if the server you are contacting is
>not that accurate to begin with then it's all moot.

I'm interested to a simply measure.
I have to measure the delay (from linux NTP sw, with the command "ntpq -p")
of several timeserver in the world: i know that the nearest timeserver is
the best (in therms of delay), but the sense of what I have to to is not to
have the best timeserver, but the measure itself, and to measure the worst
case.
In this way, with collected data, i can produce a statistic graph with the
probability of different values of delay.

My first question was:
is there a document with the performance (in general) or someone have
measured delay before and have collected data?
If exist this document I think that in the list of the different
performances, as you have explained before, it could be present also the
delay, that is the data that I need.

>> For me it would be enough to know the difference between a timeserver in
>> Italy, in USA, in Japan (for example) contatting them from Italy.

>Again, it is going to vary based on general Internet congestion, which
>backbone(s) you are on, etc. What might work great for you could be
horrible

We know that the internet congestion is a variable information, not a
constant; the delay is a function of the internet congestion, so it is a
statistic function.
So only with a set of measure I can generate this function.

>> In this moment i'm doing my tests (from Italy) with a Stratum 1 NTP
server
>> (GPS) in Francofort, but this server is located in my Company LAN.
>> Is there a real difference between Internet and a protected LAN or the
>> result could be similar?

>If your stratum 1 servers are located on your LAN, then you can expect
>usually around 10 ms or so of accuracy to that server. Over the Internet
>(depending on your connection and servers locations) it could still be as
>low as 10 ms (unlikely) but more reasonable would be around 50 ms, or even
>as high as over 100 ms.
Ok.

Thanks for the quickly response, but i hope that is clearer than before what
I need, and the sense of my questions.

I'll wait a response from anybody who knows what I need, or have a link for
information.
Best Regards,
Elio.



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