[ntp:questions] Is this normal?
David.Russell at dowjones.com
Wed May 12 00:07:10 UTC 2010
>Wow. that is a looooong time. If it is really on the same local network,
>it should be much shorter than that. What is causing the delays-- bad
>router/switch, or is the local network a modem controlled network?
Turns out the actual time is about 1.7ms. For some reason the device I am looking at is reporting an extra couple of milliseconds. That might be an issue :)
Our "Local" network includes Gig connections between data centers about 20 miles apart. The round trip times for devices in the same building are on the order of 200us including time spent in the stratum 1 server. Sorry for the confusion, I didn't mean to imply that it was the local subnet.
>What poll interval are you using on the ntp?
Maxpoll of 5 (32 sec)
>Did you write the implimentation of ntp that you are asking whether it
It came with the box and I don't have access to the code. I can just use it and query its statistics.
>And what is this "device"?
A router; doing nothing except running NTP for the purposes of the testing.
From: questions-bounces+david.russell=dowjones.com at lists.ntp.org [mailto:questions-bounces+david.russell=dowjones.com at lists.ntp.org] On Behalf Of unruh
Sent: Tuesday, May 11, 2010 10:59 AM
To: questions at lists.ntp.org
Subject: Re: Is this normal?
On 2010-05-10, Russell, David <David.Russell at dowjones.com> wrote:
> Content-Type: text/plain; charset="us-ascii"
> I am trying to verify the correct implementation of NTP on a device that is configured to poll a GPS based dedicated time server on the local area network. The round trip times to this stratum 1 vary between 3.3 and 3.4ms.
Wow. that is a looooong time. If it is really on the same local network,
it should be much shorter than that. What is causing the delays-- bad
router/switch, or is the local network a modem controlled network?
> I have plotted the offset vs drift in the included jpg. The drift rate varies between -3 and -3.2 us/s and the offset is +/- 200us. Note that the first part of the graph is when NTP started.
> My questions are that given that a device has excellent network access to a good stratum 1 server should the drift rate vary this much? Can I infer anything from the data regarding proper computations in the code, timestamping of the packets or even the system clock?
Sorry, that can in no way be called excellent network access. It is very
poor network access. With the huge variablility of the offset, one would
expect variability of the rate. What poll interval are you using on the
Did you write the implimentation of ntp that you are asking whether it
works correctly? And what is this "device"?
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