[ntp:questions] Server offset included in served time?
Unruh
unruh-spam at physics.ubc.ca
Sat Sep 13 05:54:20 UTC 2008
Steve Kostecke <kostecke at ntp.org> writes:
>On 2008-09-12, David Woolley <david at ex.djwhome.demon.co.uk.invalid> wrote:
>> Howard Barina wrote:
>>>
>>> Does an NTP servers take into account it's estimated offset in serving time
>>> to others? If I am a server and think I am 1.5 milliseconds off from true
>>> time, will I include this in the timestamps of my ntp replies to others?
>>
>> An NTP client never thinks that its time is wrong. If it did, it would
>> be admitting that the NTP algorithms are wrong. Therefore the server
>> always serves its client's idea of the time.
>>
>> The "offset" should always be within the statistical error from the
>> current measurement history (if ntpd suspects otherwise, it steps,
>> and/or reduces the poll interval, to try to rapidly re-acquire that
>> condition). Immediately after startup, there will be little history, so
>> quite large offsets will still be consistent with that history.
>A single snapshot value is of limited value because values such as the
>offset are contantly changing. The long term stability of the clock is
>more important than a single snapshot.
Of course any ntp query is a single snapshot.
>peer.awk from the ./scripts directory in the Distribution is good tool
>for summarizing peerstats files.
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