[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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