[ntp:questions] Server offset included in served time?

Richard B. Gilbert rgilbert88 at comcast.net
Fri Sep 12 21:29:01 UTC 2008


David Woolley wrote:
> Howard Barina wrote:
>>
>> Does an NTP servers take into account it's estimated offset in serving 
>> time
> 
> There seem to have been a lot of questions asked in the last month that 
> are based on the false assumption that "offset" measures the difference 
> between the local clock and true time.  Has someone published a 
> misleading document, somewhere?
> 
>> 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.
> 
> There are people who who argue that the NTP algorithms are fundamentally 
> flawed and don't give the statistically best time in real world 
> situations.  I think they have some credibility, but NTP's inventor, 
> does not.
> 

I hope you did not mean to say that David Mills has no credibility but
what you wrote sure reads that way!!




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