[ntp:questions] Lep seconds

Joseph Gwinn joegwinn at comcast.net
Tue Jan 15 05:13:12 UTC 2008


In article <flli7r$5iu$1 at scrotar.nss.udel.edu>,
 "David L. Mills" <mills at udel.edu> wrote:

> Joseph,
> Conversely, if a client syncrhonizes to a server strictly running TAI 
> and never signals leaps, NTP will deliver TAI. NIST, USNO and I have 
> discussed this serveral times and concluded the lessor of two evils is 
> to continue with NTP on UTC.

Yep.  True enough.  But GPS emits TAI (plus an offset), so one can claim 
that configuring the NTP timeserver to emit GPS System Time (not UTC) is 
to generate what is essentially TAI.  This is widely done in the 
big-radar world.


> Dave
> Joseph Gwinn wrote:
> > In article <T1199401837 at ex.djwhome.demon.co.uk.invalid>,
> >  david at ex.djwhome.demon.co.uk.invalid (David Woolley) wrote:
> > 
> > 
> >>In article <298286.52982.qm at web55415.mail.re4.yahoo.com>,
> >>marknmbox-88 at yahoo.com wrote:
> >>
> >>
> >>>compliant.  Is there a similar mod for NTP.  I am
> >>>hoping that there is a mod that will cause NTP to
> >>>supply theoretical UTC (even if it is not ascci).
> >>
> >>Both POSIX and NTP use UTC.  Your problem is that you are not using
> >>using UTC, but, rather, using TAI.
> > 
> > 
> > Actually, POSIX does *not* use UTC in the normal sense of the word, as 
> > no leap seconds are applied.
> > 
> > The fundamental POSIX timescale counts what amount to SI seconds from 
> > the POSIX Epoch, 0h 0m 0s UTC 1 January 1970.  Every day contains 
> > exactly 86,400 seconds.
> > 
> > That said, if one drives a POSIX box via NTP from a GPS timeserver set 
> > to emit UTC (versus GPS System Time), time on the POSIX box will be 
> > pretty close to UTC.
> > 
> > Joe Gwinn

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