[ntp:questions] GPS-UTC Leap Corrections

cjc yheffen at gmail.com
Tue May 5 16:31:44 UTC 2009


On May 5, 1:11 am, hal-use... at ip-64-139-1-69.sjc.megapath.net (Hal
Murray) wrote:
> In article <485551ee-a847-45b6-a040-624dc80ce... at s38g2000prg.googlegroups.com>,
>
>
>
>  cjc <yhef... at gmail.com> writes:
> >We have some time servers with GPS clocks. One of their uses is in
> >operations centers where satellites are being flown. The satellites
> >use
> >GPS (as opposed to UTC) internally, so we want the computers on the
> >ground also to use GPS (rather than UTC). The time servers speak NTP
> >and hand out GPS time as if it were UTC. The ground computers think
> >they are on UTC, but it's really GPS.
>
> >But we'd like some of the computers to really be on UTC. I really
> >haven't
> >been able to think of a good way to have computers use the GPS time
> >given out by the time servers as a source, but then to actually offset
> >their own time by the GPS-UTC difference. Some quick Googling hasn't
> >turned anything up. Anyone have some suggestions on how to manage
> >something like this? Or are we just going to have to live 15 seconds
> >ahead of the rest of the world?
>
> The GSS satellites also tell you the offset from GPS time to UTC.
> Most of the (low cost) GPS receivers tell you UTC rather than GPS.
>
> Things get interesting around leap seconds.  Other than that,
> UTC via GPS works pretty well.
>
> What type of GPS clock/receivers are you using?
>
> --
> These are my opinions, not necessarily my employer's.  I hate spam.

I'm not sure I was clear. The time servers, a mix of Tymserver 2000
and 2100s,
are capable of converting GPS to UTC, but for policy reasons, they
have been
configured to hand out GPS time, uncorrected to UTC. This is what we
want.
We most definitely want some of the systems that sync to these clocks
on
GPS time.

But for some systems, it'd be nice to have them on real UTC. They'd be
using
an NTP server giving out GPS time, but we want them to have UTC on the
system
clock. It doesn't look like there is a way to do this short of hacking
NTP source
code, which is not really feasible for this case. We'll either live
with the offset or
sync them to a different time server (another Tymserver 2100) that is
handing out
real UTC via NTP or switch that other time server to GPS so our entire
operation
is an island of GPS time in the Internet.




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