[ntp:questions] How to keep Linux server in Chicago and Mumbai in sync to within 5 microseconds

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Wed Jan 12 21:07:17 UTC 2011


In article <20110112162440.AB9F81CC0B at ptavv.es.net>,
 "Kevin Oberman" <oberman at es.net> writes:

>GPS satellites broadcast time in TAI, not UTC. Currently the offset
>between TAI and UTC is 15 seconds.

Actually, they broadcast GPS time which is offset from TAI by
the number of leap seconds that had already happened when they
started using GPS time.

They also include the offset from GPS time to UTC so you can get
UTC from GPS satellites.  (They also include leap second warnings
so you can do the right thing when leap seconds happen.)


From
  http://tycho.usno.navy.mil/leapsec.html
As of 1 January 2006,
        TAI is ahead of UTC   by 33 seconds.
        TAI is ahead of GPS   by 19 seconds.
        GPS is ahead of UTC   by 14 seconds.

We've had one more leap second since 2006, so that would be 34 and 15.

http://maia.usno.navy.mil/ser7/tai-utc.dat
 1999 JAN  1 =JD 2451179.5  TAI-UTC=  32.0       S + (MJD - 41317.) X 0.0      S
 2006 JAN  1 =JD 2453736.5  TAI-UTC=  33.0       S + (MJD - 41317.) X 0.0      S
 2009 JAN  1 =JD 2454832.5  TAI-UTC=  34.0       S + (MJD - 41317.) X 0.0      S

-- 
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