Hi Paul!
On Fri, May 24, 2013 at 9:28 PM, Paul G <[email protected]> wrote:
> I have four GPS receivers into four different computers. I've assumed that I
> should be able to get small offsets between them but to do so I need
> to set time1. If that's the correct approach how do I pick the "right"
> system to be the benchmark. So far I've just been assuming that
> the purpose built M. Tharp server should have the lowest latency but I'm not
> sure -- in any case, at present, I can't adjust it.
>
> Each machine in the truncated table below (except 210) has a time1
> value derived in an ad hoc fashion.
>
> l r refid st delay offset jitter
> ==================================================
> 1 o22.0 .PPS. 0 0.000 -0.001 0.001
> 2 +244 .PPS. 1 0.068 0.000 0.006
> 2 *210 .GPS. 1 0.514 -0.008 0.136
> 2 +192 .PPS. 1 0.455 0.008 0.032
>
>
> I feel as if this topic should be clearly explained somewhere but I've been
> unable to find it.
My recent experience with 4 stratum 1 servers (one of them an
appliance from Meinberg - great box BTW) is that you will never have
every server in sync with each other due to the latency and delays of
the network (even LAN, same segment as is in this case). I don't depend
on external NTP servers.
My Meinberg NTP server:
$ ntpq -p 10.0.2.1
remote refid st t when poll reach delay offset jitter
==============================================================================
LOCAL(0) .LOCL. 10 l 8 16 377 0.000 0.000 0.001
+GENERIC(0) .GPS. 0 l 13 16 377 0.000 0.000 0.001
oPPS(0) .PPS. 0 l 7 16 377 0.000 -0.001 0.001
-10.0.2.2 .PPS. 1 u 37 64 377 0.199 0.007 0.031
-10.0.2.3 .PPS. 1 u 6 64 377 0.171 -0.004 0.008
+10.0.2.4 .PPS. 1 u 51 64 377 0.157 -0.002 0.009
My Garmin 18 LVC on the roof:
$ ntpq -p 10.0.2.2
remote refid st t when poll reach delay offset jitter
==============================================================================
oGPS_NMEA(0) .PPS. 0 l 5 16 377 0.000 0.000 0.004
+10.0.2.1 .PPS. 1 u 2 16 377 0.157 0.005 0.013
+10.0.2.3 .PPS. 1 u 1 16 377 0.144 -0.001 0.004
+10.0.2.4 .PPS. 1 u 16 16 377 0.140 -0.002 0.004
My Sure GPS board on the window sill:
$ ntpq -p 10.0.2.3
remote refid st t when poll reach delay offset jitter
==============================================================================
oGPS_NMEA(0) .PPS. 0 l 13 16 377 0.000 0.001 0.004
+10.0.2.1 .PPS. 1 u 10 16 377 0.166 0.003 0.008
+10.0.2.2 .PPS. 1 u 5 16 377 0.138 0.004 0.004
+10.0.2.4 .PPS. 1 u 8 16 377 0.140 0.001 0.004
My 2nd Sure GPS board on the same window sill:
$ ntpq -p 10.0.2.4
remote refid st t when poll reach delay offset jitter
==============================================================================
oGPS_NMEA(0) .PPS. 0 l 7 16 377 0.000 0.000 0.004
+10.0.2.1 .PPS. 1 u 4 16 377 0.201 0.000 0.011
+10.0.2.2 .PPS. 1 u 3 16 377 0.136 0.002 0.004
+10.0.2.3 .PPS. 1 u 2 16 377 0.140 0.001 0.004
For me < 10 us offsets is OK and acceptable between stratum 1 machines.
I believe this is what is expected.
Regards,
Miguel
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