[ntp:questions] offset of two acts servers

rtxo gnu at wraith.sf.ca.us
Fri Feb 3 00:34:42 UTC 2006


Hi Folks--

I've setup a host with gps and wwv audio and the wwv audio gets down
to within 100 microseconds of the gps routinely. As an experiment, I
added two external ntp servers to this configuration. Both of these acts
external servers are "close," being within 20 millisecond ping times.

Oddly, one of the acts hosts is consistently 3-5 milliseconds behind,
and the other 3-5 milliseconds ahead:

gnu at smidge.wraith.sf.ca.us[244] ntpq -p -n
      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.20.0    .GPS.            0 l   31   64  377    0.000   -0.001   0.008
+127.127.36.0    .WV20.           0 l   34   64  376    0.000   -0.082   0.027
x69.25.96.13     .ACTS.           1 u  804 1024  377   17.315   -4.407   0.358
x207.126.98.204  .ACTS.           1 u  572 1024  377   14.020    3.622   0.184

Quite curious. The jitter on the network connection to these hosts typically
is less than a millisecond, although I've seen some Big Combers roll in, the
internet being what it is.

I wonder whats going on with these hosts. The refclock_acts driver code has
a comment that claims the acts adjusts for the round trip delay.

../Steven




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