[ntp:questions] Which public servers for adjustment?

Helmut Wollmersdorfer helmut at wollmersdorfer.at
Mon Dec 20 19:51:56 UTC 2004


Each of my two servers has 3 radio clock receivers (DCF77, HBG75, MSF60).

Calibrating against two stratum 1 servers gave around 40ms delay. Other 
radioclockd users here reported values around 20ms.

Here is a typical result of ntpq -d one hour after restart and more 
public servers than necessary:

via2:~# ntpq -p
      remote      ... st t when poll reach   delay   offset  jitter
=================...==============================================
-ntp1.esat.net   ...  1 u   96  128  377   60.335  -15.919   5.050
-ntp1.ien.it     ...  1 u  104  128  137   82.738    6.799   3.418
-212-82-32-15.ip ...  1 u   10  128  377   72.336    3.288   3.574
-192.168.0.10    ...  1 u  115  128  377    0.227   -3.985   0.140
*SHM(0)          ...  0 l   91  128   77    0.000    1.035   0.495
+SHM(1)          ...  0 l   20   64  373    0.000    0.739   2.203
+SHM(2)          ...  0 l   87   64  376    0.000   -0.637   1.000
-nav.metrologie. ... 14 u   24   64  377   15.396  -13.001   9.449
xmbox.eunet.at   ...  2 u   22  128  377   12.494   43.665   5.553
-orfroufh5.apa.n ...  2 u   16  128  377   14.235  -14.594   7.367
-ntp2.ptb.de     ...  1 u   22  128  377   33.400  -13.700   4.573
  LOCAL(0)        ... 13 l   14   64  377    0.000    0.000   0.004

SHM(0) is DCF77 with "prefer" in ntp.conf.
esat.net is from pool.ntp.org.
ien.it and 212-82-32-15 are the servers used for calibration.

Looking to the offsets above there are two groups of public servers:
1) -13 to -16 ms
2)  +3 to  +7 ms

The difference between 1) and 2) is around 20ms.

What's the correct time?
To use GPS is not possible.

Will it help to remove "prefer" for some hours from SHM(0), and specify 
  a low stratum, to let the references "fight" against each other within 
ntp's logic?

Helmut Wollmersdorfer



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