[ntp:questions] Behavior when one server is erroneous

Christopher J. Burian cburian at ll.mit.edu
Fri Jan 16 21:20:11 UTC 2004


I'm testing a CDMA-based, Palisade-compatible time source.  Most
of the time it works fine.  But in marginal reception conditions,
the device thinks it is synchronized but is not, and appears to
be off by up to a second.  I'm working with the manufacturer on 
that problem.  

What I wanted to bring to the attention of ntpd developers is
that the daemon appears to do some sort of weighted averaging
of the three mostly correct servers and the one bad server.
Shouldn't the algorithm perhaps vote to reject servers notably
different from consensus?  And when jitter is bad, shouldn't
the polling time be more frequent?

Regards,
Chris

ntpq> pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.29.1    .CDMA.           0 l    7   16  377    0.000  -26.916 116.099
+155.34.100.67   .GPS.            1 u  184  512   37    3.277  450.174  80.107
+155.34.3.123    .GPS.            1 u  185  512   37    5.223  450.440  79.103
+155.34.3.8      155.34.3.123     2 u   23   64  377    0.002  574.188  25.114
ntpq> pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
x127.127.29.1    .CDMA.           0 l   10   16  377    0.000  -226.84  99.691
x155.34.100.67   .GPS.            1 u  331  512   37    3.277  450.174  80.107
x155.34.3.123    .GPS.            1 u  332  512   37    5.223  450.440  79.103
*155.34.3.8      155.34.3.123     2 u    5   64  377    0.002  583.724  14.496
ntpq> pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.29.1    .CDMA.           0 l   16   16  377    0.000  -671.47 141.500
x155.34.100.67   .GPS.            1 u   22  256   17    3.357  -74.293  46.467
 155.34.3.123    .GPS.            1 u   21  256   17    5.096  -19.350  72.238
 155.34.3.8      155.34.3.123     2 u   56   64   76    0.919  -21.359 177.973
ntpq> pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.29.1    .CDMA.           0 l    5   16   37    0.000  -75.688  41.494
 155.34.100.67   .GPS.            1 u   20   64    1    9.419  750.087   0.002
 155.34.3.123    .GPS.            1 u   21   64    1    5.276  746.882   0.002
 155.34.3.8      155.34.3.123     2 u   20   64    3    0.002  288.527 457.307
ntpq> pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.29.1    .CDMA.           0 l   11   16  377    0.000  295.474  70.632
+155.34.100.67   .GPS.            1 u  183  512   37    3.707  784.915 144.207
+155.34.3.123    .GPS.            1 u  183  512   37    5.202  897.152 125.242
+155.34.3.8      155.34.3.123     2 u   25   64  377    0.002  1129.50 168.278



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