[ntp:questions] Re: drift/offset

Folkert van Heusden folkert at vanheusden.com
Thu Feb 3 13:56:23 UTC 2005


> >If I look at the grap of the drift/offset of my ntp-server, everything
> >seems to be rather jumpy:
> >http://keetweej.vanheusden.com/ntp_graph.png
> >The drift can be explained by a bad crystal on the motherboard, but the
> >offset puzzles me: that server is connected to a DCF77 receiver! It is
> >also syncing to some time-servers on the net.
> >Might it be that I'm doing something wrong?
> >
> Your system is obviously performing poorly!  Whether you are doing 
> something wrong or not is a question we can't answer without knowing 
> exactly what you are doing.
> Can you post your ntp.conf file?   Does your DCF77 receiver give you a 
> PPS signal?  If so, are you using it?

No, just a time-indication every minute.
It's this one: http://www.gude.info/english/frame-mouseclock.htm

my ntp.conf:
-----------
# DCF77 receiver
# "Der DCF77 Sender steht in Mainflingen (50 0 Nord, 09 00 Ost), etwa 25 km südöstlich von Frankfurt/Main."
# http://www.maporama.com/
# Mainflingen: 50 1' 54" , 9 1' 33" 50.0318 , 9.026
# Gouda/2804 RR: 52 1' 37" , 4 42' 15" 52.0272 , 4.7044
# http://www.fcc.gov/mb/audio/bickel/distance.html
# -> 374.766km
# speed of light: 299 782.458 km/s
# 1.25012652ms vertraging
# time1 ... ?
# fudging time1 overrides the default delay in the PARSE driver, which for
# mode 14, RAW DCF at 50baud, is 258ms (RAWDCF_BASEDELAY in refclock_parse.c)
server 127.127.8.0 prefer mode 14
fudge  127.127.8.0 time1 0.25925012652
# keetweej
peer 192.168.64.99

#server ntp.xs4all.nl iburst prefer
server 194.109.22.18
#server ntp2.nl.uu.net
server 193.79.237.14
#server ntp3.fau.de
server 131.188.3.223
#server ntps1-1.cs.tu-berlin.de
server 130.149.17.8
#
server time.windows.com
server time.apple.com
server clock.redhat.com

driftfile /etc/ntp/drift

authenticate no

restrict default nomodify
restrict 127.0.0.1
restrict 192.168.64.99
restrict 192.168.0.0 mask 255.255.0.0 nomodify
restrict 192.168.64.1
restrict 194.109.22.18
restrict 130.149.17.8
restrict 131.188.3.223
restrict 193.79.237.14


> Looking at the graph of your drift and offset measurements, I think I 
> see correlation between the drift and the offset measurements.   If 
> there is correlation, one could be cause and the other effect or both 
> could be effects due to some other cause.
> Since your drift measurements are being made with respect to your DCF77 
> receiver and network servers the problem could be either the crystal 
> oscillator or the time sources!    The offsets could be explained by 
> "clock hopping"!

Hopping between servers you mean? Because (unscientific approach: ) every
time I look (ntpq -c pe) it always seems to use my dcf receiver.

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*GENERIC(0)      .DCFa.           0 l   47   64  367    0.000   10.298  12.457
+keetweej.intran 131.188.3.223    2 u    7   64  377    0.467    6.608  10.577
-auth1.xs4all.nl 193.79.237.14    2 u   81   64  376    7.967   -6.370   7.870
+ntp1.NL.net     .GPS.            1 u   44   64  377   18.415   -3.600   9.333
+ntp3-rz.rrze.un .DCFp.           1 u   33   64  377   26.334    2.004   7.096
+sombrero.cs.tu- .PPS.            1 u  108   64  356   25.123    7.413   8.219
-time.windows.co 192.43.244.18    2 u   29   64  377  175.538  -15.622  14.507
-time0.apple.com 17.254.0.49      2 u    9   64  377  165.564   -6.926   8.140
+clock3.redhat.c .CDMA.           1 u   26   64  377  188.041    6.197   9.578

> Was your system synchronized with the same source for the entire 
> period?   What is your poll interval for that source?

I have not changed those settings

> Can you post the output of ntpq -p?

You'll find it above.


Thanks!


Folkert van Heusden

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