[ntp:questions] Re: Question to NTP developers

David L. Mills mills at udel.edu
Sat Aug 26 16:14:19 UTC 2006


Eugen,

I say for the >third< time: the ntpdc billboards are misleading and 
wrong. See the ntpq billboards with truthful tally codes and jitter 
estimates. The GPS and PPS offsets you claim are zero, which is very 
rarely the case in normal operation. Remember, at least some NMEA 
drivers do the PPS thing internally and do not rely on the atom driver. 
In such cases you are completely on your own and any errant behavior 
should be reported to the driver author.

Dave

Eugen COCA wrote:
> David L. Mills wrote:
> 
>>Eugen,
>>
>>It's not a good idea to use ntpdc for precision comparisons; ntpq is
>>much more useful and truthful.
>>
>>The display makes no sense. How is it that the GPS and PPS show huge
>>jitter while the offsets are zero? Take a look with ntpq at
>>rackety.udel.edu and note the offset and jitter.
> 
> 
> Dave,
> 
> on the best of my servers, ntpq/pe looks like:
> 
>      remote           local      st poll reach  delay   offset    disp
> =======================================================================
> =GPS_NMEA(1)     127.0.0.1        0   64  377 0.00000 -0.000000 0.03049
> =ntp3.usv.ro     80.96.120.253    1   64  377 0.00049  0.000053 0.04402
> =gps-1.mit.edu   80.96.120.253    1  256  377 0.14613  0.000446 0.12549
> =ntp2.usv.ro     80.96.120.253    1   64  377 0.00026 -0.000012 0.06828
> =gps-2.mit.edu   80.96.120.253    1  256  377 0.14575  0.000113 0.10460
> =ptbtime1.ptb.de 80.96.120.253    1  256  377 0.04861 -0.001742 0.10022
> =ptbtime2.ptb.de 80.96.120.253    1  256  377 0.04829  0.000012 0.11932
> *PPS(1)          127.0.0.1        0   16  377 0.00000 -0.000000 0.01567
> =ntp-p1.obspm.fr 80.96.120.253    1  256  377 0.05722  0.000721 0.09496
> =ntps1-1.cs.tu-b 80.96.120.253    1  256  357 0.05438 -0.000242 0.09479
> 
> 
> and at the server you indicated is:
> 
>      remote           local      st poll reach  delay   offset    disp
> =======================================================================
> =239.1.1.1       128.4.1.1       16   64    0 0.00000  0.000000 4.00000
> =SPECTRACOM(1)   127.0.0.1        0   64  377 0.00000 -0.000007 0.03073
> *PPS(0)          127.0.0.1        0   16  377 0.00000 -0.000008 0.01608
> =mizbeaver.udel. 128.4.1.1        1   64  377 0.00410 -0.000018 0.05716
> 
> I must run the servers with kernel sync disabled in order to see the
> differences between the to situation: kernel PPS or driver 22. I wonder
> if it make sense to put "flag3 1" - enable kernel pps in the line for
> the 22 driver, say "127.127.22.1 flag3 1" ?
> 




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