[ntp:questions] Re: ntp client over satellite and no CMOS battery

David L. Mills mills at udel.edu
Fri Oct 7 01:35:00 UTC 2005


Tim,
A good deal of quality design time went into the statistical analysis of 
errors and the manner in which statistics are presented to the 
application, in this case via ntp_gettime(). You don't want to know 
anything other than the carefully maintained maximum error and estimated 
error statistics. Neither the stratum of the server nor the poll 
interval nor the precision nor any other statistic is necessary to 
evaluate the quality of time. The maximum error and estimated error 
already take those factors into account. You really don't want to second 
guess what the server is doing, just that it and the local client are 
providing dependable statistics.

As I said in my last, your clock is Big Ben and NTP is manipulating the 
number of farthings, h'apennies, pence, shillings, pounds and guineas on 
the pendulum. [Gawd, after 33 years since decimalization, I'm not sure I 
remember how to spell all that coinage.]

Dave

Tim wrote:

> On Wed, 05 Oct 2005 18:34:08 +0000, Brian T. Brunner sent:
> 
> 
>>missing from the ntpd design(?): some system-readable TimeIsGood flag set
>>by ntpd for applications to use where they must have trustable time. alt:
>>TimeStateIs flag with values of LOST (no net, no idea what time it is),
>>SEEKING (found a source, getting time), and SYNC (time is good) alt:
>>SEEKING_n for n ranging 1 to the "minimum acceptable set size" for your
>>site; SYNC means the highest minimum has been met.  This allows different
>>applications to decide when is the time sufficiently good for that
>>application.
> 
> 
> Are you saying that the stratum information can't provide you with
> adequate information about how much faith to put in your time, or that the
> output from ntpstat (three different example results below) isn't machine
> parseable in some useful way?
> 
> synchronised to local net at stratum 8
>    time correct to within 12 ms
>    polling server every 64 s
> 
> unsynchronised
>   time server re-starting
>    polling server every 64 s
> 
> synchronised to NTP server (83.137.103.134) at stratum 3
>    time correct to within 264 ms
>    polling server every 64 s
> 




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