[ntp:questions] how will this effect stability

marknmbox-88 at yahoo.com marknmbox-88 at yahoo.com
Fri Feb 16 18:37:54 UTC 2007


Folks - 

My question generated some excellent discussion and
went a long way.  I want to thank everyone who
participated.

Just one final email from me - I need to have the time
converge much more quickly.  Can anyone suggest
someway to force the time to converge quickly if the
transit times are unbalanced but consistent?  Is there
a way to  estimate a fudge value?

                         Mark

--- "David L. Mills" <mills at udel.edu> wrote:

> Uwe,
> 
> While USNO is committed to Kalman filters, NIST is
> committed to ARIMA 
> methods. Both of these methods are quasi linear and
> don't work well in 
> the messy Internet. The ntpd method uses seriously
> crafter nonlinear 
> amputation of delay spikes followed by nonlinear
> selectio and averaging 
> algorithms. Think of this approace as a noise
> limiter and bandpass 
> filter used on high-end communications receivers.
> 
> Dave
> 
> Uwe Klein wrote:
> 
> > Terje Mathisen wrote:
> > 
> >> Uwe Klein wrote:
> >>
> >>> Terje Mathisen wrote:
> >>>
> >>>> Please let huffpuff run for a few days while
> plotting frequency and 
> >>>> offset values, my guess is it will turn out to
> be darn stable. :-)
> >>>>
> >>>> Terje
> >>>>
> >>> some data to gloat over:
> >>> huffpuff is at 160000 added ~19:00 on the 14th
> >>> t-online was added later.
> >>>
> >>> t-online.png is the ntp server of my provicer
> ntp1.t-online.de over dsl
> >>> ptb.png is the same to ptbtime1.ptb.de , dsl and
> then some more hops
> >>> robert.png is to another host on the local
> network.10Base100
> >>>
> >>> http:// home.foni.net/ ~kuttersegeln/ntp/
> >>
> >>
> >>
> >> So, are you happy with those results?
> > 
> > I am holding my breath.
> > 
> > ( one thing I noticed this morning is that ntpd
> hops between
> >   the two Stratum 1 servers )
> > 
> > ( wouldn't a Kalman Filter Type approach work
> better with
> >   time sources of comparable quality? )
> > 
> > enabled more logging and wrote some scripts to
> collect and plot data.
> > going to post some more images tonight.
> > 
> > One thing I noticed is that logfile statements
> position in the config
> > file is significant.
> > i.e. when logfile stuff ist last in the config the
> initialisation
> > logging goes to default ( syslog )
> > Does the same apply to things like the "tinker"
> stuff?
> > 
> > 
> >>
> >> You will always see horrible delay/offset values,
> but the local clock 
> >> should coast over those periods, keeping the
> local frequency pretty 
> >> stable.
> >>
> >> In fact, plotting the clock frequency numbers
> alongside the other 
> >> values would be a very nice way to determine
> if/when things have 
> >> stabilized.
> >>
> >> You should see either a straight line, or a
> sawtooth/sinus curve which 
> >> corresponds to the air condition in your server
> room.
> > 
> > I kept the heating on this night, at its permanent
> location later on temp
> > ist kept ~ constant ( central heating, no climate
> control ).
> > 
> >>
> >> Terje
> > 
> > G!&Tks
> > uwe
> > 
> >>
> 
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