[ntp:questions] Re: ref clock for network POP locations

Heiko Gerstung heiko.gerstung_removeme_ at meinberg.de
Thu Sep 28 08:20:52 UTC 2006

Jeff W. Boote schrieb:
> I have some network locations where I have no way to access GPS or CDMA. 
> But, I would still like to have a very accurate time source. (I would 
> like sub-microsecond accuracy from NTPD if I can get it.) These 
> locations are in telco-hotels, so they are typically very well shielded 
> making any broadcast technology unworkable. (We are not using sonet - so 
> getting time from there is also not an option.)
> I was thinking that it might be possible to get an oscillator to provide 
> a PPS signal, and then use a very well connected (possibly even a 
> dedicated network link with no router/switch) network peer as the 
> preferred peer. Is this a reasonable solution? Can anyone suggest 
> anything better?
> The PPS would need to be calibrated... Is the normal ntp calibration 
> reasonable for this? I would guess it depends on the oscillator...
> If this is a reasonable solution, does anyone have recommendations for 
> oscillators? Most of the ones I have seen want a reference source of 
> their own. This of course does not work in my case...
> Thanks,
> jeff
> P.S. I will happily add information to the wiki on this after figuring 
> out how to do it. (If?)

Hi Jeff,

as already mentioned, sub-microsecond accuracy is not a possibility with 
NTP these days. Did you check out PTP (IEEE 1588) instead 

We offer a NTP appliance that has its own free-running OCXO-HQ that is 
disciplined by NTP over the network. Using a very smooth filtering and 
applying only very small corrections allows us to get down to 50 to 100 
microsecond accuracy in an "ideal" network environment, i.e. 

The model is called LANTIME/NDT (Network Disciplined Timeserver) and you 
can find it on our website (www.meinberg.de, see Products section).

I would say that you have to check out PTP if you really need to sync 
down to the nanoseconds ...

Best regards,

Meinberg radio clocks: 25 years of accurate time worldwide

MEINBERG Radio Clocks

Stand alone ntp time servers and radio clocks based on GPS, DCF77 and 
IRIG. Rackmount and desktop versions and PCI slot cards.

More information about the questions mailing list