Richard B. Gilbert schrieb:
Heiko Gerstung wrote:
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.)
<snip>
Hi Jeff,
as already mentioned, sub-microsecond accuracy is not a possibility
with NTP these days. Did you check out PTP (IEEE 1588) instead
(ieee1588.nist.gov)?
That is not true. You can get microsecond accuracy or better using a
reference clock. What you can't do is get that kind of accuracy over
the internet.
I was referring to sub-microsecond accuracy over the network, it seems
that the OP has no chance to use a hardware ref clock.
My only knowledge of PTP is based on some earlier messages here but I
believe that it must have the same problems as NTP over the internet.
PTP uses hardware timestamping at the MII/PHY level, this will not help
when you use the Internet, but maybe the OP has his own nice WAN with
low-jitter connections available. You can get in the lower nanoseconds
with PTP over Ethernet, but only in very small networks or by using
PTP-aware infrastructure components like switches with integrated
hardware timestamping..
<commercial for $1000+ product snipped>
The mentioned LANTIME/NDT is basically an oscillator that is disciplined
by NTP. And yes, its too expensive for using it at home :-)
Best regards,
Heiko
--
Meinberg radio clocks: 25 years of accurate time worldwide
MEINBERG Radio Clocks
www.meinberg.de
Stand alone ntp time servers and radio clocks based on GPS, DCF77 and
IRIG. Rackmount and desktop versions and PCI slot cards.
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