On 6/29/21 8:52 PM, Eric S. Raymond wrote:
Richard Laager via devel <devel@ntpsec.org>:
On 6/29/21 3:41 PM, Eric S. Raymond via devel wrote:
Well, first, the historical target for accuracy of WAN time service is
more than an order of magnitude higher than 1ms.
My two NTP servers are +- 0.1 ms and +- 0.2 ms as measured by the NTP pool
monitoring system across the Internet.
That's quite exceptionally good. It's normally hard to get to within an
order of magnitude of that on a LAN, let alone a WAN.
If this is surprising to you, perhaps I'm quoting the wrong thing. I was
referring to the variance in the clock offset as plotted here:
https://www.ntppool.org/scores/69.89.207.99
https://www.ntppool.org/scores/69.89.207.199
https://www.ntppool.org/scores/2600:2600::99
https://www.ntppool.org/scores/2600:2600::199
There are only two systems involved, but in practice, IPv4 and IPv6 can
have different paths through the Internet.
Do you have any theory of why your deviation is that low?
Not particularly. Presumably it's just because of GPS PPS + good network?
Both systems are GPS PPS. One uses a ublox demo board. The other gets
its PPS from a telecom GPS primary reference source (that is also a BITS
source for SONET and a telephone switch).
The ublox one is the better of the two even thought it only has an
indoor antenna. I think the GPS in that telecom PRS is not so great, and
the oscillator is a TCXO, not Rubidium.
Both servers are (older) server-grade hardware, dedicated to this task
(way overkill even for public pool servers). ntpd at this moment is
using ~22% of a single Intel Xeon L5420.
They have 2x 1 Gig network connections (because that's standard here for
redundancy) with two switches (a 1G then a 10G) before they hit my "core
router". I'm the ISP.
The ublox uses gpsd via SHM while the other uses the ntpd PPS driver. I
fiddled with maxpoll a bit to optimize.
The BITS clock PPS:
server 127.127.22.0 minpoll 3 maxpoll 3 prefer
fudge 127.127.22.0 refid PPS
The ublox PPS:
server 127.127.28.1 minpoll 1 maxpoll 1 prefer
fudge 127.127.28.1 refid GPS
--
Richard
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