On 24/02/2013 23:11, [email protected] wrote:
I can't find or figure out how to validate my ntp results.
I (currently) have two Linux boxes with PPS via the NMEA driver from
Garmins (18 & 18x) and a Sure board connected to a purpose built
NTP server. When I set up my first Garmin all of my remote offsets
were negative which seemed unlikely so I set time1 to 5.3ms which
also seems unlikely but which brought me into congruence with some
nearby stratum 1 servers.
Below is the output* from an intermediate machine on my home network
(3Mb ADSL) which is temporarily connected to several servers.
192.168.0.2 is running with time1 5.3ms.
192.168.0.244 is running with time1 132us.
192.168.0.210 is the appliance and has currently has no adjustments.**
Should I expect /all/ (ignoring the high jitter ones) of the remote
clocks to have negative offsets?
Is there a sensible to way to make this assessment purely within the
NTP system?
remote refid st t when poll reach delay offset jitter
==============================================================================
+192.168.0.2 .GPS. 1 u 14 16 377 0.109 -5.429 0.006
*192.168.0.244 .GPS. 1 u 1 16 377 0.112 0.000 0.008
+192.168.0.210 .GPS. 1 u 15 16 377 0.567 -0.001 0.007
-216.66.0.142 130.207.244.240 2 u 54 64 377 63.526 -7.131 0.192
-38.229.71.1 204.123.2.72 2 u 25 64 377 67.175 -4.368 0.472
-63.240.161.99 72.26.198.233 3 u 19 64 377 70.797 -3.284 0.320
#204.235.61.9 128.105.201.11 2 u 17 64 177 73.331 -9.732 0.426
-216.229.4.69 216.229.0.179 2 u - 64 377 78.848 -4.987 1.337
-199.7.177.206 64.147.116.229 2 u 13 64 377 86.072 -7.451 0.235
#2604:180::8138: 164.244.221.197 2 u 56 64 377 91.521 -33.681 25.573
-198.101.234.139 128.138.140.44 2 u 35 64 377 97.360 -2.065 0.584
#2604:2880::870: 139.78.135.14 2 u 23 64 377 115.057 -12.785 22.738
-207.7.148.214 204.123.2.5 2 u 2 64 377 123.982 -8.091 0.747
*This billboard is sorted by delay.
**You'd have to recompile the control software.
For comparison, my results with a number of different stratum-1 servers
are here:
http://www.satsignal.eu/ntp/ntp-offsets.txt
This includes FreeBSD, Linux, and Windows stratum-1 servers.
Unless those PCs are very slow, I would suggest that the time1 value
should be well under 1 millisecond, and likely under 50 microseconds.
My own results mostly show a positive offset for remote servers, which I
put down to asymmetry on my consumer Cable Modem connection (30 Mb/s
down, 3 Mb/s up).
The remote servers are a mixture of pool and other servers, some
stratum-2 and some stratum-3. Be aware that some of the "national"
stratum-1 servers can be rather overloaded, producing poorer performance
than the better stratum-2 servers. Equally, servers in the pool may
well be not as good as the best stratum-2 servers. So it's a little pot
luck!
Does that help?
--
Cheers,
David
Web: http://www.satsignal.eu
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