On 12/27/2012 01:41 AM, Michael Tharp wrote:
The good news is that the disciplining algorithm I lifted from my
previous GPSDO project works quite well, and I have the gritty details
of measuring the PPS worked out. If I can get the Trimble working
tomorrow I might have much better results soon, otherwise I'm traveling
for a few days so it'll have to wait until the new year.
And here we go, it works. Much more reasonable, tens-of-microseconds
jitter figures.
[root@rei ~]# ntpq -pn
remote refid st t when poll reach delay offset
jitter
==============================================================================
-138.236.128.36 216.218.254.202 2 u 21 1024 377 68.819 3.228
0.641
+108.59.14.130 209.51.161.238 2 u 298 1024 377 34.920 1.167
0.288
+108.61.73.244 96.47.67.105 2 u 300 1024 377 39.524 1.135
1.604
-64.6.144.6 128.252.19.1 2 u 772 1024 377 84.329 6.609
0.252
*172.24.0.6 .GPS. 1 u 2 16 377 0.320 -0.073
0.016
-172.24.0.66 135.34.116.162 3 u 237 1024 377 0.197 0.130
0.581
x172.24.0.68 172.24.0.6 2 u 291 1024 377 0.237 113.341
77.665
-172.24.0.1 172.24.0.6 2 u 287 512 377 0.123 2.382
0.876
[root@maruko ~]# ntpq -pn
remote refid st t when poll reach delay offset
jitter
==============================================================================
-67.18.187.111 129.7.1.66 2 u 965 1024 37 66.695 1.952
0.842
+174.129.25.69 131.188.3.221 2 u 753 1024 377 35.926 1.734
0.250
*2001:470:1:15b: 132.239.1.6 2 u 513 1024 377 107.240 0.982
0.373
-172.24.0.1 172.24.0.6 2 u 786 1024 377 0.187 2.960
1.027
+172.24.0.6 .GPS. 1 u 55 16 377 0.356 -0.008
0.060
-172.24.0.64 108.59.14.130 3 u 912 1024 377 0.301 0.058
0.685
x172.24.0.68 135.6.140.0 3 u 938 1024 377 0.378 243.604
166.234
[root@hanmyo ~]# ntpq -pn
remote refid st t when poll reach delay offset
jitter
==============================================================================
*172.24.0.6 .GPS. 1 u 25 64 377 0.399 -2.390
0.258
172.24.0.64 172.24.0.6 2 u 9 1024 377 0.134 -2.273
0.708
-172.24.0.66 135.34.116.162 3 u 342 512 377 0.216 -2.607
1.728
172.24.0.68 172.24.0.6 2 u 300 512 377 0.092 245.910
124.378
-72.251.251.11 62.192.15.212 3 u 22 1024 377 122.988 -0.097
1.585
+67.18.187.111 129.7.1.66 2 u 270 512 377 66.916 -1.235
3.977
-199.7.177.206 64.147.116.229 2 u 368 512 377 59.035 3.838
1.815
+50.97.210.169 131.107.13.100 2 u 8 1024 377 100.003 2.547
1.025
hanmyo (172.24.0.1) is a small "digital engine" computer that I use as a
router; it is pretty much 100% idle, has no fans, and is located in a
closet where it is temperature stable. At the same time, it shows by far
the highest jitter figure so I'm guessing its clock is not very good. I
will have to probe around and see if there is something I can replace,
because it is the best candidate for characterizing the performance of
my little NTP server. It's hard to get quality measurements when the
peer boxes are just ordinary desktops.
I've only been testing this new firmware for ~30m so I will let it soak
while I'm traveling and when I get back the numbers should look even better.
-- m. tharp
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