On 11/12/2012 21:46, David Woolley wrote:
David Taylor wrote:
On 10/12/2012 21:18, David Woolley wrote:
Jeroen Mostert wrote:
For what it's worth, after all of that, the offset is steadily
zigzagging between 27 and 41 ms, which I'm guessing is about the best
you can hope for on a Windows machine with Internet sync. There have
not been any major time step adjustments.
Offsets should be scattered around zero. If they are all the same sign,
something is wrong.
What happens if the link to the Internet is rather asymmetrical? For
example, here I am stuck with 30 Mb/s down, but only 3 Mb/s up.
If there is an actual asymmetry in the delays (the slow uplink may have
lower delays, because it is unloaded!), the offsets will still be spread
across zero, but zero will not correspond to the true time.
So, if the PC also has a stratum-1 clock connected (e.g. PPS), to which
it was synced, then the offsets would be spread across the the non-zero
difference between "computed true time from the Internet" and UTC,
wouldn't they? In this example:
C:\Users\David>ntpq -p narvik
remote refid st t when poll reach delay offset
jitter
==============================================================================
*pixie .PPS. 1 u 20 32 377 0.153 0.371
0.024
+FEENIX .PPS. 1 u 25 32 377 0.217 0.308
0.018
+Stamsund .PPS. 1 u 25 32 377 0.221 0.420
0.050
uk.pool.ntp.org .POOL. 16 p - 1024 0 0.000 0.000
0.001
-utserv.mcc.ac.u 194.66.31.14 2 u 800 1024 377 23.998 10.566
7.972
-linnaeus.inf.ed 129.215.64.32 2 u 9 1024 377 29.272 3.559
3.337
-ntp.uk.syrahost 192.93.2.20 2 u 36 1024 377 27.957 4.717
1.551
-cpc2-derb13-2-0 213.248.206.227 2 u 922 1024 377 26.324 3.124
3.752
-ntp1.exa-networ 33.117.170.50 2 u 750 1024 377 42.560 4.435
1.156
-ntp2.warwicknet 195.66.241.2 2 u 660 1024 377 22.819 4.221
4.440
PC Narvik is synced to a local stratum-1 server, and the WAN servers
listed below the POOL entry, mostly have offsets in the 3-4 millisecond
region, suggesting (if I understand this correctly) that the delay
introduced by the asymmetry of the WAN may be in the 3-4 millisecond region.
--
Cheers,
David
Web: http://www.satsignal.eu
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