On 12/14/21 5:23 PM, Hal Murray wrote:
Out of curiosity, since you monitor NIST Gaithersburg, if you were to average
over the offsets for a whole month, what kind of value would you get? Surely
it is close to zero but I am curious how close. Within 1ms?
It depends. Mostly on the routing between you and NIST. If you are closer,
the routing is more likely to be symmetric.
From my experience, routing is generally stable on the scale of months. There
are short (hours) changes when a fiber gets cut or a router gets busted.
There are long term changes as people add fibers and/or change business deals.
There are some cases where a stable routing will produce 2 answers: x% of the
packets will be slightly faster/slower than most of them. I think what's
going on is that the routers are doing load sharing on multiple paths, hashing
on the address+port. Or something like that. So it's a roll of the dice
which path you get.
--------
I'm in California.
NIST has NTP servers at 3 locations in the Boulder CO area: NIST, WWV, and
Univ of Colorado. (Google maps says WWV is 60 miles north of Bouler. Univ of
Colorado is a few miles from NIST.)
From a cheap cloud server (Digital Ocean) in San Francisco, the RTT to NIST is
31.5 ms, to WWV is 32.1 ms, to Univ of Colorado is 54.5 ms. The time offsets
are about 1 ms for NIST and WWV and 12 ms for Univ of Colorado.
From my home (AT&T via Sonic), 30 miles south of San Francisco, the RTTs are
61 ms for NIST and WWV and 81-82 for Univ of Colorado. Offsets are 6-7 ms for
NIST and WWV and 4-5 ms in the other direction for Univ of Colorado.
Might be a localized routing phenomenon. Using my verizon connection from
Northern Virginia the results are awful for time-e-g.nist.gov:
remote refid st t when poll reach delay offset jitter
==============================================================================
-192.168.1.219 68.69.221.61 2 u 56 64 377 0.400 -0.290 0.035
*192.168.1.224 .PPS. 1 u 1 16 377 0.184 0.087 0.017
-129.6.15.26 .NIST. 1 u 32 64 377 93.087 -37.940 7.867
However from my AWS machine in Oregon:
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^- 152.63.13.177 3 6 377 63 -2011us[-2011us] +/- 128ms
^+ 209.182.153.6 2 7 377 65 -959us[ -959us] +/- 86ms
^- 64.139.66.105 3 6 377 128 -5838us[-5838us] +/- 134ms
^+ 129.6.15.26 1 6 377 64 -2075us[-2075us] +/- 37ms
^* 173.66.105.50 1 8 377 438 -448us[ -870us] +/- 38ms
-mike
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