[ntp:questions] Compensating for asymmetric delay on a per-peer/server basis?

Rich Wales richw at richw.org
Sat Sep 13 05:46:43 UTC 2014


Replying to Charles Elliott:

> The offset may be a function of distance.  Try this experiment:
> Set up your ntp.conf file to have three servers . . . :
> 1.  A relatively unused stratum 1 or 2 server as close to you as possible
> 2.  A relatively unused stratum 1 or 2 server about 1,000 miles away
> 3.  A relatively unused stratum 1 or 2 server more than 2,000 miles away

OK, here is information taken from two local servers under my control.

==============================================================================

This first machine (171.67.203.16) is on the Stanford University campus.  The
first two peers listed below are located on the Stanford campus; the third
peer is also run by Stanford but is about 50 miles east of the campus.

+171.64.7.105    .PPS.            1 u 1012 1024  377    0.465   -0.045   0.076
+171.64.7.67     .PPS.            1 u  217 1024  377    0.584   -0.043   0.081
*204.63.224.70   .PPS.            1 u  737 1024  377    1.803   -0.031   0.252

This next peer is my home machine (the one I described earlier as being
connected to the Internet via a cable modem), with its own local GPS clock.

-68.65.164.12    .PPS.            1 u   13   16  372    8.168   -2.126   4.585

Finally, these two servers are in Utah (Xmission) and Poland.

-198.60.22.240   .GPS.            1 u  721 1024  377   18.931    0.239   0.045
-213.222.200.99  .PPS.            1 u  833 1024  377  172.099   -4.083   1.167

==============================================================================

Now, here is the info from my home machine (68.65.164.12).  First, my local
GPS reference clock:

*127.127.28.1    .PPS.            0 l   14   16  377    0.000   -0.003   0.025
x127.127.28.0    .GPS.            8 l    7   16  377    0.000  -37.762  13.399

Next, my campus machine (see above for details):

-171.67.203.16   204.63.224.70    2 u    2   16  333    9.689    2.146   3.930

And finally, the same two remote servers (in Utah and Poland) that I used on
my campus machine:

+198.60.22.240   .GPS.            1 u   45   64  377   35.222    6.542   2.864
+213.222.200.99  .PPS.            1 u   18   64  377  191.192    4.890   8.968

==============================================================================

Any thoughts?

Rich Wales
richw at richw.org


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