[ntp:questions] why do internet servers not poll at longer intervals

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Tue Feb 14 19:25:53 UTC 2012

Hi all,

I have my USB GPS working pretty good at this point on both Windows and 
Linux.  I have some more Linux specific questions that I'll post later.  
At the moment, I'm working on Windows.  As has been suggested by others, 
I know I can get hugely better accuracy using a different GPS and PPS, 
and I plan to experiment with that when I get time and money.  (I've 
been ignoring lots of other household things while pursuing this 
project.)  For the moment, I just want to get optimum performance out of 
the equipment that I have.  For my immediate needs, +/- 6-10 ms accuracy 
is perfectly adequate for what I'm doing.

Here's a recent ntpq -p printout:

C:\Windows\system32>ntpq -p
      remote           refid      st t when poll reach   delay   offset  
*GPS_NMEA(5)     .GPS1.           0 l    1    8  377    0.000   -1.181   
+nist1-ny.ustimi .ACTS.           1 u   25   64  377   53.990    3.458   
#  .ACTS.           1 u   42   64  377   59.998   22.534   
+india.colorado. .ACTS.           1 u   36   64  377   63.986    1.739   
+ping-audit-207- .ACTS.           1 u   50   64  377   83.998    0.715   

Note that my GPS is closely synchronized with 3 of the 4 NIST Stratum 1 
servers.  I have intentionally set the fudge factor on the GPS so this 
is the case.

Now, here are the relevant server lines in ntp.conf:

server                prefer minpoll 3 maxpoll 3 mode 72
fudge time2 0.2950 refid GPS1

server nist1-ny.ustiming.org       prefer minpoll 6 maxpoll 13
server nist1.columbiacountyga.gov         minpoll 6 maxpoll 13
server utcnist.colorado.edu               minpoll 6 maxpoll 13
server nist1.aol-ca.truetime.com          minpoll 6 maxpoll 13

Now, note that the NIST servers are being polled every 64 seconds.  This 
thing has been running this way since yesterday evening.  However, in 
the configuration file, those servers are allowed to poll up to every 2 
hours.  My question is, why are the internet servers being polled so 
often continuously even though I have a stable GPS source available 
which is the currently selected active clock?  If I comment out the GPS 
line, the internet servers will eventually go back to polling at longer 
intervals.  Note that I don't want to get banned from using any of these 
public servers for hitting them too often.




(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

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