[ntp:questions] Frequency Offset

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sun Feb 26 07:39:52 UTC 2012

"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in message 
news:X_ednYrcXr9Hz9TSnZ2dnUVZ_rCdnZ2d at giganews.com...
> Get ready for a shock.  NTPD needs thirty minutes or more to get a 
> reasonable facsimile of the correct time.  To get the microseconds 
> right, NTPD needs more like ten hours!  It's not a very good fit for 
> running 9AM to 5PM.  You set it running and leave it running 24x7!

Richard, my systems, for the most part, do run 24 x 7.  You can see from 
the graphs I have already referenced that "correct" time is reached within 
a minute or two of starting ntpd.  For me, "correct" is the millisecond 
level.  The FreeBSD stratum-1 server is run 24 x 7, and from cold may 
perhaps take several hours to get to the microsecond level, but that 
doesn't bother the applications I run.

But I do have a PC which works only during the day, and that PC, running 
Windows Vista with a Wi-Fi connection to local stratum-1 servers was down 
to its minimum jitter (1 ms) and offset (~+/- 1 ms) within a minute of 
starting this morning.  Of course, it takes some care in configuring NTP 
to get the best results - here's an idea of what's in the ntp.conf file 
for that PC:

# Use drift file
driftfile "C:\Tools\NTP\etc\ntp.drift"

# Use specific NTP servers
server 192.168.0.A iburst minpoll 5 maxpoll 5 prefer
server 192.168.0.B iburst minpoll 5 maxpoll 5
server 192.168.0.C iburst minpoll 5 maxpoll 5

# Use pool NTP servers
server 0.uk.pool.ntp.org iburst minpoll 10
server 1.uk.pool.ntp.org iburst minpoll 10
server 2.uk.pool.ntp.org iburst minpoll 10
server 0.nl.pool.ntp.org iburst minpoll 10
server 1.nl.pool.ntp.org iburst minpoll 10

Servers 192.168.0.A/B/C are local stratum-1 servers with GPS/PPS sync, one 
FreeBSD, one Windows XP and one Windows 7/32.


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