[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.

Cheers,
David 



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