[ntp:questions] Re: SNTP Client/Server questions

david.lindauer at honeywell.com david.lindauer at honeywell.com
Thu Aug 17 13:34:19 UTC 2006

Hal Murray wrote:
> That depends on how often you poll and how much your clock drifts.
> "several seconds" is a long time relative to round-trip delays to
> a nearby time server.  Let's ignore those delays for now.
> Several PCs I have access to are off by slighly more than 100 ppm.
> There are 86K seconds per day.  Call it 100K.  So a crystal error of
> 10 ppm would turn into a clock error of one second per day.
> So you would have to poll 10 times per day - once every 2 hours.
> Back to network delays.  Does your link to the outside world get
> overloaded at times?  That may confuse things.
yes that pretty much agrees with our notion of PC clocks...  although
some of what we get is much worse.

Our main concern is that the clocks at the lowest tier agree with each
other within a couple of seconds...  the real time isn't quite so
important but we are trying to get a feel for whether we can keep them
reasonably close to the real time without a full NTP client in our part
of the system.  Reasonably close being within a few seconds, and this
assuming there aren't local network problems with polling once an hour.

This is just one possible configuration... there are other
configurations we are considering some of which are more accurate than
this and some less...

More information about the questions mailing list