[ntp:questions] Re: This is tougher than I thought?
David J Taylor
david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Tue Jan 24 15:55:02 UTC 2006
> Thanks for answering, David, Danny, Maarten...
> David: I think you just saved my life since that code is really
> helpful and is pretty much exactly what I need. I can port it to VC++
> or use it directly from VB. Thank you a lot!!!
> Some more questions:
> 1. I know this is a stupid question probably, but I'm still gonna ask
> it: synchronizing via SNTP should discard network latencies right? So
> if I got a lag of 5 seconds to a server, I should still get the time
> within a pretty accurate margin.
As Richard has said, delays to the server and back to yourself should be
tens of milliseconds - perhaps more on dial-up. If you use servers local
to you (same country or continent), that would be best. Try to avoid
servers on another continent (e.g. using US servers from Europe) as there
will be a satellite delay as well. But all well under one second.
If you set the Originate time, you can measure the round-trip time, and
hence improve your estimate of the real time with respect to the server
you queried, but for a quick "look at the wall clock" type of measurement,
you can skip that complication.
> 2. Why do some servers have "stratum" = 1 and other = 2?
Stratum is (essentially) the number of "hops" you are away from a known
reference source, as Richard explained. An absolute source of time, like
a GPS receiver, radio clock, or atomic clock would be "stratum 0" although
you don't see that term used.
More information about the questions