[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


Axonn wrote:
> 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!!!

You're welcome!

[]
> 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.

Cheers,
David 





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