The path is variable. Internet routing is constantly in flux as routes are injected and retracted.
On Feb 20, 2012, at 19:56, Brooke Clarke <[email protected]> wrote: > Hi Bob: > > It was my understanding that the receiving station knows the path taken, is > that the case? Or are you saying even when it's the same path the time delay > has large variations? > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/Brooke4Congress.html > > > Bob Camp wrote: >> Hi >> >> Since the network is being measured, I suspect that using it as the time >> reference would present a basic problem. >> >> Bob >> >> >> >> On Feb 20, 2012, at 2:07 PM, Jim Lux<[email protected]> wrote: >> >>> On 2/20/12 10:31 AM, Bob Camp wrote: >>>> Hi >>>> >>>> Simple answer: >>>> >>>> A rack mount cesium standard is as good as you can get. Figure on 15 ns >>>> per day of drift. That gets you to 15 us in 1000 days. You may or may not >>>> get one that drifts that little, a lot depends on little details. For> >>>> 3 years, consider an ensemble of cesiums. At $50K each cost can go up >>>> pretty fast. >>>> >>>> There is nothing out there that will do better stand alone for less money. >>>> Either you get a sky view or you change the budget.... >>>> >>>> Bob >>>> >>>> >>> >>> But he *does* have the ability to have an external network connection.. So >>> the real question is whether one could come up with a better-than-NTP >>> scheme to get the 100 (or 10) microseconds. >>> >>> I suspect that with sufficiently controlled network paths (which might be >>> doable in a widescale deployment) and a tweaking of the NTP stuff, you >>> might be able to get it to work. >>> >>> 100 microseconds out of a day is 1E-10, which is actually a fairly liberal >>> drift spec for an OCXO or even a TCXO. (which are things like ppb/day) >>> >>> Maybe there's a particular time of day (or day of week) when network >>> uncertainties are minimal, or can be bounded. So what you really need is a >>> onboard oscillator that is good at "carry over" between periodic >>> calibration checks. >>> >>> >>> One question about the 100 microsecond spec.. is that a worst case at any >>> instant, or is it an average spec over a day (so a consistent diurnal >>> variation would cancel out) >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
