Folkert van Heusden wrote: > Hi, > > I've heard that NTP acts funny when it tries to sync over an ADSL > line. > That seems to be the case indeed: [] > And there it is: 20ms offset. From what I've heard this is caused by > ADSL being asymetric. > Now I was wondering, can't this be fixed by telling the NTP daemon how > much asynchronous the line is? I mean: it can be easily measured what > the down- and upload bandwidth is.
Folkert, Have you measured and removed the delay for the DCF77 device? There receiver bandwidth will cause a delay, as will the propagation delay of the radio signal. Compared to GPS, at this location servers on a 10Mb/s down / 384Kb/s up Internet Cable Modem connection show an offset of 2 - 3ms, and I would expect ADSL to be similar. (Although the throttling technique in a CM is different to ADSL). The asymmetry issue is an interesting one. Whilst I don't see anything being added to NTP to cope with the problem, could one (in a test environment) achieve anything by measuring the delay from both ends? This would give you eight timing measurements instead of four. Cheers, David _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
