"Richard B. Gilbert" <[EMAIL PROTECTED]> writes: >Unruh wrote: >> [EMAIL PROTECTED] (Kay Hayen) writes: >> >>> Hello David, >> >>>>> When I say "restrict" it is our own system that decides that ">x ms" >>>>> offset is too bad and prevents ntpd from talking to it any further with a >>>>> "restrict" command. If all 2 servers of an "other host" are "restricted", >>>>> it will crash the software. >>>> You are overriding NTP's selection algorithms. Effectively you are no >>>> longer running NTP. >> >>> How would it be difference from using the restrict command manually? >> >>> And why would it not be NTP? >> >>>>> All of that is own our making and control. >>>>> >>>>> Regarding the poll values. I am not sure why we do it the external NTPs >>>>> as well. Could be that the dispersion can be brought down quicker this >>>>> way >>>> You are misusing "dispersion". Dispersion is an estimate of worst case >>>> drift and reading resolution errors. >> >>> Well, dispersion is going down only with more samples to base estimation >>> on, >>> isn't it? And we need that quick, if we want the server to influence the >>> hosts behind it quickly, say after a "NTP LAN" failure ended (some people >>> have dedicated LANs for NTP). >> >>>>> on "entry hosts" and allow the "other hosts" to synchronize faster with >>>>> them, or could be that we never considered it worthwhile to optimize it >>>>> away. Well yes, but between 2 queries from the same client the ntpd will >>>>> have made a certain adjustment. If the client gets to know this value, it >>>>> will have to >>>> ntpd is making adjustments at least every 4 seconds (old versions) and >>>> as often as every clock tick. It does this by adjusting frequency not >>>> by directly adjusting time. >> >>> I was not concerned with how the kernel makes the adjustments, but rather >>> that >>> the a fixed time change over the period is known. The slew rate is known, >>> isn't it? >> >>> Let me use a car analogy, these things work. :-) >> >>> Lets assume a three lane high way with 3 cars that try to drive at the same >>> speed. The car to the left is driving at (near) constant speed. The driver >>> in >>> the middle accelerates and braces according to his motor behaviour as well >>> as >>> the observed difference in speed between him and the other one. Now what >>> should the driver to the right do? >> >> The cars have the road as a reference. However without the road, how does >> car 3 know that car 2 is accelerating and decelerating and that it is not >> hiw own car that is misbehaving? He does not. All he >> can do is collect more cars and use the average behaviour to determine who >> is behaving badly.
>Car 3 has a speedometer! Yes, that is with reference to the road. Car three should thus completely ignore the other two cars and use his speedometer. Ie, put up a GPS receiver with a PPS and use that as your time source, and ignore all the other ntp time sources, except perhaps as sanity checks (eg if you r speedometer breaks you should get to know about it by occasionally looking at the other cars) >> >> With two other cars only as a reference there is no way of deciding which >> is weird. >> >> And if he has the road as a reference, then use the road, not either of the >> other cars ( ie buy yourself a GPS receiver with PPS and then you will not >> have to worry about what other cars are doing). >> >> >>> In my view, he could take the acceleration of his neighbour into account >>> when >>> making estimates of his own error. >> >>> Best regards, >>> Kay Hayen _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions