On 2011-11-10, David Lord <[email protected]> wrote: > unruh wrote: >> On 2011-11-10, balaji u <[email protected]> wrote: >>> my device is connected with a NTP server(stratum 5), which shows round- >>> trip delay with its primary reference (stratum 3 server) as 550 to 720 >>> msec and dispersion as 70 to 160. >> >> That is pretty huge. How is it connecting? pony express? Why are you >> using such a bad server? (720ms is enough time for the signal to circle >> the earth 5 times. Or I guess if it uses a sattelite as part of the link >> it could generate delays like that) >> >> >>> Whether this could be a problem for my NTP client?. The question >> >> Since ntpd jumps if the time gets out by 128 ms, your delay is getting >> to the point where successive timings could have offsets of that order. >> And ntpd doing jumps a fair amount of the time is not a good idea. >> >>> arises because my NTP server is sending packets with its Root delay >>> and Root Dispersion values which could create some problem on the NTP >>> client side. >> >> Why are you using such a bad server for your server? Buy a gps receiver >> and get usec accuracy for your server and then you can stop worrying. >> Or find some better servers to serve your server. >> > > I use mobile broadband and have seen latencies of several seconds > when the link has been idle. When the link is loaded the lowest > latencies have been about 150ms. That's why I joined the pool so > that I could use burst against my own server without worrying. > > Ntp seems to get my netbook within a few milliseconds. > > The valleys here have steep sides and tops are about 300m above > the road. Even mobile broadband isn't always accessible.
As I said, I would worry about hopping-- ie ntpd thinking you are out by 128ms, stepping the clock, only to step back again a few polls later. (eg, for a while your route is "highly" assymetric, leading ntpd to think it really is >128ms out, and then for some reason it goes assymetric the other way.) Now, there is of course no way you can get a good time in those situations, but the stepping of the clock is probably more worrysome than the poor time accuracy. That is a problem with the highly non-linear stepping algorithm of ntpd. > > > David _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
