[ntp:questions] NTP rootdelay and rootdispersion problem

David Lord snews at lordynet.org
Thu Nov 10 16:40:33 UTC 2011


unruh wrote:
> On 2011-11-10, balaji u <ubalaji83 at gmail.com> 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.


David



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