[ntp:questions] NTP absolute accuracy?
jdo at stanford.edu
Tue Jul 3 04:51:18 UTC 2007
Root Dispersion sounds like the one, although it seems to be a bit
conservative. Pls, let me know when you find out whether it's a double-sided
edge (+/-) or not.
"Jason Rabel" <jason at extremeoverclocking.com> wrote in message
news:006701c7bcd6$9480a2f0$0a00a8c0 at Inspiron...
> Taken from RFC-1305:
> Root Dispersion is the number indicating the maximum error relative to the
> primary reference source at the root of the synchronization subnet, in
> So depending on your stratum, it *should* (from how I read it) add up all
> the errors from you and up the chain of servers to the stratum 1 server.
> I'll have to verify this when I get home tonight.
> One thing I'm not sure about is for instance: if your root dispersion is
> 40ms, I'm not sure if it mean +/- 40ms (a total of 80ms) or +/- 20ms (a
> total of 40ms). Dr. Mills or someone on the NTP development team can
> probably clear this up.
> You can poll for root dispersion quite easily via another program, and if
> exceeds your bounds then you can do whatever.
>>I guessed so since it wouldn't be possible under the network environments
>>you pointed out.
>>Then, my question is how to detect a case with absolute time inaccuracy
>>beyond a certain limit? Is the Root Dispersion the best indicator? How
>>Offset and RTT? Also, I'm wondering whether there is any way to find out
>>status of network connection such as software and hardware delays---are
>>there any parameters about them?
>>Basically, I'm trying to find or combine parameters to detect a certain
>>outage case where absolute time inaccuracy exceeds my limit. Let me know
>>anyone has experience on this.
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