On 3/17/2012 3:20 PM, David J Taylor wrote:
"Ron Frazier (NTP)" <timekeepingntpl...@c3energy.com> wrote in message
news:4f64d793.9010...@c3energy.com...
[]
Hi David,
I'm not sure what will happen if you simultaneously prefer and
noselect the local server. Assuming the local stratum 1 server is
the most stable time source, you'll get a much better picture of what
the internet servers are doing relative to it if you allow it to be
selectable as well as being preferred. When you graph it, if the
local server is the active clock, all the lines for the internet
servers will be gathered around and relative to the local server.
When I tried to do things the other way around, with an internet
server preferred, the graph looked awful because there was so much
variation. Also, if your local server starts reporting time that
looks too far from the internet servers, regardless of who's fault it
is, ntp will clock hop over to the internet servers.
I don't THINK your internet servers will ever poll above their
default minpoll value of 6, or 64 seconds.
I realize you don't have a gps attached to this pc, but the iburst
lines reminded me of something. I read somewhere that having iburst
on internet server lines, if a local gps is attached, could prevent
the PC from synchronizing to the gps before it synchronizes to the
internet. On my pc with the gps attached, I don't use the iburst
command.
Sincerely,
Ron
Ron,
The local stratum-1 server shows without a tally code against it in
the ntpq -p output, so it's being recorded in the peerstats, but not
used for syncing. The noselect msut override the prefer.
After about three hours running, the Internet servers are all at 512
seconds poll interval. The averaged jitter has been below 1
millisecond for the last couple of hours. The offset is reporting
between -0.7 and -1.8 milliseconds, and the frequency is stabilising
very nicely (because of the long poll interval). I'll leave this
running overnight and tomorrow to see how it handles temperature
changes and any Internet access changes, and to get a few more points
on the graph.
Come to think of it, my comment about the polling interval not
increasing may only apply to a local refclock, not a local server.
One caveat is that I am using the most recent NTP (ntpd 4.2.7p263 from
Dave Hart's download page), and that with Windows-8, it may be using
the new precision time system call. From my own tests, this is
similar, on earlier versions of NTP, to setting the environment
variable NTPD_USE_INTERP_DANGEROUS, thus forcing the NTP time
interpolation to be used.
Can you elaborate more about what NTPD_USE_INTERP_DANGEROUS does?
Sincerely,
Ron
The configuration I have is:
- cable modem (with built-in router, but working as a bridge by
putting my own router in a device in the DMZ).
- Samknows network monitor (modified WRT54GL router)
- WRT54GL router running DD-WRT firmware
- Netgear 8-port consumer 1 Gb/s switch (G5108)
- wired connection to ~2 year old laptop PC
I only mention this to show that (a) it's not a direct connection and
(b) there's no wireless involved. My aim here is simply to see what
performance may be had with just Internet servers. The PC is only
running NTP and monitoring software - no user programs and no
interactive work, so it is a best-case scenario.
Cheers,
David
--
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
Ron Frazier
timekeepingdude AT c3energy.com
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