"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.
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.
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
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