Hello Professor Mills!
Please let me get back to your comment:
The peer offset is recorded for each client/server exchange. Let it run
for a few hours and record the time of day and the offsets at the
beginning and end. Subtract and divide by the interval. It's really not
complicated.
The calculation is not complicated, that's correct. Getting the precise
time is. Please see the example as follows.
According to "Plan B", NTP is configured with "disable ntp". I ran a
cron job to query the peer clock variables using ntpq -c 'rv
<assoc_id_of_peer>' at 9:00 and 10:00. The billboards are attached below
as reference.
During the two "measurements", the offset (peer.offset) increased by
975.174 ms.
Given the cron jobs where started on time (which I doubt :-), the
"measurement" interval was 3600 s, thus the daily time offset of my
system clock will be:
975.174 / 3600 * 86400 / 1000 s = 23.40 s
However, the difference in peer.reftime (8:58:38.253 to 9:58:47.253)
gives an interval of 3609 s, thus the extrapolation yields:
975.174 / 3609 * 86400 / 1000 s = 23.35 s
The difference in peer.org is 3615.973 s, so the rule of proportions gives:
975.174 / 3615.973 * 86400 / 1000 s = 23.30 s
And finally peer.rec gives a time difference of 3616.977 s, making a
daily time offset of
975.174 / 3616.977 * 86400 / 1000 s = 23.29 s
I'd like to know, which calculation is most accurate. What is the
timestamp to record when reading the offset?
Cheers
Daniel Kabs
PS: The billboards look like this
# Reading at 9:00 AM
assID=32468 status=9614 reach, conf, sel_sys.peer, 1 event, event_reach,
srcadr=10.0.0.254, srcport=123, dstadr=10.0.2.100, dstport=123, leap=00,
stratum=1, precision=-18, rootdelay=0.000, rootdispersion=6.516,
refid=DCFa, reach=377, unreach=0, hmode=3, pmode=4, hpoll=6, ppoll=6,
flash=00 ok, keyid=0, ttl=0, offset=-19583.268, delay=0.718,
dispersion=3.282, jitter=49.301,
reftime=c79eaf2e.40eef1ba Thu, Feb 16 2006 8:58:38.253,
org=c79eaf2e.c3a5c1c6 Thu, Feb 16 2006 8:58:38.764,
rec=c79eaf42.628d5410 Thu, Feb 16 2006 8:58:58.384,
xmt=c79eaf42.5a03d577 Thu, Feb 16 2006 8:58:58.351,
filtdelay= 33.29 2.73 0.72 2.75 2.80 2.54 5.90 2.70,
filtoffset= -19604. -19601. -19583. -19565. -19547. -19531. -19516. -19497.,
filtdisp= 0.03 1.01 1.95 2.90 3.86 4.80 5.79 6.75
# Reading at 10:00 AM
assID=32468 status=9614 reach, conf, sel_sys.peer, 1 event, event_reach,
srcadr=10.0.0.254, srcport=123, dstadr=10.0.2.100, dstport=123, leap=00,
stratum=1, precision=-18, rootdelay=0.000, rootdispersion=6.714,
refid=DCFa, reach=377, unreach=0, hmode=3, pmode=4, hpoll=6, ppoll=6,
flash=00 ok, keyid=0, ttl=0, offset=-20558.442, delay=0.679,
dispersion=3.734, jitter=45.116,
reftime=c79ebd47.40cf6be3 Thu, Feb 16 2006 9:58:47.253,
org=c79ebd4e.bcd4562e Thu, Feb 16 2006 9:58:54.737,
rec=c79ebd63.5c88509b Thu, Feb 16 2006 9:59:15.361,
xmt=c79ebd63.5a01abd1 Thu, Feb 16 2006 9:59:15.351,
filtdelay= 9.81 0.70 9.66 0.68 9.13 2.84 0.69 1.74,
filtoffset= -20618. -20595. -20581. -20558. -20538. -20524. -20508. -20490.,
filtdisp= 0.03 1.02 2.01 2.99 3.93 4.88 5.82 6.80
_______________________________________________
questions mailing list
[email protected]
https://lists.ntp.isc.org/mailman/listinfo/questions
