[ntp:questions] Clock Offset

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Thu Dec 20 02:10:39 UTC 2012


--Original Message-----
> From: questions-
> bounces+edward.mischanko=arcelormittal.com at lists.ntp.org
> [mailto:questions-
> bounces+edward.mischanko=arcelormittal.com at lists.ntp.org] On
> Behalf Of David Woolley
> Sent: Wednesday, December 19, 2012 3:59 PM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] Clock Offset
> 
> Mischanko, Edward T wrote:
> > How can my local clock have a negative offset when none of the
> *** selected peers have a negative offset?  Is it possible?
> 
> It is not clear what you mean by "local clock" and "offset",
> here.  For
> the normal NTP meanings of these, the offset of the local clock
> is zero
> by definition.
> 
> Could you provide the ntpq, or other, output on which you are
> making
> this observation, and indicate which fields you are using.
> 
> In the normal ntpd sense, the offset of the local clock is
> always zero
> and the offsets of other sources should be randomly scattered
> around
> zero, if the time is properly synchronised (the distribution may
> not be
> symmetric, but can never be one sided, once the clock is locked.
> 
> Offset is measured relative to the estimated time measurement
> from the
> upstream server.  It is not relative any absolute standard of
> time,
> except after adding all the intermediate errors.
> 
> _______________________________________________
> questions mailing list
> questions at lists.ntp.org
> http://lists.ntp.org/listinfo/questions
[Mischanko, Edward T] 

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

H:\>ntpq
ntpq> peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
#XXX.XXX.0.1     XXX.XXX.104.1    4 u   81  256  377    1.229   -0.089   1.032
#XXX.XXX.1.1     XXX.XXX.104.1    4 u  134  256  377    2.752   -0.153   2.626
#XXX.XXX.106.1   XXX.XXX.104.1    4 u    5  256  377   14.078   -0.212  10.713
#XXX.XXX.109.1   XXX.XXX.104.1    4 u    1  256  377    1.419   -0.027   3.646
#XXX.XXX.110.1   XXX.XXX.104.1    4 u   72  256  377    4.818    1.455   0.074
#XXX.XXX.112.1   XXX.XXX.104.1    4 u   53  256  377    1.687   -0.287   2.336
+XXX.XXX.120.1   XXX.XXX.104.1    4 u   32  256  377    1.581    0.278   0.267
*XXX.XXX.121.1   XXX.XXX.104.1    4 u    9  256  377    1.445    0.568   0.079
+XXX.XXX.122.1   XXX.XXX.104.1    4 u  116  256  377    1.614    0.319   2.084
+XXX.XXX.123.1   XXX.XXX.104.1    4 u   90  256  377    1.397    0.175   0.829
+XXX.XXX.124.1   XXX.XXX.104.1    4 u  137  256  377    1.817    0.177   1.680
+XXX.XXX.125.1   XXX.XXX.104.1    4 u   13  256  377    1.637    0.319   1.317
+XXX.XXX.126.1   XXX.XXX.104.1    4 u  136  256  377    1.424    0.391   1.456
+XXX.XXX.129.1   XXX.XXX.104.1    4 u  166  256  377    1.840    0.269   2.631
+XXX.XXX.131.1   XXX.XXX.104.1    4 u  179  256  377    1.588    0.535   1.723
#XXX.XXX.134.1   XXX.XXX.104.1    4 u  127  256  377    1.566   -0.181   0.996
+XXX.XXX.255.100  XXX.XXX.104.1    4 u    4  256  377    0.595    0.390   0.893
#XXX.XXX.255.200  XXX.XXX.104.1    4 u  241  256  377    0.518    0.605   0.159
+XXX.XXX.43.1     XXX.XXX.255.100   5 u   41  256  377    1.294    0.338   1.265
#bhw-ads04.ameri XXX.XXX.242.249  5 u   49  256  377    0.526  -12.523  22.696
#bhw-ads03.ameri XXX.XXX.242.249  5 u  172  256  377    0.554   10.323  12.585
#ihe-ads01.ameri XXX.XXX.250.248  4 u  163  256  377    1.398  -20.111  15.070
#bhw-mcads01v.mi XXX.XXX.250.248  4 u  134  256  377    0.723   -4.204  11.482
#na-mc-ads01v.mi XXX.XXX.250.248  4 u  189  256  377    1.530   -0.315   3.858
ntpq> rv
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.7p335 at 1.2483-o Dec 18 15:57:25.96 (UTC-06:00) 12  (1)",
processor="x86", system="Windows", leap=00, stratum=5, precision=-19,
rootdelay=17.559, rootdisp=157.869, refid=XXX.XXX.121.1,
reftime=d47cefe7.6ab0443f  Wed, Dec 19 2012 20:01:11.416,
clock=d47ceff7.50f120f0  Wed, Dec 19 2012 20:01:27.316, peer=30980, tc=8,
mintc=3, offset=-0.157823, frequency=1.480, sys_jitter=0.148133,
clk_jitter=0.383, clk_wander=0.023, tai=35, leapsec=201207010000,
expire=201212280000, ctr_frequency=-1.68
ntpq>

Notice individual selected peers have positive offsets, but my clock offset after averaging is negative?

Regards,
Ed


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