[ntp:questions] large dispersion

Richard B. Gilbert rgilbert88 at comcast.net
Wed May 30 16:29:56 UTC 2007


Dave wrote:
> On May 25, 9:28 am, Dave <dave.deconsult... at gmail.com> wrote:
> 
>>On May 24, 8:09 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
>>wrote:
>>
>>
>>
>>
>>>Dave wrote:
>>>
>>>>On May 23, 1:16 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
>>>>wrote:
>>>
>>>>>Dave wrote:
>>>>
>>>>>>I'm experiencing large values of dispersion when I use 'ntpq -p':
>>>>>
>>>>>>3:22pm:ntp>ntpq -p
>>>>>>    remote           refid      st t when poll reach   delay
>>>>>>offset    disp
>>>>>>==============================================================================
>>>>>>*10.2.100.10     .GPS.            1 u   25   64  377     0.46
>>>>>>943.557  439.36
>>>>>>3:22pm:ntp>
>>>>>
>>>>>>but when I look at the peerstats log file, my dispersion is low:
>>>>>
>>>>>>3:22pm:ntp>tail /var/ntp/ntpstats/peerstats.log
>>>>>>54243 54804.018 10.2.100.10 9634 0.617563 0.00046 0.31154
>>>>>>54243 54868.013 10.2.100.10 9634 0.813226 0.00043 0.32210
>>>>>>54243 54932.018 10.2.100.10 9634 0.099169 0.00046 0.55225
>>>>>>54243 54996.010 10.2.100.10 9634 0.300057 0.00047 0.28690
>>>>>>54243 55060.014 10.2.100.10 9634 0.584358 0.00044 0.31111
>>>>>>54243 55124.009 10.2.100.10 9634 0.781632 0.00047 0.32353
>>>>>>54243 55188.014 10.2.100.10 9634 0.065932 0.00043 0.55287
>>>>>>54243 55252.013 10.2.100.10 9634 0.657674 0.00044 0.37859
>>>>>>54243 55316.018 10.2.100.10 9634 0.943557 0.00046 0.43936
>>>>>>54243 55380.013 10.2.100.10 9634 0.139388 0.00044 0.59772
>>>>>>3:23pm:ntp>
>>>>>
>>>>>>I'm also concerned with the large amount of maximum/estimated error
>>>>>>when I use the xntpdc command 'kerninfo':
>>>>>
>>>>>>xntpdc> kerninfo
>>>>>>pll offset:           0 us
>>>>>>pll frequency:        -391.137 ppm
>>>>>>maximum error:        524704 us
>>>>>>estimated error:      408368 us
>>>>>>status:               0089
>>>>>>pll time constant:    2
>>>>>>precision:            1 us
>>>>>>frequency tolerance:  512 ppm
>>>>>>pps frequency:        0.000 ppm
>>>>>>pps stability:        512.000 ppm
>>>>>>pps jitter:           200 us
>>>>>>calibration interval: 4 s
>>>>>>calibration cycles:   0
>>>>>>jitter exceeded:      0
>>>>>>stability exceeded:   0
>>>>>>calibration errors:   0
>>>>>>xntpdc>
>>>>>
>>>>>>Here is the output of the pstats command:
>>>>>
>>>>>>xntpdc> pstats 10.2.100.10
>>>>>>remote host:          10.2.100.10
>>>>>>local interface:      10.2.100.5
>>>>>>time last received:   3s
>>>>>>time until next send: 61s
>>>>>>reachability change:  2947s
>>>>>>packets sent:         59
>>>>>>packets received:     59
>>>>>>bad authentication:   0
>>>>>>bogus origin:         0
>>>>>>duplicate:            0
>>>>>>bad dispersion:       15
>>>>>>bad reference time:   0
>>>>>>candidate order:      1
>>>>>>xntpdc>
>>>>>
>>>>>>And lastly, my ntp.conf file:
>>>>>
>>>>>>3:25pm:inet>more ntp.conf
>>>>>>server 10.2.100.10             # NTP server
>>>>>
>>>>>>driftfile /etc/ntp.drift          # Drift available for next restart
>>>>>>logfile /var/ntp/ntp.log       # NTP logging
>>>>>
>>>>>>statsdir /var/ntp/ntpstats/
>>>>>>statistics loopstats peerstats clockstats
>>>>>>filegen loopstats file loopstats.log type day link enable
>>>>>>filegen peerstats file peerstats.log type day link enable
>>>>>>filegen clockstats file clockstats.log type day link enable
>>>>>>3:25pm:inet>
>>>>>
>>>>>>Anyone have any ideas? I have a GPS signal coming in to a Brandywine
>>>>>>NTA-100, which is configured at 10.2.100.10. Thanks in advance!
>>>>>
>>>>>If you are using "X"ntpdc you would appear to be using a version that
>>>>>may be as much as ten years old!   Just what are you using and what are
>>>>> you running it on?
>>>>
>>>>Wow you're right. Heres the version printout:
>>>>xntpdc 3-5.93e Mon Sep 20 15:47:24 PDT 1999 (1)
>>>
>>>>I'm running this on a Sun Fire 4200, Solaris 10. Something this old
>>>>comes installed on Solaris 10?
>>>
>>>Yup!
>>
>>>I think it has something to do with the fact that there is, as yet, no
>>>RFC for NTP V4.  There is a committee, God help us, working on one.  I
>>>think it has been about a year now with no visible results!
>>
>>>I'd suggest grabbing a more recent version of the code from somewhere.
>>>Sun Freeware and Blastwave sites should both have Solaris versions more
>>>recent than what Sun ships.  There have been quite a few fixes and
>>>enhancements since 3-5.93e.
>>
>>>If you want/are able to build your own, try the ntp.org web site; there
>>>are links there to download the source to the stable and development
>>>versions which are, I believe, at 4.2.something.
>>
>>I just downloaded ntp v4.2.4 from sunfreeware.com and I'll give that a
>>try. I'll let you know how it goes!
> 
> 
> 
> Ok so I have the new version loaded and its been running for about 24
> hours now. I still have a large amount of jitter (reported on by ntpq -
> p):
> 2:50pm:freadd_user>ntpq -p
>      remote           refid            st t when poll   reach
> delay    offset     jitter
> ========================================================
> *10.2.100.10     .GPS.            1 u    3    64     377     0.461
> 91.914   385.406
> 
> 
> But using ntpdc, I see the correlation in the offset values (msec vs.
> sec), but are jitter and dispersion supposed to mean the same thing/
> have anything to do with each other?
> 

Dispersion is the difference between your clock and the atomic clock 
which, in principle, is at the root of things.  Jitter is  a measure of 
the variation in round trip delays between the server and your system.




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