[ntp:questions] basic questions about the leapsecond

David L. Mills mills at udel.edu
Mon Dec 15 17:08:26 UTC 2008


Guys,

See http://www.eecis.udel.edu/~mills/ntp/html/ntpd.html#leap for what 
actually is in the implementation. As visivle here, the Spectracom 
(GPS/WWVB) driver, ACTS telephone modem driver and WWV audio driver do 
correctly display leap information. The Meinberg GPS receiver, EndRun 
CDMA receiver and audio IRIG driver do not display leapsecond 
information.  The USNO and NIST servers do not show leap bits in the VME 
or ACTS associations, but that might not be significant until the day 
before the leap. Our servers pogo.udel.edu and rackety.udel.edu are 
correctly configure and the leap warning bits in the driver associations 
correctly set. To check a server near you, run ntpq, as and rv commands 
for the system peer and verify the leap bits are set to 01,

As mentioned in the documentation, it is not necessary to run Autokey to 
download the leapseconds file from NIST. It is availabe via FTP from the 
pub directory and leap-seconds file.

Dave

Martin Burnicki wrote:

>Hi Antonio,
>
>Antonio M. Moreiras wrote:
>  
>
>>Hi...
>>
>>I'm a bit worried regarding the leapsecond, since I'm not finding much
>>documentation about it... I have a simple (but unanswered) doubt: Do I
>>have to manually configure something?
>>
>>Could you point some docs?
>>    
>>
>
>Here's some basic information:
>http://www.meinberg.de/english/info/ntp.htm
>
>  
>
>>We have the following structure repeated 3 times:
>>
>>+------- --+ 1 PPS +--------+  IRIG  +-------+   +-----------+
>>|Atomic Ref|------>|IRIG Gen|------->|NTP st1|-->|pub NTP st2|
>>+----------+ 10Mhz +--------+ + 1PPS +-------+   +-----------+
>>                                        ^            ^
>>                                        |            |
>>
>>                                     other st1    other st2
>>
>>- 1 st1 server is freebsd + ntpd + IRIG audio
>>- 1 st1 server is symmetricom syncserver S250
>>- 1 st1 server is spectracom netclock 9283
>>
>>At the IRIG generator we have to manually set the leapsecond bit.
>>
>>Could anyone tell me if these servers could read the leap bit correctly
>>from IRIG signal? Specially IRIG audio?
>>
>>How could I test it at NTP? (Since I have made the adjust at IRIG gen
>>how could I tell if ntp can read it correctly?)
>>
>>We have also 2 systems with GPS:
>>
>>+---+  NMEA  +-------+
>>|GPS|------->|NTP st1|
>>+---+ + 1PPS +-------+
>>
>>One of them is a Trimble Acutime 2000, and the other is a Garmin 18LVC.
>>Do I have to worry about these ntp servers?
>>    
>>
>
>Please note your NTP servers need to receive a leap second announcement e.g.
>one day *before* the leap second actually occurs, otherwise they can not
>handle the leap second correctly.
>
>Leap second announcements can be received from an upstream NTP server, from
>a reference time source, (IRIG, GPS, ..), or from a leap second file. It is
>important to check whether *both* the reference time transport format (IRIG
>frame type or NMEA format) and also NTPs reference clock driver configured
>for that refclock support leap second announcements.
>
>Most commonly used IRIG frame formats have not specified a leap second
>announcement flag, but some formats like IEEE1344 support this. So it
>depends on the IRIG format you are using if a leap second announcement
>arrives at your IRIG receiver.
>
>I'm also not sure whether NMEA supports leap second announcements. E.g. the
>parse driver (type 8) does. For an NTP server it is *not* sufficient if
>only the leap second is transmitted as second 60 in a time string).
>
>If your NTP servers run NTP v4 then the best way is to install the NIST leap
>second file. See:
>http://support.ntp.org/bin/view/Support/ConfiguringNTP#Section_6.13.
>
>Don't forget to enable autokey on your servers since otherwise the leap
>second file will not be evaluated.
>
>
>Martin
>  
>




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