[ntp:hackers] ITU and Leap second elimination

juergen perlinger juergen.perlinger at t-online.de
Wed Oct 2 22:35:04 UTC 2013


On 10/02/2013 02:04 AM, Danny Mayer wrote:
<snip>
> Just to clarify something. NTP disciplines the clock by adjusting the
> frequencies of the ticks. The goal is to keep the clock synchronized
> to the earth's rotation. If you want uniformity then the frequency
> needs to be kept constant and NTP is not the tool to use. These are
> very opposite goals. You cannot have both. 
I'm not sure if i got this straight. AFAIK, NTP assumes UTC as the time
scale, which is why the leap second announcement is important to NTP(D).
Not that NTP woudn't work as well with TAI, but it's based on UTC. I
might stand corrected, though. It wouldn't be the first time in this thread.

But I think there is a misinterpretion here. The frequency is not
synchronised to earth rotation. The whole idea of leap seconds was to
make the duration of a second in UTC the same as in TAI -- simply a SI
second. The one that is now based on a Caesium time normal. (Sorry, NIST
references not available due to government shutdown, I won't comment
further on that.) The tricks employed by various NTP implementations to
avoid disruptive behaviour around a radix change (aka leap second) are
an artifact that is based on amelioration strategies on systems that do
not support variadic radix representations. Most of them try to keep to
the motto 'natura non saltat'. But in my understanding the duration of a
second in NTP is a second in UTC is a second in TAI.




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