[ntp:questions] Leap second to be introduced in June

Harlan Stenn stenn at ntp.org
Tue Jan 13 20:40:26 UTC 2015

Martin Burnicki writes:
> Terje Mathisen wrote:
>> I hate to admit it, but I'm starting to believe Google's approach,
>> where they smear the leap second over something like a day, might be
>> one of the better workarounds.

This won't work for a bunch of folks.  Other folks *hate* this approach
because it means that during this 24-hour period the reported time is
off by both frequency *and* offset.

>> It means that any sort of timing done during this time period will be
>> off by the smear ratio/frequency offset, i.e. on the order of 1.5e-5
>> or so.

GTSAPI timestamps will properly account for this.

>> Even for benchmarking runs an error of this magnitude will be down in
>> the noise, the remaining problems are for stuff like telescope
>> control.

For most folks I agree with you.  There will be cases where it's not
true and I'd expect to see an increasing number of these cases moving

>> For distributed logging you have to use the same method for every
>> single node, but that is the case today as well. :-(

GTSAPI timestamps will, I believe and expect, solve this issue.

>> I.e. with one domain smearing and another stepping, the times between
>> them will be skewed over the entire smearing period.
> Agreed, and it would be good to know the smear interval, so that 
> different systems can smear in the same way.

That's really an NTPv5 problem, as we've expected everybody to play by
the same rules as far as NTP goes, and there are a number of ways this
is not true, and I expect the number of cases to increase.  NTP needs to
know the rules its peers/servers are playing by to avoid instability:

- leap smear
- TAI or UTC?
- expected offset to correct time not yet applied
- correction algorithm and specs

Harlan Stenn <stenn at ntp.org>
http://networktimefoundation.org - be a member!

More information about the questions mailing list