Re: Predictable Internet Time

[Phillip Hallam-Baker <[e-mail]>]

Agree 100%

Hence my proposal for supporting multiple time scales for different
purposes:


1) TAI: Use this and only this for any and all purposes that involve
recording the time an event took place. Including forensic and scientific
purposes.

2) PIT: Use this for inter-machine communications. It may also be used to
present TAI in a human readable form because the mapping from TAI to PIT is
fixed.

3) Local Time Zones: For human display purposes


>From the conversation it seems that the best definition for PIT would be

PIT = TAI  + Smear ( Lag (UTC, 50 years ))



On Tue, Jan 3, 2017 at 12:27 PM, Stewart Bryant <[e-mail]>
wrote:

>
> Smearing worries me.
>
> If you have an application where tiny fractions of a second make no
> difference, then
> a slow smear is a good approximation to no leap second.
>
> However, there are some highly accurate implementations of NTP, and some
> highly
> sensitive applications that use it, and having a long term interval error,
> which is what
> happens during a smear, is harmful to those applications.
>
> It seems to me that it might be better to freeze NTP on the current leap
> second
> offset. Provide the current leap second offset to the application as a
> parameter
> and let the application deal with it as it chooses.
>
> - Stewart
>
>
> On 03/01/2017 14:08, Tony Finch wrote:
>
>> Joe Touch <[e-mail]> wrote:
>>
>>> Smearing leads to differing interpretations of elapsed time for two
>>> reasons:
>>>
>>> 1) smearing isn't unambiguously specified
>>> 2) smearing doesn't match the clock standards set by the ITU (who
>>> defines UTC)
>>>
>> Since leap smear is becoming more popular, it would be sensible to try to
>> get a consensus on the best way to do it if you do it. Clearly
>> organizations that do leap smear think (2) leap seconds are too much
>> trouble so it's better to diverge from official time in a controlled
>> manner.
>>
>> To clear up (1) there are a few technical choices on which people seem to
>> be working towards some kind of agreement...
>>
>> * If you centre the smear period over the leap second, your maximum error
>>    from UTC is 0.5s, which seems to be preferable to starting or ending
>> the
>>    smear period on the leap second
>>
>> * Linear smear works better than sigmoid smear, since it minimizes the
>>    rate divergence for a given smear period, and NTP's algorithms react
>>    better
>>
>> * Longer smear periods are better, because they give NTP more time to
>>    react to the rate change, and they minimize the rate difference
>>
>> It looks to me like a 24h leap smear from 12:00 UTC before the leap to
>> 12:00 UTC after the leap has a good chance of becoming more popular than
>> other leap smear models.
>>
>> Tony.
>>
>
>