Re: Predictable Internet Time

Stewart Bryant <stewart.bryant@gmail.com> Tue, 03 January 2017 18:35 UTC

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Subject: Re: Predictable Internet Time
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From: Stewart Bryant <stewart.bryant@gmail.com>
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Date: Tue, 3 Jan 2017 18:35:03 +0000
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Yes, the system should use a leap-second-free constant-duration-seconds 
time for everything. It is only humans that need the variable jumpy 
version of time presented to them, and that is a UI issue.

- Stewart


On 03/01/2017 18:25, Joe Touch wrote:
> We really need to separate the frames of reference of time - there's no
> need for smear for internal "seconds since epoch" time. Smear only
> renders UTC values incorrect,, which is an invitation to have financial
> and legal transactions fail and report local events (e.g., rates, etc.)
> incorrectly.
>
> We shouldn't propagate an incorrect solution.
>
> Joe
>
>
> On 1/3/2017 6:08 AM, Tony Finch wrote:
>> Joe Touch <touch@isi.edu>; 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.