Re: [Ntp] Antw: Re: Antw: [EXT] comments on draft‑mlichvar‑ntp‑ntpv5‑03

[Ulrich Windl <[e-mail]>]

>>> Miroslav Lichvar <[e-mail]> schrieb am 24.11.2021 um 13:09 in
Nachricht <YZ4rYlSynuH2RWpu@localhost>:
> On Wed, Nov 24, 2021 at 12:37:00PM +0100, Ulrich Windl wrote:
>> I had always wondered whether MAXDISP wasn't just some arbitrary larger
>> number; Couldn't it be 1 second as well?
>> Is there any specific reasoning behind?
> 
> MAXDISP is the threshold when the server is considered unsynchronized
> after it stops updating its clock. It should be larger than any
> normally expected dispersion to not block synchronization.
> 
> With the default PHI of 15 ppm, it takes 16/15e‑6 seconds (about
> 12.3 days) for the dispersion to accumulate 16 seconds. In the worst
> case it should cover up to 15 strata updating clocks at a maximum
> polling interval.
> 
> I think 1 second would be too small.

But doesn't that value also say "the reference clock can be off by as much as
MAXDISP"?
Considering that values above MAXDIST (1s) are ignored anyway, I wonder.
Probably the real reason is that 16 needs five left shifts until it is less
than MAXDIST (samples until server is accepted).

It's all a lot of heuristics, possibly still rooting from the time when it was
important to avoid integer overflows in the math.

With MAXDISP being just one second, the first sample from a server will
probably make it a valid one.

Regards,
Ulrich

> 
> ‑‑ 
> Miroslav Lichvar