[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 09:53 in
Nachricht <YZ39jGBrF+zeiYm3@localhost>:
> On Wed, Nov 24, 2021 at 08:32:09AM +0100, Ulrich Windl wrote:
>> I wonder: Up to NTPv3 floating‑point math was avoided, but starting in
NTPv4
>> floating‑point math is used.
> 
> That is up to the implementation. The specification doesn't require
> floating‑point math, but it is easier to implement if you can use it.
> 
>> If so, are those many special fixed‑point formats justified (outside of
>> packets)?
> 
> For internal calculations, you could keep everything in the 64‑bit
> format. Even in the NTPv5 packet we could do that, if we don't mind
> wasting 16 octets per packet. The specification would certainly be
> simpler.
> 
> I implemented recently some of the NTPv5 ideas in chrony in an
> experimental extension field. I noticed there is a minor compatibility
> issue with the proposed time32 format and NTPv4. The maximum value is
> not really 16, but slightly less than that. That means it cannot reach
> the MAXDISP value from RFC5905. To avoid having to work with two
> different MAXDISP values, we could specify an infinite value for the
> maximum 32‑bit value of the type.

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?

> 
> ‑‑ 
> Miroslav Lichvar