Re: [Ntp] Antw: Re: Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts

Harlan Stenn <stenn@nwtime.org> Thu, 12 September 2019 11:03 UTC

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From: Harlan Stenn <stenn@nwtime.org>
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Date: Thu, 12 Sep 2019 04:03:19 -0700
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Subject: Re: [Ntp] Antw: Re: Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts
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On 9/12/2019 3:15 AM, Ulrich Windl wrote:
>>>> Miroslav Lichvar <mlichvar@redhat.com> schrieb am 12.09.2019 um 11:46 in
> Nachricht <20190912094603.GN21704@localhost>:
>> On Mon, Sep 02, 2019 at 05:52:33AM ‑0700, Harlan Stenn wrote:
>>> The thing is that NTP is a complete specification with a goal of time
>>> synchronization that includes *known behavior in the face of impulse
>>> response*.
>>>
>>> If one uses different algorithms with different impulse response
>>> behaviors, this can trigger oscillations and even unstable tracking (the
>>> wheels fly off the bus).
>>
>> This was discussed a bit on the last meeting.
>>
>> Does anyone have an example of a PLL that is unstable when cascaded
>> with a different loop? If something works well enough to be stable
> 
> I think it was the old Dave Mills consensus like: "It's only NTP if it
> provides the same output for the same input". So if you think of some
> improvements, they still would not be allowed (I had some discussions while
> implementing PPS in the Linux kernel)

It's not only about instability.

It's about known and agreed-upon impulse behavior.

-- 
Harlan Stenn, Network Time Foundation
http://nwtime.org - be a Member!