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

"Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de> Thu, 12 September 2019 12:33 UTC

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Date: Thu, 12 Sep 2019 14:33:31 +0200
From: "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de>
To: "ntp@ietf.org" <ntp@ietf.org>,<stenn@nwtime.org>
References: <20190828103752.GI24761@localhost> <3f4b55ca-02d9-a470-229b-40860866efbf@nwtime.org> <20190828111458.GJ24761@localhost> <e50112dd-f918-1135-74c8-a738ecb70b70@nwtime.org> <55867E75-9813-466B-8E57-0E157DE5AEB9@meinberg.de> <d308b5d4-3d6e-981b-3dfc-9d5938bad78d@rubidium.se> <252618a3-d2fb-d5b1-baa4-72b16ef0f845@nwtime.org> <e5b16adb-eddb-fadd-4940-9d97685a36e4@rubidium.se> <20190902124303.GF15024@localhost> <24c6b80b-2bbb-e555-9eaf-34f964947d6e@nwtime.org> <20190912094603.GN21704@localhost> <D92F920B020000B67ED719BE@gwsmtp.uni-regensburg.de> <5FEC8C46020000E66A6A8CFC@gwsmtp.uni-regensburg.de> <0FA08C67020000EC822C0D04@gwsmtp.uni-regensburg.de> <85F2C64C020000776A6A8CFC@gwsmtp.uni-regensburg.de> <5D7A1AD9020000A100033ABD@gwsmtp.uni-regensburg.de> <edb8aa94-a667-a68a-b7e1-f18495c81aab@nwtime.org>
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Subject: [Ntp] Antw: Re: Antw: Re: Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts
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>>> Harlan Stenn <stenn@nwtime.org> schrieb am 12.09.2019 um 13:03 in
Nachricht
<edb8aa94-a667-a68a-b7e1-f18495c81aab@nwtime.org>rg>:

> 
> 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.

But is the overshoot really well-defined NTP behavior? Are you saying that
anything that doesn't overshoot is not NTP?

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