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

Watson Ladd <watsonbladd@gmail.com> Thu, 12 September 2019 14:10 UTC

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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> <5D7A3B1B020000A100033ACB@gwsmtp.uni-regensburg.de>
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From: Watson Ladd <watsonbladd@gmail.com>
Date: Thu, 12 Sep 2019 07:10:42 -0700
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To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
Cc: NTP WG <ntp@ietf.org>, Harlan Stenn <stenn@nwtime.org>
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Subject: Re: [Ntp] Antw: Re: Antw: Re: Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts
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On Thu, Sep 12, 2019, 5:33 AM Ulrich Windl <
Ulrich.Windl@rz.uni-regensburg.de> wrote:

> >>> 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?
>

The problem is cascading can cause the overshoot to grow as I understand it.

>
> >
> > --
> > Harlan Stenn, Network Time Foundation
> > http://nwtime.org - be a Member!
> >
> > _______________________________________________
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> > ntp@ietf.org
> > https://www.ietf.org/mailman/listinfo/ntp
>
>
>
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