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

Miroslav Lichvar <mlichvar@redhat.com> Thu, 12 September 2019 09:46 UTC

Return-Path: <mlichvar@redhat.com>
X-Original-To: ntp@ietfa.amsl.com
Delivered-To: ntp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 5580E120273 for <ntp@ietfa.amsl.com>; Thu, 12 Sep 2019 02:46:14 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.901
X-Spam-Level:
X-Spam-Status: No, score=-6.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id urpnZaeT9MGM for <ntp@ietfa.amsl.com>; Thu, 12 Sep 2019 02:46:11 -0700 (PDT)
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id D11BB1200B7 for <ntp@ietf.org>; Thu, 12 Sep 2019 02:46:11 -0700 (PDT)
Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 530842A09D0; Thu, 12 Sep 2019 09:46:11 +0000 (UTC)
Received: from localhost (holly.tpb.lab.eng.brq.redhat.com [10.43.134.11]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 963405D6A5; Thu, 12 Sep 2019 09:46:09 +0000 (UTC)
Date: Thu, 12 Sep 2019 11:46:03 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Harlan Stenn <stenn@nwtime.org>
Cc: ntp@ietf.org
Message-ID: <20190912094603.GN21704@localhost>
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>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <24c6b80b-2bbb-e555-9eaf-34f964947d6e@nwtime.org>
User-Agent: Mutt/1.12.0 (2019-05-25)
X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 12 Sep 2019 09:46:11 +0000 (UTC)
Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/V8wrNtl8-WRX1WZeexWqA0-RvRM>
Subject: Re: [Ntp] Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts
X-BeenThere: ntp@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: <ntp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ntp>, <mailto:ntp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ntp/>
List-Post: <mailto:ntp@ietf.org>
List-Help: <mailto:ntp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ntp>, <mailto:ntp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 12 Sep 2019 09:46:14 -0000

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
when synchronizing a clock of an NTP client to a stable reference
clock in different network conditions, how could it cause its own
clients to become unstable?

-- 
Miroslav Lichvar