IETF Logo Mail Archive

Re: [Ntp] Antw: [EXT] Re: NTPv5 draft

Kurt Roeckx <kurt@roeckx.be> Tue, 01 December 2020 15:00 UTC

Return-Path: <kurt@roeckx.be>
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 C6F343A1345 for <ntp@ietfa.amsl.com>; Tue, 1 Dec 2020 07:00:31 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_PASS=-0.001, URIBL_BLOCKED=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 P_abXXBd_xZD for <ntp@ietfa.amsl.com>; Tue, 1 Dec 2020 07:00:29 -0800 (PST)
Received: from excelsior.roeckx.be (excelsior.roeckx.be [195.234.45.115]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id B739A3A1348 for <ntp@ietf.org>; Tue, 1 Dec 2020 07:00:29 -0800 (PST)
Received: from intrepid.roeckx.be (localhost [127.0.0.1]) by excelsior.roeckx.be (Postfix) with ESMTP id 040D0A8A0D90; Tue, 1 Dec 2020 15:00:27 +0000 (UTC)
Received: by intrepid.roeckx.be (Postfix, from userid 1000) id B2A5F1FE0DDE; Tue, 1 Dec 2020 16:00:26 +0100 (CET)
Date: Tue, 01 Dec 2020 16:00:26 +0100
From: Kurt Roeckx <kurt@roeckx.be>
To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
Cc: mlichvar@redhat.com, Dieter Sibold <dsibold.ietf@gmail.com>, "ntp@ietf.org" <ntp@ietf.org>
Message-ID: <20201201150026.GR971977@roeckx.be>
References: <20201111161947.GG1559650@localhost> <AA848C67-CFB7-43FC-B190-FD3911360373@gmail.com> <20201201081203.GB1900232@localhost> <2B8C7410-DFA7-4A87-A33E-F50FFA96D0F9@gmail.com> <20201201100305.GK1900232@localhost> <20201201102540.GO971977@roeckx.be> <5FC637EC020000A10003D344@gwsmtp.uni-regensburg.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <5FC637EC020000A10003D344@gwsmtp.uni-regensburg.de>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/vSSZfR2ozrFoAc9G5VNkV4NF9WM>
Subject: Re: [Ntp] Antw: [EXT] Re: NTPv5 draft
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: Tue, 01 Dec 2020 15:00:32 -0000

On Tue, Dec 01, 2020 at 01:32:44PM +0100, Ulrich Windl wrote:
> >>> Kurt Roeckx <kurt@roeckx.be> schrieb am 01.12.2020 um 11:25 in Nachricht
> <20201201102540.GO971977@roeckx.be>:
> > On Tue, Dec 01, 2020 at 11:03:05AM +0100, Miroslav Lichvar wrote:
> >> On Tue, Dec 01, 2020 at 10:51:22AM +0100, Dieter Sibold wrote:
> >> > Uncertainty and maximum error are different. The uncertainty interval will
> >> > always be smaller or equal to the max. error.
> >> 
> >> Can you describe an example how would the server determine the
> >> uncertainty?
> > 
> > When talking about uncertainty, we talk about confidence interval.
> > We can never be sure what the maximum error is. We typically talk
> > about an expanded uncertainty of 95%, saying that in 95% of the
> > cases the error will be smaller than the uncertainty.
> > 
> > The 95% comes from 2 * sigma, which covers 95.45%. And we'll write
> > that as k=2 in case of a normal distribution. For NTP, in most
> > cases, it will not be a normal distribution, and you'll need a
> > different k factor for the 95%.
> 
> Hi!
> 
> Yes, but which? How to get the right number?

There are various documents that explain it to you. I suggest
reading something like EA-4-02, which has has many examples.


Kurt

v2.23.0 | Report a Bug | By Email