From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x231.google.com (mail-lf0-x231.google.com [IPv6:2a00:1450:4010:c07::231]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 65F0D3B29E for ; Sun, 26 Nov 2017 02:25:49 -0500 (EST) Received: by mail-lf0-x231.google.com with SMTP id f131so21345424lff.12 for ; Sat, 25 Nov 2017 23:25:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=JwdVRbRiG7aOk/4duP3Qh45PZurgUcfgEyoGKEolqkE=; b=ZYjMzURKFxMzTO7ZTyPoR2C17h8kDxjteGgZosvoEJC4gw84E92od1M4f13eKqo7l6 3w4FWCH3ovs4BxrD//1RwAihv6SIkE3JErtrn8icVVxPM/AzHhmfhl2PTMPXeaO6dySv 1bHS9VZ1IHY1d99CY2Ws/P41vHtxcC8C3sXR+l9veyhTWW7utfdWBPyT733QMBhWK5v5 atX4kjjtI12YpX4nmEu4ITMkPlwe9X301U/VrxMXv9SNjrxduWGW6SDDOjM4QyX+UrOP 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(PST) MIME-Version: 1.0 References: <20171124092021.DC01D40605C@ip-64-139-1-69.sjc.megapath.net> In-Reply-To: From: Caleb Cushing Date: Sun, 26 Nov 2017 07:25:36 +0000 Message-ID: To: Neil Davies Cc: Hal Murray , bloat@lists.bufferbloat.net Content-Type: multipart/alternative; boundary="94eb2c1cd798cbfc1b055eddb1aa" Subject: Re: [Bloat] Steam In Home Streaming on ath9k wifi X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 26 Nov 2017 07:25:49 -0000 --94eb2c1cd798cbfc1b055eddb1aa Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable ping from laptop C:\Users\xeno>ping 192.168.1.105 -n 100 Pinging 192.168.1.105 with 32 bytes of data: Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D5ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128 Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128 Ping statistics for 192.168.1.105: Packets: Sent =3D 100, Received =3D 100, Lost =3D 0 (0% loss), Approximate round trip times in milli-seconds: Minimum =3D 3ms, Maximum =3D 5ms, Average =3D 3ms On Fri, Nov 24, 2017 at 3:35 AM Neil Davies wrote: > On 24 Nov 2017, at 09:20, Hal Murray wrote: > > > neil.davies@pnsol.com said: > > There are a few more issues - the relative drift between the two clocks > can be as high as 200ppm, though typically 50-75ppm is what we observe, b= ut > this drift is monotonic. > > > 200 ppm seems pretty high, but not off scale. If ntpd is running and not > getting confused by long queuing delays, it should correct the drift to > well > under 1 ppm. If you turn on loopstats, you can graph it. > > > I=E2=80=99m saying that is the maximum rate of drift between two clocks e= ven > when they are under NTP control. As you say below the clock rates > are not completely stable they are temperature dependent. > When we did this with the guys at CERN we could > correlate the results with the workload (see below for references). > > We=E2=80=99ve got ~1M experiments using this approach across various netw= orks, > the numbers are what we are seeing in practice. > > The caveat is that, after a while (i.e several 100s) the clock drift can > make > a significant difference (i.e a few ms) in the one-way delay estimation. > > > If you are blasting the network and adding long queuing delays, ntpd can > easily get confused. > > There is another quirk to keep in mind. The temperature coefficient of > the > crystal is ballpark of 1 ppm per C. Things can change significantly if a= n > idle system starts flinging lots of bits around. > > > Also NTP can make changes at one (or both) ends - they show up as distinc= t > direction changes in the drift. > > > I'm not sure what you mean by "direction change". I'd expect a graph of > the > time offset vs time to be linear and the slope would have a sharp change > if > ntpd changed it's "drift" correction and/or maybe a rounded bend as a > system > warmed up. > > > Don=E2=80=99t forget you are measuring the difference in the rates betwee= n two NTP > clocks, > hence the change when one of the NTP systems decides to change the drift > rate > the relative rate can change direction. > > > ---------- > > Are you happy with whatever you are doing? Should we try to set things > up > > so ntpd works well enough? How close would you like the times to be? = =E2=80=A6 > > > Yep, we=E2=80=99re very happy - we don=E2=80=99t care that there is a lin= ear clock drift > (we > can correct for that) and the step changes are infrequent and can be > eliminated > from the long term analysis. > > You might find =C2=A74.4 (esp =C2=A74.4.5) and =C2=A75.6 in > https://cds.cern.ch/record/1504817/files/CERN-THESIS-2013-004.pdf > interesting. It illustrates these sort of issues. > > > > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > Bloat mailing list > Bloat@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat > --=20 Caleb Cushing http://xenoterracide.com --94eb2c1cd798cbfc1b055eddb1aa Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
ping from laptop

C:\Users\xeno>ping 192.168= .1.105 -n 100

Pinging 192.168.1.105 with 32 bytes = of data:
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D5ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D4ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D3ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D3ms TTL=3D128
Reply from = 192.168.1.105: bytes=3D32 time=3D4ms T= TL=3D128
Reply from 192.168.1.10= 5: bytes=3D32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
<= div>Reply from 192.168.1.105: bytes=3D= 32 time=3D3ms TTL=3D128
Reply from 192.168.1.105: bytes=3D32 time=3D4ms TTL=3D128
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On Fri, Nov 24, 2017 at 3:35 AM Neil Davies <neil.davies@pnsol.com> wrote:
<= blockquote type=3D"cite">
On 24 Nov 2017, at 09:20, Hal Murray <hmurray@megapathds= l.net> wrote:


neil.davies@pnsol.com said:
Th= ere are a few more issues - the relative drift between the two clocks
ca= n be as high as 200ppm, though typically 50-75ppm is what we observe, butthis drift is monotonic.

200 ppm seems pretty high, b= ut not off scale.=C2=A0 If ntpd is running and not
getting confused by = long queuing delays, it should correct the drift to well
under 1 ppm.= =C2=A0 If you turn on loopstats, you can graph it.

I=E2=80=99m saying that is the maximum rate of drift between two clocks e= ven
when they are under NTP control. As you say below the clock r= ates
are not completely stable they are temperature dependent.
When we did this with the guys at CERN we could
correlate= the results with the workload (see below for references).

We=E2=80=99ve got ~1M experiments using this approach across vario= us networks,=C2=A0
the numbers are what we are seeing in practice= .=C2=A0

The caveat is that, after a while (i.e sev= eral 100s) the clock drift can make
a significant difference (i.e= a few ms) in the one-way delay estimation.=C2=A0

If you are blasting the network and adding long queuing delays, ntpd can =
easily get confused.

There is another quirk to keep in mind.=C2= =A0 The temperature coefficient of the
crystal is ballpark of 1 ppm per= C.=C2=A0 Things can change significantly if an
idle system starts flin= ging lots of bits around.


Also NTP can= make changes at one (or both) ends - they show up as distinct
direction= changes in the drift.

I'm not sure what you mean = by "direction change".=C2=A0 I'd expect a graph of the
ti= me offset vs time to be linear and the slope would have a sharp change if <= br>ntpd changed it's "drift" correction and/or maybe a rounde= d bend as a system
warmed up.

Don=E2=80=99t forget= you are measuring the difference in the rates between two NTP clocks,
hence the change when one of the NTP systems decides to change the dr= ift rate
the relative rate can change direction.

<= div>

----------

Are you happy with whatever you are doing? = =C2=A0=C2=A0Should we try to set things up
so ntpd works well enough?=C2=A0 How close would you like the ti= mes to be? =C2=A0=E2=80=A6


Yep, we=E2= =80=99re very happy - we don=E2=80=99t care that there is a linear clock dr= ift (we
can correct for that) and the step changes are infrequent= and can be eliminated
from the long term analysis.
You might find =C2=A74.4 (esp =C2=A74.4.5) and =C2=A75.6 in=C2= =A0
interesting.=C2=A0 It illustr= ates these sort of issues.=C2=A0




--
These are my opinions.=C2=A0 I hate spam.




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