From: Dave Taht <dave.taht@gmail.com>
To: Jan Ceuleers <jan.ceuleers@gmail.com>
Cc: "Eric S. Raymond" <esr@thyrsus.com>, bloat-devel@lists.bufferbloat.net
Subject: Re: Preliminary results of using GPS to look for clock skew
Date: Fri, 23 Sep 2011 02:38:02 -0700 [thread overview]
Message-ID: <CAA93jw6=O2x-Gy4b99UwAA77iXbAj4Vpd3018AGqZxMqaqvQqQ@mail.gmail.com> (raw)
In-Reply-To: <4E7C4CDE.4060308@gmail.com>
On Fri, Sep 23, 2011 at 2:09 AM, Jan Ceuleers <jan.ceuleers@gmail.com> wrote:
> On 09/22/2011 04:24 AM, Jonathan Morton wrote:
>>
>> When the *network* is loaded, the latency to the NTP server changes. That
>> is likely to confuse ntpd - it certainly did when I lived on an analogue
>> modem.
>
> Look at the huff'n'puff filter for how ntpd addresses this concern.
>
> http://www.eecis.udel.edu/~mills/ntp/html/huffpuff.html
In the case of the cosmic background bufferbloat detector idea, I'm
interested in collecting the data
that ntp is currently *filtering away* as a means to measure various
delays across a wide base of machines,
thus collecting rawstats on the client seems like the best approach.
The point is not to derive accurate time
from multiple, possibly badly varying, data sources, but to see how
badly varying the data sources are!
It would be best to be doing so passively, however, at the server, and
I've been toying with the idea of
creating a new ntp message type to do so. With clients often behind
nat there is no good way to
supply what a ntp host thinks is the current time to a data collecting
server elsewhere.
The huff n puff filter is a great idea, however I note it relies on
ntp running for a long time, and many (most?)
clients restart ntp on every interface change (example, a dhcp
refresh, or wakeup from suspend)
Secondly, adding the refclock with noselect keyword seems like a
useful means of comparison.
Thirdly - as much as I would like to get a PPS signal, that seems
impossible with the hardware we are
currently playing with. That said, delays/variations of 10ms are not a
real problem as the bufferbloat signal
can often be measured in close order of seconds.
>
> Jan
> _______________________________________________
> Bloat-devel mailing list
> Bloat-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat-devel
>
--
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://the-edge.blogspot.com
next prev parent reply other threads:[~2011-09-23 9:38 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-21 23:02 Eric Raymond
2011-09-22 0:18 ` Dave Taht
2011-09-22 2:11 ` Eric Raymond
2011-09-22 2:24 ` Jonathan Morton
2011-09-22 2:29 ` Eric Raymond
2011-09-23 9:09 ` Jan Ceuleers
2011-09-23 9:38 ` Dave Taht [this message]
2011-09-23 12:10 ` Jan Ceuleers
2011-09-23 12:50 ` Rick
2011-09-24 14:50 ` Jan Ceuleers
2011-09-22 9:08 ` Dave Taht
2011-09-22 17:15 ` Rick Jones
2011-09-22 17:34 ` Dave Taht
2011-09-22 17:43 ` Rick Jones
2011-09-22 17:58 ` Dave Taht
2011-09-23 10:57 ` Aidan Williams
2011-09-23 10:10 ` Dave Taht
2011-09-23 9:09 ` Jan Ceuleers
2011-09-23 9:24 ` Jan Ceuleers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAA93jw6=O2x-Gy4b99UwAA77iXbAj4Vpd3018AGqZxMqaqvQqQ@mail.gmail.com' \
--to=dave.taht@gmail.com \
--cc=bloat-devel@lists.bufferbloat.net \
--cc=esr@thyrsus.com \
--cc=jan.ceuleers@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox