Re: [Bloat] [tsvwg] how much of a problem is buffer bloat today?

[Jim Gettys <jg@freedesktop.org>]

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On Thu, Mar 21, 2013 at 1:50 PM, Oliver Hohlfeld <
oliver@net.t-labs.tu-berlin.de> wrote:

> (cross posting to bloat)
>
> On 03/13/2013 04:28 PM, Fred Baker (fred) wrote:
> > On Mar 13, 2013, at 10:23 AM, Eliot Lear <lear@cisco.com> wrote:
> >
> >> I don't have an answer to that question, but Mark Allman from ICIR did
> >> attempt to characterize buffer bloat on the Internet through an
> >> empirical study that appeared in the January edition of CCR.  You can
> >> find a reference to that paper at the following URL:
> >>
> >> http://www.sigcomm.org/ccr/papers/2013/January/2427036.2427041
> >>
> >> Eliot
> >
> > Well, yes, he says that in his gigabit FTTH network he doesn't see
> megabit-scale problems.
>
> Marks paper is /not/ about measuring buffer bloat in an FTTH network.
> While he uses the FTTH network as /vantage point/, the paper actually
> measures buffer bloat in various remote networks.
>
> Marks paper is not the only study suggesting the extend of the problem
> to be modest. The presented results are in line with recent findings by
> Chirichella and Rossi [1]. Based on unpublished work, I can confirm the
> low magnitude of the problem. I analyzed passive measurements of
> residential users traffic from multiple continents (~60 million IPs
> originating from 50\% of all ASes) and rarely find excessive RTTs that,
> among other problems, can indicate the presence of buffer bloat.
>

I believe you are actually measuring the *fraction of the time* your
measurements show bad latency, rather than the fraction of paths that may
suffer from significant bufferbloat at various times due to excessive
buffering.

Buffers only fill when they are being used and that only happens when
saturation occurs.

The best data I've seen on how widespread the problem is is the ICSI
Netalyzr scatter plots results, which (in color) are in my blog.
http://gettys.wordpress.com/2010/12/06/whose-house-is-of-glasse-must-not-throw-stones-at-another/
These must be flavored by understanding that those tests top out at about
20Mbps, and that (to keep the time that netalzyr takes to run sane) stops
at about 5 seconds of buffering.

I encourage everyone to run netalyzr and/or the mlabs tests for bufferbloat
on your own broadband connections, or do simple copy and ping tests inside
your own house over wifi to your local file servers....
                                                               - Jim


> In summary, bloated buffers exist and buffer bloat can be demonstrated,
> but current findings suggest that it rarely occurs in practice. One
> potential reason being that users do not often sustainably utilize
> their uplink capacity and fill-up their potentially large queues.
>
> Oliver
>
> [1] To the Moon and back: are Internet bufferbloat delays really that
> large?
> http://perso.telecom-paristech.fr/~drossi/paper/rossi13tma-a.pdf
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