rscheff at gmx.at
Mon Feb 7 22:54:57 PST 2011
I've created a simplistic simulation of bufferbloat with ns2-2.34.
Since bandwidth x latency x time-per-frame are scale invariant (if each
frame represents less time, the simulatied bandwidth goes up / latency goes
down), I choose parameters which fit best with good graphical results.
Perhaps one should add some line-graphs next to the sender, showing the
evolution of the congestion window, or the bandwidth utilized.
The simulated tcp stack was an older variant of Linux.
The animation is released under CC 3.0 - I explicitly invite you to ie.
voice over the animation, use parts of it (ie. time-lapse for beverity) etc.
----- Original Message -----
From: "Jim Gettys" <jg at freedesktop.org>
To: <esr at thyrsus.com>
Cc: "Eric Raymond" <esr at snark.thyrsus.com>; <bloat at lists.bufferbloat.net>
Sent: Monday, February 07, 2011 8:56 PM
Subject: Re: [Bloat] Overview modifications
> On 02/06/2011 03:20 PM, Eric Raymond wrote:
>> Jim Gettys<jg at freedesktop.org>:
>>>> Change in progress -- append to the "Hating" paragraph the following
>>>> sentence: "Lossy networks such as wireless actually show less chaotic
>>>> behavior under load than clean ones." Is this correct and adequate?
>>> It's not chaotic behaviour. In fact, it is much more worrying: it
>>> is periodic (oscillatory) behaviour. Chaos is good, in this case.
>> Dave also says my take is wrong and is promising to suggest a correction.
>> I have enough other stuff to do that I'll wait on that.
>>> My nightmare, is that as traffic shifts over more and more to
>>> saturated links as XP retires, we end up with self synchronising
>>> behaviour on a local, regional or global scale, and havoc ensues,
>>> and parts/all of the Internet stop working. Whether these fears are
>>> justified, I do not know.
>>> Think: we may be a column of soldiers in cadence approaching a bridge...
>> New graphs at the end of "From Highway to Network":
>> We also have some worries about the future. For various reasons
>> (including the gradual retirement of Windows XP) more and more
>> Internet traffic is now running over saturated links. In this new
>> environment, we think there is a possibility that bufferbloat
>> and defects in management strategies might produce
>> behaviour in network traffic - packet floods and network resonance
>> a local, regional or global scale that could be a greater threat to
>> the Internet than the congestion-driven near-collapse of the NSF
>> backbone in 1986.
> It's not just bufferbloat: a number of network technologies are bunching
> up packets and injecting them into the Internet with periodic bursts.
> Unfortunately, I don't have good references to this; I gather this is true
> of both wireless and wired technologies.
>> This is a classic "black swan" situation in Nassim Taleb's sense; in
>> today's Internet-dependent economy there is a potential for nearly
>> inacalculable havoc in the worst case, but we don't even know in
>> principle how to estimate the overall risk. Bufferbloat mitigation
>> might keep us out of some very serious trouble, and is worth
>> on those grounds alone.
> It's actually a general fear of any periodic behaviour; I'm just spooked
> to see it in such long period TCP traffic.
> Van warned me about time based congestion phenomena in general.
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