[e2e] bufferbloat paper

Detlef Bosau detlef.bosau at web.de
Mon Jan 14 03:31:18 PST 2013

Am 07.01.2013 19:36, schrieb Mark Allman:

in his paper;

> As queues grow so does delay through the net-
> work. While delay does not have an appreciable impact on
> bulk TCP transfers it can degrade delay-sensitive traffic such
> as Internet telephony conversations.

Seems to me as if we were not talking about networks but about money 
pumping and the € crisis.

However, I have to thank for this statement.

At least one aspect in TCP congestion control, particularly in equation 
based flavours, is the frequently written nonsense of estimating 
possible rates by the "latency bandwidth product", which should be 
called "latency throughput product".

So, the higher the latencies are, the higher the "bandwidth estimators" 
will be => full buffers cause rates to increase.

Sounds to me like a prime example for a iatrogenic problem.

A second remark:

> This phenomenon is
> caused by a general over-buffering in router queues that hold
> traffic that cannot be immediately forwarded.

Is this the correct diagnosis? (Excuse me, I always have in mind € and 
the most powerful women in the world. Our divine leader always wants to 
earn (!) money by austerity. Let  the poor starve to death - so the rich 
get rich as they deserve.)

What causes a queue to overrun? Is the reason ALWAYS, that traffic 
cannot be immediately forwarded? (I strongly believe, that there ARE 
such cases.
However, these are very particular cases and we should have a very 
careful look at them.) Or could it bee, that we simply put too much data 
into our buffers?
So, we should not only have a look at the SERVICE patterns - but at the 
ARRIVAL patterns as well.



For those who do not believe me in my first statement, I strongly 
recommend to read
> @article{ meyer,
>     author ="Michael Meyer and Joachim Sachs and Markus Holzke",
>     title  ="{Performance Evaluation of A TCP Proxy in WCSMA Networks}",
>     journal ="IEEE Wireless Communications",
>     year = "2003",
>     month = "October"
> }

an impressive example of HOW BADLY delays in networks can be misunderstood.

Recovery delays (i.e. there are endless retransmissions of the same data 
along the radio link) are mistaken as "delay" used in the "delay 
bandwidth product" and to make things worth the "bandwidth" is given by 
the gross data rate.

Yes, I was strongly advised not to criticize colleagues in this way. 
However, as computer scientists take a published theorem for a proven 
theorem, it must be possible to say that a paper is crap when the paper 
is crap.

Detlef Bosau
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The nonsense that passes for knowledge around wireless networking,
even taught by "professors of networking" is appalling.  It's the
blind leading the blind. (D.P. Reed, 2012/12/25)

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