[e2e] Reacting to corruption based loss

[Detlef Bosau]

(I apologize when this is received twice, but apparently it was not
sent properly the first time) 
On Tue, 7 Jun 2005 07:18:09 -0400, Wesley Eddy wrote

> 
> This idea is sort of discussed in the ETEN paper Craig sent a link to
> earlier.  One approach that it describes (CETEN_A) adapts beta between
> 1/2 and 1 based on the rate of congestion events reported.  In the
> October 2004 CCR, there is a paper that goes into greater depth on
> CETEN; "New Techniques for Making Transport Protocols Robust to
> Corruption-Based Loss" by Eddy, Ostermann, and Allman.



I think, this range for beta illustrates the problem quite well. In
cases of low corruption rates, the so modified TCP congestion control
will behave quite similar to what we know from, e.g. TCP/Reno etc.

The mentioned approach sets beta to (1+e/p)/2, where p = e+c.
e is the corruption loss rate and c the congestion loss rate.

However, with large error rates (0.8, 0.9 or even close to 1) the so
modified beta will practically suspend the congestion control
mechanism.

Of course, this may increase the network load along the path and will
thus in turn increase congestion drop and therefore lower beta
again. I´m not quite sure about the resulting dynamics.

For the moment, I consider the mechanism using error rates as 0.1 or
so, which Wesley mentioned some days ago. In that case, let´s take for
granted that anything is just fine.

My question is: How dow we deal with _high_ corruption rates like 0.8
or 0.9, typically met in mobile wireless networks?

In other words: It´s again my question whether there exists a general
consensus on whether we should attempt to handle even those large
error rates e2e? Or whether local recovery / PEP etc. should be used?

Besides the pure congestion dynamics, we should in addition think of
possible network load caused by e2e retransmission.

Perhas, the question is an old one. But for me, it´s simply of
interest to know the "common position" here:

Should we treat path with corruption loss larger than, say, 80 % with
e2e-means, e.g. CETEN? Or should we, in case those corruption loss
occurs on a mobile access line to the Internet, make use of proxies
here?

I´m just curious and unsafe about the "common" position.
-- 
Detlef Bosau
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