[e2e] Reacting to corruption based loss

[Detlef Bosau]

Craig Partridge wrote:
> 
> 
> >In my opinion, and I´m willing to receive contradiction on this point,
> >it is a matter of the Internet system model. Why couldn´t we continue
> >to assume loss free links? Is this really a violation of the End to End
> >Principle when we introduce link layer recovery? Or is it simply a well
> >done seperation of concerns to fix link issues at the link layer and to
> >leave transport issues to the transport layer?
> 
> Take a peek at Reiner Ludwig's (RWTH Aachen) dissertation which says that,
> in the extreme case, link layer recovery and end-to-end recovery don't mix --
> and we know from the E2E principle that some E2E recovery must be
> present.  (I believe there's also work from Uppsala showing that you
> need at least some link layer recovery or TCP performance is awful --
> what this suggests is we're searching for a balance point).

I totally agree here.

My concern is the loss differentiation debate in wireless networks,
particularly in mobile wide area networks (GSM, 3G...).
(There are quite a few wireless networks where packet corruption is
extremeley rare or neglectible. Think of properly set up WaveLANs for
example. In my opinion, there is no urgent need to treat them different
to wireless networks.)

However, in mobile networks, it often makes sense to use local recovery
schemes and / or performance enhancing proxies. My own work exactly
deals with such situations. (And no, I do _not_ attempt to propose yet
another PEP %-)). Nevertheless, I got some strong criticism because PEP,
connection splitting etc. would violate the E2E principle, violate TCP
semantics etc. Of couse, each of these objections deserves most careful
consideration. E.g. a PEP which breaks TCP E2E reliability like the
original I-TCP approach can hardly be used. However, even with
connection splitting, TCP E2E reliability can be maintained, following
Rajiv Chakravorty, Sachin Katti, Jon Crowcroft, and Ian Pratt. "Flow
Aggregation for Enhanced TCP over Wide Area Wireless.", INFOCOM 2003.

Basically, if we consider 3G networks for access networks only, the
alternatives are:
First: PEP and connection splitting must not be used, hence there is a
need for loss differentation tu react appropriately.
Second: In case of severe loss or other "non TCP compliant behaviour" in
access networks, it makes sense to use PEP, connection splitting etc. to
make corruption loss neglectible from the E2E point of view. Of course,
great care must be taken to have _all_ E2E semantics properly
maintained. 

In case of the second alternative, it may be necessary to obey the
particular needs/E2E semantics of the transport protcol / application in
use.

I´m just curious, whether there is a general consensus on this matter. 

DB
 
-- 
Detlef Bosau
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