[e2e] TCP Loss Differentiation

Lachlan Andrew lachlan.andrew at gmail.com
Fri Mar 13 16:00:46 PDT 2009

Greetings Detlef,

2009/3/13 Detlef Bosau <detlef.bosau at web.de>:
> David P. Reed wrote:
>> My main point was that these loss processes are not characterizable by a
>> "link loss rate".  They are not like Poisson losses at all, which are
>> statistically a single parameter (called "rate"), memoryless distribution.
>>  They are causal, correlated, memory-full processes.  And more  importantly,
>> one end or the other of the relevant link experiences a directly sensed
>> "loss of connectivity" event.
> Does anybody happen to have some good reference for this one? Something
> like: "The failure of poisson modelling of mobile wireless links" or
> something
> simuilar?
> What I have seen so far, simply assumes the contrary and uses Gilbert Markov
> Models and the like.

Although the Gilbert model is far from perfect, it is very much better
than a Poisson model for wireless.  They are correlated and
"memory-full", and have the notion of "loss of connectivity" (i.e.,
being in the bad state).  It certainly can model the case you describe
of periods of a broken connection interleaved with excellent

Although your work may need better wireless models, I think that for
most people on this list the law of diminishing returns means that
going from Poisson to Gilbert is enough.

David, could you explain what it means for a stochastic process to be
"causal"?  My understanding was that a filtration on a random process
is always causal in the sense of having being increasing in one
direction, while the time reverse of the underlying random process is
always another valid random process, albeit a different process except
in the case of reversible processes.


Lachlan Andrew  Centre for Advanced Internet Architectures (CAIA)
Swinburne University of Technology, Melbourne, Australia
<http://caia.swin.edu.au/cv/landrew> <http://netlab.caltech.edu/lachlan>
Ph +61 3 9214 4837

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