[e2e] Why do we need TCP flow control (rwnd)?

Craig Partridge craig at aland.bbn.com
Fri Jul 11 10:29:21 PDT 2008

You achieve research by looking at the points more carefully.

* Analysis is useful when employed correctly.  For instance, for all
  that Poisson is terrible, if you can prove a negative result with
  Poisson arrivals (e.g. service model Zed is a disaster even if
  arrivals are Poisson) that's a very strong result (as we know
  Poisson is nicer than real traffic -- per Christian's note).

* Simulators validated by real world experiments are very valuable
  testing environments (I have access to such a simulator for testing
  wireless systems -- worth its weight in gold).

* Observations are extremely valuable when carefully documented such that
  the reader can determine if the observations show a general truth or
  a specific situation.  Remember, we learned a lot during the various
  congestion collapses of the late 1980s [and there was more than one], by
  observing each one and comparing what we learned.  Different collapses
  had different morphologies -- one I still remember is when the Atlantic
  satellite link got so overloaded that each connection's fair share of
  the capacity was less than one TCP segment...

Or, to make this short -- we make progress by being (a) careful and (b)
smart (in that order).


In message <486C037C.4060300 at web.de>, Detlef Bosau writes:

>Good rant.
>And I coudln't agree more.
>Only one problem remains.... And that's a very honest question:
>If we agree upon some facts:
>- Poisson processes and Markov prossesses are of little use in 
>networking research,
>- Analysis is not really helpful (and frankly spoken, I hardly believe 
>those analytical TCP models, which are around),
>- Simulation can prove anything and nothing,
>- Observation is not reproducible and not systematic,
>so, if we agree upon the fact, that research on networking is basically 
>impossible, _how_ can we accomplish research on networking then?
>It's of course allowed - and it's always scientifically correct to do so 
>- to put in question anything we have.
>But if we only see blind alleys, how do we find a way out?
>Detlef Bosau                          Mail:  detlef.bosau at web.de
>Galileistrasse 30                     Web:   http://www.detlef-bosau.de
>70565 Stuttgart                       Skype: detlef.bosau
>Mobile: +49 172 681 9937

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