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

David P. Reed dpreed at reed.com
Tue Jul 1 18:31:02 PDT 2008

I am reminded of the fact that one can fit an exponential curve to any 
two points, and that with enough epicycles, one can keep the earth 

Curve fitting ex post is hardly following the scientific method.   Is 
there any reason to believe that the *actual* process by which packets 
arrive at the network are driven by a Poisson-style process?  Of course not.

So the value of having curve-fit a Poisson model to some range of time 
scales is merely ease of model fitting.  That's not trivial, but it's 
hardly worthy of suggesting to students of networking that they *ought* 
persist in such assumptions.

One can just as easily presume a hidden Markov model of some structure, 
tuned to "curve fit" the data.   The advantage being that one *might* 
imagine a "learning algorithm" based on Viterbi or some such that would 
let the system adapt by measurement and prediction of the load variation 
over time.

Just a thought on the meta process of science as exploration of the 
*unknown* vs. orthodoxy driven by mathematical presumptions.

We'd be arrogant to assume that network applications will always 
henceforth be modeled by the curves we fit today.

slblake at petri-meat.com wrote:
> Quoting John Day <day at std.com>:
>> No kidding. There are some textbook authors who have helped with this
>> too.  I was shocked to see Stallings say in one of his books, something
>> to the effect of 'In the early 90s we discovered network traffic wasn't
>> Poisson.'  (!)  We had known *that* since the 70s!!! I remember prior
>> to 1976 scouring the literature looking for work that was closer to
>> real, i.e. didn't assume Poisson, or would give us the tools to get
>> closer to real.
> The following paper may be of interest to those following this thread:
> T. Karagiannis, M. Molle, M. Faloutsos, and A. Broido,
> "A Nonstationary Poisson View of Internet Traffic",
> IEEE Infocom 2004.
> http://www.ieee-infocom.org/2004/Papers/33_3.PDF
> Regards,
> // Steve

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