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

Ted Faber faber at ISI.EDU
Fri Jul 11 13:33:46 PDT 2008

On Fri, Jul 11, 2008 at 01:49:39PM -0400, Craig Partridge wrote:
> Hi Dave:
> My understanding of the literature (and I don't claim to be an expert)
> is that between the late 1950s and the mid 1970s, the telephony system
> fit Poisson very well (for arrivals and departures of phone calls and
> the like) and that this was an essential driver to the introduction
> of statistical muxing in the telephone system.  As modems, faxes, changes in
> charging models, etc. came along, that changed but that it was true
> (a sort of golden moment for the statisticians) and drove advances.
> But I wasn't there....

I think David is drawing the distinction between a Poisson process,
which is defined pretty precisely and something that produces events
with a Poisson distribution.

True Poisson processes are rare; the only one I can think of off the top
of my head is radioactive decay.  Series of events that are Poisson
distributed are markedly easier to find.  The pseudorandom number
generator on my machine (which is certainly not a Poisson process) can
be massaged to create a sequence of events that are Poisson distributed.

I believe that the statements that the telephone interrarrivals were
Poisson distributed and that they were not generated by a Poisson
process are both true.

This is like the fact that my students aren't Normal, but I still grade
on a bell curve. :-)  (Yes, yes, I know, I don't need to hear about the
various laws of large numbers; that sentence was a joke...)

Ted Faber
http://www.isi.edu/~faber           PGP: http://www.isi.edu/~faber/pubkeys.asc
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