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

Lachlan Andrew lachlan.andrew at gmail.com
Tue Jul 1 11:02:18 PDT 2008

2008/7/1 Jim Gettys <jg at laptop.org>:
> On Tue, 2008-07-01 at 08:54 -0700, Lachlan Andrew wrote:
> The individual human pokes a web browser to visit another page.
> Embedded on that page are often tons of images or other objects, not
> necessarily at the same web site.
> So an individual human often initiates anywhere from one, to many, many,
> many TCP connections all at once.

True.  I wasn't addressing the question of *what* arrives as a Poisson
process: It may be TCP connections, or batches of TCP connections like
you mention.

I was meaning to address the statement that it is bad to model
congestion collapse by people continuing to pound a congested link
with Poisson traffic.  My point was that, for a core/edge link,
individuals each only need to pound once, and we can still have a
(batch) Poisson process during the congestion interval.  An individual
leaving the system because of congestion doesn't stop the Poisson-ish
arrivals of new individuals (flows, bursts, ...) coming.

Again, this only applies to edge/core links.  Whenever a single
individual produces a significant fraction of the traffic, I entirely
agree that the Poisson model doesn't apply.


Lachlan Andrew Dept of Computer Science, Caltech
1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA
Ph: +1 (626) 395-8820 Fax: +1 (626) 568-3603

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