[e2e] Are we doing sliding window in the Internet?

Greg Skinner gds at best.com
Wed Jan 10 15:07:36 PST 2007

On Wed, Jan 10, 2007 at 07:28:43PM +0000, Jim Gettys wrote:
> On Wed, 2007-01-10 at 19:56 +0100, Detlef Bosau wrote:
> > I don´t think that this is a "proof". I think, the congavoid paper has a 
> > very sound theoretical foundation.
> Yes, and the motivation and theory worked out in reaction to the real
> world experience and analysis of the network failing.
> If theory had been understood in the first place in advance of the
> Internet's congestion collapse, Van would never have worked on the
> problem; presumably one would try to avoid what one forsees.

Depending on what you mean by "theory", one could argue that the basis
of the congavoid paper is in control theory, which was well understood
in the 1980s.  OTOH, its application to the Internet and TCP/IP
implementations of that time was not well understood.

> > If the congestion collapses in the eighties were as bad as you say and 
> > if there was a solution, this surely would not have been ignored.
> For parts of the internet, it really was that bad, and it would
> *certainly* have taken much longer before the work was validated and
> deployed, had it been done on a small minority system or as a research
> prototype model.

For Detlef's benefit, there are archives of the tcp-ip mailing list
where the early discussions on congestion avoidance in the emerging
Internet were held.  Most people involved in this discussion today
will read the emails of the past and recognize the problem that was
being discussed based on what has been studied and published.  Go to
http://securitydigest.org/tcp-ip/#archives, follow the July 1986 link,
and start with the subject "TCP retransmission efficiency". Follow the
discussions from there.  You'll eventually get to VJ's results.

Jim does note correctly that:

> Had [congavoid changes] been done in the Twenex implementation,
> while it might have been noticed, its impact would have taken far
> longer and could even conceivably been ignored.

Benefit of making the changes on a widely used platform was that
congestion was considerably reduced, validating the research.

IMO, it would have been great if more control theory could have been
applied to early Internet design.  Fortunately, VJ kept plugging
enough that he was able to push his ideas through, providing the
bedrock for the R&D in network performance that came afterward.


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