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

Jim Gettys jg at laptop.org
Wed Jan 10 11:28:43 PST 2007

On Wed, 2007-01-10 at 19:56 +0100, Detlef Bosau wrote:
> Jim Gettys wrote:
> >> What do you mean by "research into systems"? The term "system" extremely 
> >> general.
> >>     
> >
> > If you go look at Van's LCA presentation referenced, you'll see it is
> >   
> Could you give me a pointer please? Unfortunately, I don´t know this talk.

There is a link in the following article, as I posted before.

> > rethinking TCP's implementation in a real system.  That is systems
> > research.  Maybe I should have said research in implementations and
> > algorithms.
> >
> >   
> As I said, I don´t know the talk yet. However, rethinking TCP´s 
> implementation in a real system should be done independent from a 
> concrete operating system.
> Of course, one should consider the difficulties encountered in real 
> systems. But then, we should abstract from concrete systems and look for 
> general principles how we can avoid difficulties und learn from our 
> experiences in the past.

I think you will see that by analyzing and solving the real problems in
Linux he came up with principles that are (potentially) transferable to
many systems.

Doing it independently of a real system would have not proved the points
he proved in that work Van reported on at LCA last year.

> > Simulation of protocols does not fit what I'm talking about here.
> >
> >   
> What are the alternatives? You can build testbeds and you can trace real 
> traffic.
> At least we should exploit these befor deploying premature protocols.

Certainly; but they are at most "doing your homework"; but they cannot
substitute for deployment or testing at scale on a real network.

> > Without a control, experimental science becomes hand-waving anecdotes
> > (which typifies research in many fields, unfortunately).
> >
> >   
> There is no argument about this.
> The dissent is first, what is experimental science? To me, engineering 
> is not purely experimental but always should rely on sound theoretical 
> work and include then proper experiemnts.

In a real science, theory and experiment go hand in hand; you can't know
what problems are worth trying to apply or develop theory for without
experience and experiments, and you can't validate any theory without

> 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.

> What was experienced practically was the problem and the relevance of 
> congestion control.
> The rest is proper work.
> I still think on a remark of some computer science professor who even 
> told me that the timeouts could be only determined by experiments.
> And even these timeouts are based on sound conceptional work in Van´s paper.

You seem to think that theory exists in a vacuum from experience and
experiment.  It doesn't.  The theory was worked out in reaction to the
situation at hand.

> > system of that era. Had it 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.
> >   
> 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.
                         - Jim

Jim Gettys
One Laptop Per Child

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