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

Jim Gettys jg at laptop.org
Wed Jan 10 07:18:17 PST 2007

On Wed, 2007-01-10 at 15:16 +0100, Detlef Bosau wrote:
> Jim Gettys wrote:
> >
> >
> > I have to fundamentally disagree when it comes to systems research.
> >
> > If you are doing research into *systems*, an academic exercise using a
> > marginal system can only be justified if you are trying a *fundamental*
> > change to that system, and *must* start from scratch.  Most systems
> > research does not fall into that category.
> >
> >   
> 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
rethinking TCP's implementation in a real system.  That is systems
research.  Maybe I should have said research in implementations and

Simulation of protocols does not fit what I'm talking about here.

> > Doing such work outside the context of a current system invalidates the
> > results as you cannot inter compare the results you get with any sort of
> > "control".  This is the basis of doing experimental science.  Giving me
> >   
> Why does research "outside the context" of a current system invalidate 
> results? Could you perhaps provide a concrete example for this?

I saw what looked to be very nice results showing better caching
behavior in memory systems, done on an obsolete version of Linux a
couple years ago.  But since that version was so out of date, the data
showing improvement over baseline had to be taken with a large *block*
of salt, since so much had been done in the base operating system in the
meanwhile.  The data had become an apples and orange comparison. If I
can remember enough to dig up the paper, I'll send a pointer.

Without a control, experimental science becomes hand-waving anecdotes
(which typifies research in many fields, unfortunately).

> > results that some "improvement" helps Linux 2.4.24, when current Linux
> > is 2.6.19, or whatever, essentially invalidates the result, due to the
> > extensive changes between versions.
> >
> > Much of why Van's research was able to be taken seriously by the Linux
> > community and has had impact was precisely in that he had done the work
> > on a recent version of Linux (independent of whether the code was ever
> >   
> One prominent example for Van´s research is the congavoid paper. Linux 
> did not yet exist when this work was done.
> Does that invalidate this work?

I still have scars on my back from the internet collapse in the mid
'80's. Things were so bad we were at times reduced to Federal Express
between Cambridge and Palo Alto.

The *proof* that made people take the congestion avoidance work
seriously that I remember was the application of Van and Mike Karel's
patches to 4.2BSD that made the internet (and the individual machines)
work again.  

Those patches preceded the paper, if I'm not mistaken of the history.
The proof was in the implementation of the algorithms in widely used
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.
                                       - Jim

Jim Gettys
One Laptop Per Child

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