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

Detlef Bosau detlef.bosau at web.de
Wed Jan 10 10:56:36 PST 2007

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.

> 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.

> 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 

At least we should exploit these befor deploying premature protocols.

> 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.

Second: Can experimental deployment replace a solid research? I don´t 
think so.

>> 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.

So, there was an opportunity to learn from.

More drastically spoken. We all know about the Titanic disaster. And 
about the Takoma bridge disasater.
Do these invalidate academic research for, how it is called in englisch, 
naval engineering and civil engineering?
I don´t think so. I think proper research prevented a number of 
disasters like these.

And it was proper research, when we learnt from the Takoma bridge 
disaster and eventually, after decades of research, the Akashi-Kaikyo 
bridge could be completed.
> 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.  

First: How many nodes did the Internet have that time?
Seconde: How many operating systems and implementations for TCP/IP 
support have been around that time?

To the best of my knowledge, the "Internet" was an experimental test bed 
that time. We must not compare this situation to the actual one.

> 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

I don´t think that this is a "proof". I think, the congavoid paper has a 
very sound theoretical foundation.

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.

> 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.


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