[e2e] Simulator for wireless network

Jim Gettys jg at laptop.org
Mon Apr 16 15:19:05 PDT 2007

On Mon, 2007-04-16 at 10:57 -0700, Joe Touch wrote:
> Detlef Bosau wrote:
> > S. Keshav wrote:
> >>
> >>
> >> This is the reason why 'proof by simulation', for computer systems, at
> >> least, is farcical. Not only are simulators known to be buggy, but
> >> they are also simulating a system that is too loosely coupled to be
> >> adequately modeled.

> > 
> > Is a "proof by implementation" is better?
> > 
> > I don´t think so. Implementations are known to be buggy. Implementations
> > are known to not behave as expected.

Yes, operating systems are known to be buggy: and you get them fixed if
you want to get real results.  

Oh, you say you can't get the bugs fixed?  Then choose a different
operating system.....  Responsible vendors get their bugs fixed when you
bring them to their attention, or the code is available for you to fix.

And the insight gained when the implementation not behaving as you
expect you learn that your programs are broken. That is also of great
value.  Would that many/most HTTP implementations understood the
underlying TCP protocol; unfortunately, most implementers do not.

No one said that experimental science was easy.... (says one who worried
about how HTTP would run across the actual internet, rather than a
simulator; Craig, thanks again for shepherding us crazies through the

Having said the above, I note that some particular tools, such as those
that can inject delay in network paths, or losses in those paths, in
combination with measurements across real networks can give additional
insight into the likely behavior of real systems in different
circumstances that you may not easily be able to test directly.  Those
tools have good value. But there is no substitute for real measurement.
                                  - Jim
Jim Gettys
One Laptop Per Child

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