Re: [tcpm] Separate header checksums and WiFi

Michael Welzl <michael.welzl@uibk.ac.at> Wed, 31 January 2007 17:13 UTC

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Subject: Re: [tcpm] Separate header checksums and WiFi
From: Michael Welzl <michael.welzl@uibk.ac.at>
To: Joe Touch <touch@ISI.EDU>
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On Wed, 2007-01-31 at 17:54, Joe Touch wrote:
> Michael Welzl wrote:
> > On Wed, 2007-01-31 at 16:58, Joe Touch wrote:
> ...
> >> There was a separate issue - you need to *know* the header is intact.
> >> For TCP, there's no separate header checksum to provide that
> > 
> > Well, that's what my proposal added  :)
> 
> Did your experiment measure that aspect? That's the key question - how
> many packets have recoverable headers...

Yes! It's a sad, sad story (well, for me it was  :)   ).
See the tables on pages 62ff of
http://www.welzl.at/research/projects/corruption/index.html

To give you an example, in the measurement on page 61,
we had approx. 479k received packets, of which 178 were
received with errors and 14 had an intact header checksum.

That's the approximate order of magnitude... tens or
hundreds, if not less, out of hundreds of thousands.

By the way, I'd like to point out that all the credit
for this measurement goes to the master student who
did it, Mattia Rossi - he really put a lot of effort
into this. BTW, he's now in Australia (Perth), taking
a break, and soon looking for a job there AFAIK;
his email address is (hopefully still working?)
mattia.rossi@uibk.ac.at and I'm cc'ing him.

Cheers,
Michael


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