[e2e] Re: [Tsvwg] Really End-to-end or CRC vs everything else?

Luigi Fratta fratta at elet.polimi.it
Tue Jun 12 06:37:52 PDT 2001

please remove my name from this mailing list.


At 08.47 12/06/01 -0400, David P. Reed wrote:
>At 06:57 PM 6/11/01 -0700, Christian Huitema wrote:
>>What is at stake here is whether we want a safety belt or an alarm bell.
>I would argue that the current TCP isn't a very good alarm bell, because it 
>doesn't detect too-smart-for-their-own-good, friendly "adversaries" (such 
>as NATs that recompute the entire checksum correctly after making serious 
>changes to the contents) that inadvertently weaken the detection.
>  Note that, if you really follow the e2e argument, this
>>is OK: the only way to be certain that the back-up went well is by
>>computing a strong checksum over the whole volume, not by trusting TCP.
>Indeed.  But then the IETF ought to spread the gospel to the folks who are 
>responsible for FTP and SMTP, for example.  These poor souls typically 
>believe that TCP provides a *reliable* stream, where the word reliable is 
>implicitly defined as *perfect*.
>>In fact, it is all a matter of probabilities and arbitrations. The
>>transmission system should be good enough that the backup is OK most of
>>the time, so that the e2e checksum (volume) only fails rarely, so that
>>the cost of correction is acceptable...
>I assume you mean by transmitting the whole file again.
>- David
>WWW Page: http://www.reed.com/dpr.html
Prof. Luigi Fratta
Dipartimento di Elettronica e Informazione
Politecnico di Milano
Piazza Leonardo da Vinci, 32
20133  MILANO
Tel.+39-02-2399-3578   Fax.+39-02-2399-3413
email.  fratta at elet.polimi.it

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