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

David P. Reed dpreed at reed.com
Tue Jun 12 05:47:21 PDT 2001

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

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