[Mageia-discuss] Switzerland Mirror Switch.ch

Michael Scherer misc at zarb.org
Thu Feb 17 23:31:43 CET 2011

Le jeudi 17 février 2011 à 19:48 +0100, Juergen Harms a écrit :
> >> Well, in fact, given the way tcp work, I do not see how it could
>  >> suffer from a transmission problem.
> Tcp corrects errors with a certain likelyhood. I do not know what 
> CRC-something is used by ftp - for CRC-16, depending on the type of 
> error and the package length, probablilities are smaller than 10 power 
> -6 (I did these figures many years back, rapid googling does not provide 
> any evident figures). Anyhow, with this order of magnitude, and with the 
> 100 M bytes(!) of a typical largish package, the probability of 
> receiving an apparently good package which after all is not so good is 
> non-negligeable. Doing another check at the application level therefore 
> may be of substantial merit. Would be good to get input from somebody 
> who is more competent.

IP and TCP both have error detections with 16 bits checksum. And the
chance that a error slip in such a way that it is not detected by
neither checksums, and at the same time that the error happen at the
physical level ( ie, cable level ) and do not happen more than once are
really really rare. 

Even if you would cause such a error, you would likely not be able to.

Michael Scherer

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