Re: Rumors about the death of the ARPANET


haverty@CCV.BBN.COM
Mon, 21 Mar 88 12:01:26 -0500


Vint/Frank - my recollection of some of the conflagrations around
checksumming is that the end-end checksum is valuable even if the
piecewise error control is perfect (10 to however many you like);
what the end-end often catches are plain and simple bugs deep down
in the middle of the path, e.g., a pointer off-by-one in a packet
switch buffer under some obscure condition and the like. Since
software is never debugged fully until you retire it, such situations
will crop up, and according to Murphy will happen at the worst time.
What would be interesting is to see if there is a way to design
a simple end-end "checksum" designed to catch errors which are not
like those in communications media, i.e., result from bugs, configuration
mistakes, etc., rather than line noise and the like.
Jack



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