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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: TCP "reliability"Jonathan, > >(2) Data is correctly delivered in the face of corruption. TCP's 16-bit > > checksum falls short of a 32-bit CRC in its ability to detect > > corruption, and hence TCP leaves something to be desired here. > > stricly, what you say is unquestionably true. Right ... I put the numbers of bits in for a reason :-). > But I think you are > conflating two quite distinct properties here: 32-bit error-detecting > codes (EDCs) and the kinds of errors which a (32-bit) CRC guarantee to > catch, versus the errors which to which a transport-level error chehck > is, empirically, subjected. > > It turns out that, on the best data we (I and Craig Partridge) have on > empirically-observed transport-level errors, CRCs are just not a whole > lot better than a 32-bit mod-M additive sum (where M ~= 2^32). I think that's fair, and I certainly don't want to argue with empirical data - my wife claims the first rule of engineering is "never argue with results" ... and she's always right ;-). However, when looking at TCP, we have to deal with the 16-bit checksum that exists and really cannot be changed at this juncture. Thanks, --David --------------------------------------------------- David L. Black, Senior Technologist EMC Corporation, 42 South St., Hopkinton, MA 01748 +1 (508) 435-1000 x75140 FAX: +1 (508) 497-8500 black_david@emc.com Mobile: +1 (978) 394-7754 ---------------------------------------------------
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