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Article #46Re: CRC-16
From: Marc Kaufman
Date: Tue, 12 Aug 1986 04:20
Date: Tue, 12 Aug 1986 04:20
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1441 bytes
Thanks for the correction. Note that my example was 17 bits, even if I used the wrong polynomial. The problem is, that this represents only three (3) symbols in the newer RF modems (64- or 256- QAM, etc.). In addition, a symbol error in a differentially encoded modem will cause an error in the next symbol (as the phase is corrected). With trellis coding, the error may propogate to two or more symbols before the codes get back to normal. Just possibly (I have not looked in detail) the generated errors may just cancel the CRC error in some cases. In any event, short polynomials become less useful as the number of bits in a symbol increases. Either the makers of modems should select their transition rules to preserve effectiveness of the CRC, or we should look for better error checking polynomials.
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Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU Path: arc1-ca.pugleaf.net!utzoo!decvax!ucbvax!SHASTA.STANFORD.EDU!kaufman From: kaufman@SHASTA.STANFORD.EDU (Marc Kaufman) Newsgroups: mod.protocols Subject: Re: CRC-16 Message-ID: <8608120853.AA06492@ucbvax.Berkeley.EDU> Date: Tue, 12-Aug-86 00:20:28 EDT Article-I.D.: ucbvax.8608120853.AA06492 Posted: Tue Aug 12 00:20:28 1986 Date-Received: Tue, 12-Aug-86 09:47:25 EDT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 12 Approved: protocols@red.rutgers.edu