Cell Relay Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: CR: Re: Single bit header error correction in ATM Specific TC
Hi all. At 11:15 10/05/1999 -0400, Paul Koning wrote: > >I've seen CRCs used in several places (not just ATM HEC) >supposedly for single bit error correction. It's never looked >like a good idea to me. If the block being protected is more >than a few bytes long, the probability of miscorrection >becomes uncomfortably high. And in the case of ATM, you >just do not get any useful benefit out of doing header error >correction. It depends upon the burst error pattern. On optical fiber, it is very common to find single-bit errors OR a large run of bit errors. In these cases, the CRC-8 used to protect a 40-bit block is fine since there are only 40 possible single-bit errors. On copper, bit error patterns vary widely so error correction is, indeed, a bad idea!! This is why the CCITT/ITU-T originally proposed the HEC for multiple-bit error detection/single-bit error correction; they also originally proposed ATM to run exclusively over SONET/SDH. Once copper media were introduced, e.c. was dropped (along with pointers!). Later! /kessler ==================================================================== Gary Kessler +1 802-658-9848 (direct) SymQuest Group +1 802-658-9801 (fax) 30 Community Drive +1 802-351-0210 #4045 (pager) South Burlington, VT 05403 gkessler@symquest.com http://www.symquest.com http://www.sover.net/~kessfam/gck Send PGP encrypted mail to kumquat@sover.net... PGP Public Key: http://www.sover.net/~kessfam/gck/kumquat_pubkey.html
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