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Second Level Error Detection System for Run Length Encoded Noncoded Information Data

IP.com Disclosure Number: IPCOM000079873D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Garcia, JE: AUTHOR

Abstract

Error detection is provided at the uncoded bit level as a second level over the transmission error detection, to insure virtually error free NCI communications.

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Second Level Error Detection System for Run Length Encoded Noncoded Information Data

Error detection is provided at the uncoded bit level as a second level over the transmission error detection, to insure virtually error free NCI communications.

In a noncoded information (NCI) transmission system, undetected transmission errors may render the output copy virtually unintelligible. This is due to the fact that undetected transmission errors may cause decoding errors that propagate. The susceptibility of error propagation is dependent upon the particular coding scheme employed. Some known non-interline-dependent schemes using run-length codes are minimally susceptible to propagation of errors; but interline-dependent schemes, such as predictive or referencing run- length codes may be quite susceptible to error propagation.

In most run-length coding schemes such as the ones described above, a unique word may be used to describe an end-of-scan (EOS) indication. This method is quite commonly used to signify the end of one scan and the beginning of another. This EOS signification could also be used to indicate the last white run-length of the page (quite commonly the right-hand margin), so that no new coded bits are added to provide EOS significations.

Now, at a given resolution, the number of bits available for coding in a line are known. If the bits resulting for the decoded run-length codes are counted, upon the reception of an EOS indication this number should be less than the number of bits known to be available. If any time during the decoding procedure the number of decoded bits becomes greater than the number of bits available, it can be assumed that an undetected transmission error has occurred. Upon this indication, decoding is stopped and a search is begun for the unique EOS code to provide a "sync" point for commencing the decoding again. For Dual-Mode codes not only the EOS code, but also the E0S code "shifted by two" should be searched, because the error could have caused an erroneous change of the bit- mode indicator.

The described scheme will stop most undetected transmission errors from propagating, and will result in one line of data being lost. Th...