TAILIEUCHUNG - Error Detection and Correction

Data can be corrupted during transmission. For reliable communication, error must be detected and corrected are implemented either at the data link layer or the transport layer of the OSI detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination | Prof. Choong Seon HONG Error Detection and Correction 9장 Error Detection and Correction Types of Errors Detection Error Correction Error Detection and Correction Data can be corrupted during transmission. For reliable communication, error must be detected and corrected are implemented either at the data link layer or the transport layer of the OSI model Type of Errors Type of Errors(cont’d) Single-Bit Error ~ is when only one bit in the data unit has changed (ex : ASCII STX - ASCII LF) Type of Errors(cont’d) Multiple-Bit Error ~ is when two or more nonconsecutive bits in the data unit have changed(ex : ASCII B - ASCII LF) Type of Errors(cont’d) Burst Error ~ means that two or more consecutive bits in the data unit have changed Detection Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination Detection(cont’d) Redundancy Detection(cont’d) Detection methods VRC(Vertical Redundancy Check) LRC(Longitudinal Redundancy) CRC(Cyclic redundancy Check) Checksum Detection(cont’d) VRC(Vertical Redundancy Check) A parity bit is added to every data unit so that the total number of 1s(including the parity bit) becomes even for even-parity check or odd for odd-parity check VRC can detect all single-bit errors. It can detect multiple-bit or burst errors only the total number of errors is odd. Detection(cont’d) Even parity VRC concept Detection(cont’d) LRC(Longitudinal Redundancy Check) Parity bits of all the positions are assembled into a new data unit, which is added to the end of the data block Detection(cont’d) CRC(Cyclic Redundancy Check) ~ is based on binary division. Detection(cont’d) CRC generator ~ uses modular-2 division. Binary Division in a CRC Generator Detection(cont’d) Binary Division in a CRC Checker Detection(cont’d) Polynomials CRC generator(divisor) is most often represented not as a string of 1s and 0s, but as an algebraic polynomial. Detection(cont’d) A polynomial representing a .

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