Longitudinal Redundancy Check

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What Does Longitudinal Redundancy Check Mean?

a longitudinal redundancy check (LRC) is an error-detection method for determining the correctness of transmitted and stored data.


LRC verifies the accuracy of stored and transmitted data using parity bits. It is a redundancy check applied to a parallel group of bit streams. The data to be transmitted is divided into transmission blocks into which additional check data is inserted.

This term is also known as a horizontal redundancy check.

Techopedia Explains Longitudinal Redundancy Check

LRC generally applies to a single parity bit per bit stream. Although simple longitudinal parities only detects errors, a combination with additional error control coding, such as a transverse redundancy check, are capable of correcting errors.

LRC fields consist of one byte containing an eight bit binary value. LRC values are calculated by transmitting devices, which append LRC to messages. The device at the receiving end recalculates the LRC on receipt of the message and compares the calculated value to the actual value received in the LRC field. If the values are equal, the transmission was successful; if the values are not equal, this indicates an error.

LRC is generated through the following steps:

  1. Add all bytes in messages excluding the starting colon and the ending the carriage return line feed
  2. Add this to the eight-bit field and discard the carries
  3. Subtract the final field value from FF hex, producing one’s complement
  4. Add one, producing two’s complement

In a system environment where a data stream is accepted from a host during host-initiated operations, LRC calculations are performed and appended to every received data block. The resulting blocks are stored by the subsystems. As data passes through the subsystem, LRC calculations are performed. If the host requests data later, a data block is sought along with the previously calculated LRC. The same LRC exclusive or calculations are performed and compared with stored LRC values as data is transferred to the host. If the stored value matches the newly calculated values, the data is considered to be valid.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.