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A vertical redundancy check (VRC), also called a parity check or character parity, adds one parity bit to each data unit so a receiver can detect certain transmission errors. The sender and receiver must agree on even or odd parity. VRC can detect some corrupted data, but it cannot identify or repair the bad bit on its own.
What is VRC in computer networks?
VRC is a basic error-detection method used in data communications. For each protected character or other data unit, the sender adds one extra bit—the parity bit. The receiver counts the 1 bits in the received unit and checks whether the total follows the agreed parity rule. A mismatch signals that an error may have occurred.
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The name “vertical” is used for this character-level parity check. It is commonly described simply as a parity check. Manonmaniam Sundaranar University’s VRC explanation and a Wiley chapter excerpt on data communications describe parity as one of the basic error-control methods.
How does the VRC parity bit work?
Before sending data, the sender chooses the parity bit to make the full unit—including that bit—contain the required number of 1s. Both ends must use the same convention:
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- Even parity: the complete unit must contain an even number of 1 bits.
- Odd parity: the complete unit must contain an odd number of 1 bits.
For example, the seven-bit data 1100001 contains three 1s. With even parity, append a 1, giving 11000011. The resulting eight-bit unit contains four 1s, an even total. This example places the parity bit at the end; a protocol or representation may assign it a different position.
What errors can VRC detect?
A single flipped bit changes the count of 1s by one, so it changes the unit’s parity. The receiver can therefore detect a one-bit error when it checks the received unit against the expected rule. IEEE Technology Navigator describes parity-check codes as detecting single-bit errors, while noting that parity alone does not correct them: IEEE Technology Navigator: Parity check codes.
VRC can miss corruption when an even number of bits change. For example, flipping two bits may leave the total parity even when even parity is in use. The check then passes despite the altered data. A passing parity check is therefore not proof that the data arrived unchanged.
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No. A parity mismatch tells the receiver that the unit fails the agreed check, but a single parity bit does not reveal which data bit changed. VRC alone cannot locate the error or reconstruct the original data. A system that needs correction requires additional error-control information or a retransmission process; those capabilities are not provided by the VRC check itself.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What are VRC’s trade-offs?
VRC is simple and adds one check bit to each protected unit. Its limitation is the narrow set of errors it reliably flags: a one-bit change alters parity, but changes in pairs can preserve it. Other methods, including longitudinal redundancy checking (LRC) and cyclic redundancy checking (CRC), are also used for error detection. Their relative suitability depends on the system and error patterns; there is no universal ranking implied by the basic VRC definition.
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