ITPEC FE Morning April 2023 Question 6
Which of the following is an error detection method where, on the sender side, the data sent accompanies a remainder of the data bit sequence divided by a specific generator polynomial, while on the receiver side, error detection is performed by checking if the received bit sequence is divisible by the same polynomial?
Explanation
CRC — the cyclic redundancy check appends the remainder of dividing the data by a generator polynomial.
The sender treats the data bits as a polynomial, divides it (modulo 2) by the agreed generator polynomial and appends the remainder as check bits. The transmitted sequence is then exactly divisible by the generator, so the receiver divides it again: a remainder of 0 means no error was detected. CRC is good at catching burst errors and is used in Ethernet frames and on storage devices.
Answer (a)
Why not others:
- •(b) Hamming code — adds check bits computed as parities over chosen bit positions, which can locate and correct a single-bit error; there is no polynomial division
- •(c) Horizontal parity check and (d) Vertical parity check — add a parity bit that makes the number of 1s in each row or column even (or odd); they count bits and divide nothing
Key rule: Parity counts 1s, a Hamming code places parity bits so that one error can be located and fixed, and CRC divides by a generator polynomial and checks the remainder.
Basic Theory · AI-written, may contain errors
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