Error detection and correction

Error detection and correction is about methods to make sure that information or data is not corrupted, and still makes sense. The techniques help reliable delivery of digital data over unreliable communication channels.

Detecting an error
There are different ways to make sure an error can be detected. This is done by adding more data or information to the data transmitted. Adding more data than needed is called redundancy.

Repetition codes: The data is broken up into blocks. Each block is then sent a number of times. 
Parity bits can be used. The parity bit is 1 for an odd number of ones, and 0 for an even number (or vice versa)
Checksums
Cyclic redundancy checks
Hamming codes
Hash function
Longitudinal redundancy check
Transverse redundancy check
Polarity schemes

Correcting an error
There are two main ways to correct an error:
 Automatic repeat request (ARQ) - The receiver detects an error and automatically requests a repetition
 Forward error correction

 Other websites 
 Error control --Citizendium

Category:Information theory