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Two-dimensional parity, as discussed in the exercise, makes it possible to detect and correct single bit errors, but two-bit errors and burst errors (a sequence of bits that have all been altered or some of which have been altered) are still undetected. Fig. 23.3.2 shows a 2-dimensional parity scheme using even parity. A single bit error is detected at the intersection of a row and a column that has an incorrect parity bit.
Of course the bits really aren't transmitted in a two-dimensional form. Several methods of actually sequencing the bits onto the wire are possible -- either transmit each column at a time or each row at a time. |
