 The
2dimensional parity scheme can
correct all
1 bit errors
Example:
Transmitted data:
11110000
10101010
11111111
10100101
Received with one bit in error:
11110000
10101010
11011111 < odd parity
10100101
^

odd parity

The receiver can
tell
which bit was in
error from the
parity check !!!
Therefore:
 The receiver can
take the initiative to
correct
the received message !

 The
2dimensional parity scheme
can
detect all
2 bit errors...
but it
cannot
correct
the error.
Example:
Transmitted data:
11110000
10101010
11111111
10100101
Received with 2 bits in error:
11110000
10111010 < odd parity
11011111 < odd parity
10100101
^^

odd parity

The errors can be detected.
However,
the receiver
cannot
correct the error:
 The cause of error is
ambiguous:
Original data:
11110000
10011010
11111111
10100101
Error pattern #1:
11110000
10001010 < odd parity
11011111 < odd parity
10100101
^^

odd parity
Error pattern #2:
11110000
10111010 < odd parity
11101111 < odd parity
10100101
^^

odd parity

Both cases will result in the
same parity pattern !!!
The receiver cannot tell
which of these
2 error cases
has occured....
So the receiver
can not correct
the error

