Bias bit

The bias bit = 0 for even parity
The bias bit = 1 for odd parity

Example (1) For synchronous transmission the transmitter is to transmit the ASCII character Z. If you received 0101 1000 at the receiver is there an error?

Note: The ASCII value of Z is 101 1010 but when you transmit it a P will be appended to it and the LSB is the first to be transmitted so you are really transmitting 0101 101P

if you XOR the last bit the preceedingh bit the function will be :b7 + b6 + b5 + b4 + b3 + b2 + b1+ b0 = P

so to check whether 1100 0011 is correct we xor it bit per bit:
the xor = 0 +1 + 0 + 1 + 1 + 0 + 0 + 0 =1 but for odd parity the parity bit must be zero and numbers of ones must be odd so by parity checking there's an error

Example (2) If the received data for letter S is 1100 0010 for even parity is there an error

note: that when an even number of bit errors occurs Class 3 probability will occur for parity checking.

1.1 VERTICAL REDUNDANCY CHECK

• Is an error detection scheme that uses parity to determine if a transmission error has occurred within a character .
• VRC is the XORing result of bits within a single character.
• The VRC bit for each charcter is computed in the vertical direction.

1.2 HORIZONTAL OR LONGITUDINAL REDUNDANCY CHECKING

• Is an error detection scheme that uses parity to determine if a transmission error has occurred in a message.

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