Therefore, your data stream must include a process called error checking. Error checking is accomplished by adding some kind of standard information to each byte. In a simple computer data network, the handshaking informa- tion is called the parity bit, which tells the device receiving each byte whether the sum of the ones and zeroes inside the byte is odd or even. This value is called a checksum. If the receiving device discovers that the parity bit is not correct, it instructs the transmitter to send the same byte again.