Parity Checking
One of the oldest and simplest
A single bit added to each character
- Even parity: number of 1’s remains even
- Odd parity: number of 1’s remains odd
Receiving end recalculates parity bit
- If one bit has been transmitted in error the received parity bit will differ from the recalculated one
Simple, but doesn’t catch all errors
- If two (or an even number of) bits have been transmitted in error at the same time, the parity check appears to be correct
- Detects about 50% of errors