### Syllabus Detail

- Methods of error detection and correction in digital data transmission, including parity bit, checksum. 12 ATAR

### Background

- When sending anything over the internet, there is always problems and corrections to data that you don't often see.
- Packets of data, which contain your email, or image or doc you are sending, often don't get dellvered correctly.
- Therefore, we need an automatic way for them to fix themselves up. Or error correct.

### Parity Bit Error Correction

- This is a check bit method.
- It adds one more bit ( a 0 or a 1) based on even parity setup or odd parity setup.
- If even parity setup (which is most common) then a 1 is added to the right hand end, only if there is an odd number of ones.
- eg 1001001 has an odd number of ones.... so we add a 1 to the right hand end, to make the number of 1s change from 3 to 4 (even parity)
- it now becomes 10010011
- If a 1 or a 0 gets flipped because of interference when getting sent over the network, then the number of ones might be wrong.
- If the number of 1s is wrong, it automatically asks for it to be sent again.
- Jenna on Youtube gives more explanation.

### Checksum Error Correction (works by using the modulus)

- This uses a calculation to check if all the bits are added up correctly.
- If when summed up, doesn't match the number added to the right hand end of the number (the checksum), it must be wrong and the message must be sent again.
- So how does it work?
- The message or image is converted to bits or numbers.
- The numbers are added up.
- The previously agreed to number, is divided into the total of the numbers.
- The remainder or modulus, is added to the right hand end of the number to be sent, and then sent with the message.
- If the message is received and upon checking it notices that the checksum on the right hand side, does not match the calculation, it asks for a resend.
- Eddie Woo explains on youtube.

Found an error or have an enhancement? Please let us know via this contact form