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