Networks and CommunicationsCommunication Media and Software, Network design and creation, connectivity standards, protocols, security, operating systems.

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.
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