Error Detection and Correction

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  • Error Detection And Correction.
    • Parity Checks
      • - to ensure that a single word or byte of data has been transferred within the system correctly
      • - a bit in each byte or word is reserved to be the parity bit
      • - the parity bit is set to 1 or 0 depending on the data
      • - if the data is corrupted, then the parity check is likely to fail
      • - a specific bit in a byte is the parity bit/ 8th bit/ MSB in a byte is the parity bit.
        • - the sum of the bits in a byte is odd if odd parity is being used/ even is even parity is being used
          • - when a byte is received it's parity is checked
            • - if the parity of the byte has changed an error has occurred/ at least 1 bit has flipped
    • Checksums
      • - to ensure that a block of data hs been transferred within the sytem correctly
      • - extra words of data are added to a block of data that are worked out from the value of the data in the block
      • - at a later stage the checksum is worked out again, and compared with the original, to ensure the data has not been corrupted at some stage in the system
      • - an algorithm is applied to a block/ packet of data to create a checksum.
        • - the checksum is appended to the block/ becomes part of the block
          • - then the block is received the checksum is recalculated using the same algorithm
            • - if it differs, then an error has occurred.
    • Cyclic Redundancy Check
      • - particular type of checksum
      • - commonly used to verify blocks of data stored on disks or transmitted across networks
    • Echo Checking
      • - feature of data transmission in which the data received is returned to the point of origin for comparison with the original data in order to check it
      • - when data is received a copy is transmitted back to the sender/ course
        • - where it is compared with the original
          • - if it differs the original data is retransmitted
            • - echo checking is an automatic process
    • https
      • communicate protocol
      • - ensures secure communication between a browser and a web server
      • - authenticates the website and ensures the privacy if data while in transit
      • - uses TLS or SSL
    • Encryption
      • - data is encoded / scrambled before transmission
      • - using a key / cipher / algorithm
        • - data is encoded / scrambled before transmission
        • - intercepted data is meaningless / unreadable without the key
          • - it is decrypted upon receipt
    • Digital Certificate
      • - an encrypted messaged provided by a certification authority
        • - confirming that the sender is who they claim to be
          • -  it is attached to the message and includes a digital signature
            • - which can be confirmed by sending a secure message to the certification authority

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