Error Checking
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Name the four type of error checking method
Parity Bit, Majority Voting, Checksum, Check digit
Describe how Parity Bit error checking works.
• An extra bit is added to the start/end of a bit pattern. • When the data is transmitted it specifies where the parity bit was added and whether odd/even parity was used . • When the data is received it checks whether the amount of 1’s adds to odd or even (according to what was specified when the data was sent) • If the 1’s don’t add up to what was specified, the receiver knows to request that the data is resent
What is the start bit called? What is the end bit called?
The most significant bit The least significant bit
When is parity bit checking typically used.
During transmission of 7-bit ASCII
What are the negatives of using Parity bits
• It doesn’t specify where an error has occurred so the error can’t be corrected due to this • It can be reliable as if multiple errors occur it could mean that it won’t recognise an error has occurred.
Describe how Majority Voting error checking works.
Every bit is multiplied by 3 For example 110 becomes 111 111 000 So then the majority of each bit is taken when received
Describe 3 advantages of using Majority Voting.
1) It specifies where the error occured 2) The error can be fixed easily 3) It can tell when multiple errors have occurred
Describe how Checksum error checking works.
• A checksum algorithm is applied to the data • It returns a value which is then transmitted with the data. • The receiver recalculates the checksum and compares the values. • If they’re the same value, it knows no error has been made.
Describe how Check Digit error checking works and what it’s used for
An extra digit is placed at the end of a string of numbers. It’s used to recognise and prevent human errors when entering or assigning identification numbers.
Give a real world example of where a check digit is used.
They’re used to identify a product (an ISBN or barcode) or verify a user (an IBAN) or a social security number)
How is the check sum digit produced?
Check digits are digits produced by algorithms that often use modulo arithmetic
What’s a disadvantage of majority voting error checking?
Has a longer transmission speed because it triples the length of the bit pattern that’s being sent