Error Checking

Question 1

Name the four type of error checking method

Answer 1

Parity Bit, Majority Voting, Checksum, Check digit

Question 2

Describe how Parity Bit error checking works.

Answer 2

• 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

Question 3

What is the start bit called?

What is the end bit called?

Answer 3

The most significant bit

The least significant bit

Question 4

When is parity bit checking typically used.

Answer 4

During transmission of 7-bit ASCII

Question 5

What are the negatives of using Parity bits

Answer 5

• 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.

Question 6

Describe how Majority Voting error checking works.

Answer 6

Every bit is multiplied by 3
For example 110 becomes 111 111 000
So then the majority of each bit is taken when received

Question 7

Describe 3 advantages of using Majority Voting.

Answer 7

1) It specifies where the error occured
2) The error can be fixed easily
3) It can tell when multiple errors have occurred

Question 8

Describe how Checksum error checking works.

Answer 8

• 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.

Question 9

Describe how Check Digit error checking works and what it’s used for

Answer 9

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.

Question 10

Give a real world example of where a check digit is used.

Answer 10

They’re used to identify a product (an ISBN or barcode) or verify a user (an IBAN) or a social security number)

Question 11

How is the check sum digit produced?

Answer 11

Check digits are digits produced by algorithms that often use modulo arithmetic

Question 12

What’s a disadvantage of majority voting error checking?

Answer 12

Has a longer transmission speed because it triples the length of the bit pattern that’s being sent