Error Checking and Correction

Question 1

Define parity bit:

Answer 1

A method of checking for errors in the code based on counting the digits

Question 2

Define even parity:

Answer 2

Checking for errors by counting the digits - the parity bit makes sure the number is even, and if it comes in odd, you’ll know there’s been an error

Question 3

Define majority voting:

Answer 3

When each digit is sent multiple times and the most common digit received is assumed to be the correct one

Question 4

Define check digit:

Answer 4

A digit added to the end of the number that is used for checking

Question 5

How is a check digit created:

Answer 5

By taking the digits of the number and manipulating them in some way to make 1 digit

Question 6

What’s a common way of calculating a check digit:

Answer 6

Modulo-11

Question 7

How is modulo-11 calculated:

Answer 7

Give all the numbers a weighting from 2 up starting from the last digit, multiply the digit by the weighting, add all those together, divide by 11, take the remainder away from 11, and that’s the check digit

Question 8

How does even parity work:

Answer 8

Sender calculates the sum of the digits - if it’s even, the parity bit is a 0, if it’s odd, it’s a 1 to make sure the total sum including the parity bit is even. The receiver checks the sum of the digits for the received value. If it’s odd, it knows an error has occurred and requests that the data is resent. If it’s even, it knows the data is likely to be correct and accepts it