Information Coding Systems Error Checking

Question 1

Convert Computer Science to ASCII

Answer 1

067 111 109 112 117 116 101 114 032 083 099 105 101 110 099 101

Question 2

What causes errors?

Answer 2

Bits can change during transmission because of different interference.

Question 3

What is a parity bit?

Answer 3

Parity bits - check that bits are likely to be correct
ASCII 7 bit leaves an additional bit free. An additional bit can be added to add odd or even parity to the data. (parity bit) This is the MSB.

Question 4

How do parity bits work?

Answer 4

If the data is checking for ODD Parity, the bit added will ensure that there are an ODD number of 1’s and vice versa for EVEN parity.

Question 5

What are disadvantages of parity bits?

Answer 5

Parity Bits will ONLY check for errors and cannot identify or correct the error. It may also fail if there are an even number of errors:
1011011 is sent with ODD Parity and so the parity bit is 0.
1000011 is received. 2 errors have occurred but the parity bit of 0 will not catch it.

Question 6

How does majority voting work?

Answer 6

Each bit within the data is sent 3 times. Majority Voting will select the data in the majority of each 3 bits.

Question 7

If the DATA = 1011 what would the Majority Voting Transmission be?

Answer 7

DATA = 1011
Majority Voting Transmission = 111000111111
Received = 101001110111