Character Encoding & Error Detection

Question 1

What is character encoding?

Answer 1

It means representing letters and symbols using binary. This is needed because machines can only directly process binary information.

Question 2

What is ASCII?

Answer 2

It stands for American Standard Code for Information Interchange.

ASCII uses 7 bits to store each character. This means that there are 128 possible characters that can be represented.

Question 3

What are the limitations of ASCII?

Answer 3

It only allows a small number of characters to be represented.

It’s an American standard and only enables communication in English.

Question 4

What is Unicode?

Answer 4

It uses more bits per character than ASCII (typically between 8-32 bits)

Question 5

Why was Unicode introduced?

Answer 5

It was introduced to support a larger range of characters due to increased international communication/support for multiple languages.

Question 6

What are parity bits?

Answer 6

An 8th ASCII bit that is added as a parity bit to detect any errors.
It will not be able to tell you which digit is wrong, so isn’t corrective.

Question 7

If odd parity is used…

Answer 7

The 8th bit is added to ensure there is an odd number of ones in total.

Question 8

If even parity is used…

Answer 8

The 8th bit is added to ensure there are an even number of ones in total.

Question 9

What are the limitations of parity bit?

Answer 9

1. Not corrective - does not reveal which bit/s changed during transmission.
2. If an even number of bits changes, the errors won’t be detected.

Question 10

How does check digit work?

Answer 10

The sender generates the check digit using a function and appends it to the value being sent.

The receiver recalculates the check digit based on what it receives.

If the recalculated check digit is not equal to the received check digit they assume an error has occurred.

It is not corrective.

Question 11

What is majority voting?

Answer 11

It is the only error detection method which can correct errors in the data sent.

It works by the sending device tripling each bit in the bit pattern that is sent.
The receiver then determines the modal bit from each triplet and determines the original binary pattern.

Question 12

What is the limitation of majority voting?

Answer 12

Majority voting is space inefficient, as you are tripling the amount of data that you are sending.

This makes transmission take longer.