Data Representation - Error Checking

Why is error checking necessary?

There is a risk of corruption when transferring data (due to electrical interference, faulty hardware etc.)

What is the sender's job in a parity bit check?

Counting the number of 1s in the bit pattern and adding the correct parity bit

What is the receiver's job in a parity bit check?

Counting the number of 1s in the bit pattern and checking if it matches the type of parity

What does the receiver do when no error has been detected in a bit pattern?

It accepts the packet of data as correct

What does the receiver do when an error is detected in a bit pattern?

It requests the sender for the packet of data to be resent

What error checking method does ASCII use?

Parity Bit

What is a parity bit check vulnerable to?

Having an even number of bits in a bit pattern changed

What is the sender's job in majority voting?

Sending each bit in a bit pattern three (an odd number of) times

What is the receiver's job in majority voting?

Accepting the bit that appears the most from each triplet

What is the disadvantage of majority voting?

It is slow and expensive as the amount of data transferred is tripled

What is the sender's job in a checksum check?

Applying a checksum algorithm to the bit pattern and appending the result of that algorithm (value) to the end of the bit pattern

What is the receiver's job in a checksum check?

Applying the same checksum algorithm as the sender to the bit pattern and checking if the result is the same as the checksum value appended to the received bit pattern

What types of codes is a checkdigit check used for?

For decimal codes, often identification numbers such as bank account numbers or ISBNs

What is the sender's job in a checkdigit check?

Applying a checkdigit algorithm to the decimal code and appending the result of that algorithm (value) to the end of the decimal code

What is the receiver's job in a checkdigit check?

Applying the same checkdigit algorithm as the sender to the decimal code and checking if the result is the same as the checkdigit appended to the received decimal code

What is ISBN-13?

A checkdigit algorithm where:

-the digits are alternately multiplied by 1 and 3

-the sum of the products is found

-the sum is divided by 10 to determine the remainder

-the checkdigit is the result of ten minus the remainder if the remainder was not 0

-the checkdigit is 0 if the remainder was 0

What type of error is checkdigit most effective at detecting?

A transposition error

(adjacent letters swapped around)