Error Detection

Question 1

What are parity checks?

Answer 1

• when data is transmitted, parity bit is sent by the transmitting end and odd or even parity is checked at the receiving end
• parity bit is set to either 0 or 1 at start of transmission to make total number of 1s odd or even.
• the 1s counted at receiving end and is wrong number of bits are ‘on’ to 1, error detected and data resent

Question 2

What is a parity block check and when is it used

Answer 2

• used when sending multiple bytes in one transmission block.
• each byte will have its own parity bit
• final parity byte is used which contains a parity bit for each column
• error in transmission can be detected in exact position and identified and corrected

Question 3

What is a checksum?

Answer 3

Is calculated by using algorithm to sum all the data to be sent in a transmission
- check sum sent with transmission and recalculated at the end using same method
- if start and end do not match, data has changed during transmission

Question 4

What is a echo check

Answer 4

• performed by asking recipient computer to send back an exavt copy of the data.
• data is compared with original
• if both copies match, data is without error

Question 5

What does ARQ stand for

Answer 5

Automatic repeat request

Question 6

What are ARQs

Answer 6

Computers using ARQs will automatically send back a positive acknowledgment of a Data packet if deemed correct
- or they will ask for data to be resent is error detected
- if no acknowledgement returned within certain time period a timeout is registered and sending computer resends packet
- process repeats until packet received is correct or until ARQ limit is reached

Question 7

What are check digits

Answer 7

• a additional digital at the end of a string of other numbers
• check digit recalculated on data entry
• if matches with the one at end of the number, the numbers are deemed correct and in the right order

Question 8

How to calculate check digits, (module 11)

Answer 8

1. Times the check digit and weight togehter
2. All them all up
3. Divide by 11 and find reminder
4. Substrat reminder from 11

Question 9

How to calculate check digits, ISBN- 13

Answer 9

1. Times odd check digits with 1
2. Times even with 3
3. Add odd and even sums together
4. Divide sum by 10 and find reminder
5. 10 - reminder

Question 10

Plaintext -

Answer 10

Original message/ data file

Question 11

Ciphertext -

Answer 11

Encoded message using encryption algorithm and key

Question 12

What is Symmetric encryption and how does it need to be transferred?

Answer 12

• private key encryption
• uses pre-shared key to encode and decode data
• key must be transferred separately to recipient so only they can decrypt

Question 13

What is asymmetric encryption and how is it transferred?

Answer 13

• public key encryption
• uses 2 separate but related keys
• public key is shared with others and used to encrypt a message so it can be deciphered by the intended recipient with their private key

Question 14

What is a danger of using symmetric encryption?

Answer 14

Anyone that obtains key can encrypt/decrypt the message