Data Transmission

Question 1

What is the structure of data packets

Answer 1

Header
- IP of sender and receiver
- size of packet
- number sequence of packet

Payload
- where the message is stored

Trailer
- checks message if its the right one by identifying the end of the packet (uses CRC)

Question 2

Packet Switching

Answer 2

When each packet of a message takes a different path to increase efficiency, but they can arrive to the destination in the wrong order and therefore need to be ordered

Question 3

Simplex

Answer 3

Data can be sent in one direction only
E.g printer

Question 4

Half-duplex

Answer 4

Data can be sent in both directions, but not at the same time
E.g walkie-talkie

Question 5

Full-duplex

Answer 5

Data can be sent in both directions at the time of
E.g using broadband internet connection

Question 6

Serial data transmission

Answer 6

Data is sent one bit at a time down a single channel/wire
E.g USB connection

Question 7

Parallel data transmission

Answer 7

Several bits of data are sent down several wires/channels at the same time - each wire/channel transmits each bit
E.g using the internal circuits of a computer

Question 8

USB

Answer 8

Universal serial bus
Computer automatically detects the device

Question 9

Parity check

Answer 9

• can be odd or even
• counts number of 1’s to see if message is corrupted or not
• if number is correct then add 0 as the parity bit but if it’s wrong add 1

Question 10

What do you use to find where the error is in parity

Answer 10

• criss cross
• parity blocks

Question 11

Checksum

Answer 11

• data block is about to be transmitted - check sum is calculated
• calculation is done by an agreed algorithm - agreed by sender and receiver
• checksum is sent with the data block
• receiving computer calculates checksum and compares
• if incorrect is sent request is made for resend

Question 12

Echo check

Answer 12

• data is sent
• data is returned
• data is compared and re-sent if any errors are found

Question 13

Check digit + the 2 diff types

Answer 13

The final digit included in a code, its calculated from all the other digits in the code
- ISBN 13 and Modulo 11

Question 14

How do you calculate ISBN 13

Answer 14

1 - add all odd numbered digits
2 - add all even numbered digits and do result ×3
3 - add results together and divide by 10
4 - minus remainder from 10, if remainder is 0 that’s the check digit

Question 15

How do you calculate modulo 11

Answer 15

1 - each digit is given a number starting from 2, right to left
2 - digit is multiplied by it’s number and all digits are added together
3 - result is divided by 11
4 - remainder is subtracted from 11, if remainder is 10 check digit is 1 or X

Question 16

ARQ

Answer 16

Automatic repeat requests
- uses positive and negative acknowledgements
- uses timeout - time interval allowed to pass before an acknowledgment is received