Unit Two- Data Transmission

Question 1

How is Data sent?

Answer 1

in Packets

Question 2

What does a Packet Structure look like?

Answer 2

Split to three parts:
header
payload
trailer

Question 3

What does a header contain? (4)

Answer 3

IP address of sender + receiver
The sequence number of the Packet
The size of the packet

Question 4

What does the Payload contain?

Answer 4

actual data that is being sent (usually 64 KiB)

Question 5

What does the Trailor contain?

Answer 5

Some way of identifying the end of packet
an error checking method
(CRC)

Question 6

What does the term Switching mean?

Answer 6

To pass along to to forward

Question 7

What are the two types of switching?

Answer 7

Packet Switching
Circuit Switching

Question 8

What is Packet Switching? (3)

Answer 8

1. each packet of data takes its own route
2. a sequence number is added
3. a hop number is added

Question 9

What are hop numbers?

Answer 9

the number of hops a packet can take
–> to ensure they don’t bounce around and get lost

Question 10

What is circuit switching?

Answer 10

1. Each packet of data takes the same route

Question 11

Simplex data transmission meaning

Answer 11

data can be sent one direction only

Question 12

Half duplex data transmission meaning

Answer 12

data can be transferred both ways both one at a time

Question 13

Full duplex data transmission meaning

Answer 13

data can be transferred both way at the same time

Question 14

Serial Data transmission meaning

Answer 14

data is sent one bit at a time down a single wire

Question 15

Parallel Data transmission meaning

Answer 15

several bits of data sent over several wires

Question 16

What is the full form of USB?

Answer 16

Universal Serial Bus

Question 17

What happens when a USB connects a device to a computer?

Answer 17

1. computer detects device
2. device is recognized and the appropriate device driver is loaded

Question 18

Benefits for Packet Switching (4)

Answer 18

1. no need to tie a single communication line
2. possible to overcome faulty lines
3. easy to expand passage usage
4. high data transmission rate

Question 19

Drawbacks of Packet Switching (3)

Answer 19

1. packets can be lost and need to be resent
2. Doesn’t work the best with RTS
3. delay while packets are being organized

Question 20

Benefits of USB (6)

Answer 20

1. automatic detectors
2. connections only go one way
3. industry standard
4. different data transmission rates
5. no external power sources needed
6. backward compatible

Question 21

Drawbacks of USB (2)

Answer 21

1. supports maximum of 5m
2. slower data transfer rates

Question 22

Why do you need to check for errors?

Answer 22

1. electrical inferences
2. packet switching (loss of synchronization)
3. skewing of data

Question 23

What are Parity Checks (2)

Answer 23

1. uses even or odd parities (number of 1’s)
2. Parity blocks + criss-cross methods can be used to determine the exact data that has been changed

Question 24

What are Check Sums? (2)

Answer 24

1. Calculated y an agreed algorithm using the block of data
2. The checksum is recalculated by receiver and compared

Question 25

What is an Echo Check? (3)

Answer 25

1. Data sent back to the sender as soon as the receiver gets it 2. it is compared to the data originally sent 3. it is resent if any errors occur

Question 26

What are check digits?

Answer 26

1. check values are calculated with different methods - ISBN 13 - Modulo 11 2. generated digit is added on the end

Question 27

What can Check digits detect? (4)

Answer 27

1. incorrect digits entered 2. transposition errors 3. extra digits in the number 4. phonetic errors

Question 28

How to calculate ISBN-13 numbers (5)

Answer 28

1. add all odd placed numbers 2. add all even placed number then multiply by three 3. add the two values 4. divide by 10 5. subtract the remainder from 10

Question 29

How to calculate Modulo-11 numbers (5)

Answer 29

1. give the number a weighting value (start from 2, go towards the left) 2. multiply the digit with the weighting value 3. total all the sum 4. divide total by 11 5. subtract remainder from 11

Question 30

What is Automatic Repeat Request? (4)

Answer 30

1. uses positive, negative acknowledgements and timeouts 2. if no errors are detected, a positive acknowledgement is sent 3. if error is detected, a negative acknowledgement is sent and data is re-transmitted 4. a timeout set by the sender, if there is no acknowledgement in this time, data is resent automatically