Chapter 2

Question 1

What is the structure of a data packet?

Answer 1

Header
Payload
Trailer

Question 2

What does the header contain?

Answer 2

Origin Address (IP)
Destination Address (IP)
Packet Number

Question 3

What is the payload?

Answer 3

The data being sent, broken down into small parts, each going in one packet.

Question 4

What is the trailer?

Answer 4

The last part of the packet, signalling that the packet is over.

Question 5

The process of transmitting packets is called _____________. Packets are sent via a ___________. Which servers the packets travel through is determined by a ___________

Answer 5

Packet Switching
Network
Router

Question 6

What is the difference between serial and parallel data transmission.

Answer 6

Serial = Only one packet at a time can travel along a single wire
Parallel = 2 or more packets can travel along 2 or more wires.

Question 7

What are the advantages AND disadvantages of serial transmission?

Answer 7

Data should arrive in order of sequence
Less chance of errors in data (interference)
Cheaper than Parallel

Slower than Parallel
Needs a start bit and stop bit, to indicate when data starts and stops being sent.

Question 8

What are the advantages AND disadvantages of parallel transmission

Answer 8

Computers already use parallel, and don’t have to convert data to serial.
Faster than Serial

Bits arrive out of order, need rearranging
More chance of errors in the data (interference)
More expensive

Question 9

What is the difference between simplex, half-duplex, and duplex transmission

Answer 9

Simplex = Data can travel in one direction only
Half-duplex = Data can travel both ways, but not at the same time
Duplex = Data can travel both ways, at the same time.

Question 10

What are the advantages and disadvantages of a USB (universal serial bus)

Answer 10

Easy to use
Fast transmission
Appears in most devices
Drivers to operate hardware must only be downloaded once
Can power a device simultaneously

Ethernet and others are faster
Limited to 5 meters long cables

Question 11

Name 3 error detection methods that can be used to check if data sent is correct

Answer 11

Checksum
Parity Check
Echo Check

Question 12

The _______ bit goes at the start of the _______, to check if the sum of bits in the byte is odd and even.

Answer 12

parity
byte

Question 13

If an odd parity check is run, and the byte looks like this, what is the parity bit: 0 1 1 0 0 1 1 _

Answer 13

1

Question 14

If an even parity check is run, and the byte looks like this what is the parity bit: 1 0 0 0 1 1 1 _

Answer 14

0

Question 15

What is an echo check?

Answer 15

When the receiving device returns the data to the sending device to ensure that it is correct, then followed by a confirmation from the sending device.

Question 16

What happens in an ARQ if the data has no errors

Answer 16

The receiving device receives one packet
It checks that it has no errors.
It sends a positive acknowledgement to the sending device.

Question 17

What happens in an ARQ if the data has errors

Answer 17

The receiving device receives one packet
It checks if it has no errors.
If it has error(s),
It sends a negative acknowledgement to the sending device.
The sender must send the packet again

Question 18

What is checksum?

Answer 18

The sender calculates a value to add to the packet
The receiver calculates the same value
If the values match, a positive acknowledgement is sent

Question 19

What is check digit used for?

Answer 19

To ensure that no errors occur during data input

Question 20

What is data called before and after encryption?

Answer 20

Before: plaintext
After: cipher text

Question 21

An encryption algorithm is called an ______________

Answer 21

Encryption Key

Question 22

The process for symmetric encryption is:

Answer 22

Plain text is encrypted into cipher text by an encryption key
The cipher text and encryption key are sent separately to the receiving device.
The same key is used to decrypt the cipher text into plain text.

Question 23

The process of asymmetric encryption is:

Answer 23

Plain text is encrypted into cipher text by a public key. (of the receiver)
Cipher text sent to receiving device.
Cipher text is decrypted using a private key.