unit 2

Question 1

What does a packet of data in a unit contain?

Answer 1

• packet header
• payload
• trailer

Question 2

What does the packet header include?

Answer 2

• destination address
• packet number
• originator’s address

Question 3

Process of packet switching:

Answer 3

• Data is broken down into packets
• Each packet could take a diff route
• A router controls the route a packet takes
• Packets may arrive out of order
• Once last packet arrives packets are reordered.

Question 4

Different methods of data transmission:

Answer 4

• serial
• parallel
• simplex
• half-duplex
• full-duplex

Question 5

Serial data transmission

Answer 5

A transmission method where data is sent one bit at a time down a single wire.

Question 6

what is packet switching?

Answer 6

A method of transmitting data packets across a network.

Question 7

Advantages & disadvantages of serial

Answer 7

Ad
- sent one bit at a time, arrives in order of sequence, less chance of data getting mixed up.
- sent along single wire so less chance of interference(error in data)
-only one wire is needed for a serial tansmission cable, so cheap to buy

Dis
-data sent one bit at a time so data transmission is slower.
- additional data may need to be sent to indicate to the recievinf device when transmission has started(start and stop bit).

Question 8

Parallel

Answer 8

a transmission method where data is sent multiple bits at a time down multiple wires.

Question 9

Advantages & disadvantages of parallel

Answer 9

Ad
- data sent multiple bits at a time, transmission is quicker.
- no need to convert to serial transmission to transmit data across a network.
Dis
- as data sent multiple bits at time, bits not arrived in order, increases risk of skewed data.
-multiple wires means more chance of interference, more errors in data.
- multiple wires, expensive

Question 10

simplex

Answer 10

transmission method where data is transmitted in a single direction only.

Question 11

half-duplex

Answer 11

transmission method where data is transmitted in both directions, but in one direction at a time.

Question 12

full duplex

Answer 12

transmission method where data is transmitted in both directons at the same time.

Question 13

what is the USB interface and how is it used to transmit data?

Question 14

advantages & disadvantages of USB interface

Answer 14

Ad
- simple interface. USB cable to devixe can only fit into USB one way. Less errors in connecting devices are made.
- Speed of USB connection is high, data can be transferred quickly.
- A USB connection can be used to charge a device.

Dis
- length of a USB cable is limited
- Transmission speed high but not as high as other types of connection.

Question 15

Types of error detection methods that check data after transmission

Answer 15

-parity check
-checksum
-echo check

Question 16

Why do we need to check for errors?

Answer 16

in process of data transmission errors can occur due to interference. E.g data loss, data gain

Question 17

parity check

Answer 17

error detection method that adds an additional bit to each byte to create an odd or even sum. If even amount of 1´s, even parity.

Question 18

checksum

Answer 18

error detection method that performs a calculation on the data to create a checksum value.Checksum values are compared after transmission to see if they match.

Question 19

error check

Answer 19

error detection method that send a copy of the transmitted data back to the sender to be compared with the original data sent.

Question 20

ARQ(automatic repeated request)

Answer 20

error detection method that uses acknowldgement and timeout to see if data has arrived correctly after transmission.

Question 21

negative acknowldegement

Answer 21

• sending device transmits the first data packet.
• recieving device recieves the data packet and checks it for errors.
• If recieving device detects no errors, no further action is taken.
• if recieving device does detect errors it will send a negatiev acknowledgement back to sender.
• If sender recieves - ack then means data sent incorrectly so can resend data packet.
• timeout set by sending device, if doesnt recieve - ack before time out, it doesnt wait to send next data packet.

Question 22

positive acknowledgement

Answer 22

-sending device transmits the first data packet.
- receiving device receives the data packet and checks it for errors.
- once receiving device knows has been sent data error free, sends + ack.
- if sending device no receive + ack within set timeframe, timeout occurs.
- when timeout occurs, the sending device resends data packet. Keep doimg this when timeout occurs unil gets a + ack.

Question 23

encryption

Answer 23

A method of securing data for storage of transmission that scrambles it and makes it meaningless.

Question 24

encryption key

Answer 24

type of algorith used to encrypt data

Question 24

plain text

Answer 24

data before encryption

Question 25

cipher text

Answer 25

data after transmission

Question 26

Symmetric encryption & method

Answer 26

Type of encryption that uses same key to encrypt and decrypt data.

• plain text encrypted into cipher using encryption key.
• cipher text and encryption key sent separately to receiving device.
• same key used to decrypt the cipher text back into plain text.

Question 27

Asymmetric encryption & method

Answer 27

Type of encryption that uses two diff keys to encrypt and decrypt.

-plain text encrypted into cipher text using a public key. Type of encryption algorithm,
- cipher text transmitted to recieving device.
- cipher text cannot be decrypted using public key, decrypted using private key.