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Question 1

Structure of a packet

Answer 1

-Header
-Payload
-Trailer

Question 2

State three components of the header

Answer 2

Destination address
Originator’s address
Packet number

Question 3

payload

Answer 3

content to be sent

Question 4

trailer

Answer 4

has data that indicates the end of the packet and error checking information

Question 5

packet switching

Answer 5

1) Data is broken down into packets
2) As packets are sent through the network they could each take a different route
3) The router will control the route the packets go through
4) as packets arrive they may be out of order so it will need to be rearranged

Question 6

serial transmission

Answer 6

one bit is sent at a time over a single wire

Question 7

parallel transmission

Answer 7

many bits are send at a time over multiple wires

Question 8

simplex

Answer 8

data can only travel in one direction

Question 9

half-duplex

Answer 9

data travels in both directions but not at the same time (along only one cable)

Question 10

full-duplex

Answer 10

data can move in both directions simultaneously using two cables

Question 11

advantages and disadvantages of parallel

Answer 11

advantages:
- faster
- can send multiple bits at the same time

disadvantages:
- crosstalk (a signal in one line creates disturbance in another line)
- skew (as each wire has different properties, the data may arrive at different times, so you must wait until all the bits are sent until you can send the next set of bits. This slows down the data transfer - to solve this the transmission distance needs to be decreased)

Question 12

advantages and disadvantages of serial transmission

Answer 12

advantages:
- no issue of crosstalk or skew
- cheaper as there is only one wire
- better for long transmission distances

disadvantages:
- slower fro short distances

Question 13

A CPU communicates with RAM using parallel transmission.
Describe the reasons why parallel transmission is used over serial transmission
in this case.

Answer 13

• RAM and CPU are located very close together on a motherboard meaning they don’t really suffer from skewing.
• The lines on the CPU/RAM and motherboard are all hard wired with enough distance between them meaning they don’t suffer from crosstalk
• There are large amounts of data need to be transmitted between CPU and RAM so using
  parallel transmission more data can be transmitted more quickly

Question 14

USB

Answer 14

Universal serial bus (USB) is a serial cable that is commonly used to connect external devices to computers, laptops, tablets and smartphones

Question 15

disadvantages and advantages of USB

Answer 15

BENEFITS
It cannot be inserted incorrectly

Supports different transmission speeds

High speed transmission

Automatically detected (not connected) // automatically downloads drivers

Powers the device (for data transfer)

Backward compatible

Question 17

what is encryption

Answer 17

The purpose of encryption is to encode a file or data into something that cannot be read or understood

Question 18

need for encryption

Answer 18

for privacy and personal information not to be stolen or seen by unwanted poeple

Question 19

Symmetric encryption

Answer 19

• a key is shared between the sender and the receiver
  -This key encrypts the data before it is transmitted
  -The receiver uses the key to decrypt the data

Question 20

Asymmetric encryption

Answer 20

In asymmetric encryption, two keys are created by the receiver. Private key and the public key.
This means that anyone can
encrypt the data with public key, but only the receiver can decrypt it with the private key.

Question 21

Decrypt

Answer 21

decode encrypted data back into plaintext

Question 22

Encrypt

Answer 22

encode data into an unreadable form

Question 23

Plaintext

Answer 23

text that hasn’t been encrypted

Question 24

Shared key

Answer 24

the secret key that is used to encrypt and decrypt the data

Question 25

Public key

Answer 25

a key that anyone may see and use to
encrypt data before it is sent to someone

Question 26

Private key

Answer 26

the key used to decrypt data

Question 27

Error checking

Answer 27

Parity bits
Check digits
Check sums
Echo checks
Automatic Repeat reQuests (ARQ)

Question 28

Parity bits

Answer 28

check hoe many ones a data has. If its supposed to be even then you should have an even number of ones.
If not change the last but to the correct number to make it even. Do the same if the number of ones is supposed to be odd

Question 29

Check digits

Answer 29

A check digit is an additional digit at the end of a set of other numbers designed to check for mistakes in input or transmission

Question 30

Checksums

Answer 30

The file is run through an algorithm that produces a checksum which it also sends
When the file arrives, the receiving computer generates the checksum and compares it with the checksum that was sent
If the checksums don’t match, the file may have been corrupted or altered in transmission

Question 31

Echo check

Answer 31

The data is transmitted to the receiver
The same data is then echoed back to the transmitter
The transmitter compares the data with the original. If it isn’t the same, the data is transmitted again

Question 32

Automatic Repeat reQuests

Answer 32

The sender first sends a block of data
The receiving computer then sends back an acknowledgement
When the sender receives the acknowledgement it sends the next block of data
If the acknowledgement is not received after a period of time, a timeout occurs and the data is resent
This process continues until the acknowledgement is received