Unit 2

Question 1

what are data packets

Answer 1

a packet is a small unit of data that being transmitted

Question 2

what is the structure of a data packet

Answer 2

header
payload
trailer

Question 3

what does the header contain

Answer 3

senders IP address
Recievers IP address
Packet number

Question 4

what does the payload contain

Answer 4

data/part of the message

Question 5

what does the trailer contain

Answer 5

bits to show end of packet

Question 6

what is packet switching

Answer 6

data packets are sent through different routes so that data transfer is efficient

Question 7

what are the advantages of packet switching

Answer 7

packets can take different routes to get to their destination
this ensures message is delivered despite the unavailability of a route

Question 8

describe the process of packet switching

Answer 8

data is broken down into packets
each packet takes a different route
a router controls the route a packet takes
the packets are reassembled at the destination

Question 9

what is simplex data transmission

Answer 9

when data is sent in one direction only
computer to a printer

Question 10

what is half duplex data transmission

Answer 10

when data is sent in both directions but not at the same time
walkie talkies

Question 11

full duplex transmission

Answer 11

when data is sent in both directions at the same time
broadband internet connection

Question 12

serial data transmission

Answer 12

one bit at a time over a single wire/channel
connecting a computer through a USB connection

Question 13

advantage of serial data transmission

Answer 13

works well over long distances since data is fully synchronised in the correct order

Question 14

disadvantage of serial data transmission

Answer 14

transmitted at a slower rate than parallel data transmission

Question 15

parallel data transmission

Answer 15

when several bits of data is sent down several channels/wires at the same time
used in the internal circuits of a computer

Question 16

advantage of parallel data transmission

Answer 16

works well over short distances
faster than serial transmission

Question 17

disadvantages of parallel transmission

Answer 17

data can become skewed(mixed)
the longer the wire, the worse it becomes

Question 18

what is the USB

Answer 18

Universal Serial Bus
form of serial data transmission
allows both half duplex and full duplex transmission
standard method for transmission of data

Question 19

benefits of USB

Answer 19

become industry standard
is backward compatible
automatically detected when plugged in
no need for external power source
easy to add more USB ports

Question 20

drawbacks of USB

Answer 20

only supports cable length of 5 metres
early forms of USB may not be supported by computers
data transfer rate is slow

Question 21

how can errors occur during data transmission

Answer 21

interference
problems due to packet switching
skewing of data

Question 22

what is parity checking

Answer 22

it can be called even or odd
one of the bits is reserved for a parity bit and the number of 1’s is counted. the even or odd parity check will make the total number of 1s even or odd

Question 23

what is the problem with parity checks

Answer 23

sometimes more than 1 byte it corrupted but the parity is maintained
this is why other methods are needed to ensure errors are never missed

Question 24

what are parity blocks

Answer 24

a block of data is sent and the number of 1bits are totalled horizontally and vertically.
this identifies that an error has occurred and where the error is

Question 25

what is checksum

Answer 25

used to check if data has been changed or corrupted following data transmission
data is sent in blocks and an additional value, the checksum, is sent

Question 26

what is the process of checksum

Answer 26

the checksum is calculated from a block a data
the calculation is done using an agreed algorithm
checksum is transmitted with the block of data
the reciever recalculates from the block of data
if the checksums are the same, no error occured otherwise a request is made to resend the data

Question 27

what is echo check

Answer 27

when data is sent to one device, it is sent back to the reciever
the sender then compares the sets of data to check if errors occur

Question 28

what is the problem with echo check

Answer 28

it isnt known whether the error has been made while sending the data or recieving it meaning it isnt reliable

Question 29

what is check digit

Answer 29

the final digit included in a code
calculated from all other digits in the code
example- ISBN

Question 30

what is check digit used for

Answer 30

used to identify errors that occur in data entry caused by mistyping or misscanning

Question 31

What are ARQ’s

Answer 31

Automatic Repeat Requests
used to check data following data transmission

Question 32

How do ARQ’s work

Answer 32

the reciever sends back a positive or negative acknowledgements to the sender and the data is the resent depending
also uses timeouts where if no data is recieved by the sender, the data is automatically resent

Question 33

what is plaintext

Answer 33

the data being sent is known as plaintext

Question 34

what is cyphertext

Answer 34

the data once it has gone through an encryption algorithm

Question 35

what is symmetric encryption

Answer 35

the same key is used to encrypt and decrypt the encoded message

Question 36

disadvantage of symmetric encryption

Answer 36

the encryption key can always be intercepted which brings about the question of security

Question 37

what is asymmetric encryption

Answer 37

uses 2 keys called the private and public key
the private key is known only to the computer user
the public key is known to everybody

Question 38

process of asymmetric encyption

Answer 38

a matching pair of keys is generated
the public key is then sent to user 2 from user 1
user 2 encrypts their own message with the key and sends the encrypted data back to user 1
the private key is used by user 1 to decrypt the data