Data transimmsion

Question 1

data packet

Answer 1

header (IP address of sender and receiver&size of packet)
payload (the actual data)
trailer (error checking)

Question 2

benefits of data packets

Answer 2

no need to tie up a single communication line
high data transmission rate
overcome busy line by rerouting

Question 3

drawbacks of data packets

Answer 3

packets could be lost and need to be resent
there is usually a delay at the destination causing the packets to have to re order themselves.
doesn’t work well with real time streaming

Question 4

simplx data tranmission

Answer 4

one direction only

Question 5

half duplex data transmission

Answer 5

both directions but not at the same time (walkie talkie)

Question 6

full duplex data transmission

Answer 6

both directions at the same time (internet)

Question 7

serial data transmission

Answer 7

sends 1 bit at a time through 1 channel only
better for long distance transfer
data arrives in order
less expensive

Question 8

parallel data transmission

Answer 8

sends multiple bits at a time through multiple channels
better for short distance
will arrive out of order
more expensive

Question 9

benefits encryption

Answer 9

helps hide data from hackers
original data is known as plain text
after encryption it is called cypher text

Question 10

symmetric encryption

Answer 10

uses encryption key to encrypt and decrypt
not the most secure

Question 11

asymmetric encryption

Answer 11

2 keys (public and private)
public key is used to encrypt messages meaning anyone can do it
private key is used to decrypt messages and only maker of key has private key

Question 12

why do we error check

Answer 12

interference
problems durning packet switching
corrupting data

Question 13

parity check

Answer 13

even parity check means that there are an even number of 1 bits
odd parity check means that there are an odd number of 1bits

Question 14

check-sum

Answer 14

check sum is calculated when data is being sent using an agreed algorithm
then data is sent along with the checksum
receiver recalculates the checksum using the algorithm
if checksums match then the data has not been tampered with

Question 15

echo-check

Answer 15

data is sent from sender to receiver
data is resent back to sender
sender compares the 2 datas
if difference is found then sender resents data as error has occurred

Question 16

check digit

Answer 16

final digit in code
used in barcode
ISBN-13
Modulo-11

Question 17

ISBN-13

Answer 17

add all odd numbers
(add all even number)*3
add odd +even /10
find remainder and subtract it from 10 to find check digit

Question 18

Modulo-11

Answer 18

each digit is given a weight
digit * weight
divide total by 11
remainder -11= check digit

Question 19

ARQ

Answer 19

Automatic repeat request
They use an acknowledgement and time-outs.
When a receiving device detects an error following data transmission, it asks for the data packet to be re-sent. If no errors are detected, a positive acknowledgement is sent to the sender. The sending device will re-send the data packet if:
* a request to re-send data has been received, OR
* a time-out has occurred
The whole process is continuous until the data packet received is correct or until the time-out is reached