2. data transmission

Question 1

how is data transmitted

Answer 1

by breaking it down into smaller chunks called packets

Question 2

what is a packet

Answer 2

A packet is a small unit of data that can be transmitted from a sending device to a receiving device via a network communication protocol.

Question 3

what is the sturcture of a packet, and what does each layer contain

Answer 3

packet header:
senders and receivers ip address, packet number
payload:
data/ part of the message
trailer:
bits to show the end of the packet

Question 4

what is packet switching and explain its process

Answer 4

a way of transmitting data, process:
- Data is broken down into packets
- Each packet could take a different route
- A router controls the route a packet takes
- Packets may arrive out of order
-Once the last packet has arrived, packets
are reordered

Question 5

what are the 2 transmission methods

Answer 5

serial and parallel transmission

Question 6

descirbe serial transmission

Answer 6

a single wire is used to connect the sending device to the receiving device. Bits are transmitted one at a time.
more reliable over long distances, slow so not suitable for transmission of large files over short distances

Question 7

describe parallel transmission

Answer 7

multiple wires are used to connect the sending device and the receiving device. Several bits are sent simultaneously down the wires
faster, however bits can arrive out of order so might need rearranging before complete transmission, expensive method to implement over longer distances

Question 8

what are the types of data transmission

Answer 8

Simplex data transmission
Half-duplex data transmission
Full-duplex data transmission

Question 9

describe simplex data transmission

Answer 9

only one device can transmit data; as such, data moves in one direction only eg only from senders device to receiving, for example using a usb cable to send info to a printer

Question 10

describe half duplex transmission

Answer 10

here both the sending device and the receiving device can transmit data, but not at the same time. This means that data can move in both directions, but only in one direction at a time. eg walkie talkies

Question 11

describe full duplex transmission

Answer 11

where both the receiving device and the sending device can send and receive data at the same time, i.e. data is transmitted in both directions simultaneously eg. iphone call

Question 12

what dos usb stand for

Answer 12

universal serial bus

Question 13

what is a USB

Answer 13

a hardware device that enables you to connect your peripheral devices to your computer so that those devices can exchange data with the computer.

Question 14

USB uses what type of transmission

Answer 14

serial, through one mire one bit at a time

Question 15

advantages of using USB

Answer 15

-universal, used in almost all common devices
-can transfer power as well as data, even at the same time

Question 16

disadvantages of using USB

Answer 16

-there are multiple different connectors (updates, changes the size and pattern of the usb)

Question 17

why were error detection methods established

Answer 17

to ensure that transmission errors are detected as early as possible as many errors can happen during data transmission due to interference, e.g. data loss, data gain and data change

Question 18

what does parity check use

Answer 18

using a parity bit at the end or start of the binary number and sent along with the data

Question 19

how does parity check work

Answer 19

there are two established checks
even parity check: total number of 1’s in a byte is even
odd parity check: total number of 1’s in a byte is odd
The sending and receiving computers must both agree on which parity to use – even or odd, if the type of parity check isnt the same for the sender and receiver, an error has been made

Question 20

what is a disadvantage of parity check

Answer 20

they cannot tell us exactly which bit has been corrupted or changed during transmission

Question 21

what is a checksum

Answer 21

another type of error detection method. In this method, data is sent in blocks together with a calculated value known as the checksum. receiver calculates the checksum if equal to senders checksum= no error different= error during transmission

Question 22

what are the rules for checksum

Answer 22

1- if number of bytes in a block is less or equal to 255 than that is the checksum number
2- if bigger than:
-divide sum of bytes in block by 256
-convert this value int integer and round down
-multiple integer value by 256
-subtract,sum of bytes- calculated value

Question 23

describe echo check

Answer 23

method of error detection where the receiving computer sends back an exact copy of the data to the sending computer. The sending computer then compares the data it originally sent to the data it has received back. the sending computer performs the error checking and not the receiving computer,

Question 24

state one disadvantage of echo check

Answer 24

is difficult to tell whether the data was corrupted in transit to the destination or on its way back. Another disadvantage is speed, because the complete data has to be sent twice.

Question 25

what is a check digit

Answer 25

A check digit is an extra digit added to a number calculated from the existing digits in the number and used to check the integrity of the data entered.

Question 26

what are some uses for check digit

Answer 26

ISBN, barcodes, product codes etc

Question 27

how do you calculate if an ISBN has been transmitted correctly using check digit

Answer 27

1- remove last digit of number
2- create a pattern of 1 and 3 under each value remaining eg:
1 6 2 0
1 3 1 3
3- multiply each value by the pattern beneath eg:
(1x1)=1
(6x3)=18
(2x1)=2
(0X3)=0
4-add all the answers together and round the total down eg:
(1+18+2+0)= 21=20
5.subtract un rounded answer by rounded eg:
21-20= 1
6. compare value obtained by check digit

Question 28

what is an automatic repeat request (arq)

Answer 28

A set of rules used for error control during transmission. A receiving computer may request the sending computer to resend the packet if errors are detected.

Question 29

Describe the ARQ

Answer 29

1- when data is received to receivers end the computer sends a short message called an acknowledgment, indicating weather there was any errors, (positive acknowledgment= no errors, negative acknowledgment= errors)

2. if there was a negative acknowledgment, the receiving computer will request the sending computer to resend the data
3. process is repeated until receiving computer receives complete package or until the time out has run out (defined fix time)

Question 30

what is encryption

Answer 30

a type of security measure, in which a message is made unreadable to anyone without the decryption key/ algorithm

Question 31

what is un encrypted text called

Answer 31

plain text

Question 32

what is encrypted text called

Answer 32

cipher text

Question 33

what are the two types of encryption

Answer 33

symmetric and asymmetric

Question 34

describe symmetric encryption

Answer 34

A simple method of encryption where the same key is used to encypt and decrypt the data.
less safe, because of malicious user intercepts key it can decrypt message very easily

Question 35

describe asymmetric encryption

Answer 35

A more complex method of encryption where two different keys are used to encypt and decrypt the data, a public key (used by everyone visiting a website) and a private key (receivers key used to decrypt).
more reliable compared to symmetric encryption