Data Transmission

Question 1

What is the structure of a packet

Answer 1

• packet header
• payload
• trailer

Question 2

What does the packet header include?

Answer 2

Destination address
Packet Number
Sender’s adress

Question 3

What is the process of packet switching?

Answer 3

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 4

What different methods can data be transmitted

Answer 4

Serial
Parallel
Simplex
Half-duplex
Full-duplex

Question 5

How is data transmitted through simplex

Answer 5

The data is transferred in one direction

Question 6

How is data transmitted through half duplex

Answer 6

The data can travel in both directions however not at the same time

Question 7

How is data transmitted through full duplex

Answer 7

The data is transmitted in both directions at the same time

Question 8

How is data transmitted through serial transmission

Answer 8

Data bits are sent one at a time via a single cable

Question 9

How is data transmitted through parallel transmission

Answer 9

Several bits of data can be sent simultaneously via a series of canles

Question 10

What is a USB?

Answer 10

A universal serial bus is a form of serial data transmission allows for both half and full duplex

Question 11

What are the advantages of serial transmission

Answer 11

Lower interference than parallel
More reliable over longer distances
Cheaper to set up

Question 12

What are the advantages of parallel transmission

Answer 12

Very fast data transfer

Question 13

What are the disadvantages of parallel transmission

Answer 13

More prone to interference
Data may arrive out of order known as skew
Limited to very short distances

Question 14

What are the advantages of the USB

Answer 14

Very well supported
Connected devices are automatically detected
It can notify the transmitting device to re-transmit data if detect errors

Question 15

what are the drawbacks of the USB

Answer 15

limited distance of around 5m
Many devices no longer support older standards
Newer versions have slower data transfer

Question 16

What are common methods of error checking

Answer 16

Parity checks
Checksums
Echo checks
Automatic Repeat Query

Question 17

What is the process of parity checks

Answer 17

When sending a byte of data, we can use the Most Significant Bit as a parity bit
With even parity, we set the MSB to be 1 or 0 so that the total number of bits- including the parity bit-is even
With odd parity, we set the MSB to be 1 or 0 so that the total number of bits- including the parity bit- is odd
With the method, simple errors can be spotted nut there is no way to tell exactly where the error occurred

Question 18

What is the process of parity block checks

Answer 18

When send a block of data, parity checks can be performed both horizontally and vertically on the whole block
These checks can spot that an error has occurred and where, allowing the receiving device to fix the error

Question 19

What is the process of checksums

Answer 19

A checksum is calculated by using an algorithm on the data to be transmitted
This checksum is added to the transmission and sent along with it
The receiving device re-calculates the checksum and compares the new one with the original
If the checksums do not match and it is assumed an error has occurred

Question 20

What is the process of echo checks

Answer 20

The receiving device returns an exact copy of the data it has just received
The data is compared to what was originally sent. If it is different, it is assumed that an error has occurred and the original data is resent

Question 21

What is the process of check digits

Answer 21

A check digit is the last digit included in a code or other identification number
* Calculated from all other digits in the code
* Commonly used with barcodes, ISBN numbers and Vehicle Identification Numbers

Question 22

What is the process of Automatic Repeat Query (ARQ)

Answer 22

• The destination device receives the data transmission along with an error detection code
  
  • The code is used to determine if the data contains any transmission errors
  • If no errors have been detected, a positive acknowledgement is sent back
  • After a pre-determined amount of time, if the sending device hasn’t received any form of acknowledge, it will automatically re-send the data
    It will keep doing this until it either receives a positive acknowledgement or a pre-determined number of attempts to re-send the transmission have taken place

Question 23

What is encryption?

Answer 23

Encryption is the process of encoding a message so it can only be read by the sender and intended recipient- this is especially useful when transmissions including personal or sensitive information

Question 24

What is symmetric encryption

Answer 24

• uses the same private key to encode and decode data
  
  • This key must be transmitted in some way prior to sending an encrypted message
    However, shared private keys can be intercepted, making this method less secure

Question 25

What is asymmetric encryption

Answer 25

• Uses two separate but related keys
  
  • The public key is shared with others and used by the recipient to encrypt a message
  • In this way, a message can only be deciphered by the intended recipient with their private key
    Private keys must be never shared