Data Transmission

Question 1

Data packets?

Answer 1

a small part of a data that is transmitted over a network ; after transmission all data are reassembled to form the original data.

Question 2

a packet header?

Answer 2

• IP address of the sender
• IP address of the receiver
• sequence number of packet (allowing correct reassembly)
• Size of the packet in bytes

Question 3

the payload?

Answer 3

contains the actual data in the packets

Question 4

a trailer

Answer 4

• method of identifying the end of the packet
• some form of error checking to ensure packet arrives error-free

Question 5

Cyclic redundancy checks (CRCs)?

Answer 5

a method of error checking in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer, the same calculation is repeated at the receiving station.

Question 6

packet switching?

Answer 6

a method of transmission in which a message is broken into many data packets, which can then be sent along pathways independently of each other

Question 7

benefits of packet switching?

Answer 7

• There is no need to tie up a single communication line
• it is relatively easy to expand package usage
• a high data transmission rate is possible

Question 8

Drawbacks of packet switching?

Answer 8

• packets can be lost
• more prone to errors with real-time-streaming
• a delay at the destination whilst the packets are being re-ordered

Question 9

Hopping?

Answer 9

Sometimes, the packets get lost because they keep bouncing around from the router and never reach the destination. Hopping is used to overcome this problem. A hop number is added to the header of each packets, and this number is reduced by 1 every time it leaves a router. When it gets to 0, the packet is deleted and is resent.

Question 10

Simplex data transmission?

Answer 10

Occurs when data can be sent in ONE DIRECTION ONLY.
e.g. A computer to a printer

Question 11

Half-duplex data transmission?

Answer 11

Occurs when the data is sent in BOTH DIRECTIONS but NOT AT THE SAME TIME.
e.g. walkie-talkie

Question 12

Full-duplex data transmission?

Answer 12

Occurs when the data can be sent in BOTH DIRECTIONS AT THE SAME TIME
e.g. Broadband internet connection

Question 13

Serial Data transmission?

Answer 13

Occurs when data is sent ONE BIT AT A TME over SINGLE WIRE
(Can be simplex, half or full duplex)

Question 14

Parallel data transmission?

Answer 14

Occurs when SEVERAL BITS OF DATA are sent down SEVERAL WIRES
(can be simplex, half or full duplex)

Question 15

What’s the problem with parallel data transmission over a longer distance?

Answer 15

Data can become skewed; data arrives unsynchronised

Question 16

Compare between Serial and Parallel data transmissions.

Answer 16

1. Serial has less risk of external interference than with parallel, due to fewer wires.
2. Parallel has a faster rate of transmission than serial, due to more wires.
3. Serial is more reliable over longer distances; parallel works well over shorter distances.

Question 17

Definition for Universal Serial Bus (USB)?

Answer 17

a type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port.

Question 18

What are the four wires for USB?

Answer 18

Red + black for power
White + green for data transmission

Question 19

Describe the process when a device is plugged into a computer using one of the USB port.

Answer 19

1. The computer automatically detects that a device is present.
2. The device is automatically recognized, and the appropriate software is loaded up so the computer and the device can communicate effectively.
3. if a new device is detected, the computer will look for the device driver that matches the device, if not, the user is prompted to download the software.

Question 20

Benefits + Drawbacks of USB

Answer 20

Benefits:
1. Devices plugged in are automatically detected by the computer.
2. Can support different data transmission rates.
3. No need for an external power source since cable supplies +5V

Drawbacks:
1. Has a limited length of 5m
2. Power limitations for high-powered devices.
3. Limited data transmission speed compared to newer technologies.

Question 21

Causations for errors in data transmission

Answer 21

• Electrical Interference
• Problems during packet switching
• skewing of data (only in parallel)

Question 22

What are the three different ways in which data can be checked for errors?

Answer 22

1. Parity checks
2. Checksum
3. Echo check

Question 23

Parity check?

Answer 23

Could make use of either EVEN or ODD parity checks
e.g, the data is 101010; you use an odd parity check, the result would be 0

Question 24

Checksum?

Answer 24

It works by calculating a value (the checksum) based on the data being sent, usually by adding up the values of all the data bits. This checksum is then sent along with the data. Upon receiving the data, the receiver performs the same calculation. If the calculated checksum matches the received checksum, the data is considered correct; if not, an error is detected.

Question 25

Echo check?

Answer 25

In an echo check, the system sends a message or data to the receiver, and the receiver sends the same message back (echoes it) to the sender. The sender compares the original message with the received echo. If they match, the data is assumed to have been transmitted correctly. If there is any difference, it indicates that an error occurred during transmission.

Question 26

Check digits?

Answer 26

An additional digit is appended to a number to check if the entered number is error-free, it is a type of data entry check. e.g. ISBN13

Question 27

Automatic Repeat Requests (ARQs)?

Answer 27

it makes use of acknowledgment and timeout to automatically request re-sending of data if the time interval before positive acknowledgment is too long.

Question 28

what is an eavesdropper?

Answer 28

another way of saying hacker

Question 29

Plaintext and cipher text

Answer 29

plaintext is the original text, cipher text is when data has gone through encryption algorithm

Question 30

Symmetric encryption?

Answer 30

a type of encryption in which the same encryption key is used for both to encrypt and decrypt the message.

Question 31

Asymmetric encryption?

Answer 31

a type of encryption that uses public key and private keys to ensure data is secure.

Question 32

quantum computer?

Answer 32

a computer that can perform very fast calculations