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Computer Science by DY > 2 Data Transmission > Flashcards

2 Data Transmission Flashcards

1
Q

Data sent over long distance is usually broken into ______ _______

A

data packets

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2
Q

What are the 3 parts of a dat packet

A

headler

payload

trailer

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3
Q

What is in the header? (4)

A

IP address of the sender

IP address of the receiver

Sequence number of the packets

Size of the packet (in bytes)

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4
Q

What does the payload contain? (1)

A

The actual data in the packets (64KiB)

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5
Q

What does the Trailer contain? (2)

A

Methods of identifying the end of a packet

Some forms of error checking to ensure packet arrives error free

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6
Q

Define packet switching

A

method of transmission in which a message is broken up into a number of packets

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7
Q

Describe how packet switching occurs (4)

A

Each packet sent independently from start point to end point

At the destination, packets reassembled into their correct order

At each stage of transmission, there are nodes that contain a router

Each router determines the route the packet needs to take

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8
Q

Benefits of packet swtiching(3)

A

no need to tie up a single communication line

possible to overcome failed, busy, faulty lines by rerouting packets

high data transmission rate is possible

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9
Q

Drawbacks of packet switching(3)

A

packets can be lost and need to be resent

method is prone to errors with real time streaming

delay at destination while the packets are restructured

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10
Q

Why might pathways become clogged (2)

A

packets keep bouncing around from router to router

Lost packets mount up, clogging the system

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11
Q

What is simplex transmission mode

A

data can be sent in only one direction only

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12
Q

What is half-duplex transmission mode

A

When data is sent in both directions but not at the same time

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13
Q

What is full-duplex transmission mode

A

Both directions at the same time

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14
Q

What are the two types of data transmission (2)

A

Serial data transmission

Parallel data transmission

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15
Q

What is serial data transmission (2)

A

ONE BIT AT A TIME over a SINGLE WIRE/CHANNEL

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16
Q

What is parallel data transmission? (2)

A

SEVERAL BITS OF DATA over SEVERAL WIRES/CHANNELS

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17
Q

Advantage of serial data transmission (4)

A

reliable over long distances

Data arrives in order as bits transmitted through single wire

less risk of external interference than parallel

less expensive than parallel data transmission (fewer wires)

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18
Q

Disadvantage of serial data transmission (2)

A

relatively slower than parallel data transmission

not suitable for transmitting data over short distances

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19
Q

Advantage of parallel data transmission (2)

A

faster than serial data transmission

works well over short distances

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20
Q

Disadvantage of parallel data transmission (2)

A

expensive than serial (requires more hardware)

bits can arrive out of synchornisation (skewed)

21
Q

What does USB stand for

A

Universal Serial Bus

22
Q
A
23
Q
A
24
Q

What happens when a device is plugged into a USB? (3)

A

computer automatically detects that device is present (small change in voltage in the USB cable)

device is automatically recognised, appropriate device driver loaded so that computer and device can communicate

if a new device detected, computer looks for device driver that matches device

25
Q

Benefits of USB systems (4)

A

industry standard

Devices automatically detected and device drivers automatically loaded

backwards compatible (older versions still supported)

connections can only be one way, prevents incorrect connection being made

26
Q

Drawbacks of USB systems (2)

A

Very old USB versions not supported

maximum cable length is roughly 5 metres

27
Q

What are the 4 ways of data can be checked for errors (4)

A

Parity checks

checksum

echo check

Automatic repeat request (ARQ)

28
Q

Why might errors occur during data transmission

A

Interference

skewing of data

probelsm during packet switching

29
Q

Describe what a parity check is (2)

A

A method used to check if data has been transmitted properly

makes use of even parity and odd parity

30
Q

What is a parity bit

A

a bit added to a byte of data to ensure that the byte follows the correct even or odd parity protocol

31
Q

What is a parity block

A

A horizontal and vertical parity check on a block of data being transmitted

32
Q

What is the limitation of parity check? (1)

A

Cannot tell which bit has been corrupted or changed

33
Q

Describe the checksum process (5)

A

when a block of data is about be transmitted, checksum value calculated

checksum transmitted with block of data

at the receiving end, checksum is recalculated using the blocks of data

recalculated checksum is compared with the initial checksum value

If they are the same, no errors have taken place during transmission

34
Q

Describe the process of echo check (3)

A

a copy of data is sent back to the sender

the returned data is compared with original data by the sender’s computer

if there are no diffrerences, then data sent without errors

35
Q

Describe the process of Automatic repeat request (ARQ) (3)

A

uses positive and negative acknowledgements and timeout

receiving device receives an error detection code as part of the data transmission (used to detect where data has any errors)

If no error detected, positive acknowledgment sent to sender

36
Q

What happens if an error is detected in a computer system that uses ARQ (1)

A

negative acknowledgement sent to sender and requests data to be resent

37
Q

What happens if no acknowledgement of any sort has been received by the sending device after a certain amount of time (ARQ) (1)

A

resends data until positive acknowledgement is sent to sender

38
Q

What is the original data being sent also known as in encryption?

A

plaintext

39
Q

Define encryption

A

the process of making data meaningless using encryption keys; without the correct decruption key the data cannot be decoded [unscrambled]

40
Q

What is symmetric encryption

A

both parties given identical secret key to encrypt or decrypt information

41
Q

What is the main problem with symmetric encryption

A

if hacker gains access to the key, they can decrypt the information

42
Q

What is asymmetric encryption

A

type of encryption that uses both public and private key to ensure data is secure

43
Q

define public key

A

a key known to everyone

44
Q

define private key

A

a key known to the receiver

45
Q

Describe the process of asymmetric encryption (3)

A

Sender encrypts data using public key

Encrypted data is sent to the receiver

Receiver decrypts the encrypted data using a MATCHING private key

45
Q

Advantage of asymmetric encryption

A

much more reliable compared to symmetric key

46
Q

What is check digit

A

extra digit added to a number that is calculated from the existing digits in the number.

47
Q

Examples of when check digit is used (2)

A

ISBN

barcodes

(used to check for errors during data entry)

48
Q
A

Computer Science by DY (10 decks)

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