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Computer science paper 1 > Data transmission > Flashcards

Data transmission Flashcards

1
Q

Why is data broken down into packets:

A

Small chunks of data are easier and quicker to route over the internet than big chunks of data

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2
Q

What is TCP?

A

Transmission Control Protocol, used for organising data transmission over networks

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3
Q

Structure of packet

A

Header
Payload
Trailer

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4
Q

Packet header structure:

A

Originating IP address
Destination IP address
Packet number

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5
Q

What does trailer contain:

A

Checksums

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6
Q

Packet switching summarised:

A
  • Data is broken down into packets each 64KiB in size
  • Each packet could take a different route
  • A router controls the route a packet takes by taking the most available path
  • Packets may arrive out of order
  • Once the last packet has arrived, packets are reordered by receiving computer using packet number in header
  • If packet is missing or corrupted, it is requested again
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7
Q

Advantages of serial transmission over parallel:

A
  • more effecient over longer distances
  • Less prone to errors of electrical interference where skewing and cross talk can occur
  • Data will arrive in order
  • Cheaper to purchase
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8
Q

Disadvantages of serial transmission

A
  • Slower than parallel
  • only small quantities of data can be transmitted at a time
  • as distance of wire increases, cost increases
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9
Q

advantages of parallel transmission

A
  • fast
  • large quantities of data can be transmitted at one time
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10
Q

disadavantages of parallel transmission:

A
  • expensive to purchase
  • not suitable over long distances since its more prone to errors of electrical interference like:
  • skewing
  • cross talk
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11
Q

advantages of simplex

A
  • cheap as only one wire used
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12
Q

disadvantages of simplex

A
  • slow (one bit at a time)
  • might require two sets of wires for bidirectional transmission; expensive
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13
Q

advanatges of half-duplex

A
  • cheaper than simplex for bidirectional transmission (only one wire required)
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14
Q

disadvantaegs of half-duplex

A
  • slower than full duplex as data travels in only one direction at a time
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15
Q

advantages of full-duplex

A
  • faster as data can travel in both directions simultaneously
  • receiver does not have to wait for the sender to stop before they can start transmitting their data
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16
Q

disadvantages of full-duplex

A
  • Full-duplex is expensive
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17
Q

serial use:

A

good for long distances
e.g
transmitting data over a telephone line

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18
Q

parallel use

A

good for short distances
e.g
- computer to printer
- cpu to ram
- or when long distance not needed

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19
Q

Simplex uses

A

Transmitting data from a computer to a printer.

The printer doesn’t need to send data back to the computer

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20
Q

Half-duplex uses

A

walkie-talkie

downloading and uploading data which dont need to occur at same time

21
Q

full duplex uses

A
  • Broadband connections to the internet
  • downloading and uploading
  • Phone convos (may interrupt each other)
22
Q

USB interface; when device connected by USB to computer, what happens?

A

computer:
automatically detects that the device has been connected

automatically recognises and loads the appropriate device driver so that the device can communicate with the computer

23
Q

what if device in USB port is new? what does computer do?

A

If the device is new, the computer will look for a matching device driver.

If one cannot be found then the user must download and install an appropriate driver manually

24
Q

Disadvantages of USB:

A
  • cannot be used over very long distances, limiting its use
  • Older versions of USB have limited transmission rates
  • Very old USB standards may not be supported in the near future
25
Q

What causes errors?

A

Errors can occur during data transmission due to interference,

data loss,
data gain
data change (flipped bits)

26
Q

Limitations of parity check

A

only check that an error has occurred, they do not reveal where the error occurred

do not reveal transposition errors

27
Q

drawback of parity block check

A

Does not detect transposition error
(two bits flip at same time)

28
Q

Checksum drawback

A

do not reveal where error is

29
Q

Echo Check

A
  • Receiving computer sends copy of data back to sending computer for comparison.
  • sending computer compares the two sets of data for any errors in transmission process
  • if data does not match, error occured, data is automatically retransmitted
30
Q

drawback of echo check

A

not reliable;

it is unknown if error occured when sender transmit the data or receiver transmit a copy for checking

31
Q

Automatic Repeat Query (ARQ)

A

ARQ is a protocol that notifies the sender that an error has occurred and that the data received is incorrect.

  • error detected = negative acknolwdegment sent by receiver
  • timeout occurs (no ack sent) = data automatically resent
  • no error detected = positive ack

process is repeated until all data has been received and positevely acknowledged

32
Q

Check digit

A
  • block of data transmitted alongside additional digit (check digit) which is calculated using custom made algorithm
  • When data received, check digit value is calculated using the algorithm in the trailer of the packet
  • Receiver checks calculated check digit with received check digit
  • if same = no error,
  • if different = error occured, a resend request is sent and data is retransmitted
33
Q

Encryption:

A

encoding data into a form that is meaningless using an algorithm from plaintext to ciphertext

34
Q

Symmetric encryption:

A
  • same key (algorithm) used to encrypt and decrypt data
  • before data transmission, key first shared between sender and receiver
  • sender uses key to encrypt data from plaintext to ciphertext
  • receiver uses same key to decrypt data from ciphertext to plaintext
35
Q

symmetric encryption drawback

A

If hacker gains access to shared key then they can decrypt data in transmission

36
Q

Two keys of asymmetric encryption

A

Private key: only available to receiver to DECRYPT data

Public key: available to sender(everyone) to ENCRYPT data

37
Q

Asymmetric encryption:

A
  • Two keys generated by receiver, public and private key, public key shared with receiver, private key kept secret by sender.
  • public key used by anyone who wishes to send message to receiver, by encrypting data through public network
  • public key cannot decrypt data, only secret private key with receiver.
  • receiver decrypts data with private key
38
Q

Advantage of asymmetric

A

key is not shared, so more secure than symmetric, because hacker cannot find out the key algorithm

39
Q

Plaintext:

A

text before encryption, its meaningful

40
Q

Ciphertext

A

text after encryption, it is meaningless

41
Q

what controls route of packets

A

router

42
Q

Why is check digit used and where

A

used to detect errors in manual data entry

Used in:
- bar codes
- ISBN (International Standard Book Number)

43
Q

How strength of encryption can be improved

A

Uses a more complex encryption algorithm

Increase the length of the key

44
Q

Benefits of USB

A
  • devices automatically detected and load device drivers, simplifying process for user
  • Newer USB standards are backwards compatible with older USB standards
  • industry standard
  • Cable connectors fit in only one way. This prevents incorrect connections and ensures compatible data transmission
  • It can charge the device
45
Q

How parity check works

A
  • sender and receiver agree before transmission if odd or even parity used (protocol)
  • A parity bit is added to each byte of data, to make the number of 1s match parity type
  • receiver checks value of parity type by counting the number of 1’s in the byte
  • If the number of 1’s does not match the agreed parity then an error has occurred, retransmission if automatically requested
46
Q

Checksum

A
  • sender performs a calculation on data to be transferred following an algorithm
  • the calculated checksum value and its algorithm is sent along data packets, in its trailer
  • after transmission, receiver follows checksum algorithm on data received and compares with received checksum value
  • if same = no error,
  • if different = error occured, a resend request is sent and data is retransmitted
47
Q

what is a USB

A
  • Universal Serial Bus
  • It is a method of data transmission
  • Uses serial transmission
  • bits of data are sent one at time down a single wire
48
Q
  1. Checks for errors on data entry:
  2. Compares two calculated value to see if error occured:
  3. Will not detect transposition errors
  4. Sends additional values when data is transmitted from a computer to another
A
  1. Check digit
  2. Check digit and Checksum
  3. Parity check
  4. Checksum and Parity check

Computer science paper 1 (14 decks)

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