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CS > T2: Data transmission > Flashcards

T2: Data transmission Flashcards

1
Q
A
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2
Q

What are the parts of a data packet?

A

Packet header
Payload
Trailer

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3
Q

What does the packet header contain?

A

destination address
packet number
originator’s address

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4
Q

What are the steps of packet switching?

A
  1. Data is broken into packets and given a sequence number
  2. Each packet will take a different route to the next depending on the quickest route
  3. The router controls the route that the packet takes
  4. When packets arrive, they are reordered based on their packet number
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5
Q

What is serial transmission?

A

Data bits are sent one at a time down one cable at high speeds

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6
Q

What is serial transmission used in?

A

USB

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7
Q

What are the disadvantages of serial transmission?

A

Lower transmission speeds

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8
Q

What are the advantages of serial transmission?

A

Lower interference
More reliable over long distances
Smaller, cheaper connections to produce

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9
Q

What are the advantages of USB?

A

Backwards compatible
Cannot be inserted upside down
Do not need an additional power source ~ 5V power
Industry standard

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10
Q

What are the disadvantages of USB?

A

Only supports cable lengths of 5m
Slower data transfer speeds
Limitations of backwards-compatability

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11
Q

What is parallel transmission?

A

Several bits of data sent simultaneously across several wires

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12
Q

What is parallel transmission used for?

A

Printer cables or internal device connections

REALLY SHORT

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13
Q

Disadvantages of Parallel transmission?

A

Data corruption commonly occurs over long distances
Skewing
Can only be used for short distances

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14
Q

What is skewing?

A

When data bits travel parallel to each other can move at different speeds causing them to arrive out of sync

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15
Q

Advantages of Parallel transmission?

A

Very fast data transfer
Can send data in both directions at the same time

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16
Q

What is simplex transmission?

A

Data travels only in one direction down a single cable

17
Q

What is an example of simplex transmission?

A

Sending data from the computer to a monitor as it never needs to go the other way

18
Q

What is half-duplex transmission?

A

Data can travel in both directions along a single cable, but not simultaneously

19
Q

What is an example of half-duplex transmission?

A

Printer parallel cables
Text is sent to a printer, and the printer can send ‘Out of paper’ messages back; but only when the computer has finished sending text

20
Q

What is (full) duplex transmission?

A

Data can travel in both directions simultaneously using two communication channels

21
Q

What is an example of (full) duplex transmission?

A

Networking or Internet cables to transmit and receive at the same time

22
Q

what are error detection methods

what errors can occur

A
  • parity check (odd or even)
  • checksum
  • checkdigit
  • echo check

data gain, data loss, data change

23
Q

how does parity check work

A

if it’s even: the parity bit needs to be 1 if the 1s in the data are odd, and it’s 0 if the 1s in the data are already even
if it’s odd: the opposite
- the sender and receiver agree on which parity is used

put in the beginning

24
Q

disadvantage of parity check and how to fix

A
  • if two bits were swapped, this method wouldn’t pick it up
  • using parity blocks where you can figure out the problem with the help of multiple bytes and bits
25
Q

how does checksum work

A
  • when a block of data is about to be transmitted, the checksum is calculated from the block of data
  • the calculation is done using an agreed algorithm
  • the checksum is then transmitted with the block of data
  • at the receiving end, the checksum is recalculated
  • the re-calculated checksum is then compared to the checksum sent with the data block
  • if an error is detected, a request to resend the data is sent

put at the end

26
Q

how does echo check work

A
  • a copy of the data is sent back to the sender
  • the returned data is compared with the original data by the sender’s computer
  • if there are no differences, then the data was sent without error
  • if the two sets of data are different, then an error occurred at some stage
    during the data transmission.
27
Q

what are types of checkdigit algorithms

A
  • ISBN 13
  • Modulo 11

put at the end

28
Q

what are uses of check digits

A
  • standard book numbers (ISBN)
  • bar codes
29
Q

when are checkdigits used

A
  • to detect errors in data-entry
  • or miscanned barcodes
30
Q

checkdigit

what is it / how found roughly

A
  • a check digit is calculated through complicated ways
  • another calculation is made to see if the remainder ends up being 0
31
Q

define what does ARQ stand for

A

automatic repeat query

32
Q

how is ARQ used to stablish that data is received without error

A
  • uses positive and negative acknowledgements and timeout (this is the time interval allowed to elapse before an acknowledgement is received)
  • the receiving device receives an error detection code as part of the data transmission
  • if no error is detected, a positive acknowledgement is sent back to the sending device
  • however, if an error is detected, the receiving device now sends a negative acknowledgement to the sending device and requests re-transmission of the data
  • a time-out is used by the sending device by waiting a pre-determined amount of time ….
  • … and if no acknowledgement of any type has been received by the sending device within this time limit, it automatically re-sends the data until a positive acknowledgement is received …
  • … or until a pre-determined number of re-transmissions has taken place
  • ARQ is often used by mobile phone networks to guarantee data integrity.
33
Q

how is data encrypted using symmetric encryption

A

the same key is used to encrypt and decrypt the message

34
Q

how does assymetric encryption work

A
  • a matching pair of keys (private and public) is created
  • the public key is sent to the other person
  • the person encrypts data to ciphertext using public key
  • only matching private key can unlock
  • in order for two way communication to work, everyone will need their own private key

CS (9 decks)

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