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IGCSE Computing > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

Three components of a packet

A
  • Header
  • Payload
  • Trailer
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2
Q

What’s in the Packet header

A
  • IP of sending device
  • IP of receiving device
  • Sequence number of the packet
  • Packet size
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3
Q

What’s in the packet payload

A

The actual data being sent

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4
Q

What’s in the packet trailer

A
  • Identification of the end of the packet
  • Error checking method (CRC)
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5
Q

Describe the process of packet switching [5]

A
  • Each packet follows its own route
  • Routers determine the journey of each packet
  • Routing selection depends on number of packets waiting to be processed
  • The shortest possible path is always taken
  • Packets reconstruct once the final packet is received
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6
Q

Benefits of Packet Switching

A
  • No need to tie up single communication line
  • Overcome failed or busy lines via other route
  • Easy to expand package usage
  • High data transmission rate possible
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7
Q

Drawbacks of packet switching

A
  • Packets can be lost and need to be resent
  • Prone to errors with real time streaming
  • Delay at destination while packets are reordered
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8
Q

What is hopping/hop numbers

A

A hop number is added to a packet and increases by 1 every time it switches router. If it hits maximum hops then it’s resent from computer.

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9
Q

Simplex

A

Sent from one direction only

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10
Q

Half duplex

A

Can send in both directions but not at same time

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11
Q

Full duplex

A

Data can be sent both ways simultaneously

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12
Q

Serial data transmission

A

One bit at a time

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13
Q

Parallel Data transmission

A

Multiple streams of bits

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14
Q

Benefits of Serial Data transmission

A
  • cheaper
  • reliable over long distances
  • can send data long distances
  • less risk of external interference
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15
Q

Benefits of parallel data transmission

A
  • Faster
  • works well over short distances
  • easier to program input/output operations when parallel is used.
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16
Q

Disadvantages of serial data transmission

A
  • slow data transfer
17
Q

Disadvantages of parallel data transfer

A
  • expensive hardware
  • can arrive out of synchronisation
18
Q

Describe the steps when a USB is plugged in

A
  • computer detects device
  • device is recognised and drivers are loaded
  • if the device is new there will be search for drivers
19
Q

Benefits of USB

A
  • Incorrect connections cannot happen
  • can support wide range of transmission rates
  • easy to add more ports
  • backward compatibility
20
Q

What is parity check

A

An error check to determine if data has been changed or corrupted based on the number of 1-Bits in a byte of data.

21
Q

How does parity check work?

A
  • parity can be odd or even
    — based on the number of 1 bits
    An agreement is made between the sending an receiving computer to determine whether odd or even parity will be used.
  • once string of numbers has been received it is checked.
22
Q

What is checksum

A
  • error checking method
  • an additional value is added to the end of a block of data.
23
Q

How does Checksum work?

A
  • When a block of data is about the transmitted checksum is calculated
  • algorithm is agreed soon by sending and receiving computer
  • check sum is transmitted w/data block
  • once received, checksum is calculated and compared
  • if error then computer will send data again
24
Q

What is echo check and how does it work?

A
  • error checking method that sends the data back to sender to check
25
Q

What is check digit

A
  • Final digit in a code
  • used to identify errors in data entry
26
Q

What is symmetric encryption

A
  • uses an encryption key
  • same key used to encrypt and decrypt the encoded message
27
Q

What is asymmetric encryption?

A
  • uses a public and private key
  • public key is known by sender and receiver
  • private key is linked to public key
  • only receiver has the private key
28
Q

Plaintext

A

Original message before it’s put through encryption

29
Q

Ciphertext

A

Encrypted ciphertext

IGCSE Computing (9 decks)

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