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Year 10 Computer Science > Unit 2 Computer Science > Flashcards

Unit 2 Computer Science Flashcards

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1
Q

What are data packets?

A

Data which is broken down into smaller pieces when being sent over long distances

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2
Q

What is the size of a data packet?

A

64 KiB (Kibibyte)

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3
Q

Give me an advantage of data packets

A

Each packet can be sent to a different route to reach its destination so it would be great if a specific route was very busy

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4
Q

Give me a disadvantage of data packets

A

The data packets will need to reassemble the data when it reaches its destination

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5
Q

What is the structure of a data PACKET?

A

They have a HEADER consisting of:
- Contains Ip address of sender and receiver
- Sequence number of packet (indicates overall position of packet in data sequence)
- Size of packet (to know if packets have arrived intact)

They have a PAYLOAD consisting of:
- The actual data (info being sent)

They have a TRAILER consisting of:
- The method of identifying the end of the packet
- Error-checking methods

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6
Q

What is a cyclic redundancy check?

A

It is an error checking method and first, the computer counts all the 1-bits (not 0, they ignore) in the payload and stores it as a hex value in the trailer. When the receiving computer gets the packet, it counts the number of 1-bits and compares to the value in the trailer, if they match, no error has occurred, but if they don’t match then an error has occurred and the packet must be resent

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7
Q

What is packet switching?

A

It is a method of data transmission when data is broken down into many packets and sent individually to the receiver (can be through different routes) and the packets are then reassembled in the receivers computer as the original data.

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8
Q

What are the advantages of packet switching?

A
  • High data transmission speed
  • Easy to add more packets and data
  • Possible to overcome failed or busy routes
  • It doesn’t rely on only 1 line of communication (it can use others)
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9
Q

What are the disadvantages of packet switching?

A
  • Packets could get lost
  • More errors can occur when live-streaming
  • Delay on the receiver when packets are re-ordered
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10
Q

How does a packet get lost?

A

They can get lost by bouncing between routers and never reaching its destination

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11
Q

What happens when packets bounce between routers for too long?

A

It can slow down network and cause network congestion (traffic in network)

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12
Q

What method is used to prevent network congestion?

A

The method is called hopping and it is when each packet has a hop limit in the header and each time the packet passes a router it minuses the hop limits number by 1 and if the number reaches 0 then the packet is killed

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13
Q

What are the 3 things to be considered when transmitting data?

A
  • Direction of data transmission (one or both directions)
  • Method of transmission (how many bits can be sent at the same time)
  • Making sure data is received in correct order
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14
Q

What is Simplex data transmission? And give an example

A

It is a type of data transmission and Simplex is when data is sent in 1 DORECTION ONLY. Example: computer to printer

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15
Q

What is Half-duplex data transmission? And give an example

A

It is a type of data transmission and Half-duplex is when data is sent in BOTH DIRECTIONS but NOT at the SAME TIME. Example: walkie talkie

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16
Q

What is Full-duplex data transmission? And give an example

A

It is a type of data transmission and Full-duplex is when data is sent in BOTH DIRECTIONS at the SAME TIME. Example: landline phones

17
Q

What is Serial data transmission? And give an example

A

It is a type of data transmission METHOD and Serial is when data is sent ONE BIT AT A TIME over a single wire. Example: keyboard to computer

18
Q

What is Parallel data transmission?

A

It is a type of data transmission METHOD and Parallel is when MULTIPLE BITS of data are sent over several wires at the same time

19
Q

What are the FEATURES of Serial data transmission?

A
  • Better for longer distances (Telephone lines)
  • Cheaper than parallel
  • Usually used when size of data transmitted is small
  • Its slower than parallel
20
Q

What are the FEATURES of Parallel data transmission?

A
  • Better for shorter distances (internal circuits)
  • Expensive because more hardware is required
  • Usually used when speed is necessary (large size of data)
  • Faster than serial
21
Q

What does USB stand for and what type of data transmission is it?

A

It stands for Universal serial bus and it is a form of serial data transmission

22
Q

What type of data transmissions does USB allow?

A

USB allows both half and full duplex data transmissions

23
Q

What does USB consist of?

A
  • Four-wire shielded cable (protection against electromagnetic interference)
  • Two powers are used for power and Earth (one for support power to device and one for earth connect for safety)
  • Two wires are used in data transmission (2 wires carry signal)
24
Q

What are the advantages of USB?

A
  • They are automatically detected
  • They only fit in one way preventing incorrect connections
  • Different data transmission rates
  • Is compatible with older USB ports
  • An industry-standard (global)
25
Q

What are the disadvantages of USB?

A
  • Transmission rate is less than 120MB/s (Max speed data can be transmitted at)
  • Max cable length is 5m
26
Q

Name methods of error detection:

A
  • Parity checks
  • Checksum
  • Echo check
  • Check digit
  • Automatic repeat requests
27
Q

How are parity checks used?

A

The computer remembers the amount of ‘1’ bits in a byte of data and the parity can be either even or odd depending on the amount of ‘1’ bits in the byte if its an odd number of it (when added), then its odd parity but if its an even number of it (when added), then its even parity. Usually, the main bit which is on the left side of the byte is called the parity bit and decides if odd or even parity is being used.

28
Q

What are the limitations with parity checks?

A

Two bits may change during a transmission and the error of which bit changed is not found. To overcome this issue, parity blocks will be used to organize data in a grid with row and column parity bits and this method helps by looking for differences in the parity bits.

29
Q

What is Checksum?

A

It is a method of error detection and is done by adding the total binary value in a set of data before and after the package is sent (the checksum values). If any changes in the checksum values are spotted after being sent, then the package is resent

30
Q

What is Echo check?

A

It is a method of error detection and is done by the receiver sending back the data to the sender for verification, the sender then compares the received and the original data for errors. This is a stupid method of error detection as we wont know if error has occurred when sending the data to the receiver or when sending back the data to the sender.

31
Q

What are Check digits?

A

Check digits are digits added to the end of a data string based on the other digits in the string and when data is transmitted, receiving system calculates the check digit and compares it to the one sent and if there is a difference, an error has occurred

32
Q

What is Automatic Repeat Requests? (ARQ’s)

A

It is a method of error detection and is done by the receiver giving confirmation to the sender that the packet was received correctly, and without confirmation, the packet will continuously be resent until conformation is given

33
Q

What is Encryption?

A

It is when you turn data into an unreadable form so it wont make sense to hackers etc

34
Q

What is Plaintext?

A

Original data being sent

35
Q

What is Cypertext?

A

New text produced after encryption

36
Q

What is Symmetric encryption?

A

It is when an encryption key is used to both encrypt and decrypt data (same key MUST be used)

37
Q

What is Asyemetric encryption?

A

It is when a private and public encryption key is being used and public can be used by anyone but private can be used by only 1 user. The receiver would generate the private and public key and would send the public key to anyone who wants to send them a secret message. The person who sends the secret message can then encrypt the message with the public key and send the encrypted message to the user with the private key. The data can only be decrypted using the private key by the user

Year 10 Computer Science (3 decks)

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