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iGCSE CS 25 > 2.1 & 2.3 Data Transmission and Encryption > Flashcards

2.1 & 2.3 Data Transmission and Encryption Flashcards

1
Q

What is serial data transmission?

A
  • Method of data transmission
  • each bit is sent one after another …
  • over a single wire (channel)
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2
Q

What is parallel data transmission?

A
  • Method of data transmission
  • Multiple bits (often 8 bits) sent at the same time …
  • using multiple wires (lines)
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3
Q

Advantages and disadvantages of serial transmission are?

A
    • more accurate/fewer errors over a longer distance
    • less expensive wiring (single wire)
    • less chance of data being skewed/out of synchronisation
    • slower, less data sent at once dues to only one wire
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4
Q

Advantages and disadvantages of parallel transmission are?

A
    • faster, more data sent at once due to more wires
    • less accurate/more errors over a longer distance
    • more expensive wiring (multiple wires)
    • more chance of data being skewed/out of synchronisation
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5
Q

Uses of serial transmission?

A
  • Medium to long distances e.g. Ethernet, Telephone Wire
  • USB (Universal Serial Bus)
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6
Q

Uses of parallel transmission?

A
  • Short distances
  • Fast internal data transfer within a computer system (buses)
  • IC’s (Integrated Circuits)
  • Older printers
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7
Q

Explain duplex data transmission and give an example

A
  • Direction of data transmission is both ways at the same time (simultaneously)
  • Examples: Telephone call, broadband connections, video conferencing
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8
Q

Explain half-duplex data transmission and give an example

A
  • Direction of data transmission is both ways but not at the same time (not simultaneously)
  • Examples: Walkie Talkie, Intercom
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9
Q

Explain simplex data transmission and give an example

A
  • Direction of data transmission is one way only (unidirectional)
  • Examples: radio/tv broadcast, microphone to computer, computer to speaker
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10
Q

What are Integrated Circuits?

A
  • self-contained circuits with many separate components (e.g. transistors, diodes) etched into a tiny silicon chip.
  • Uses parallel transmission for …
  • …sending data internally in computer systems
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11
Q

What are the drawbacks of integrated circuits?

A
  • Less flexible - individual component or components cannot be removed or replaced – whole IC must be replaced
  • Limited power rating
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12
Q

What are the benefits of integrated circuits?

A
  • Small size – Thousands times smaller than discrete circuits
  • Small weight due to miniaturised circuit
  • Low cost due to mass production
  • Low power consumption because of their smaller size
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13
Q

What is USB?

A

Universal Serial Bus

  • Uses asynchronous serial transmission for …
  • … sending data externally
  • … (to and from peripherals / between devices)
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14
Q

Advantages of USB are?

A
  • Devices plugged into the computer are automatically detected
  • The connectors can only fit one way; this prevents incorrect connections being made
  • Industry standard; this means that considerable support is available to users
  • Supported by many operating systems
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15
Q

Explain what happens when a USB device is plugged into a computer

A
  • The computer automatically detects a device (due to a small change in the voltage level)
  • A known device is automatically recognised, and the appropriate device driver is loaded
  • If a new device is detected, the computer will look for and install the device driver
  • If this is not available, the user is prompted to download the device driver
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16
Q

Disadvantages of USB are?

A
  • Limited distance: the maximum cable length is presently about 5 metres
  • Current transmission rate is slower than Ethernet (although USB 3.0 is over 10 time faster than USB 2.0)
17
Q

Data sent over long distances is broken up into data packets. State the 3 parts of a data packet.

A
  • packet header
  • payload
  • trailer
18
Q

The packet header of a data packet consists of …

A
  • Ip address of the sending device
  • IP address of the receiving device
  • The sequence/packet number of the packet
  • The protocol
  • The packet size (in bytes)
19
Q

The payload of a data packet consists of …

A

the actual data being sent

20
Q

The trailer of a data packet consists of

A
  • a way to identify the end of the packet
  • error checking information (Checksum/CRC’s)
21
Q

How are Cyclic Redundancy Checks (CRCs) used to check data packets:

A
  • Sending computer adds up all the 1 bits in the payload and storing this as a hex value in the trailer before it is sent
  • Once the packet arrives, the receiving computer recalculates the number of 1 bits in the payload
  • The receiving computer then checks this value against the one sent in the trailer
  • If the two values match, then no transmission errors have occurred;
22
Q

Explain how packet switching works …

A
  • Data is broken down into packets
  • Each packet is given a sequence number and sent on its way.
  • Each packet may take a different route to the next depending on the quickest route at the time.
  • Routers control the route that a packet takes.
  • Packets may arrive out of order
  • Once the last packet has arrived, the sequence numbers are used to put them back into order.
23
Q

State 3 benefits of packet switching

A
  • There is no need to tie up a single communication line
  • It is possible to overcome failed, busy or faulty lines by simply re-routing packets
  • A high data transmission rate is possible.
24
Q

State 3 drawbacks of packet switching

A
  • Packets can be lost and need to be re-sent
  • The method is more prone to errors with real-time streaming
  • There is a delay at the destination whilst the packets are being re-ordered
25
Q

Message data before it is encrypted is known as …

A

Plain Text

26
Q

Message data after it has been encrypted is known as

A

Cipher Text

27
Q

Describe the steps involved in encryption

A
  • An encryption algorithm is used to scramble/encrypt the data
  • The original data is called the plain text
  • A key is used to encrypt the data
  • The key is applied to the plain text
  • Plain text is encrypted into cipher text
28
Q

Describe the process of decryption

A
  • An algorithm is used to decrypt the text
  • The encrypted data is called the cipher text
  • A key is used to decrypt the data
  • The key is applied to the cypher text
  • Cypher text is decrypted back into plain text
29
Q

Encryption is used to …

A
  • store information securely
  • transmit messages securely.
30
Q

Describe a disadvantage of symmetric encryption

A
  • When sending symmetrically encrypted data …
    • the key must be sent separately to the cipher text
  • If the key is intercepted when being transmitted it is …
    • easy to decrypt cipher text with the algorithm and the key
31
Q

How can we improve encryption?

A
  • Increase the length (number of bits) of the key e.g. 8 bit to 64 bit
    • … which means there are more possible combinations for the key
    • …and less chance of decryption by brute force
  • Choose a more secure algorithm
32
Q

How many keys do symmetric and asymmetric encryption use?

A
  • Symmetric encryption uses an encryption algorithm and a single shared key
  • Asymmetric encryption uses an encryption algorithm and 2 keys
    • a public key and
    • a private key
33
Q

Explain how a symmetric key used to encrypt a message could be passed securely from User A to User B using asymmetric encryption

A
  • The symmetric key is encrypted by User A using the public key of User B
  • User A then sends the encrypted symmetric key to User B
  • User B decrypts the symmetric key by applying their own private key

Magic!

34
Q

Explain asymmetric encryption

A
  • Everyone has their own public and private key
  • Private key is kept secret
  • Encryption algorithm and public keys are freely available
  • To send a message securely the receivers public key is used to encrypt the message
  • The receiver can then descrypt the message with their private key
35
Q

Give a disadvantage of asymmetric encryption

A

It is slower than symetric encryption due to the longer key lengths and the complexity of the encryption algorithms

iGCSE CS 25 (8 decks)

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