Chapter 2 (2.1, 2.2, 2.3) Data Transmission Flashcards

1
Q

packets

A

A small part of data is transmitted over a network usually 64 KiB

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2
Q

What are the 3 components of a packet

A

Header
Payload
Trailer

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3
Q

Header

A

IP Address of sender and receiver

sequence number of packet - so that all the data can get reassembled

Size of packet In bytes

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4
Q

Payload

A

The actual data

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5
Q

Trailer

A

Method of identifying the end of
the packet

Error checking method

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6
Q

Cyclic Redundancy Checks

A

Sending computer adds all the 1 bits in the payload and sends as a hex value in the trailer.
Receiving the computer recalculates the 1 bits and compares the value to the one in the trailer.

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7
Q

Router

A

Receives a data packet and decides where to send next based on the information in the header

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8
Q

Packet switching

A

Method of data transmission where data is broken down into packets and sent independently from the start point to the endpoint.
Packets get reassembled at the destination.

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9
Q

General process of packet switching

A

Data is broken down into packets
* Each packet could take a different route
* A router controls the route a packet takes (always selects the shortest path available)
* Packets may arrive out of order
* Once the last packet has arrived, packets are
reordered

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10
Q

Benefits of packet switching

A

High transmission rate
there is no need to tie up a single communication line
it is relatively easy to expand package usage

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11
Q

Drawbacks of packet switchign

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.

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12
Q

Node

A

stages in a network that receive and transmit data packets.

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13
Q

real-time streaming

A

Transmission of data for live events. It is sent as it is received or generated.

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14
Q

Hop number

A

A number in the header that helps terminates lost packets so that the network doesn’t get clogged.

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15
Q

Factors considered why transmitting data

A

» the direction of data transmission

» the method of transmission

» how will data be synchronised

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16
Q

Simplex

A

Can be transferred only in one direction.

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17
Q

Half-duplex

A

Can be transferred in both directions, but only one at a time.

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18
Q

Full-duplex

A

Can be transferred in both directions, simultaneously.

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19
Q

Serial

A

Sending data down one channel/wire one bit at a time

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20
Q

Serial advantage

A

More reliable over longer distances

Data wont get skewed

Less expensive

21
Q

Parallel

A

Sending data down multiple channels/wires multiple bits at a time. (Usually 1 byte at a time)

22
Q

Parallel advantage

A

Faster rate of transmission than serial

Works better in shorter distances

easier to program input/output operations when parallel used

23
Q

Skewed data

A

Data arrives with bits that are unsynchronised.

24
Q

Universal Serial Bus (USB)

A

Serial data transmission which has become industry standard for connecting a computer to a device via a USB port.

25
Q

What happens when a device is plugged into a computer using a usb port

A

» the computer automatically detects that a device is present (this is due to a small change in the voltage on the data signal wires in the USB cable)
» the device is automatically recognised, and the appropriate device driver software is loaded up so that the computer and device can communicate
effectively
» if a new device is detected, the computer will look for the device driver that matches the device; if this is not available, the user is prompted to download the appropriate driver software

26
Q

USB Advantage

A

Industry standard - is compatible almost everywhere.
Plug and play - no external drivers need to be installed in order to use it
Different transmission rates 1.5mbps - 5gbps

27
Q

USB Disadvantage

A

Only up to 5m
V1 USB Isn’t supported on new computers

28
Q

Parity

A

Error checking method to check whether data has been changed or corrupted. This method is based on the number of 1 bits in the byte. If odd number then odd parity, if even number then even parity

29
Q

Parity bit

A

A bit added to the MSB of a byte to ensure that the byte follows either the even or odd parity protocol.

30
Q

Parity block

A

Horizontal and vertical parity check on a block of data that is being transmitted.

31
Q

Parity byte

A

Extra byte of data sent at the end of a parity block. Made of the parity bits from the vertical checks of a data block.

32
Q

Checksum

A

Error detection method that is calculated from the block of data that has been sent. Value is sent after each block.

33
Q

Process of checksum

A

» 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 by the computer using the block of data

» the re-calculated checksum is then compared to the checksum sent with the data block

» if the two checksums are the same, then no transmission errors have occurred; otherwise a request is made to re-send the block of data.

34
Q

Check digit

what errors can it detect

A

Calculated from other digits in the code and detect errors in data entry.

Incorrect digit entered
Transposition errors
Omitted or extra digits
Phonetic errors

35
Q

ARQ - Automated Repeated Requests

A

Error checking method that uses a system of acknowledgements and timeouts. If the sender receives a negative acknowledgement from the receiver or it doesn’t receive any acknowledgement at all before the timeout, it will resend the data until a positive acknowledgement is received or a pre-determined number of re-transmissions has taken place. If the sender receives a positive acknowledgement then data has been transferred successfully.

36
Q

Echo check

A

Data is sent to a receiver, and then the receiver sends that data back to the sender to get compared. If it is corrupted, the sender resends the data .

37
Q

encryption

A

Process of making data useless without encryption keys. The correct key is required to decode the data.

38
Q

Symmetric encryption

A

The same encryption key is used to encrypt and decrypt a message.

39
Q

Asymmetric encryption

A

Uses public and private keys to ensure that data is secure.

40
Q

Public key

A

Key that is known to all users

41
Q

Private key

A

Key that is only known to a single user.

42
Q

What is an eavesdropper

A

Person that intercepts data being transmitted on a wired/wireless network

(hacker)

43
Q

What is plaintext
what is ciphertext

A

plaintext– the original text/message before it is put through an encryption algorithm

ciphertext – encrypted data that is the result of putting a plaintext message through an encryption algorithim

44
Q

What is an encryption Algorithm

A

a complex piece of software that takes plaintext and generates ciphertext

45
Q

Explain how asymmetric encryption works

A

First - Receiver uses an algorithm to generate a matching pair of keys. A public key and a private key

Second - The public key is sent to the sender.

Third - The sender uses the public key to encrypt the data (ciphertext) and sends it back to the receiver

Fourth - Receiver uses the matching private key to decrypt the ciphertext

46
Q

Can you use a public key to decrypt data in asymmetric encryption?

A

No

47
Q

Quantum computers

A

Very fast computers that can do calculations at a high speed. Performs calculations based on probability not 0 and 1 values. This means it can process a lot more data than a normal computer.

48
Q

Causes for errors in data transmission

A

» interference (all types of cable can suffer from electrical interference, which can cause data to be corrupted or even lost)

» problems during packet switching

» skewing of data (parallel data transmission - cause data corruption if the bits arrive out of synchronisation).

49
Q

Drawback of symmetric encryption

A

The security issue of keeping the key a secret since the same key is used by the sender and receiver