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Computer Science Paper 2 > Communication And Networking > Flashcards

Communication And Networking Flashcards

1
Q

What is a symbol?

A

Pattern of bits represented by a signal

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2
Q

What is Baud Rate?

A

The number of signal changes in medium per second

1 baud = 1 symbol change per second.

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3
Q

What is bit rate?

A

Number of bits transmitted over medium per second.

Bit rate = Baud rate X Number of bits per signal.

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4
Q

What is bandwidth?

A

Range of frequencies in which a medium is capable of transmitting. - Higher bandwidth = higher bit rate.

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5
Q

What is latency?

A

Difference in time between action being initiated and it’s effect being noticed.

Usually increases with distance.

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6
Q

What is a protocol?

A

Set of rules relating to communication between devices.

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7
Q

Explain serial data transmission

A

Data sent 1 bit at a time over communication line.

Used for long distances computationally

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8
Q

Explain parallel data transmission

A

Numerous communication lines used to send multiple bits at a time

More lines used - more bits per second

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9
Q

What is skewing?

A

Data sent via parallel transmission arrives at slightly different times - each line slightly different. Over longer distances - bits may not be received together. - Long distances leads to overlapping.

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10
Q

What is crosstalk?

A

Communication lines packed to close - data can jump to another line causing data corruption.

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11
Q

State an advantage of serial over parallel

A

Doesn’t suffer crosstalk or skew - more reliable over long distances.
Cheaper than parallel to install.

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12
Q

What is synchronous transmission?

A

Clock signal shared by sender and receiver used to time when data is sent.

Often used within processor for FE cycle.

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13
Q

What is asynchronous transmission?

A

Use of start-stop bits rather than clock speed. Start-stop bits indicate duration of transmission.
Start bit always opposite stop bit.
Sender must use same baud rate and synchronise clock speed for duration of transmission.

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14
Q

What is a physical network topology?

A

Physical architecture of a network - Use of interconnected components

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15
Q

What is a star network topology?

A

Each client connected to central hub. Hub receives packet and sent to correct recipient.

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16
Q

Name some advantages and disadvantages of star topology.

A

Adv:
- Packets sent to recipient.
- Easy to add and remove clients
- no collisions - each device has own cable
- Failure of cable doesn’t affect network.

Disadv:
- Central point of failure (hub)
- Expensive to install

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17
Q

What is a bus topology?

A

Connects clients to single ‘backbone’ cable. Terminators placed at either end.

No need for central hub - just connect via backbone.

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18
Q

State some advantages and disadvantages of bus topology.

A

Adv:
- No central hub, less likely to fail.
- Cheaper to install - just cost of cable

disadv:
- packets sent via backbone - every client on network receives packets.
- High chance of collisions - 1 main cable connects many clients.
- Backbone failure brings down network

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19
Q

What is a logical network topology?

A

Flow of data packets within a network - Delivers packets to all clients on network.

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20
Q

What is meant by mixing topologies?

A

Connect clients in star topology, can run as a bus topology - sends packets to all devices.

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21
Q

What is client-server networking?

A

One or more central servers providing services to clients.

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22
Q

How does client-server networking work?

A

Clients on network request services form servers - respond with requested service.

  • File storage
  • Mail management
  • user accounts
  • print queues.
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23
Q

What is peer-to-peer networking?

A

Services provided by clients, not servers.

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24
Q

How does peer-to-peer networking work?

A

Each client has equal status
one client will be responsible for file management, another for mail storage etc.

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25
Q

Name a disadvantage of peer-to-peer

A

Each client must be running and fully operational - client responsible for files is faulty, no device can access their files.

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26
Q

Name some advantages of peer-to-peer.

A

More cost effective - no need for powerful server.
- Easier to set up and maintain.
- High performance without server.

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27
Q

How does wireless networking work?

A

Devices connect to wireless access point (WAP) which connects to network.

Allows for communications without cables.

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28
Q

What is WiFi?

A

Wireless Local Area Network (wLAN) based on international standards.

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29
Q

How are wireless networks secured?

A

Encryption. WPA or WPA2.

30
Q

What is WPA?

A

WPA - WiFi Protected Access - requires new client enters password to connect to network.

WPA2 is slightly better than WPA with a longer password required.

31
Q

What is SSID broadcast? What does disabling SSID broadcasting do?

A

Service Set Identifier - Name of the network.

Disabling SSID broadcast means devices need to enter the name of network to connect. `

32
Q

What is a MAC address filter

A

MAC - Media Access Control

Filtering MAC addresses will mean only specific devices can connect to a network. MAC blacklists block specific devices connecting.

33
Q

What is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)?

A

Protocol used to avoid data collisions caused by simultaneous transmission.

34
Q

How does CSMA/CA work?

A

Device listens to communication channel - check weather is idle - Only send if channel is free.
.

35
Q

What does CSMA/CA do if the channel is busy? What is Exponential Backoff Algorithm?

A

If channel busy, wait random time before checking again.
Exponential backoff algorithm - used to increase time period device waits with each check of the channel.

36
Q

What is Request To Send / Clear To Send (RTS/CTS)?

A

Protocol which adds additional step to CSMA - Once transmitting device checked channel is idle, sends request to send (RTS) - If channel is idle, receives Clear to send (CTS). Otherwise waits before starting CSMA again.

37
Q

Why is RTS/CTS required?

A

CSMA is not effective against hidden nodes - Cannot see some parts of network.

38
Q

What is the Internet?

A

Network of interconnected computer networks - Uses end-to-end communication protocol.

Mostly wired network with cables passing under major oceans.

39
Q

What is an Internet Service Provider (ISP)?

A

Company which provides customers with access to internet.
Largest ISP’s are national Internet Service Providers - Provide local ISP’s.

40
Q

What is packet switching?

A

Data / message split into numerous packets, then transmitted via best possible route and assembled at recipient.

41
Q

How do packets reach recipient from sender?

A

Packets pass through number of routers through best possible route. Each router it passes through, a ‘hop’ occurs.

42
Q

What is TTL?

A

Time To Live
Each packet has finite number of hops it can do defined by it’s Time To live.
When TTL ends, packet is ‘dropped’ and sender resends packet.

43
Q

What are the components of a packet?

A

Sender Address - Where packet was sent from.

Receiver address - intended recipient

Packet contents - Data packet is holding

TTL - Number of hops

Sequence number - Number of packets in a message. Identifies which position this packet is in relation to others.

44
Q

What are routers and what are they used for?

A

Hardware which sends packets to recipient via fastest route - Lowest hops, least congested etc.

Hold tables relating to fasted routes for specific devices.

45
Q

What is a gateway?

A

Hardware device which connects 2 networks with different protocols together.
Modifies packets so that it can travel across different protocol networks.

46
Q

What is a URL?

A

Uniform Resource Locator

Address assigned to files on the internet.

47
Q

Name the parts of the URL

A

Protocol - HTTP, HTTPS etc

Subdomain - Points to web server hosted at following domain - WWW .

Domain - Name of organisation - BBC

Directory - Where the file is being requested from - /news

Subdirectory - further location of file being requested - /technology

Name - What the file is called. - /index

File extension - Usually HTML

48
Q

What is a domain name?

A

Identifies organisation or individual on internet - uses alphanumeric characters

49
Q

What are fully qualified domain names?

A

Domain which specifies exact resource - only interpreted in one way.

https://bbc.co.uk/news/index.html

50
Q

What are IP addresses?

A

Identifier assigned to every computer on the network.

51
Q

What is a DNS?

A

Domain Name Server - DNS used to translate domain into corresponding IP address.

Each domain has direct relationship with IP address.

52
Q

How do DNS’ work?

A

Table of domain names and corresponding IP stored.
If domain client is requesting doesn’t exist on certain DNS, passed onto another DNS.

53
Q

What are Internet Registries?

A

Organisation responsible for allocation of IP addresses.

There are only 5 in the world.

54
Q

What is the purpose of an internet registry?

A

Protect depleting pool of IP addresses.
When new IP requested, checks for prev allocated now unused before allocating brand new.

55
Q

What are Firewalls?

A

Regulates packets passing through network.
Software or hardware, and can work as proxy server to perform packet filtering and stateful inspection.

56
Q

What is packet filtering?

A

Method firewalls use to block or accept packets based on their source ip and the protocol they are using

57
Q

What is stateful inspection?

A

Method used by firewalls which involves examining the contents of the packet before deciding to allow it through firewall.

Can sometimes keep track of what’s being sent - block anything not related to current activity.

58
Q

What is a proxy sever?

A

sits between public and private network - manages every packet passing through 2 networks.
Data sent from private network adopts proxy address - some level of anonymity.

59
Q

Explain how symmetric encryption works.

A

Both sender and receiver share same private key - used to encrypt and decrypt.

Sender and receiver exchange keys - can be vulnerable to interception.

60
Q

Explain how Asymmetric encryption works.

A

use of 4 different keys - each device has pair of mathematically related keys ( public and private)

Message encrypted with recipients public key, corresponding private key can decrypt.

61
Q

What are digital signatures?

A

Used to verify sender of a message - check message not tampered.

62
Q

How do digital signatures work?

A

Digest of message created - hashing / checksum - Value depends on content of message.

Digest is encrypted with senders private key

Encrypted digest appended to message.

Message + digest encrypted with recipients public key - only decryptable by recipients private key.

Recipient receives and decrypts message and digest. - Digest matches means message was really sent by sender.

63
Q

What are digital certificates?

A

Verifies ownership of key pair used in asymmetric encryption.
- Used to check fake key pair isn’t being used.

64
Q

What is included in digital certificates?

A

Serial number, owners name, expiry date, owners public key and certificate authority’s digital signature.

65
Q

What are worms?

A

Malicious software which can self-replicate within network or by users downloading infected files.

66
Q

What are Trojans?

A

Type of malware disguised as benign file - email attachments / malicious websites

67
Q

What are Viruses?

A

Malware requiring host file - usually executable files

68
Q

How can malware be prevented?

A

Update software - particularly antivirus software.

Install antivirus software

Train employees about risks of opening suspicious files.

69
Q

What is TCP / IP

A

Transmission Control Protocol / Internet Protocol - Used in all parts of the internet.

70
Q

What are the 4 distinct layers in the TCP/IP stack?

A

Application - Selects correct protocol to transmit data.

Transport - Establishes virtual parth - end-to-end connection between sender and receiver.

71
Q
A

Computer Science Paper 2 (6 decks)

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