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Computer Science > 3.5 Networks > Flashcards

3.5 Networks Flashcards

1
Q

What is required for a computer network?

A

Two or more computers

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2
Q

How is the network formed?

A

Either wirelessly or through cables

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3
Q

What is the purpose of a network?

A

To Exchange information and data between other devices and to share recources

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4
Q

What is a network?

A

A computer network is created when two or more computers are connected through a connection either physically or wirelessly

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5
Q

What is the internet?

A

It is a connection of networks, no one person or organisation owns the internet - this is know as collective or distributed ownership.

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6
Q

What is the world wide web?

A

A service which is offered on the internet

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7
Q

Networks: Benefits

A

Data sharing, collaboration
Security
Communication
Remote access
Roaming (same computer no matter where you log in)
Centralised management
Files are saved to a network server

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8
Q

Networks: Risks

Or disadvantages

A

Data breaches
Viruses
Malware
Expensive
Network speed could slow down
Hacking
Reliant on hardware

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9
Q

PAN

A

Personal Area Network - connects electronic devices within a user’s immediate area, it only ranges a few meters (an example would be Bluetooth)
A PAN is anywhere in the world as long as you are there.

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10
Q

LAN

A

Local Area Network - a computer network within a limited area
A LAN operates across a small geographical area such as a school, hotel using their own cabling using their own cabling or wireless
A LAN is owned and controlled/managed by a single person or organisation
A WLAN includes a router that allows devices to connect wirelessly

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11
Q

WAN

A

Wide Area Network - the technology that connects your computers, data centres, cloud applications, and clouds storage together.
Operate over a wide geographical location in which the computers communicate using resources supplied by a ‘third party carrier’ such as BT
The largest WAN is the world

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12
Q

Standalone

A

A computer that is not connected to any other computer via a network

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13
Q

What is a Data Packet?

A
  • A small unit of information transmitted over a network, such as the internet, from one device to another
  • Each communication is split into smaller pieces called packets
  • Each packet will contain the same number of bytes
    In addition to holding the payload, each packet is marked with the packet number so that the packets can be put together by the receiver
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14
Q

IP address

A
  • Internet Protocol - the unique identifying number assigned to every device connected to the internet
  • Like every front door in the world, every computer in the world has an IP
  • IP addresses are four 8-bit numbers (0-255) separated by dots - 32 bits in total
  • It is set in software and can therefore be changed
  • It is hierarchical* - this means that it includes network, subnet, and host components - similar to a house address
  • IP addresses are used by routers to determine the best path to the destination

*contains lots of different bits of information

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15
Q

Circuit switching

A

When you make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call

  • This is called ‘circuit switching’
    It works fine for phone calls, but there could never be enough lines for all the billions of people sending data across the internet

Packet switching solves this problem

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16
Q

Packet switching

A

Each packet is 512 bytes
Each packet is given a header containing:
- The IP address it is going to
- The IP address it is coming from
- The sequence number on the packet
- The number of packets in the whole communication
Error checking data

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17
Q

Router

A

Routers are a piece of hardware capable of routing packets from one place to another based on the IP address.
They make up the ‘backbone’ of the internet
Your home router, routes packets to the different devices on your home network
Internet routers route packets around the world like a mail sorting office

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18
Q

Network Interface Card (NIC)

A

It may be wireless with an antenna or wired with a network cable socket
It is built into networked device
Most modern computers and phones incorporate the NIC into the motherboard

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19
Q

MAC address

A

Media Access Control (MAC) is assigned to each Network Interface card by the manufacturer
Your computer may have more than one MAC address if it has both ethernet and WiFi connection
A smartphone will have two different MAC addresses, one for WiFi, one for Bluetooth

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20
Q

Switch

A
  • Switches connect each node (computer) in a network
  • They know the MAC address of all connected computers and devices
  • When a packet of data arrives, they can send it directly to the correct computer
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21
Q

Hub

A
  • Hubs also connect each node in a network but do not look at the MAC address.
  • They send the data to all connected computers
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22
Q

What is a Star Topology?

A

Computers and other devices (known as nodes) all connect to the central switch/hub

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23
Q

What is a Bus Topology?

A

Computers and other devices (known as nodes) are all connected to a central backbone cable
Terminators are at each end of the cable to absorb signals and prevent them reflecting back down the cable
Packets are broadcast to all devices on the network

24
Q

Advantages of a Star Topology

A
  • Better performance – as traffic increases the network performance will not be effected.
  • If one cable fails the other computers are not affected
  • No collisions – if switch is used
  • Better security (if switched is used) as data is not broadcast to all machines
25
Q

Disadvantages of a Star Topology

A
  • Expensive - requires additional hardware such as the central switch and network cables
  • Reliance on central device - if the central switch fails the whole network goes down
26
Q

Advantages of a Bus Topology

A
  • Cheaper to install as less cable is required
  • Easy to add more devices as they only need to connect to a central cable
27
Q

Disadvantages of a Bus Topology

A
  • The single cable is shared by many devices so there will be many ‘collisions’ of data if data is sent at the same time
  • If the cable is damaged, the whole network fails
  • Potential security risk as packets are broadcast to all devices on the network
28
Q

What is the process of authentication?

A

Authentication is the process of verifying a user or device before allowing access to a system of recourses

29
Q

What is encryption?

A

Encryption is encoding data so that it can no longer be easily understood
- The process of converting plaintext into ciphertext

30
Q

What is plaintext?

A

The original message to be encrypted

31
Q

What is ciphertext?

A

The encrypted message

32
Q

What is a key in encryption?

A

A sequence of numbers used to encrypt or decrypt, often data using a mathematical formula

33
Q

What is the encryption algorithm?

A

The formula for encrypting plaintext
Two inputs: plaintext and a secret key

34
Q

What is a public key?

A

A single key is used to encrypt and decrypt a message and must be given to the recipient of your message to decrypt the data

35
Q

What is private key encryption?

A

Two keys are used - one (public key) to encrypt and the other (private key) to decrypt the data
This is more secure as it means that you never have to send or reveal your decryption key

36
Q

What is a Caesar Cipher?

A

Each letter is replaced by a letter n positions further on in the alphabet
n is the key used to decrypt the message

37
Q

What are the most common methods of WiFi security?

A

WEP (Wired Equivalent Privacy)
WPA (WiFi Protected Access)

38
Q

What is a firewall?

A
  • Checks packets entering and leaving the network to see where they are coming from and going to and what they contain
  • Packets that don’t match filtering rules are dropped
  • This is known as a packet filter
  • Firewalls can be run on dedicated hardware or as software
39
Q

What is MAC address filtering?

A

-A Media Access Control (MAC) is a unique hex number assigned to all Network Interface Cards
-A wireless router can be configured to block access to specified devices identified by their MAC addresses
- This is known as MAC address filtering and can block a specific device or only allow approved devices

40
Q

What is a network protocol?

A

A set of rules that allow devices to communicate / transfer data

41
Q

HTTP

A

Hypertext Transfer Protocol
- used for accessing and receiving web pages via the Internet
- These are written in HTML (Hypertext mark-up language)
- The protocol requests a web page from the web server
The server then sends its response which contains the web page

42
Q

HTTPS

A

secure HTTP
- encrypts the information so that it cannot be understood by an eavesdropper
- These days, most websites use HTTPS as they deal with personal data
- Some specific types of site that use HTTPS are:
○ Banks – to prevent theft
○ Online shops – for bank and log in details
○Social networks – for log in details and personal data

43
Q

FTP - What does it transfer?

A

File Transfer Protocol
- used for sending or retrieving files to or from a FTP server
- A graphical interface will allow files to be dragged from your computer to the server

44
Q

SMTP - What is this protocol used for today?

A

Simple Mail Transfer Protocol
- used for sending emails
- Email software, such as Outlook, sends the email to the SMTP server used by the company or individual
- The mail server then relays the message through various other servers known as mail relays
- Finally, the email arrives at the destination mail server

45
Q

POP - What is this protocol used for?

A

Post-Office Protocol
- Used to fetch message data and attachments from your remote mail server
- will download every new message to your local device and will no longer be available on the server.
- This is similar to the protocol of sending a letter through a post office

46
Q

IMAP - What is this protocol used for?

A

IMAP (Internet Message Access Protocol)
- Used to fetch message data and attachments from your remote mail server
- will leave the messages on a server.
- They can be accessed by multiple devices and they are only removed if the user deletes them

47
Q

TCP/IP Stack

A

A layered model that controls the different aspects of communication.

48
Q

Application Layer

A

Applications such as email clients and web browsers create data to send in this layer

49
Q

Transport Layer

A

The Transport layer creates the connection between two computers, or ‘hosts’

The two computers agree the communication settings and the size of the packets they will send and receive

Data is then divided up into packets and given a packet number

Packets are reassembled by the recipient’s Transport layer

Lost packets are resent (If TCP is used)

This layer uses the TCP (Transmission Control Protocol) or the UDP (User Datagram Protocol)

50
Q

Internet Layer

A

Responsible for routing packets

Routers operate on this layer

Source and destination addresses are written on to the packets ready
for transmission

51
Q

Link Layer

A

This is where the physical network
hardware is located.
This includes:
- Network Interface Cards (NICs)
- Cables and Wi-Fi
- The operating system’s device drivers
- The MAC address is also found at this layer

The Ethernet and WiFi suite of protocols operate at the link layer but are ONLY used inside the LAN

HTTP, HTTPS, FTP, SMTP, POP, IMAP

52
Q

Sending

Using TCP/IP Stack

A

Application - Computer application produces data for sending

Transport - Splits data into packets and numbers them

Internet - Attaches the source and destination IP address
and passes the packets to the link layer to be sent

Link - MAC address is added and packets sent along cables

53
Q

What does a router do in the TCP/IP Stack?

A

Data packets are passed from one router to another on route to their destination
Each router will ‘unpackage’ the packet to expose the IP address at the Internet layer
The router can then make an informed decisions about which port it should send the packet from
It repackages the data and sends it on its way.
The process is repeated by each router until it reaches its destination

54
Q

Receiving

A

Link - The link layer removes the MAC address and passes packets up to the Internet layer

Internet - The Internet layer removes the IP addresses and passes packets up to
the Transport layer

Transport - The Transport layer reassembles the packets in order and passes the data to the Application layer

Application - The Application layer uses the correct protocol to correctly display the data, web page or email for the user

55
Q

What is the advantages of network layers?

A

Layers are self-contained – developers can concentrate on one aspect of the network

The functionality of one layer can be changed without affecting the functionality of other layers

Ensures interoperability between providers and systems
- This means that manufacturer’s routers operating on the Internet layer, will operate with another manufacturer’s Network Interface Cards (NICs) operating on the Link layer

56
Q

What is a network layer?

A

A division of network functionality
Each layer has its own specific functions to perform
Operates independently of any other layer

Computer Science (8 decks)

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