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A-Level Computer Science > 11: Networks > Flashcards

11: Networks Flashcards

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1
Q

What is meant by a standalone machine?

A

A single computer not connected to anything else

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2
Q

What are the advantages of networks?

A
  • users can share files
  • users can share peripherals and connections to other networks such as the internet
  • users can access files from any computer on the network
  • servers can control security, software updates and backup of data
  • Communication with other people - e.g. email and social networking
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3
Q

what are the disadvantages of networks?

A
  • Increased security risks to data
  • malware and viruses spread very easily between computers
  • If a server fails, the computers connected to it may not work
  • Computers may run slower if there is a lot of data travelling on the network
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4
Q

What is meant by standards?

A

A set of hardware and software specifications that allow manufacturers to create products and services that are not compatible with each other

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5
Q

What is a protocol?

A

An agreed set of rules/standards devices follow in order to communicate with each other

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6
Q

What are common protocols used for communication over LANs/WANs?

A
  • TCP (transmission control protocol)
  • IP (internet protocol)
  • UDP (User Datagram protocol)
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7
Q

what are common protocols used for web page requests?

A
  • HTTP (Hypertext Transfer Protocol)

- HTTPS (Hypertext Transfer protocol secure)

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8
Q

What protocol is commonly used for file transfers?

A
  • FTP (File Transfer Protocol)
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9
Q

What protocols are commonly used for emails?

A
  • POP (post office protocol)
  • IMAP (internet message access protocol)
  • SMTP (simple mail transfer protocol)
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10
Q

What does TCP do?

A

Provides error-free transmission between two routers

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11
Q

What does IP do?

A

Routes packets across a WAN

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12
Q

What does TCP and IP come together to create?

A

TCP/IP protocol stack, the foundation of communication over the internet

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13
Q

What does UDP do?

A
  • Uses a simple, connectionless transmission model
  • Alternative to TCP but has no error-checking
  • Used to send short messages using datagrams, where speed is more important than accuracy
  • maintains an open, two-way connection ideal for online gaming
  • not used very much as it is significantly less reliable than TCP
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14
Q

What does the HTTP do?

A

It provides a way for a client and server to send and receive requests and deliver HTML web pages

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15
Q

What does HTTPS do?

A
  • Effectively the same as HTTP, except it adds in encryption and authentication
  • Should be used whenever a website deals with sensitive information such as passwords or bank account details
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16
Q

What does FTP do?

A
  • Used for sending files between computers, normally on a WAN
  • people often use FTP clients - software applications that sit on top of the actual FTP protocol
  • When you interact with the program, the client generates and sends the appropriate FTP commands
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17
Q

What does SMTP do?

A

Transfers ongoing emails between servers and from email clients to servers

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18
Q

What does POP do?

A

Retrieves emails from a mail server and transfers them to your device, removing them from the server in the process

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19
Q

what does IMAP do?

A

keeps emails on the mail server, maintaining synchronicity between devices

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20
Q

How do devices connect to make up the internet?

A
  • a home network would be connected via a typical wireless router
  • The router is connected to the Internet Service Provider (ISP), typically via a telephone connection or fibre optic cable
  • The ISP is connected to a Domain Name Service (DNS) and other routers that make up the backbone of the internet
  • These routers are also connected to: devices on their LANs, other routers on the WAN, and servers
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21
Q

What is meant by the concept of layering?

A
  • To divide the complex task of networking into smaller, simpler tasks that work in tandem with each other
  • The hardware and/or software for each layer has a defined responsibility, and each one provides a service to the layer above it
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22
Q

What are the advantages of layering?

A
  • Reducing a complex problem into smaller sub-problems
  • Devices can be manufactured to operate at a particular layer
  • Products from different vendors will work together
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23
Q

What is meant by TCP/IP stack?

A
  • A set of networking protocols, consisting of four layers working together.
  • All incoming and outgoing data packets pass up and down through the various layers
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24
Q

What are layers of the TCP/IP protocol?

A

Applications, Transport, Network, Data Link + (physical)

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25
Q

why does it make more sense to split physical connections from data delivery than it did when TCP/IP was originally conceived? (The fourth layer)

A

There were very few physical connection option when TCP/IP was conceived, now we have twisted pair, Wi-Fi, fibre optic etc

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26
Q

What protocols are associated with the application layer?

A
  • network application such as web browsers or email programs operate at this layer
  • FTP, HTTP, HTTPS, SMTP, IMAP
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27
Q

What protocols are associated with the transport layer?

A
  • Sets up communication between two hosts - they agree settings such as language and packets size
  • TCP, UDP
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28
Q

What protocols are associated with the network layer?

A
  • addresses and packages data for transmission. It routes packets across the network
  • IP
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29
Q

What connections would be associated with the link layer?

A
  • Network hardware and connection port standards. Operating system device drivers also sit there. Facilitates the transmission of binary via any media
  • Copper twister pair, fibre optic, Wi-Fi
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30
Q

What would happen during the application layer when a message is being sent (example)

A
  • The application layer uses an appropriate protocol relating to whatever application is being used to transmit data
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31
Q

What would happen during the transport layer when a message is being sent (example)

A
  • The transport layer uses the TCP part of the stack as well as other conversation protocols like UDP
  • It is responsible for establishing an end-to-end connection and maintaining conversations between application processors
  • Theses protocols use port numbers to track sessions and add this information to the header
  • Once the connection is made, the transport layer splits the data into packets and adds its number/sequence, the total number of packets, and the port number to each packet
  • Packets are numbered so they can be reassembled in the correct order
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32
Q

What happens during the network layer when a message is being sent?

A
  • The network layer add to each packet: the source IP address, and the destination IP address
  • Routers, which operate at this layer, use the IP address to find out where the packets are heading
  • We now have what is known as a socket: IP address + port
  • We now know: the device the packet is being sent to (IP), and the application on that device that needs the packet (port)
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33
Q

What happens in the link layer when a message is being sent?

A
  • The link layer represents the actual physical connection between network devices
  • It is responsible for adding the unique Media Access Control (MAC) address of the: source device, and destination device
  • When transmitting data between routers on a WAN, the MAC address is changed at each hop on the route
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34
Q

Why do we need both MAC and IP addresses?

A
  • Communication between devices on a LAN only requires the link layer, so only MAC addresses
  • Communication between devices on a WAN requires both the network layer, which uses IP addresses to create a packet, and the link layer frame
  • Every physical device has a MAC address, but it is not feasible for routers to know and store every MAC address in existence, as it would take too long. To solve this switches learn and store the MAC addresses for connected LAN devices only, while routers cache some IPs
35
Q

How would a message be sent between two hosts on the same network?

A
  • delivery is simple, one host can simply send to the other
  • A host may need to broadcast first if it doesn’t already know the destination MAC address
  • As traffic passes through the switch, the switch examines source and destination MAC addresses and learns which address applies to which device, eliminating the need for broadcasting in the future
36
Q

How would a message be sent between two hosts on different networks?

A
  • The data will be transmitted via a router
  • The destination MAC address will be the address of the router
  • When the frame reaches the router, the router works out where it needs to send the packet by looking at the destination IP in the header
  • The router then sends its own MAC address as the source and the next device as the destination. The router can also use the ARP protocol to find the destination MAC address if the router doesn’t already know it
  • If there are several routers on the path to the destination, the source and destination MAC addresses will be overwritten at every hop
37
Q

Summary of how a message is sent over the internet:

A
  • The original message is split apart and wrapped up in segments
  • These segments are wrapped up in packets which, in turn, are wrapped up in frames
  • Once the frames reach their final destination, they will travel up through the layers of the TCP/IP stack in reverse order, stripping off the headers and tails as they go
  • Finally the destination application receives the message
38
Q

What is meant by the World Wide Web?

A
  • A collection of files with information stored in hypertext (aka web pages), and other associated files, hosted on web servers
  • these web servers host the file and handle client requests - for example, a HTTP GET request for a page or resource
  • A web page, stored as text (HTML, CSS, JavaScript), is sent to a web browser application, which uses rules to render it correctly
39
Q

How do domain name systems allow users to access websites?

A
  • A user requests a URL via a browser
  • The browser sends the domain name to a Domain Name System (DNS)
  • The DNS maps the domain name to an IP address and returns it to the browser
  • A GET request for the web page or resource is sent to the web server using the IP address
  • The requested web page or resource is returned to the client’s web browser
40
Q

How do domain name systems allow users to access websites? (in depth)

A
  • First, the human-readable URL is received by a DNS resolver server
  • The server then queries a DNS root name server
  • The root server responds with the address of the top-level domain server (TLD) for (.com for example)
  • The resolver makes a request to the .com TLD server
  • the TLD server then responds with the IP address of the domain’s name server , google.com (eg)
  • The recursive resolver sends a query to the domain’s name server
  • The IP address of the website is then returned to the resolver from the name server
  • Finally, the DNS resolver responds to the web browser with the IP address of google.com
41
Q

What is a LAN?

A
  • Any network that covers a small geographical area, typically located on a single site
  • All the hardware for a LAN tends to be owned and controlled by the organisation using it
  • Typically connected using: UTP cable, fibre optic, Wi-Fi
42
Q

What is a WAN?

A
  • Any network that covers a large geographical area
  • When multiple LANs physically located in different areas are connected, they form a WAN
  • The infrastructure that connects LANs to form a WAN is leased from telecommunication companies who own and manage it
  • Typically connected using: telephone lines, fibre optic cables, satellite links
43
Q

What is circuit switching?

A
  • Provides the basis for traditional telephone networks
  • Creates a temporary and dedicated link of fixed bandwidth between the source and destination that only lasts until the transmission is complete
  • Using this method guarantees the quality of the transmission through dedicated bandwidth, making circuit switching excellent for data that needs a constant link end-to-end such as real-time video
  • The downside is that a lot of the potential bandwidth can be wasted
44
Q

What is packet switching?

A
  • Breaks streams of data into smaller blocks, each sent independently of one another
  • At each node, packets are sent via whichever route the node decides is the least congested - this maximises bandwidth but doesn’t guarantee the quality of the transmission
  • It also means that packets can take different routes to their destination and may arrive out of order
  • It is more affordable and efficient than circuit switching as all bandwidth can be used at once. It also requires less complex infrastructure and can easily respond if parts of the network fail
45
Q

What is the role of the server on a client-server network?

A
  • Controls access and security for a shared file store
  • manages access to the internet
  • manages printing jobs
  • provides email services
  • runs regular backups of data
46
Q

what does the client do on a client-server network?

A
  • makes requests to the server for data, connections and other services
47
Q

What are the advantages of client-server networks?

A
  • Easier to manage file security
  • Easier to back up shared data
  • Easier to install software updates to all computers
48
Q

What are the disadvantages of client-server networks?

A
  • Can be expensive to set up and maintain
  • Requires IT specialists to maintain
  • The server is a single point of failure
  • Users will lose network access if the server fails
49
Q

When are client-server networks most suitable?

A
  • Organisations with a large number of computers

- Situations where many computers need access to the same information

50
Q

What is meant by a peer and what are their responsibilities in a peer-to-peer network?

A
  • A peer is a computer connected to the network
  • A peer is equal to all other peers
  • Peers serve their own files to each other
  • Each peer is responsible for its own security and data backup
  • peers usually have their own printers
  • peers can send print jobs to other peers to process, but that peer must be switched on to communicate with the printer
51
Q

What are the advantages of a peer-to-peer network?

A
  • Very easy to maintain
  • Specialist staff are not required
  • No dependency on a single computer
  • Cheaper to set up
  • No expensive hardware
52
Q

What are the disadvantages of peer-to-peer network?

A
  • Network is less secure
  • Users will need to manage their own backups
  • Can be difficult to maintain a well-ordered file store
53
Q

When are peer-to-peer networks most suitable?

A
  • smaller organisations with fewer computers

- where fewer users need access to the same data

54
Q

What is the aim of network security?

A
  • only allow authorised users to access what they need
  • prevent unauthorised access
  • minimise the potential damage caused by unauthorised access
55
Q

What is a hacker?

A

A person who attempts to gain access to a computer system with the intent of damaging data or somehow harming the system

56
Q

What is a black-hat hacker?

A

traditional hackers that attempts to gain access with the intent to cause damage

57
Q

What are white-hat hackers?

A

Security experts employed by a company that try to find vulnerabilities in a system and fix them

58
Q

What are grey-hat hackers?

A

locate flaws in computer systems as a hobby, to inform the company so they can fix it

59
Q

What is malware?

A

any computer code written with the intent to frustrate or harm

60
Q

What are the effects of malware?

A
  • deleting, corrupting or encrypting files
  • causing computers to crash, reboot or slow down
  • reducing network speeds
  • logging keyboard input and sending them to hackers
61
Q

What is a virus?

A
  • Pieces of code capable of copying themselves and spreading throughout a system
  • Typically designed to have a detrimental effect like corrupting a file system or destroying data
62
Q

What is spyware?

A

A type of malware that covertly obtains information about a user’s computer activities by transmitting data from their device

63
Q

What is a denial of service (DoS) attack?

A
  • When an attacks floods a server with useless traffic, causing the server to become overloaded
  • DoS attacks often target web servers of high-profile organisations such as banks
  • Cost a lot of time and money to handle
64
Q

What is a distributed denial of service attack? (DDoS)

A

When multiple systems orchestrate a synchronised DoS attack against a single target

65
Q

What is an SQL injection?

A
  • A code injection technique used to attack data-driven applications
  • They are designed to exploit vulnerabilities in poorly coded database applications
66
Q

What is social engineering?

A

an umbrella term covering several different manipulation techniques that exploit error with a view to obtaining private information, access to a restricted system or money
- Egs include phishing, pharming, scareware

67
Q

What is phishing?

A

An online fraud technique used to trick users into giving personal information (eg usernames, passwords, credit card details)

68
Q

What is a firewall?

A

A piece of software or hardware configured to let only certain types of traffic through it

69
Q

How do firewalls prevent network threats?

A
  • they can block certain ports and types of traffic
  • inspect data travelling across it to see if it looks suspicious
70
Q

How do secure password systems prevent network security threats?

A

Implementing password rules such as:
- minimum length
- must be changed every x days
- uppercase / lowercase number
- can’t be the same as your last x passwords

71
Q

What is a proxy?

A
  • A physical device placed between a network and a remote source
  • all traffic travels through it on its way in and out of a network
72
Q

How does encryption prevent security threats?

A

Text can only be decrypted with a unique key, so only someone with an appropriate key will be able to translate the cipher text

73
Q

What does a modem do?

A

Transforms digital information from your computer into analogue signals that can be transmitted through wires and vice versa

74
Q

What does a router do?

A

Routes data between devices on a small home network and between devices on a network and the internet

75
Q

What are the three most popular cables?

A
  • Twisted pair
  • Coaxial
  • Fibre Optic
76
Q

Twisted pair

A
  • insulated copper wires
  • affected by noise from external magnetic fields
  • more affordable than other cables
  • provide low bandwidth
  • used for telephone networks, data networks and cable shielding
77
Q

Coaxial

A
  • made up of a solid conductor wire, a layer of insulation, a grounding conductor, and a layer of exterior insulation
  • can be affected by magnetic fields but not as bad as twisted pair
  • provide moderate bandwidth
  • more expensive than twisted pair but cheaper than fibre optic
  • used for feedlines that connect radio transmitters and receivers to antennas, as well as computer network connections, digital audio and cable television
78
Q

Coaxial

A
  • made up of a solid conductor wire, a layer of insulation, a grounding conductor, and a layer of exterior insulation
  • can be affected by magnetic fields but not as bad as twisted pair
  • provide moderate bandwidth
  • more expensive than twisted pair but cheaper than fibre optic
  • used for feedlines that connect radio transmitters and receivers to antennas, as well as computer network connections, digital audio and cable television
79
Q

Fibre-optic

A
  • Made up of thin optical fibres bundled into a single cable
  • highest noise immunity
  • high bandwidth capabilities
  • most expensive
  • used for long-distance connections between cities and countries as well as data centres and organisations transmitting large volumes of data
80
Q

Fibre-optic

A
  • Made up of thin optical fibres bundled into a single cable
  • highest noise immunity
  • high bandwidth capabilities
  • most expensive
  • used for long-distance connections between cities and countries as well as data centres and organisations transmitting large volumes of data
81
Q

What is the purpose of a Network Interface Controller (NIC)

A

Allows both wired and wireless communications between computers on a LAN or connected to a large-scale network using the Internet Protocol (IP)

82
Q

What is a wireless access point (WAP)

A

A device that creates a wireless local area network
- connects to a wired router, switch, or hub via Ethernet cable and projects a Wi-Fi signal within a designated area

83
Q

What is a hub

A
  • Allows you to connect multiple devices to one network
  • it is a passive device that broadcasts the transmissions it receives to all connected devices
  • this means the network can easily become flooded
  • just hardware
84
Q

What is a switch

A
  • Allows you to connect multiple devices to one network
  • It is an active device, meaning it can inspect transmissions and route them to the correct device
  • faster than hubs
  • has software for admin purposes

A-Level Computer Science (25 decks)

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