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Computer Science A Level OCR > 1.3.3 Networks > Flashcards

1.3.3 Networks Flashcards

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1
Q

Stand alone machine

A

A single computer not connected to anything else

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2
Q

NETWORK advantages

A
  • users can share files
  • users can share peripheral devices and connections to other networks such as the internet
  • servers can control security, backup of data and software updates
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3
Q

NETWORK disadvantages

A
  • increased security risks to data
  • malware and viruses spread more easily between computers
  • if a server fails, the computers connected to it may no work
  • computers may run slower if there is lots of data travelling on the network
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4
Q

Standards

A
  • a set of guidelines/conventions that govern how a task should be performed or how a product should function
  • a set of hardware and software specifications that allow manufacturers to create products which are compatible with each other
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5
Q

NEED for standards

A
  • standards enable different network devices regardless of their manufacturer of model to work seamlessly together .
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6
Q

Protocols

A
  • a set of rules to govern the transmission of data between devices [1]
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7
Q

Why are protocols important in a network ?

A
  • protocols ensure that all devices follow the same rules and standards [1]
  • so that they interpret data and signals in the same way [1]
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8
Q

Examples of protocols

A
  • HTTPS (hyper text transfer protocol secure)
  • HTTP (hyper text transfer protocol )
  • TCP (transmission control protocol
  • IP (internet protocol)
  • FTP (file transfer protocol)
  • SMTP (simple mail transfer protocol)
  • IMAP (internet messenger access protocol)
  • POP (post office protocol)
  • UDP (user diagram protocol)
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9
Q

What is a Logical protocol ?

A
  • a set of rules that govern the transmission of data [1]
  • these rules specify how data is represented [1]
  • examples include character sets [1]
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10
Q

TCP/IP

A
  • a networking protocol used in the routing of packets through networks
  • purpose : communication over LAN/WAN
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11
Q

HTTP

A

Used for webpage rendering/requests

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12
Q

HTTPS

A
  • a version of HTTP (also used for webpage rendering/requests) but with encryption for security
  • used for secure transactions like online banking and shopping
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13
Q

FTP

A
  • used for transmission of files over networks
  • provides authentication (username and password)
  • can manage file directories
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14
Q

SMTP ( IMAP and POP are also used )

A

the standard for sending email messages between servers

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15
Q

Physical topology

A
  • The physical layout of wires and components which form the network
  • eg bus, mesh, star
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16
Q

logical topology

A
  • the way data flows around a network
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17
Q

BUS topology

A
  • a network topology where all computers are connected to a single cable
  • the ends of the cable are plugged into a terminator
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18
Q

Bus topology advantages

A
  • cheaper to set up ( as it requires less cable)
  • doesn’t require any additional hardware
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19
Q

Bus topology disadvantages

A
  • if the backbone cable fails, the entire network gets disconnected
  • as traffic increases, performance decreases
  • low security as all computers on the network can see all data transmission
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20
Q

STAR topology

A
  • uses a central switch/computer to direct the flow of data
  • MAC addresses identify each device
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21
Q

Star topology advantages

A
  • if one cable fails, only that computer/station is affected
  • is more secure
  • no data collisions as each station/device has its own cable to the server
  • transmits data faster ( so better performance than bus topology)
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22
Q

STAR topology disadvantages

A
  • expensive to install due to switch and cabling
  • maintaining the network is difficult because if the central device goes down, network data can no longer be transmitted to any of the nodes
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23
Q

MESH topology

A
  • every node is connected to every other node
  • only one node requires a connection and all the others can share this connection
  • most commonly found in wireless technology eg. WiFi
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24
Q

MESH advantages

A
  • no cabling costs as it is wireless
  • the more nodes that are installed, the faster and more reliable the network becomes
  • this is because if there is a break in any of the connections, traffic can be routed via another route
  • new nodes are automatically incorporated into the network
  • Faster communication since data packets don’t need to travel via a central switch
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25
Q

MESH disadvantages

A
  • requires devices with wireless capabilities
  • maintaining the network is difficult
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26
Q

INTERNET STRUCTURE

A
  • Internet is a collection of interconnect networks (WAN)
  • www is just a service of the internet
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27
Q

Protocol layering + benefits

A
  • divides network protocols into layers each of which performs specific functions ( modular design ) [1]
  • used to apply protocols in order/ one after the other [1]
  • allows different layers to be worked on independently [1]
  • allowed layers to be upgraded/updated without affecting others [1]
  • allows for layers from different providers to be used interchangeably [1]
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28
Q

TCP/IP stack

A
  • stands for Transmission Control Protocol / Internet protocol [1]
  • TCP/IP is a set of rules used for communicating across a network [1]
  • each protocol belongs to a different layer [1]
  • consists of the following layers [1] :
    - application layer
    - transport layer
    - internet layer
    - link layer
  • a set of networking protocols that work together as 4 connected layers passing incoming and outgoing data packets up and down the layers during network communication
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29
Q

Application layer

A
  • based at the top of the stack
  • protocol to be used is decided based on the application (used to transmit data) [1]
  • e.g if the application being used to send the message was a web browser we could use HTTP/HTTPS , FTP [1]
  • adds encryption if HTTPS is used [1]
  • passes on data to transport layer for transmission [1]
  • gets data from the transport layer when receiving [1]
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30
Q

Transport layer

A
  • receives data/segments from the application layer
  • uses the TCP to establish an end to end connection between the source and recipient computer
  • splits up data into packets
  • each packet is labelled with the:
    - packet number
    - port number
    - total number of packets
  • packets are numbered so the can be reassembled In the correct order
  • if any packets go astray during the connection, the transport layer requests transmission of any lost packets
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31
Q

Internet layer

A
  • receives packets from the transport layer
  • adds the source and destination IP addresses
  • this layer is responsible for routing each packet across the network using IP addresses
  • all routers operate at this layer, the router uses the IP address to forward the packets
  • IP address + port number = socket
  • IP: the device the packet is being sent to
  • port: application of the device that needs the packet
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32
Q

Link layer

A
  • receives data from the internet layer to send [1]
  • adds the unique MAC addresses to the packets [1] (identifying the NICS of the source and destination computers )
  • passes layered data back up to internet layer when receiving [1]

Context :
- is the actual physical connection between network devices/nodes
- translates the digital packet into an electrical signal that can be sent over a network

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33
Q

What happens on the recipient computer ?

A
  • the layers occur again in reverse
  • link layer : removes MAC addresses
  • internet layer : removes the IP addresses
  • transport layer : removes the port number and reassembles the packets
  • application layer : presents the data to the recipient in the format it was sent
34
Q

IP address

A
  • a numerical address made from 4 numbers each between 0 and 255 (IPv4) [1]
  • which is a unique identifier for a device on a network [1]
  • is a logical address/identifier [1]
  • can be changed ( on a physical device )
  • responsible for global identification
  • indicates where a data packet is to be sent or has been sent from
  • if a domain name is associated with an IP address, the IP address is the address of the server that the website resides on
35
Q

MAC address (media access control)

A
  • is a 6 byte unique hexadecimal address assigned to a NIC card used to identify a device
  • MAC is the physical address of a computer and is hard coded into the device at manufacturing
  • MAC address identifies network devices on a local scale
  • MAC address are permanent, can’t be changed
  • can’t be found by third party
36
Q

Domain name

A

Is a unique human readable name that identifies a website on the internet and is associated an IP address on the internet

37
Q

DNS ( domain name system )

A
  • is the system used to name and organise internet resources
  • translates the domain name into its associated IP address
  • benefits : domain names are much easier to remember than IP addresses
38
Q

URL ( uniform resource locater )

A
  • is the full address of an internet resource
  • specifies the :
    - location of a resource on internet
    - resource name
    - file type
    So that the browser can request it from the website server
39
Q

Explain how the DNS plays a role in websites being loaded

A
  • the DNS is used to associate IP addresses with URLs [1]
  • the user web browser sends a request to the DNS resolver [1]
  • the resolver checks its local cache for the URL
  • if the resolver doesn’t have the URL, it forwards the request to the TLD name server [1]
  • or if the Q is 3 marks : if the server doesn’t have the domain name/ URL it passes the request recursively to another DNS resolver [1]
  • the TLD name server checks its cache for the URL
  • if not found , the TLD name server directs the resolver to the authoritative name server for the specific domain
  • the authoritative name server produces the IP address associated with the URL [1]
  • the IP address is retuned to the DNS resolver [1]
  • finally the DNS resolver sends the IP address back to the users browser or an error is communicated if no resolution can be found [1]
40
Q

Why are IP address needed or useful?

A
  • IP addresses can help identify a user [1]
  • so companies can potentially track users attempting to gain unauthorised access [1]
41
Q

LAN (Local area network)

A
  • A network that covers a small Geographical area typically located on a single site [1]
  • all infrastructure/hardware for LAN is owned by the network owner [1]
  • this makes LANs more secure than WANs which have connections owned by 3rd part companies [1]
  • LANs are typically connected using: UTP cable, fibre optic, WiFi
  • example of LAN : home WiFi networks
42
Q

LAN advantages

A
  • users on the network can communicate with each other [1]
  • users on the network can share peripheral devices/software/data [1]
  • users on the network can share files [1]
  • users in network can share internet connection [1]
  • simplifies backup procedures/central backups [1]
43
Q

LAN disadvantages

A
  • access to data and peripherals can be slow if there is a lot of network traffic
  • requires maintenance to ensure software is up to date
  • upgrades back ups can be costly
44
Q

WAN

A
  • a wide area network that covers a large geographical area and often uses third party connections [1]
  • is less secure than LAN [1]
  • a collection of LANs eg. Connecting two LANs between 2 cities makes a WAN
45
Q

Data packets

A
  • Packets are units of data
  • are small and easier to manage
  • when a message is too large to be sent as a single unit, it is divided to smaller more manageable units called packets
46
Q

Header

A
  • Each packet is composed of a :
    Header :
    - includes sender and recipient IP address
    - protocol being used
    - order of packets ( for reassembling)
    - packet length- size of the packet
    - hop limit: tells packet when to expire and discard so that it does not travel forever
47
Q

Payload

A

The actual data to be transmitted

48
Q

Trailer

A
  • signifies the end of the packet
  • may also contain :
    - checksum: a value used for error checking
    - cyclical redundancy check to detect any transmission errors
49
Q

Bandwidth

A

The maximum possible data transfer rate of a network

50
Q

Packet switching

A
  • a method of communication
  • best for data that can tolerate some delay eg. Emails, webpages
  • data is split into chunks called packets [1]
  • each packet has a header which includes the address being sent to and order of the packet [1]
  • each packet is sent is across the most efficient/optimum route [1]
  • routes can vary for each packet [1]
  • this means packets may arrive in a different order to which they were sent [1]
  • once packets arrive at the receiver/final destination they are reordered [1]
51
Q

Packet switching benefits

A
  • transmission is safer from interception [1]
  • because it is hard to intercept all the packets as they use different routes [1]
  • very efficient use of network resources [1]
  • as packets can follow different paths to the destination using more of the available bandwidth [1]
  • is more robust against network failures as packets can be rerouted/retransmitted easily [1]
  • meaning it is more reliable as if a single packet fails to reach its destination only that packet needs to be resent , not the entire data stream [1]
52
Q

Packet switching CONS

A
  • packets can arrive out of order, requiring reassembly of data packets and error checking
  • must wait for all packets to arrive before data can be received so their can be delays
53
Q

Circuit switching

A
  • A method of communication
  • where a direct link is created between two devices for the duration of the communication
  • data is transmitted as a continuous stream
  • Circuit switching requires the two devices to transfer and receive data at the same rate
  • ideal for real time services like voice calls or video conferencing that require low latency
54
Q

Circuit switching benefits

A
  • data arrives in order as it follows the same path allowing for quicker reconstruction of the data
  • enables two users to hold a call without delay in speech
  • no delays as a dedicated path is established
55
Q

circuit switching CONS

A
  • bandwidth is wasted during periods of time in which no data is being sent
  • devices must transfer and receive data at the same rate
  • using switches mean electrical interference could be produced which can corrupt or destroy data
  • ties up sections of the network which can’t be used by other data until transmission has been completed
56
Q

NETWORK THREATS

A
  • hackers
  • viruses
  • malware
  • denial of service
  • distributed denial of service
  • SQL injection
  • phishing
57
Q

Hackers

A

Individuals or groups which exploit system vulnerabilities to gain unauthorised access to data, with malicious intent

58
Q

Malware

A

Malicious software designed to harm or gain unauthorised access to a system or a network
Includes :
- worm
- virus
- Trojan horse
- spyware - records all key presses and transmits them to a third party
- ransomware - encrypts users files and demands for a ransom payment to decrypt them

59
Q

DOS (denial of service)

A

Where a computer floods a server with useless traffic causing the server to become overloaded which causes it to crash or become unavailable to users
- often target web serves of big companies - banks, e-commerce businesses etc
- may cause damage to reputation

60
Q

DDOS (distributed denial of service)

A
  • occurs when multiple systems orchestrate a synchronised Dos attack against a single target
  • instead of being attacked from one location, the target is attacked from many locations
61
Q

SQL injection

A
  • where malicious SQL statements are inserted in an entry field for execution
  • can expose databases revealing private data
  • data in databases can be amended or deleted
  • new rogue records can be added to the database
62
Q

Phishing

A

A type of fraudulent email which aims to steal sensitive info from users

63
Q

Virus

A
  • Malicious software that attaches itself to a legitimate program or file and then replicates itself to spread to other programs or files on the computer
  • viruses may delete data/damage hardware
64
Q

Worm

A
  • is a standalone software that can replicate itself over networks without any user intervention
  • unlike virus a worm can replicate itself and send copies to other users from your computer eg. By emailing
  • worms are responsible for using up :
    - bandwidth
    - system memory
    - network resources
  • causing computers to slow down and servers to stop responding
65
Q

Virus and worm comparison

A
  • both have the ability to self replicate by spreading copies of themselves
  • viruses rely on host files which are usually executable programs to be opened in order to spread themselves whereas worms don’t and can replicate on their own
66
Q

Trojan

A
  • a program that disguises itself as a legitimate program or file but when installed it can delete data or damage hardware
  • Trojan can’t self replicate
67
Q

types of NETWORK Protection

A
  • firewall
  • proxy server
  • packet filtering/static filtering
  • encryption
  • antivirus software
  • secure password
  • regular software updates
68
Q

Firewall

A
  • a hardware device or a peice of software that monitors and filters traffic/packets going to and from a network [1]
  • prevents unauthorised access to a network [1]
  • used to protect companies data/intellectual property [1]
  • used to restrict websites that can be accessed from within the company [1]
69
Q

packet filtering/ static filtering

A
  • limits network access in accordance with administrator rules and policies
  • it works by examining the source and destination IP address aswell as the ports being requested and the protocols being used
  • when access is denied by a firewall a packet can be either dropped or rejected
  • rejected packet : sends an alert to the user to notify them of the error
  • dropped packet does not
70
Q

Proxy servers

A
  • acts as an intermediary, collecting and sending data on behalf of the user
  • the privacy of the user is protected and they remain anonymous
  • the proxy server can cache frequently used website data making it faster to load
  • proxies can reduce overall web traffic
  • can be used by administrators to prevent access to sensitive or irrelevant info at work or at school
71
Q

NETWORK hardware

A
  • NIC
  • switches
  • WAPS
  • routers
  • gateways
72
Q

NIC (network interface card)

A
  • is required to connect a device to a network
  • is usually built into hardware and assigns a unique MAC address to each device
73
Q

Switch

A
  • sends packets and receives packets [1]
  • joins computers/devices together on a LAN
  • Commonly used In star topology
74
Q

WAPs (wireless access point)

A
  • allow devices to connect to a network wirelessly
  • most commonly used to connect devices to a router which can allow internet access
  • used in mesh networks
75
Q

Routers

A
  • a device that passes data between two networks [1]
  • is used to connect two or more networks together eg a LAN and a LAN or a WAN and a WAN
  • a routing algorithm is used to find optimum route eg. Dijkstras algorithm
76
Q

Gateways

A
  • a device which connects two dissimilar networks together [1]
  • are used when protocols aren’t the same between networks [1]
  • translates protocols so that both networks can have the same protocols
  • remove header data from packet before the remaining raw data is added with the new protocol of the new network in mind
77
Q

Client server network model

A
  • client computers connect to a server [1]
  • server provides access to a resource/service [1]
  • Use case : large organisations
78
Q

Client server advantages

A
  • central backups (in on location) eliminate the need for individual client backups [1]
  • centrally administered in one location [1]
  • Easier to keep data secure as files are stored in a central location and access rights are managed by the server [1]
  • data and resources can be shared between clients
79
Q

Client server disadvantages

A
  • central/single point of failure ( if the server goes down services could become unavailable) [1]
  • can be expensive to set up (require specialist staff to maintain network) [1]
80
Q

Peer to peer network model

A
  • there is no central server [1]
  • devices on the network share data [1]
  • a peer is a computer connected to the network
  • use case: home networks
81
Q

Peer to peer advantages

A
  • no dependency on a central server
  • is cheap to set up
  • enables users to share resources such as printer, router etc
  • is easier to maintain/ does not require specialist staff
82
Q

Peer to peer disadvantages

A
  • each machine is responsible for its own security and backups
  • lack of central control can lead to security issues and vulnerabilities

Computer Science A Level OCR (24 decks)

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