Networks

    Cards (25)

      • Router at home is connected to an ISP
      • ISP is connected to a DNS and other routers which make up the backbone of the internet
    • TCP/IP stack is a protocol stack which is used to switch packets across routers, allowing global communication
      It is made of 4 layers:
      • Application Layer
      • Transport Layer
      • Network Layer
      • Link Layer
    • Transport layer:
      • Sets up communication between two hosts
      • They agree settings such as language and packet size
      • Uses TCP, as well as other conversation protocols such as UDP
      • Once connection is made, the data is split into packets, the packets are numbered sequentially
      • Adds port number to packets to be used based on HTTP protocol
      • At the receiving end this layer confirms that packets have been received and requests that any missing packets be resent
      • (Adds number in sequence, total number of packets, and port number to each packet)
    • Application Layer - Used to provide services for applications that want to communicate across a network such as the internet
      • Uses high-level protocols that set an agreed standard between communicating end-points (such as IMAP for emails, HTTP(S) for web browsers, FTP for file transferring files
      • Does not determine how data should be transmitted, just specifies the rules of what should be sent
    • Network Layer:
      • Uses the internet protocol (IP) to address packets with the source and destination IP addresses
      • Router forwards each packet towards an endpoint called a socket, defined by a combination of IP address and port number
      • Each router uses a routing table to instruct the next hop
      • Routers operate at this level
    • Link layer:
      • Operates across a physical connection
      • Adds MAC address and physical NIC that packets should be sent to based on the destination IP address
      • MAC address changes each hop
      • Packets referred to as frames
    • Concept of layering is to divide the complex tasks of networking into smaller, simpler tasks that work in tandem with each other
      ADVs of layering:
      • Reduces complex problem into simpler sub-problems
      • Products from different vendors work together
      • Devices can be manufactured to work on a specific layer, making them more efficient at completing that layer than a device designed for all layers
    • Communication across a LAN only requires the link layer, which creates frames using MAC addresses whereas communication across a WAN requires the network layer, which uses the Internet Protocol to move a packet and the link layer frame
    • A network is multiple computing devices connected together
      Adv:
      • Users can share files
      • Share peripherals
      • Users can communicate with each other
      Disadv:
      • Increased security risks to data
      • Malware spreads very easily between computers
      • If a server fails, computers connected to it may not work
    • Standards - Set of hardware and software specifications that allow manufacturers to create products and services that are compatible with each other
      A key way of ensuring technology-based standards are adhered to is protocols
      Protocols - Set of rules defining common methods of data communication
    • Protocols:
      • Transmission Control Protocol (TCP) - Error free transmission between two routers
      • Internet Protocol (IP) - Routes packets across a WAN
      • User Diagram Protocol (UDP) - alternative to TCP with no error checking
      • Hypertext Transfer Protocol (HTTP/S) - way for client and server to send and receive requests and deliver HTML web pages (HTTPS adds encryption)
    • Email Protocols:
      • Simple Mail Transfer Protocol (SMTP) - Transfers outgoing emails between servers and from email clients to servers
      • Post Office Protocol (POP) - retrieves emails from a mail server
      • Internet Message Access Protocol (IMAP) - Keeps emails on the mail server, maintains synchronicity between devices
    • Hardware:
      • Modem - Transforms digital information from your computer into analogue signals that can be transmitted through wires (does this by modulating and demodulating signals sent through phone lines, coaxial cables etc)
      • Router - Routing data between devices on a network, Modem often connects to router
      • Cables - Three types of cables
      • Network Interface Controller - Allows both wired and wireless communication between computers on a LAN or widescale using IP
      • Wireless Access Point - Creates a wireless LAN, connects to a wired router to project a Wi-Fi signal
    • Hardware:
      • Hub - Allows connection of multiple devices to one network
      • Switch - Same function as hub but faster by using some software
    • Three types of cable:
      • Twisted pair - Made up of a pair of insulated copper wire, low bandwidth, cheap
      • Coaxial - Moderate bandwidth, mid-range price
      • Fibre Optic - Very thin optical fibres, high bandwidth, high price
    • Local Area Network (LAN) - Network covers a small geographical area
      Wide Area Network (WAN) - Network covers a large geographical area
      Multiple LANs physically located in different areas being connected forms a WAN
      Infrastructure that connects LANs is leased from a telecommunications company who owns it and manages it
      WANs usually connected by telephone lines, dibre optic cables, and satellite links
    • DNS system:
      1. User requests a URL via a browser
      2. Browser sends the domain name to a domain name system
      3. The DNS maps the domain name to an IP address and returns it to the browser
      4. A GET request for the web page is sent to the web server using the IP address
      5. The requested web page or resource is returned to the client's web browser
    • World Wide Web (WWW) - Service on the internet, it is a collection of files with information stored in hypertext, kmown as webpages, and other associated files, hosted on web servers
    • Circuit Switching - Creates a temporary and dedicated link of fixed bandwidth between the source and destination that lasts until transmission is complete
      • Guarantees the quality of the transmission through dedciated bandwidth, making it excellent for data that needs a constant link end-to-end such as real time video
      • A lot of potential bandwith can be wasted
    • Packet Switching - Breaks streams of data into smaller blocks, each sent independently over whichever route the node decides is the least congested
      • Maximises bandwidth
      • Does not guarantee quality of transmission
      Packet switching is more affordable and efficient as all bandwidth can be used at once, also requires less complex infrastructure and can easily respond if parts of network fail
    • Client-Server Model:
      • Server controls access and security for a shared file store, access to the internet, printing jobs, provide email services, regularly runs backups of data
      • Client makes requests to the server for data, connections, and other services
      Adv:
      • Easier to manage file security
      • Easier to backup shared data
      • Easier to install software updates to all computers
      DisAdv:
      • Can be expensive to set up and maintain
      • Requires IT specialists to maintain
      • Server is a single point of failure
      • Users will lose network access if server fails
    • Peer-to-Peer model:
      • A peer is a computer connected to the network
      • All peers are equal and are responsible for their own security and data backups, usually have own printers
      Adv:
      • Very easy to maintain
      • Specialist staff not needed
      • No dependency on a single compter
      • Cheaper to set up, no expensive hardware
      Disadv:
      • Less secure
      • Users need to manage own backups
      • Can be difficult to maintain a well ordered file store
    • Hacker - Person who tries to gain access to a computer system with malicious intent
      Malware - Umbrella term that covers any computer code written to frustrate or harm
      • Viruses - Pieces of code capable of copying themsleves and spread throughout a system
      • Spyware - Covertly obtains information about a user's computer activities by transmitting data from their device
      • Denial-of-Service (DoS) - When a server is attacked with useless traffic, cauing the system to become overloaded, can cost a lot of time and money to handle
      • SQL injection - Code injection technique to attack data-driven apps
    • Social Engineering:
      • Manipulation techniques that exploit human error
      • Phishing - disguise as a trustworthy soruce to trick users into giving personal information
      • Pharming - Malware redirects users to fraud websites
    • Proxy - Physical device between a network and a remote source, ensuring theres no direct connection between a user and a remote source