Networks

• Network


  An arrangement of two or more computing devices connected together in order to communicate with each other and share resources
• LAN (Local Area Network)


  • Covers a relatively small area
  • Usually managed by a local manager or team at the site
• WAN (Wide Area Network)


  • Connects separate LANs over a large geographical area
  • Computers can communicate with computers and users in other locations
  • Managed by several different people or parts of an organisation (collective ownership) or each LAN could be managed independently (distributed ownership)
• The internet is a global system of interconnected computer networks
• IP address


  A unique identifier for every device connected to the internet, allowing it to send and receive data
• Dynamic IP address


  Allocated from a communal pool when a device connects to the internet and returned when it disconnects, so the IP address may change next time
• Static IP address


  A permanent IP address that never changes, used for devices like routers and web servers that are constantly connected to the internet
• Domain name


  A human-friendly form of an IP address
• What happens when a web page is requested


  1. Browser sends URL to DNS server to get IP address

  2. Browser sends HTTP page request to web server

  3. Server finds the correct files and sends them to the browser

  4. Browser renders the page and displays it
• Packet switching


  A data transmission method where data is split into smaller packets that can travel independently and be reassembled at the destination
• Packet


  • Consists of a header (with destination IP, source IP, sequence number, checksum), payload (actual data), and footer
• Packets from the same transmission may travel via different routes and arrive out of sequence
• Routers keep each other informed of traffic conditions and can send packets via alternative routes if one is congested
• Wired transmission media


  Devices physically connected using cables, usually copper wire or fibre-optic
• Wired transmission media


  • Copper wire: up to 100 Gbps, susceptible to electrical interference
  • Fibre-optic: up to 100 Gbps, less susceptible to interference
• Wireless transmission media


  Use radio waves to transmit data through the air
• Wireless transmission media


  • Range: up to 100m, but can be obstructed by physical objects
  • Power consumption: high for Wi-Fi, low for Bluetooth and Zigbee
• Fibre-optic cable is better suited than copper wire to provide high-speed broadband connectivity
• Wireless LANs are easy to install and allow devices to be moved around easily
• RFID


  Radio Frequency Identification used to authenticate the identity of the passport holder
• RFID


  • No need for physical cable connection, data transmitted wirelessly
  • Risk of data transmission being intercepted is reduced because chip and reader must be within 1 m of each other
• Fibre-optic cable


  Better suited than copper wire to provide high-speed broadband connectivity
• RFID


  • Suitable for embedding within physical objects
  • RFID chip does not need its own power supply
• RFID is suitable for authenticating the identity of the passport holder
• RFID is suitable for embedding within physical objects and the RFID chip does not need its own power supply
• Wired LANs require physical cables to connect devices, while wireless LANs do not
• Wireless LANs


  • Easy to install, easy to add new devices
  • Devices can be moved around without affecting the connection, as long as they stay within signal range
  • New users can easily join the network by connecting to the wireless access point and entering the SSID and password
• Wired LANs


  • Up to 100m range, may be shorter due to physical obstacles
  • High data transfer rate up to 10 Gbps per connection
  • Low susceptibility to interference, layers of protective coverage
• Wireless LANs


  • Shorter range, may require signal boosters
  • Lower data transfer rate up to 3.2 Gbps, shared among all devices
  • High susceptibility to interference from other wireless networks or devices
  • Poor security, anyone within range can intercept transmissions
• Many networks use a combination of wired and wireless connections, with some devices connected via cables and others connected wirelessly
• Connecting a TV to the router by cable ensures sufficient bandwidth to stream content from the internet
• Devices with fixed locations can be cabled in, freeing up wireless bandwidth for devices without fixed locations
• Schools need to consider the benefits and drawbacks of cable and wireless networks when choosing a network setup
• Data transfer rate


  The speed of a network, measured in bits per second