Networks

• Network


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


  • Covers a relatively small area
  • Connects multiple devices on a single site
• WAN


  • Covers a large geographical area
  • Connects multiple LANs together
• Reasons for connecting computers on a network

  • To share data and software
  • To share printers, hard drives and other hardware peripherals
  • To share internet connections and services, such as the web and web-based software
  • To provide centralised support and backup services
  • To enable the rapid deployment of new software and updates
  • To enable people to communicate with each other using services such as email and video conferencing
  • To support collaborative working
• The internet is a global system of interconnected computer networks
• The internet is an example of a huge WAN
• LAN


  A network in a small area such as a home, school, office building or group of buildings on a single site
• WAN


  Connects separate LANs over a large geographical area to form a network of networks
• The internet is a global system of interconnected networks
• No single organisation owns the internet
• IP address


  Unique identifier assigned to every internet-connected device so it can send and receive data
• Versions of IP


  • IPv4
  • IPv6
• Dynamic IP address


  Allocated from a communal pool when a device connects to the internet and returned when it disconnects
• Static IP address


  Permanently assigned to a device that is permanently connected to the internet
• Domain name


  Human-friendly form of an IP address
• URL


  The complete web address of a particular web page, image or other resource on the internet
• 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. Web server finds correct files and sends them to browser

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


  Data travels across the internet in packets using a method called packet switching
• Packet switching process


  1. Sender's data is broken up into smaller packets

  2. Packets are directed to their destination by routers

  3. Packets may take different routes and arrive out of order

  4. Receiving computer reassembles the packets in the correct order
• Routers


  • Form a physical connection between two or more networks
  • Forward data packets from one network to another
  • Use routing tables to select the most efficient route for each packet
• Data packets from the same transmission may travel to their destination via different routes and may therefore arrive out of sequence
• Data packet


  Consists of a payload, a header and a footer
• On arrival at the destination, the receiving computer checks that each packet is complete and uncorrupted, checks that all packets have been received, and reassembles them in the correct order
• Wired transmission media


  • Copper wire
  • Fibre-optic cable
• Copper wire


  • Transmits data as electrical pulses
  • Susceptible to electrical interference
• Fibre-optic cable


  • Transmits data as pulses of light
  • Immune to electrical interference
  • Offers higher bandwidth than copper wire
• Wireless transmission media


  • Wi-Fi
  • Bluetooth
  • Zigbee
  • RFID
  • NFC
• Wi-Fi


  • High power consumption
  • Range up to 100m but can be obstructed by physical objects
• Bluetooth


  • Low power consumption
  • Range up to 10m
• Zigbee


  • Low power consumption
  • Range up to 100m
• RFID


  • Very low power consumption
  • Range up to 1m
• NFC


  • Very low or no power consumption
  • Range around 10cm
• Fibre-optic cable offers advantages over copper, but it is considerably more expensive and more fragile and difficult to handle
• RFID proximity


  Around 10 cm
• RFID signal strength


  Very low or none
• RFID use


  Contactless payment systems
• The UK issues RFID-embedded passports. The RFID chip contains biometric information used to authenticate the identity of the passport holder.
• An RFID is suitable for embedding within physical objects because the chip does not need its own power supply
• g


  Displays received information to the user
• Sending


  1. Splits outgoing data into packets and numbers them

  2. Adds a header containing a sequence number and a checksum to each packet