1.3 Networks

• Network


  Two or more computers connected together

  
• Advantages of networks


  • Resources can be shared
  • Easy communication between users
  • Software can be installed and updated remotely
  • Security measures can be easily set up and enforced
  • Site licences for software are much cheaper
• Disadvantages of networks


  • Servers and network infrastructure can be expensive
  • Large networks need dedicated staff to manage and maintain
  • Crucial servers can cause network failure if they break
  • Large networks are a target for viruses and hackers
• LAN (Local Area Network)


  Two or more computers connected together, either directly or through a central hub or router
• Features of a LAN


  • All network in one location
  • Organisation owns all hardware
  • Organisation manages the LAN
• WAN (Wide Area Network)


  Network that connects two or more LANs in different locations
• Features of a WAN

  • Connection between LANs owned by separate company
  • Connection managed by external company
• Factors affecting network performance

  • Network topology
  • Transmission media
  • Number of users
  • Bandwidth

  
• Client-server network


  Certain powerful computers (servers) provide services to other computers (clients)
• Peer-to-peer network


  Each computer stores files and acts as a server, with equal responsibility for providing data
• Network Interface Card (NIC)


  Device that connects a computer to a network, either wired or wireless

  
• Wireless Access Point (WAP)


  Transmits signals from the network so wireless NICs can connect

  
• Router


  Device that can join different networks together
• Switch


  Device that allows devices to connect to the network, redirecting traffic to the correct device
• Transmission media


  Wires, cables and fibre that physically connect network components
• Internet


  Massive wide area network with millions of servers and billions of computers connected
• World Wide Web


  Services including web pages that use the internet to distribute content
• IP address


  Unique address for each computer on a network, currently made up of 4 numbers 0-255 separated by dots
• The current IP4 system is right at the end of its life because all of the available IP addresses have been used up
• Internet


  The hardware that connects computers

  
• World Wide Web


  The services including web pages that uses the internet to distribute its content
• Accessing a website


  1. Type in the web address (URL)

  2. Domain Name Servers find the IP address of the web server

  3. Web pages are retrieved from the web server
• IP address


  The unique "address" of a computer on a network, made up of four 8-bit binary numbers separated by dots
• The current IP4 system is at the end of its life as all possible IP4 addresses have been used, so it is being replaced by IP6 which uses 6 eight-bit binary numbers
• In practice, we use domain names instead of typing in IP addresses
• Hosting


  Setting up a web server to serve web pages, which can be done on a simple computer but requires a server farm for high-traffic websites
• Cloud storage


  Secondary storage that can be accessed from any web-enabled device, provided by large companies with secure data centres
• Star topology


  • Each device connects to a central hub or switch
  • Practical limit of 24-30 devices per hub
• Mesh topology


  • Devices can connect directly to each other as well as through a hub
  • Allows high traffic and redundancy, but more complex and costly to implement

  
• Advantages of mesh topology

  • Multiple devices can transmit data simultaneously
  • Network can still function if one device fails
  • Adding devices does not disrupt other connections

  
• Disadvantages of mesh topology

  • Higher cost to implement
  • Building and maintaining the topology is difficult and time-consuming
  • High chance of redundant connections
• Wired network


  Uses cables or fibres to connect devices, with Ethernet as the standard
• Wireless network


  Uses Wi-Fi or Bluetooth standards to connect devices wirelessly

  
• Advantages of wired networks

  • Offer higher speed and bandwidth
  • Suitable for business/school environments with fixed devices
• Advantages of wireless networks

  • Suitable for portable devices and temporary connections
  • Common in homes, cafes, etc.
• Encryption


  Scrambling information so it can be safely sent without being read by others
• Encrypting a message


  1. Use a long number key

  2. Shift each letter by the corresponding number in the key
• Encryption can be cracked by powerful computers, but is generally considered secure in practice
• IP address


  The unique "address" of a computer on a network
• MAC address


  The unique hardware address of a network interface card