1.3.1

• A LAN covers a small geographical area located on a single site. LANs can be wired or wireless. Often found in businesses and schools. LANs are good because:

  • Sharing files is easier
  • Share the same hardware (printers)
  • The internet connection can be shared
  • User accounts can be stored centrally, so users can log in from any device on the network
  • You can install and update software on all the computers at once
• A WAN connects LANs that are in different geographical locations, for example a business with offices in different countries. WANs can be connected using fibre or copper telephone lines, satellite links or radio links. The internet is one big WAN.
• Bandwidth affects the performance of the network. Bandwidth is the amount of data that can be transferred in a given time, and is shared between all the devices on a network at a given time. Too many devices or too heavy use may cause congestion and slow the network. You can limit bandwidth available to individual users to address this.
• Wired connections are generally faster and more reliable than wireless. Fibre optic cable give a better performance than copper cables. Wireless performance depends on signal quality and can be affected by the range of the device, interference from other networks and physical obstructions.
• Choice of network hardware and network topology can affect performance.
• A client-server network is managed by a server. The devices connected to the server are clients. Files and software are stored centrally on the server rather than on individual client devices. Clients send requests to the server, e.g. asking for data. The server processes the request and responds. The server stores user profiles, passwords, and access information- it may request a password before fulfilling a request or deny requests to users without the right access level. Most uses of the internet work on a client-server relationship.
• Client-server pros and cons:

  Pros:

  • Easier to keep track of files as they are stored centrally
  • Easier to perform backups
  • Easier to install and update software
  • Easier to manage network security
  • Servers are very reliable and always on

  Cons:

  • Expensive to set up and needs IT specialists to maintain the network and server
  • Server dependence - if the server goes down all clients lose access to their work
  • The server may become overloaded if too many clients access it at once
• Peer-to-Peer networks don't use servers. All devices are equal, connecting directly to each other without a server. You store files on individual devices. Can be used at home, to connect devices to a printer.

  Pros:

  • Easy to maintain - no expertise or expensive hardware needed
  • No dependence on server

  Cons:

  • No centralised management - devices need their updates and security performed individually. Backups are also more complicated
  • Peer machines are less reliable and data may be lost if one fails
  • Machines are prone to slow down when other devices access them
• Wireless Access Points allow devices to connect wirelessly to a LAN. The WAP itself is connected via wires to a network allowing it to convert radio frequencies into electrical signals.
• Routers transmit data between networks. It looks at data packets and re-routes them closer to their intended destination. Receives and accepts data packets if the IP address matches that of the router. Constructs data packets ready to be sent.
• A switch connects multiple devices together on a LAN. It identifies each new device by its MAC address. Because of this, it can transmit any data around a LAN to the correct device directly.
• A Network Interface Card or Controller is built into every device that requires the use of a network. Can be wired or wireless.
• Twisted copper cables:

  Pros:

  • Cheap
  • Lightweight
  • Easily installed
  • Good bandwidth
  • Good transmission

  Cons:

  • Breaks more often
  • Affected by electromagnetic interference/ more prone to transmission distortion
  • Can lose 94% of signal strength over 100m
• Fibre optic cables:

  Pros:

  • Lightweight
  • Easily installed
  • Much harder to break
  • Very high bandwidth
  • Much faster transmission
  • Not affected by electromagnetic interference/ little to no transmission distortion
  • Only uses 3% of signal strength over 100m
• Domain Name System (DNS). A server with a database containing domain names with their linked IP address. Domain names are easier for a user to remember than IP addresses. There are many DNS servers of varying sizes. A Domain Name Service is used to translate website domain names into IP addresses.
• How a DNS works:

  • URL is typed into a web browser and sent to the local DNS
  • If the IP address is found for that domain, the DNS sends the IP back to the user’s web browser
  • If the IP address is not found, it gets passed ‘up the chain’ to the next DNS (most likely a root server). If not found still, an error is returned to the user’s browser
  • The user’s browser then contacts the webpage host server using the IP, to request the webpage to be sent
• Hosting is when a company stores your files on their servers. This could include, web pages, online file storage and video hosting services. For web pages, a web server hosting company allows webpages to be stored on their servers and accessed when requested by a client.
• Cloud storage refers to storing data in an off-site storage system which utilises file servers.

  Pros:

  • Can access data anywhere
  • Share data with others no matter their location
  • Backup and data safety is no longer your responsibility, it is the hosts
  • Access to software on demand

  Cons:

  • Dependent on having internet connection to access data
  • Users feel more concerned about their data security
• Star topology: all computers/devices have their own dedicated cable connection to the centre of the topology. The centre can be a hub, switch or server. Works best in organised environments with multiple devices where central storage of data helps e.g. schools, large businesses.

  Pros:

  • Consistent and reliable data transmission
  • If a minor cable or device fails the other computers are not affected
  • Simple to add more devices

  Cons:

  • Costly as lots of hardware required
  • If the central switch/server fails the whole network goes down
• Mesh topology:

  Full mesh or partial mesh. Used for small offices or even large cities.

  Pros:

  • Uses fewer cables with wireless technology
  • Fast
  • No single point where the network can fail

  Cons:

  • If the device connected to the internet fails, the whole system does not have connection to a WAN