by patrick


A local area network (LAN) is a group of computers within a small area, such as a house, office or school, that are connected to each other. Most academic institutions and corporate networks use LANs.

All computers/workstations connected on the LAN can communicate with one another.

some advantages of LAN:

  • Very high network speeds and data transfer rates
  • Protection from the outside world, thus creating a trusted computing environment (Firewalls are usually used to protect LAN's and to provide a secure computing environment.)
  • No need to lease telecommunication lines, such as those used for telephone, data and Internet services, once the hardware for connecting all the machines has been bought

However, are restricted to a small geographic range, limited distances, and an upper bound on the number of computers that can be connected on a single LAN.

One LAN can be connected to another LAN over any distance through telephone lines or satellite.


A Wide Area Network (WAN) is a network that covers a broad area.
  • The Internet is a WAN.
  • A network of bank cash dispensers is a WAN.
  • A school network is usually a LAN.
  • LANs are often connected to WANs, for example a school network could be connected to the Internet.
  • WANs can be connected together using the Internet, leased lines or satellite links.

Advantages of a network


  • Sharing devices such as printers saves money.
  • Site (software) licences are likely to be cheaper than buying several standalone licences.
  • Files can easily be shared between users.
  • Network users can communicate by email and instant messenger.
  • Security is good - users cannot see other users' files unlike on stand-alone machines.
  • Data is easy to backup as all the data is stored on the file server.


  • Purchasing the network cabling and file servers can be expensive.
  • Managing a large network is complicated, requires training and a network manager usually needs to be employed.
  • If the file server breaks down the files on the file server become inaccessible. Email might still work if it is on a separate server. The computers can still be used but are isolated.
  • Viruses can spread to other computers throughout a computer network.
  • There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse, eg a firewall.

Bus topologies

In a bus network all the workstations, servers and printers are joined to one cable (the bus). At each end of the cable a terminator is fitted to stop signals reflecting back down the bus.


  • easy to install
  • cheap to install, as it doesn’t require much cable

  • if the main cable fails or gets damaged the whole network will fail
  • as more workstations are connected the performance of the network will become slower because of datacollisions
  • every workstation on the network "sees" all of the data on the network – this is a security risk

Ring topologies

In a ring network each device (workstation, server, printer) is connected to two other devices, this forms a ring for the signals to travel around. Each packet ofdata on the network travels in one direction and each device receives each packet in turn until the destination device receives it.


This type of network can transfer data quickly, even if there are a large number of devices connected because the data only flows in one direction, so there won’t be any data collisions.


If the main cable fails or any device is faulty then the whole network will fail.

Star topologies

In a star network each device on the network has its own cable that connects to a switch or hub. A hub sends every packet of data to every device, whereas a switch only sends a packet of data to the destination device.


  • very reliable – if one cable or device fails then all the others will continue to work
  • high performing as no data collisions can occur

  • expensive to install as this type of network uses the most cable (network cable is expensive)
  • extra hardware required (hubs or switches) which adds to cost
  • if a hub or switch fails all the devices connected to it will have no network connection