Network Toplologies

Bus, Ring, Star

LANs

LANs- Local Area Network.A LAN covers a small area such as one site or building, eg a school or a college.


A LAN can be one of two types: wired or wireless. A wired LAN requires Ethernet cable to physically connect all computers on the network to a main device called a switch. The wireless type uses radio waves to communicate, eliminating the need for wires.

WANs

WANs- Wide area network.A WAN covers a large geographical area. Most WANs are made from several LANs connected together.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.


Linking one computer network with another is often desirable, especially for businesses that operate a number of facilities. Beginning with the local area network and going up to the wide area network, this is most easily accomplished by using existing telephony technology. Essentially, fiber optics are used to create the link between networks located in different facilities.

Networks

Advantages and disadvantages of networks


Advantages

  • 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.


Disadvantages

  • 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.

The Bus Network

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.


Advantages:

  • Easy to install.
  • Cheap to install, doesn't require much cable.


Disadvantages:

  • 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 data collisions.
  • Every workstation on the network "sees" all of the data on the network – this is a security risk.

The ring network

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 of data on the network travels in one direction and each device receives each packet in turn until the destination device receives it.


Advantage:

  • 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.


Disadvantage:

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

The star network

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.


Advantages:

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


Disadvantages:

  • 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.