Posted by admin on 5th May 2011

Networks

Networks are the hardware setups we put together to allow computers to communicate with each other. That allows us to use computers as communication devices, allowing everything from MSN messenger to iTunes this website. You’ll need to know about the hardware devices used to make networks and the different designs of networks as well as some advantages and limitations of using a networked computer.

Network Hardware

Almost every computer you buy has networking hardware built in, usually directly into the motherboard. Early in the development of networking, a network card was an add-on that could be connected to a computer to allow it to communicate on a network. A network cable is plugged into the network port on the computer. The photo shows what the most common network cables in 2010 look like. The other end of that cable will be plugged into a device with one of three names: router, switch, or hub. That piece of hardware allows messages to be transferred from one cable, from one computer, to another. Usually in your home that would be a router, which allows an internet connection to be shared between computers as well.

Over the past 10 years, networks have increasingly been becoming wireless. Wireless networks are really convenient to use, but can be slower and less secure than “wired” networks.

Some other hardware can be connected to a network. Phones and mp3 players are an obvious example, but things like printers and scanners can be networked too. This means that they can be shared between lots of users – great in an office or a school classroom where it would be really wasteful to put one printer per computer. It’s good at home too – you could print from the sofa watching TV with your wireless network.

Peer-to-peer or server/client

There are two models for networks, two ways to get things connected up. Web pages on the internet work in a server/client way. The server stores the webpages and your computer, the client, downloads. Lots of clients can connect to one central server, so it can be a source of weakness if it crashes.

Bittorrent and other types of filesharing service often work peer-to-peer. This means that each computer is an equal, connected to other computers, sending files to each other. If any one computer goes off-line, the others will keep working and sending the files to each other. Peer-to-peer services can get a bad reputation but they are also used for legal things too – BBC iPlayer has peer-to-peer sharing built in.

Network Topologies

Topologies? It’s a big word meaning ‘shapes’ – these are the shapes of networks, and the way they’re connected together affects how they work.

You’ll need to know about:

  • Star
  • Ring
  • Bus

Each one has benefits and weaknesses, make sure you can remember them.

busBus Network

Each computer is like a stop on a bus route – sending information goes along the line until it reaches the right stop. if it reaches the end of the line it goes back all the way to the other end. This arrangement uses the least cable to connect the computers, but since the data for all the computers goes both was along all the cables, there are collisions. When data collides it is lost and must be resent, slowing down transmission. Also, if the cable breaks, lots of computers can be cut off.

ringRing Network

The computers on a ring network are connected in a circle so one-way data does not need to collide. The ring needs more cable than the bus network and if it fails in one place the whole network will fail.

starStar Network

The star network is the type that is actually used most. Each computer is connected to a central hub or switch which uses quite a lot of cable. If any cable fails only one computer is affected; if the hub fails the whole network breaks. There are less collisions as the hub routes the data carefully to avoid it.

Cell NetworkCell Network

The cell network topology is not on the GCSE course but is on other courses. It’s the way that mobile phones communicate and sometimes it’s one that we use for Wifi (wireless networks) too. At the centre of each “cell” is a base station, a transmitter and receiver device that communicates with the devices in its area. The especially smart bit of this system is how the cells “hand over” devices to the next cell as they move without you being able to notice that the connection has been lost and reconnected – it should happen seamlessly.

As it is a wireless network there are no problems with individual devices and cables though high amounts of data being sent over the network will result in slower speeds. The cell structure should mean that devices are shared out as fairly as possible to reduce this, though.

Revising

Make sure you can draw the three types of network topology. When you draw them, remember to add lots of different types of device, like printer, scanner, PC, server. Make sure you know the reasons why it’s good to have a network – and the problems, like security.

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