Networks

A guide to LANs, WANs, Network Topologies and Components

Network Types

LAN

LAN stands for Local Area Network. This is a network of computers that covers a small area, such as one site or building (e.g. at home, offices, schools, shops). LANs generally have a higher data transfer rate than WANs, as there are fewer computers and a smaller network. They allow any computers on the network to share data, software and hardware.

WAN

WAN stands for Wide Area Network. This is usually a network of LANs which covers a broad region, such as a county, metropolitan area or other large area. Businesses often use this type of network to relay data, software or hardware to branches, employees and customers across the country. Most WANs are private and are made for the use of one group or company only. Due to distances and the number of computers, data transfer rates are slower than that of LANs.

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Topologies

Bus

A bus network topology connects computers(nodes) via a connection known as a bus, where each computer is connected to a single cable or 'communication line'. A terminator is used at each end of the bus to prevent signals from reflecting back. Bus topologies are useful as it easy to add or remove computers (nodes). It also allows for a high rate of data transfer, as the connection is cabled rather than wireless. This topology is a lot cheaper to install than most others, as it requires less cabling. However, any failures in the central line will cause the entire network to fail. Performance also tends to decrease as more data is transferred. This type of topology is best used as a temporary network.

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Ring

A ring network topology connects computers (nodes) together via a loop. Data is transmitted from computer to computer in one direction. This allows data to be transferred quickly between nodes, as the transfer of data is a lot more simple than that of the bus topology. This design also removes the need for a central computer. One of the problems with ring topologies, however, is that if the connection is broken, the whole network fails as data can only travel in one, fixed direction. Its design also makes it harder to add or remove computers, as doing so requires the network to be disrupted.

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STAR

A star network topology connects each computer on the network directly to the central computer or server. The way in which a star topology is set out allows it to transfer data more securely between computers (nodes) as the data goes directly to the designated computer. The star topology also has an advantage that the previous two topologies lack, and that is that if the connection to one computer fails, only that computer will be cut off - the rest of the network will remain unaffected. The design also makes it easy to add or remove computers/nodes, as they can simply be added to or removed from the star formation. Though, this type of topology still has its issues. For example, if the central computer/server fails, the network collapses and all nodes lose connection. This type of topology also requires a lot of cable, which makes it expensive to set up.

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LAN NETWORK COMPONENTS

File Server

The file server is the main computer on a network, so it needs to be more powerful than the other computers.Ideally, it should contain large amounts of RAM and Hard Disk space in order to keep up with data transfer. It is this computer that contains the user data and applications (software) for all nodes. It also contains the network OS (e.g. Windows 7). These cost anything between £500-15,000 pounds, on average.

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Network Interface Card

The network interface card, also known as the NIC, allows a computer to communicate with the file server and other computers on the network. Every computer must have one of these in order to connect to a network. Most NICs are built for a certain network, protocol and/or media, though some can support more than one type of network.These are priced at around between £4-150 on average.

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Network Cable

Network cables plug into the back of each computer (or computer processor) and link them together. They go straight into the network interface card in the computer. There are many different types, such as coaxial, optical fibre and Twisted pair. Twisted pair cabling involves twisting the two conductors together in order to block out interfering EM radiation from external sources. Optical fibre cables consist of a glass core surrounded by several protective layers. They transmit light rather than signals. Coaxial confine electromagnetic waves to the area inside the cable. Their design means that they can be twisted and bent without any negative effects on the connection. The type used depends on the network's topology, protocol and size. The price for network cables ranges between £2 and £30.

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SWITCHES

A switch, also called a multi-port network bridge, is a single connection point for a group of computers. It connects to the main computer/server and organizes communication. Think of it as a postal service: the switch receives messages from any device connected to it and sends it to the device it was meant for. Though it isn't required for all networks. You can buy these for between £5 and £90.

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WAN Network Components

Modem

Modem stands for Modulator-Demodulator. This device was first created to take digital signals from a computer and convert them to analogue, so that they can be transmitted down a telephone line.