There are different ways to send information over distances, one being the use of flags to represent different letters with people waving them accordingly. The problem with this flag signalling method is that it is unreliable and there is no guarantee that the receiver will understand the message correctly.

If a method of communcation is to work well, protocols are needed to enable 2-way communication in order to confirm successful receipt of the signal etc... (Ethernet is a good example of a protocol used for communication between computers within a network)

Data can be transferred between computers via telephone lines despite the fact that these lines are designed to carry analogue sound in the form of various tones. A modem can be used to transfer data from a computer into sound so that it can be sent over the telephone network.

The data rate possible over the telephone lines depends on the quality of audio link and frequency. There is always the possibility of overloading the system if a constant stream of data is pushed through the cables. Originally, the system was only designed for phone calls which would not result in a constant data flow rate.

Nowadays, there are networks designed specifically for digital data transmission. There are Local Area Networks (LAN) and Wide Area Networks (WAN)

LAN

A LAN is fast and can be used to transfer data over relatively short distances (up to a mile or so). Due to the small scale of a LAN, all the hardware involved with the network can easily be set up and maintained by the business internally therefore there are no rental costs for connections etc... as is the case for a WAN.

There are various network topologies (or layouts) associated with Local Area Networks:

Bus Networks involve workstations and servers being connected to a central network line which has terminators at each end. This type of network is not very flexible as it can be difficult to simply add another machine to the network as a connection will have to be made and new cabling laid. This can be combatted by using a central hub which every machine is connected to. The hub redirects data and messages in the same manner that they would travel through a bus network.

Star networks involve a central server with nodes (or user workstations) connected to it. This differs from a network with a hub at its centre as a hub simply redirects messages and cannot provide services for users.

WAN

A WAN is designed to operate over a very large region, sometimes even internationally. The infrastructure for these WANs is provided by service providers who own and maintain the country's digital communications infrastructure (NTL or BT in the UK for example). These service providers lease out connections to companies wishing to have a WAN. The links involved in a WAN are long and expensive therefore in most cases it is inappropriate or companies to be able to have connections which they own themselves.

"Distinct" routes within a WAN are routes which are completely independent from each other i.e. the same link/connection is not used by two distinct routes. If a WAN has 3 distinct routes, this means that the WAN would still be able to operate if two links failed, regardless of where they are in the WAN.

Try a Computer Systems Quiz in the Computing Students Computing Quizzes Section to test your knowledge.

Search for "Networks" on: Google | Kelkoo | Amazon | eBay (UK) | eBay (US)

Search for "Networks" on the rest of Computing Students: Networks