Revision:Networks

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Networks

What is a network?

A network is a collection of computers connected via cable or wireless technology. Each stand-alone computer may be connected to a server or hub which in-turn connects the computer to the whole network.

Why are they used?

They are used so that files and programs are based at the server (only on some networks) but they can be accessed from anywhere in the network as long as the user has the correct access rights. Peripherals such as scanners and printers can also be shared between computers in a network.

If a school/company have computers all over a building they can network them together so that documents can be sent to any computer in the network. This makes it easier for people within the building to access files. They can use any computer within the network to log-on to their user area and access their documents.

What are the advantages and disadvantages of networking computers?

Advantages:

Files can be accessed from any computer terminal within the network.

Users can send files easily and quickly to other users of the network.

Programs and documents can be shared across the network.

Peripherals can be shared across the network.

The security within a network allows restrictions to be made to prevent unwanted access to data.

Disadvantages

Can be expensive to install and maintain.

People may become dependent on the network.

If the network goes down you may not be able to access the computers.

Stand-alone computers offer more privacy.

If one computer gets a virus it can spread across the network.

What hardware and software is required?

Software

To set up a network you need programs which will handle the security and file management that a network requires. Programs such as Windows NT are designed with the ability to help a computer act as a server. Each computer needs the appropriate utilities installed from their operating system so that it can be used as a member of the network.

Hardware:

You need a network card in every computer that is going to be connected to the network, you also need network cable (such as Ethernet cable). Depending on your network you may require one or more server computers, which will act as the centre of the network. Some networks have a hub, which connects all computers together.

What are LANs (Local Area Networks)?

A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a WAN.

Most LANs connect work stations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as a laser printer, as well as data. Users can also use the LAN to communicate with each other.

There are many different types of LANs Ethernet being the most common for PCs. Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers.

What are WANs (Wide Area Networks)?

Wide Area Networks, or WANs, connect multiple sites to each other, such as a company with multiple office locations, or separate companies wishing to electronically link with business partners or customers. WANs are public or private forms of communication.

A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.

What types of network are there?

There are many types of network layouts (topology).

• Peer to peer: A type of network in which each workstation has equivalent capabilities and responsibilities. This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler, but they usually do not offer the same performance under heavy loads.

• Mesh Topology: Devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network.

• Star Topology: All devices are connected to a central hub. Nodes communicate across the network by passing data through the hub.

• Bus Topology: All devices are connected to a central cable, called the bus and backbone.

• Ring Topology: All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it.

• Tree Topology: A hybrid topology. Groups of star-configured networks are connected to a linear bus backbone.

• Satellite Transmission: Data is transferred by modem from Liverpool to London, the data is then sent via a satellite connection to the USA. Any computer in the network can access data.

How is data transferred?

Data can be transferred by modem or satellite.

• Modem: There are 2 types of modem, internal and external
  • Internal: Internal modems should be faster because they are connected directly to the mother board. If the mother board fails, the modem can be damaged.
  • External: If the mother board is damaged the modem isn't because it isn't connected to it directly. Slower because data needs to travel to the modem then get sent.
• AT command: One of the ways, which you can communicate with and configure, a modem is to use AT command sets. They are called this because they begin with the characters AT, calling the modem to Attention. Using these commands you can perform actions such as dialling. Each AT command string is in the form AT command string carriage return or enter.

There are about 50 commands, a few are listed below.

Command

Function         dial

Values            none

Command AT&Znx<cr>

Function         stores telephone number

Values                        n 0 – 9;        x dial string

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