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Computer Networks.

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Element 4.3 Computer Networks 2. Types of Networks A LAN (local area network) is a collection of computers connected together over a small area, usually a single building or site (e.g. a school). If a school was to have a LAN it would own all the equipment and be able to run the network as it sees fit. If changes need to be made to the network, such as adding new terminals, it will be relatively easy and cheap. A WAN (wide area network) consists of computers connected over a large area using telecommunications equipment, such as telephone or satellite communications links. A school could have a LAN which is connected to other schools around the country (or world) to form a WAN. WANs are more sophisticated than LANs as the operator has to deal with telecommunications companies and doesn't own all the equipment. Wires between one LAN and another are owned supplied by a telecommunications service provider, each of which has it's own regulations and service charges. Two schools with a LAN could be connected using two modems and appropriate software on each machine together with a public telephone line. This method is fairly cheap to set up with no need for much extra equipment, but data transfer is slow and the phone bills can be high. As it is a public telephone line it is not very secure and so vulnerable to hackers. Renting a dedicated leased line from a telecommunications service provider, of which you are sole user, is much more secure but more expensive. Examples of Wide Area Networks: Broadcast services These are services that use radio links. The commonest example is teletext where images from computers are sent as part of the television signal. Broadcast services also include networks with terminals or workstations linked by radio or infrared signals. This could be useful in many situations such as in supermarkets where checking stock can be done using a wireless hand-held terminal that transfers the data directly from the shelf to the main system. ...read more.


These tapes can be very large (12 Gigabytes is not uncommon). This facility is often used for backing up server information for security. Writeable CD's can also be used as auxiliary storage. However access for reloading work from these devices is generally slower than from the hard drive, either of the station of the server. Data can also be compressed in order to store it in compact form (e.g. floppy disc) Bridge These are used to connect two LAN's in the same location. It can also be used to keep two LAN's separate, only allowing specified data through it. The connection of two LAN's enables sharing of data and easier management; i.e. rather than two LAN's to manage it can be treated as one and managed from one location. It can also be used to separate segments on a single LAN. For example in a company there are many departments. Some departments require similar information but all will have their own information that only they will require. The bridge can be set so that it only allows specified information through. This speeds up the performance of the segments because they are no longer carrying all information, so of which is not required. A bridge can only connect networks that have the same topology. Gateways These are hardware devices that decide which way a packet of information needs to be sent, ensuring the information is sent in the most efficient way. This device is more intelligent than a bridge in that it can decide which way a packet of information needs to be sent. It can also connect networks of differing topologies. These are used generally to connect remote networks. A gateway/router will be used at each end of the communication line. A LAN such as the network in college includes the following components: * Workstations * File server * Network card * Print server * Fibre Optic Cabling * Ethernet Cabling * Auxiliary Storage * Server Operating System * Station Operating System A WAN ...read more.


The purpose of such software is to gather statistics about the movement of data around the network and watch for any faults. Security Security is very important to a network as data is widely distributed to many people, so there is a greater risk of misuse. Networks are vulnerable to viruses because they can pass from one computer to the whole network, causing havoc in the process. There are a number of ways to prevent viruses getting on the network and minimise the damage if they do (e.g. scan disks, make back-ups, antivirus software, etc) Storage Networks have a certain amount of storage space, each user having an allocated amount. The server can monitor the amount of space and deny access if there is not enough. System configuration This is how the network is set up, in terms of users, passwords, station connection, registration with the server and the allocation of resources (e.g. printers, scanners, etc) 8. System security methods Control of access Access of control can be divided into two groups: 1. Physical controls These prevent the user from getting to the computer or making it work. * Controlling access to the room (keypads, special cards) * Controlling access to the building (guards, locks) * Lock the computer so it can't be switched on * Lock the computers away when not in use Logical controls These prevent the user from accessing or changing certain files. There are two types of network security: user level security and share level security. In user level, each user is given a user name and password, which have to be entered to gain access to the network. Share level is when each resource on the network is given a password. Forced recognition In order to make users aware of the importance of security, clauses can be written into their contracts of employment. In government departments and the armed forces, staff have to sign the Official Secrets Act making it a crime to pass information on to outside bodies. 5 1 ...read more.

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