Many companies insist on using this method of ordering and invoicing. Teleconferencing allows a group of people to communicate, throughout the world, simultaneously using telephones and group email. Video conferencing is similar to teleconferencing plus the ability of users to see one another. These methods of communication have reduced travel costs as meetings can be held without people leaving their desks. Originally, special rooms were required for videoconferencing. This is no longer necessary as videoconferencing can now be done using standard PCs and a video camera.
In this system whiteboards can be used to produce drawings that can be transmitted electronically. Network hardware and software, and selecting appropriate network systems Network hardware- Servers A client-server network is a way of organising computers (clients) so that they can make use of the resources of one or more servers. A server is simply a computer that has resources that can be used by clients. There are a number of different types of server. A file server. This is a computer that stores all of the users’ data files. The network NOS (Network Operating System) allows accounts to be set up.
Users have to enter in a user ID and password to gain access to the network and to their own files. This system also means that users cannot access other people’s files. A print server. This is a computer that allows clients to have access to a shared printer. Print servers usually come with spooler software. Spoolers collect any jobs that have been sent to the printer, queues them and then sends them to the printer. If you sent a file to be printed straight to the computer rather than the spooler program, your computer would slow down because the printer works much slower than the computer.
The spooler program frees up an application so you can carry on working. A CD-ROM server. This is a computer that has many CD drives (or one drive that can change CD-ROMs automatically). Clients can access the information from any of the CD-ROMs currently in the CD-ROM server. A mail server. This manages mail into and out of a network. A web server. If a business wants to have an Intranet, or wants to host its own web site, then it will need a dedicated web server. The web server is responsible for storing web pages and distributing them in response to requests.
A proxy server. A proxy server on an organisation’s network is used to cache web pages. When an individual requests a web page, it is downloaded from the Internet and also stored, or ‘cached’, on the organisation’s proxy server. The next time that site is requested, however, it will be downloaded from the proxy server instead. Retrieving a web page from a proxy server is much faster than retrieving it from the Internet. The proxy server also usually acts as a security buffer between the main file server and the users on a system.
A user requests data held in a file server. This request is intercepted by the proxy server. The proxy server checks that the user is a valid user and is making a request for data that he/she is entitled to. If the user passes these checks then the proxy server gets the requested data from the file server and passes it on to the user. The user cannot access the file server directly – they must go via the proxy server. Network hardware – additional equipment In addition to clients, and various kinds of servers, a network may also need additional equipment.
1) Repeater. Repeaters are used when you want to extend a network but where there may be problems with the strength of data signals. This would be because the cable lengths between different parts of the new network have become very long; data strength (i. e. voltage) drops as the distance increases. Repeaters can be used to connect two segments of a network. It repeats data from one segment to another, enhancing the signal, as shown below. Repeaters do not segment a network and do not partition a network into sub-networks. They simply extend a network. 2) Hub.
These are used to connect many computers to one computer. For example, in a star network, all the cables from each individual computer go back and connect to a hub. The hub then connects to the server. Hubs can also boost signal strength if needs be. 3) Switch. A switch is a more ‘intelligent’ hub. It can set up communication paths between different clients and different servers, for example, at the same time. If a user has large files to transmit, or a large volume of data, then switches would be more appropriate than hubs. Newer technology replaces hubs with switches.
This allows greater speed because each station is switched in and thus has full network speed. Switches ‘learn’ which connections are required and join the corresponding ends. If, at the same time, Station 1 wishes to communicate with Print Server , Station 2 with Web Server, Station 3 with File Server and Station 4 with Mail server, this is possible as the switch will set up four independent paths. This means that data can flow at maximum speed along each as the system will be treated as four independent circuits. 4) Bridge. A bridge connects two similar LANs together.
Users think it is logically one LAN even though it is physically two. Bridges enable the users of one network to use the resources of the other. 5) Modem A modem provides a ‘dial-up connection’ for a computer. It is used typically to allow a computer (which is a digital device) to communicate with other computers using the public telephone system (which is largely an analogue system). A user cannot simply connect digital equipment to analogue equipment. The latter must convert the signals first. Modems can be used as well in networks to allow each computer on the network to, for example, connect to the Internet.
6) Network card. Each client will need a network card. This enables the client to be connected to the actual network. It is a card that is fitted to one of the free slots inside the computer. Example 1 A team of programmers all have their own PCs which they use to create programs. The team work on the same projects and share code. A suitable network is shown below. There is no need to use a switch as files tend to be small (usually text) and traffic is relatively light. Also, the data will need to travel between all stations. Example 2.
A group of people work together to produce a catalogue and price list for a large company. The catalogue consists of about 500 pages, each of which may have up to 15 colour pictures. Each picture has a description of the item and its price. A separate booklet contains just the item codes, brief descriptions and the prices. The pictures are held on a large server and all text descriptions to be used in the catalogue and in the price list are on a smaller server. This is a case where a switch is more appropriate than a hub as picture files can be very large.
Also, the people creating pictures will usually be connected to the large server while those creating the price list will mainly need access to the smaller server. A possible solution is shown below. Example 3 A primary school has two small computer rooms, near to one another, and a single server. A suitable network is shown below If the computers are to be spread around the school, instead of all in two rooms, and if access to the Internet is required from all stations, it would be better to use either a switch or a hub. Selecting a network topology.
It is important to select an appropriate topology along with any necessary additional hardware for any given situation. The topology selected will have an impact on the amount of data that can be sent, the security of the data on the network, the budget for putting the network together and the potential for future network expansion. Bus networks Bus networks are relatively easy to set up compared to star and ring networks. They comprise of one main cable. These types of networks use packet switching. When a client sends some data it is split up into packets.
Some additional information is then added to each packet, such as the destination address and recombination information. All other clients are monitoring the network, to see if it can detect any packets of information addressed to them. The problem with this, however, is that the network isn’t very secure, because packets can be intercepted from any client. When the main cable has a fault on it, the whole network goes down. Also, when a lot of clients are communicating at the same time, the network can slow down. Bus networks can be peer-to-peer or client-server. Ring networks.
As with bus networks, these types of networks use packet switching. When a client sends some data it is split up into packets. Some additional information is then added to each packet, such as the destination address and recombination information. All other clients are monitoring the network, to see if it can detect any packets of information addressed to them. The problem with this, however, is that the network isn’t very secure because packets can be intercepted from any client. When faults occur on a ring network, they can be difficult to find and one fault may bring the whole network down.
They are also slow if there are a lot of clients communicating. Star networks These are the fastest and most secure of the three networks topologies. This is because when a client wants to send information, it sends it from itself to the server, which then redirects it directly to the destination client. In addition, the server can provide extra software security. Each client has its own link with the server. That means each client needs an interface and connection with the server. This is a more expensive connection method than for a bus or ring network. However, if one client goes down, the other clients can carry on.
Collision avoidance and detection Clients will often want to send data at the same time. Networks can’t cope with more than one client’s data on the network at once. One of the jobs of a computer’s network card is to continuously monitor the network. It looks for times when the network is free. When it detects this situation, it can put it’s own data onto the network if required. This is collision avoidance. If two clients, however, see that the network is free at the same time and both put their own data on the network at the same time then the data will ‘collide’.
Collision detection is the term used to describe when clients’ network cards detect a collision. When this happens, both clients will be asked to re-send their data again in turn. New Business The Internet allows communication on a world-wide basis. This means that advertising can be relatively cheap. Organisations can advertise all round the world from a single site. There is no need to advertise in each individual country. It also means that it is easier to sell goods throughout the world. Organisations can create Web sites that advertise their goods and let users have access to their product databases.
It is also possible to allow users to order, and pay for, goods on the Internet. This means that people will be needed to create Web sites, to keep them up-to-date and to manage large databases of goods and customers. Users can transmit their details and orders over the Internet at very little cost. The main problem is security of information and people are needed to create secure systems for EDI. Another area of expansion is in providing information. For example, medical advances can be posted on the WWW that can then be accessed world-wide. Indeed, doctors can request advice using the WWW.
The use of the Internet by media reporters can mean that news can be quickly updated and that information is in electronic form. This means that it can be manipulated for use on other media. Estate agents can set up sites that enable them to sell property throughout the world. The applications are endless and you should keep abreast of modern developments as they are published in the media. E-Commerce Commerce is all about business, about the buying and selling of goods and services. Consider buying a new computer. The functions that need to take place by the buyer of the computer include.