Н. В. Моина ю. Б. Генина т. В. Шульженко чтение английской научнотехнической литературы
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Types of NetworksThe types of network are categorized on the basis of the number of systems or devices that are under the networked area. Networking is the process by which two or more computers are linked together for a flawless communication. By creating a network, devices like printers and scanners, software, and files and data that are stored in the system can be shared. It helps the communication among multiple computers easy. By computer networking the user access may be restricted when necessary. There are two types of networks: 1. Local Area Network (also referred as LAN). This system spans on a small area like a small office or home. The computer systems are linked with cables. In LAN system computers on the same site could be linked. 2. Wide Area Network or WAN is a type of networking where a number of resources are installed across a large area such as multinational business. Through WAN offices in different countries can be interconnected. The best example of a WAN could be the Internet that is the largest network in the world. In WAN computer systems on different sites can be linked. The types of networks can be further classified into two more divisions: Peer-to-peer, Client-Server, and Application-Server Networks. Each type has certain benefits and downsides, this article will describe each type, along with why it could or should be implemented. Peer-to-peer network. Nearly all operating systems come with the ability to act as some kind of a server to share resources. You can setup different computers to allow others to use its peripherals such as printers or CD-ROM drives, and other computers to allow others to read or write to its hard disk allowing sharing of files, while other computers may allow access to its Internet connection. When you allow workstation computers to become servers and share things in this manner, it is called a peer-to-peer network. For example, in a small business office, the secretary uses the best computer, and has the most drive space, she also has a fast laser printer connected to her computer. The accountant has a mediocre computer that has a color ink jet printer. The owner has a good computer with a zip drive to take work home. All of these computers are networked together, with no central server. The secretary uses the zip drive through the network to backup important documents, and also uses the ink jet printer on the accountant's computer to print out fliers. The accountant uses the laser printer on the secretary's computer to print out checks, accesses some important documents on the secretary's computer, and backs up the accounting data on the zip drive on the owners computer. The owner uses both printers on the other computers, and accesses important documents on the secretary's computer. All of the computers share Internet access through the secretary's computer. All of this gets done with no passwords or user names since all the shared devices use no access control, or other type of security measure. Also in order for the accountant's computer and the owner's computer to be able to read the companies important documents, the secretary's computer must be turned on first. Peer-to-peer networks can be implemented with very little investment costs, but in order for the network to work properly, the users must be very experienced with computers, and strict guidelines must be implemented and followed in order for the data to remain secure and archived properly. In my experience, peer-to-peer networks tend to become more of a headache instead of a help after about 6 computers, especially if your company has a moderate employee turnover. Client-server network. The client-server network model usually consists of one or more server computers that provide services and information to a number of workstation computers. These services can consist of many different roles, including: file services, web services, email services, domain name lookup services, document version system services, Internet sharing services, etc. A great example of the client-server network model is actually the World Wide Internet. On the Internet clients, or computer with web browsers, access web sites that are hosted on servers. This model differs from the peer-to-peer network model in that the servers do not dually act as a workstation, and the workstations do not act as servers, and if they do act as a server, they should be configured to allow the central servers to provide access restrictions on the shares they provide the network. For example, the network is setup with a main file server, that also stores all the users email. Every night the main file server is backed up to a secondary file server that is located in an adjacent building. The network has a network firewall computer that serves an Internet connection to the network, and forwards all email to the file server. The file server has different shares for each department so only people in that department has access to the files, and also has a company wide share that everyone in the company has access to the files. Each user also has a home directory on the main file server for personal documents that no one else can access. The network also has two large laser printers and a commercial color laser printer, all the printers are connected to the main file server through a jet direct interface. The client computers all map a drive letter (L:) to the company wide share, and also map a drive letter (M:) to the department share, and the clients can print to whichever printer they need to. The drive mappings occur during a login script that is ran when the client computer logs in to the network. Each department has at least one zip drive on its computers which is shared for backups and convenience. Each employee has a separate email account, and all e-mail messages reside on the main file server, which provides security and intactness of the e-mail. The Client-Server network model provides important services to the network safely and securely, it also allows the convenience of allowing the users to work on their own workstation machine. However, this network model can be very expensive, not only because the software can be expensive, but you also must provide adequate hardware for both the servers and the individual workstation machines, which can become very expensive with revolving hardware updates. If you have the funds to implement this type of network, the return on the investment is great, and you will have the knowledge that your network is well secured and archived. Application-server network. The final network type that will be covered is the Application Server based Networks, sometimes called Terminal Server based. The idea behind this type of network is that you basically have one high-end server or mainframe, and all the network clients are "dumb terminals", meaning that none of the processing is actually done on the terminals, instead the only job the terminals have is to provide input and show the display on the monitor. Most people equate application servers to the very old text-only terminals with no pointing devices. Today application servers are very modern, and most people running on a "dumb terminal" will think they are working on a modern standalone computer. For example, each floor has its own Application Server running a version of Linux. Each application server has basic user applications, such as Internet Browser, Word Processor, Spreadsheet Program, Email Application, Image Manipulation Program, as well as all the basic applications you should find on a computer. Each Application Server serves applications to 20 different terminals, which are older donated computers. Each terminal has the ability to run all of the above applications, print to any of the printers on each floor and has access to the main card catalog through a web-based interface. If one of the Application Servers goes down, the network is configured so that the terminals will log into one of the other floors servers until the computer is repaired. If a terminal goes down, a replacement terminal can be installed with no downtime for the entire network, with no information loss. All the Application Servers also share a single/home directory from a separate File Server, which allows the library the ability to offer an individual login name, email account and individual storage for a small charge. Along with the login name, email account and storage, the patron also has the ability to access any files he may have saved on the file server through a secure FTP server. Even though not every software package will allow you to run it off of an Application Server, the price benefits can be astounding when this type of network is implemented. If you need to provide public access to computers, or have separate departments that only need to use word processing, spreadsheets, and email, an Application Server could literally save you tens of thousands of dollars, even on a smaller network of 10–20 computers. |