Types of computer networks
Computer networks occupy an increasingly important place in the life of mankind. Networks can unite information resources of both small enterprises and large organizations occupying premises remote from each other, sometimes located even in different countries. This determines the way computers are connected to each other and, accordingly, the type of network: local, regional, corporate, global.
Imagine a polyclinic computer network with a central computer containing information about all patients. Each doctor’s office has a computer, on the screen of which, if necessary, information about a particular patient is displayed. The doctor updates them, saves them in the database of the central (main) computer, and they become available to other specialists, such as a physiotherapist, neuropathologist, cardiologist. In addition, the same information is also displayed on the computer of the registry, where the patient can order a referral for an examination or an appointment with the right doctor. The computer can also store information about the work schedule of specialists, the issuance of coupons for admission to them, etc.
A commercial enterprise can also be equipped with a computer network. Here, with its help, you can store information about goods and their cost, process sales information, keep records of the quality of the goods sold, etc. All this information is stored centrally, on the server.
A computer network can unite the computers of the entire school, installed in a variety of workplaces: in the administration offices, in the library, in computer science classes and other classrooms. You can network, for example, two or three home computers of students living in the neighborhood.
In the office, working on the network, different employees have access to the same internal sources of information for preparing various reports, scheduling and planning the overall activities of the enterprise. Special network programs allow you to automatically schedule meetings, choosing the most suitable time for all employees, the boss can check whether his orders that he sent out over the network have been completed, and so on. All the examples of networks described above are designed to process information of local importance. As a rule, such networks connect computers located at short distances (about 50-100 meters) within the building, and therefore they are called local (local). About 90% of the information circulating in such networks is information from a local organization.
A local area network is a connection of computers located at short distances from each other.
Regional and corporate networks
Often in the same office, school or clinic there is a need to obtain information from other similar organizations. In such cases, computers located not only in one or several rooms are interconnected.
Imagine a system for storing information in libraries. Here it is necessary to have a variety of information for each book: title, data on authors, publisher, number of copies available, annotation of the content, etc. If such information is made available to a large number of libraries, then it is possible to improve reader service, improve the organization of the interlibrary fund for the exchange of books. The integration of libraries into a centralized computer network allows all libraries to have access to any necessary information about books.
Both a library with only one computer and a library with a local network can be connected to the central library. A telephone line can be used to connect computers. Such a network already has regional significance. An example is the network of libraries in St. Petersburg and the Leningrad Region.
Regional network – combining computers and local networks to solve common problems of a regional scale.
Let’s also remember how train tickets are ordered. At the request of any cashier-operator, information about the availability of seats on the train, the cost of travel tickets, etc. is displayed on his monitor. At the direction of the passenger, the cashier through the network enters into the central computer a request to purchase a ticket and executes its sale. Moreover, the paid place is immediately withdrawn from further sale. Imagine that all these computers were not connected to a network. Then the point of using them would be completely lost, since after each working day one would have to make general changes about the availability of free seats in each individual computer, inform other cashiers about unsold tickets and think about how to organize ticket sales for the next day.
A centralized network easily solves such problems. Tickets for the same routes can be sold from several cities. And such a network can no longer be called a local one. It serves to process information of one firm or association of firms and therefore is called corporate (from the word “corporation” – association).
A corporate network is an association of local networks within a single corporation.
Corporate networks are intended to serve customers in various remote locations, such as hotels. They can link within the same corporation branches located in different countries. Information can be changed by employees who have access to it. The networks described above may have access to other external networks, for example, in order to obtain information from remote global databases or send e-mail messages to another network, send a fax.
Centralized data processing is not always reliable, since the failure of the central computer can lead to the loss of important information or even paralyze the network for some time. Therefore, there was a need for decentralized information processing in the network. The development of means and methods for transmitting information over long distances made possible the emergence of global networks. The idea of their construction is that powerful computers are interconnected and can exchange information on a transcontinental scale.
Global network servers provide other computers registered on them with access not only to their resources (information and software, e-mail, computer conferences), but also to the resources of other network servers and provide their users with the ability to work with information outside their computer by opening access to resources of remote machines.
In recent years, global networks have united with each other, and such an association is called the Internet (Internet). Internet users can find anything they want on this network. These are files, images, sounds created in various computer environments and stored in server file archives. They can be copied to your computer and opened with the applications they were created in. From the Internet, you can receive daily changing information: weather forecasts, exchange rates, statistical reports, theater repertoire and restaurant menus, any programs, etc.
Remote access (access to information from a long distance over the network) allows you to organize training at any distance (distance learning). For example, you can conduct a lesson at the same time in different schools of the world, communicating directly with everyone present at such a lesson, or organize lectures by famous professors for a wide range of students from around the world. Communication at a distance makes real consultations of major specialists during surgical operations, consultations, demonstrations of these operations for the training of medical personnel.
The use of global networks has become especially attractive in connection with the development of multimedia tools, that is, graphics, video and sound. Documents containing such components have become the most popular among the available information on the Internet.
In order not to get confused in the huge flows of information, there are special search engines on the network servers. They search for information, analyze it and provide the user, upon request, with the address of the location of the necessary information.
The global network provides efficient access to information on a global scale.
The global network is a combination of computers located at a remote distance for the common use of world information resources.
Communication channels for information exchange between computers
The main purpose of creating any computer network (local or global) is to ensure the exchange of information between objects (servers and clients) of the network. Obviously, for this it is necessary to connect computers to each other. Therefore, the mandatory components of any network are all kinds of communication channels (wired and wireless), for which various physical media are used. In accordance with this, networks distinguish such communication channels as telephone and fiber optic lines, radio communications, space communications, etc.
The purpose of communication channels in a computer network is easy to understand if we compare them with the transport channels of a freight or passenger transportation system. Passengers can be transported by air, by rail or by water (sea or river) routes. Depending on the medium of transportation, a means of transportation is chosen. Information is transported through computer networks. The environments in which network computers communicate determine the means by which computers are connected. If this is an environment that requires telephone communication, then the connection is made through a telephone cable. Computer connections are widely used with electrical cables, radio waves, fiber optic cables, etc.
All these are different channels of communication. The efficiency of communication in computer networks essentially depends on the following main characteristics (parameters) of communication channels:
♦ bandwidth (data transfer rate), measured by the number of bits of information transmitted over the network per second;
♦ reliability – the ability to transmit information without distortion and loss;
♦ expandability (connection of new computers and devices).
Compare the characteristics of communication channels given in the table