SHARE WITH FRIENDS:
The problem of transferring information from one computer to another has existed since the dawn of computing. Such transfer of information provides opportunities to organize the joint operation of separately used computers, to solve one problem with the help of several computers. In addition, it will be possible to specialize each computer to perform a certain task and to use the resources of computers together, as well as to solve many other problems.
Recently, many types of methods and means of information exchange have been proposed: from the simplest file transfer from computer to computer using disks, to the Internet network, which provides the opportunity to connect computers all over the world.
Often, the term "local area network" (lokalniye seti, LAN, Local Area Network) is understood as a network of small, local-sized, nearby computers, that is, a local network. But if we look at the technical indicators of some local networks, we can be sure that such a term is not clear.
For example, some local area networks allow easy communication from a distance of several kilometers or tens of kilometers. This is not only the size of one room, one building or buildings located close to each other, but also the size of a city. On the other hand, through a global network (WAN, Wide Area Network or GAN, Global Area Network), computers located on two side-by-side tables in the same room can exchange information, but for some reason, no one calls such an organized network a local network. Two nearby computers can be connected via an interface (RS232, Centronics) using a cable, or even wirelessly using an infrared channel. But such a connection is not called a local network.
Perhaps the definition of a local area network is the same as a small network, connecting not many computers. In fact, a local network in most cases includes from two to several dozen computers. However, the limited capacity of some local networks is much higher, and the number of subscribers can reach up to a thousand. Calling such a network a small network is perhaps incorrect.
Some authors define a local network as "a system that connects many computers." In this case, it is assumed that information is carried out from computers to computers without intermediaries and through a kind of transmission medium. However, today's local networks are a type of transmission medium
cannot be talked about. For example, all types of electrical cables and also fiber optic cables can be used within one network. The definition of information transmission "without an intermediary" is also not very clear, because in today's local networks, various concentrators, switches, routers (routers) and bridges (bridges) are used. It is not so clear whether these tools, which process complex information transmitted in the process of information transmission, are considered intermediaries or not.
Perhaps it is clear that a network where users do not feel the presence of a connection is considered a local network. Computers connected to a local network are like a virtual computer, their resources must be freely available to all users, and a separate computer
it should not be less convenient than using its resources. In this case, first of all, the convenience is to have clear high-speed resources, information exchange between applications is carried out without the user noticing.
In this definition, neither a slow global network nor a fast-acting serial or parallel port fit the concept of a local area network. It follows from this definition that as the speed of widespread computers increases, the speed of information transmitted over the local network must also increase. If in the recent past the data exchange rate of 1-10 Mbit/s was considered sufficient, now a medium-speed network is a network capable of transmitting information at a speed of 100 Mbit/s. Active work is also being done on devices capable of transmitting information at a speed of 1000 Mbit/s and more. A low-speed connection reduces the performance of a networked virtual computer.
Thus, the main difference between local networks and any other network is high-speed information exchange. But this is not the only difference, other factors are also important.
For example, it is necessary to drastically reduce the error in the transmission of information. Very fast, but error-prone data transmission is pointless, because it needs to be retransmitted, and therefore local networks necessarily use special high-quality communication means.
Also, one of the main technical indicators of the network is the ability to work with a large load, that is, the speed of information exchange (in other words, with large traffic). If the mechanism used to control the exchange of information in the network is not effective, then computers can wait a long time in the queue for information transfer. Even with high-speed and error-free data transfer after queue arrival, the network user still has to wait for some time to use the network resources.
In order for any information transmission control mechanism to work guaranteed, the number of computers that can be connected to the network, the number of information, must be known in advance. It is natural that any mechanism will not be able to transfer information as a result of connecting more computers to the network than planned, causing an increase in the load. Finally, as the original meaning of the word "network" should be understood as such an information transmission system, which should connect several tens of local computers.
Thus, it will be possible to form distinguishing features of local computing networks (MHT):
- availability of high-speed data transfer and high-speed transfer;
- low level of error during transmission (high-quality communication channels). The probability of a possible error in the transmission of information is at the level of 10-7 - 10-8;
- to be an effective and fast implementing mechanism of information transfer;
- the number of computers connected to the network is limited and must be specific.
It follows from the given tariff that; the global network differs from the local network in the following ways: it is intended for unlimited subscribers and low-quality channels are also used; the speed of information transmission is relatively low, and the mechanism of information exchange is not guaranteed in terms of speed. In global networks, the most important thing is not the quality of communication, but the availability of communication.
Another type of computer networks - metropolitan area network (MAN, Metropolitan Area Network) is often noted, usually they are close to global networks, and sometimes they have some characteristics of local networks. For example, it is similar to high-quality communication channels and relatively high-speed information exchange. This feature indicates that a city network can also be a local network (with MXT benefits).
In fact, it is no longer possible to draw a clear border between the local network and the global network. Most local networks have access to the global network, but the principle of information transfer, the organization of information exchange, is quite different from that generally accepted in the global network. For users of the local network, the ability to connect to the global network remains only one resource.
All kinds of digital information can be transferred from the local computing (MHT) network: information, images, telephone conversations, e-mails, etc. The issue of image transmission, especially the transmission of full dynamic images, requires high speed from the network.
Usually on the local network from the following resources; shared disk space, printers, and global networking capabilities. But these capabilities are part of the capabilities of local network tools. For example, they also carry out all kinds of inter-computer information exchange. A network subscriber can be not only a computer, but also other devices.
For example, printers, plotters. Local networks allow to organize a parallel computing system on all computers of the network. Such a system speeds up solving complex mathematical problems many times. It is also possible to control complex technological processes using local networks or to control research devices using several computers at the same time.
But it should not be recalled that local computing networks also have some disadvantages. Network development, resource management, troubleshooting, and network performance monitoring in addition to the additional cost of staff training, additional hardware, network software, and cabling. , that is, the administrator of the network must be an administrator. The network limits the portability of the computer, otherwise it is necessary to run cables to connect, moreover, the network is a favorable environment for the spread of viruses, so more attention should be paid to security issues than individual computers.
Within this topic, it is necessary to see the concepts of server and client, which are important concepts of network theory.
A server is a network subscriber, it makes its resources available to other subscribers, but it does not use the resources of other subscribers, that is, it works only on the network. There can be several servers in the network. A dedicated server is a server that serves only for network purposes. A dedicated server can handle other issues besides network maintenance.
A client is a network subscriber who uses only network resources and does not allocate his resources to the network, that is, the network serves him. A client computer is also often called a workstation. Usually, each computer can be both a client and a server at the same time. Often, the server and client are not understood as the computer itself, but rather the software applications running on the computer. In this case, the application that provides its resources to the network is the server, and the application that only uses network resources is the client.