5 Basics of working in an environment of local and global computer networks 5.1. Evolution of computer networks

The concept of computer networks is a logical result of the evolution of computer technology. The first computers of the 1950s. were big, bulky and expensive. Their main purpose was a small number of selected operations. These computers were not used for interactive work of the user, but were used in the batch processing mode.

Batch processing systems are usually built on the basis of the mainframe, which is a powerful and reliable universal computer. Users prepared punch cards containing data and program commands, and transferred them to a computer center. Operators entered these cards into the computer and gave the results to the users the next day. In this case, one incorrectly packed card could lead at least to a daily delay.

For users, it would be much more convenient to have an interactive mode of operation, which implies the ability to efficiently manage the processing of data from the terminal. However, at this stage, it was batch mode that was the most efficient mode of using computational power, since it allowed to perform more user tasks per unit time than any other modes. At the head of the corner was the efficiency of the most expensive computer device, which was the processor, to the detriment of the efficiency of work using its specialists.

In the early 1960s. Expenses for the production of processors have decreased and new ways of organizing the computational process have appeared, allowing to take into account the interests of users. The development of interactive multi-terminal time-sharing systems has begun. In these systems, several users worked on the computer at once. Each of them got at the disposal of the terminal, which helped him to communicate with the computer. At the same time, the reaction time of the computing system was small enough so that the user did not notice the parallel work with the computer of other users. By sharing a computer in this way, users could have the advantages of computerization for a relatively small fee.

The terminals, when leaving the computer center, were scattered throughout the enterprise. Despite the fact that computing power remained completely centralized, many operations, such as data input and output, became distributed. These multi-terminal centralized systems have become very similar to local area networks. In fact, each user perceived the work of the mainframe terminal in much the same way as the current work of a PC connected to the network. He had access to shared files and peripherals and was convinced of his sole ownership of the computer. This was due to the fact that the user could run the program he needed at any time and almost immediately get the result.

Thus, multi-terminal systems operating in the time-sharing mode were the first step towards the creation of local computer networks. However, before the advent of local networks, it was still necessary to overcome a long way, since multi-terminal systems, although they had the external features of distributed systems, still retained the centralized nature of information processing, and the need for enterprises to create local networks by this point in time was not yet ripe. This was due to the fact that there was simply nothing to be networked in one building. The high cost of computing did not allow enterprises to acquire several computers. During this period, the so-called Grosch law was valid, which empirically reflects the level of technology of the time. According to this law, computer performance was proportional to the square of its cost, therefore, for one and the same amount it was more profitable to buy one powerful machine than two less powerful ones, since their total power turned out to be much lower than the power of an expensive machine.

However, the need to connect computers that were at a great distance from each other, by this time was quite ripe. The development of computer networks began with the solution of a simpler task - access to a computer from terminals remote from it for many hundreds or even thousands of kilometers. The terminals were connected to computers via telephone networks via modems. Such networks allowed numerous users to remotely access the shared resources of several powerful computers of the supercomputer class. After that, systems appeared in which, along with remote connections like terminal-computer, remote connections like computer-to-computer were used. Computers were able to exchange data automatically, which is the basic mechanism of any computer network. Based on this mechanism, the first networks were used to organize a file-sharing service, synchronization of databases, e-mail, and others, which have now become traditional network services.

So, chronologically, the first global computing networks were developed and applied. It was during the construction of global networks that almost all basic ideas and concepts of existing computer networks were proposed and developed, for example, multi-level construction of communication protocols, packet switching technology, packet routing in composite networks.

In the 1970s there was a technological breakthrough in the production of computer components, which was reflected in the appearance of the LSI. Their low cost and immense functionality allowed the creation of mini-computers, which have become real competitors to mainframes. Grosz's law ceased to operate, since ten mini-computers were able to perform some tasks much faster than a single mainframe, and such a mini-computer system cost less.

Small business units could now acquire computers for themselves. Mini-computers were able to perform the tasks of managing technological equipment, warehouses and solving other problems, corresponding to the level of an enterprise unit, i.e., the concept of distribution of computer resources throughout the enterprise appeared, but all computers of one organization continued to operate independently.

Over time, the needs of computer users increased, there was a need to be able to exchange data with other closely located computers. For this reason, enterprises and organizations began to use the connection of their mini-computers and developed the software necessary for their interaction. As a result, this led to the emergence of the first local area networks. They were still significantly different from modern networks, in particular, in the device pairing. Initially, a variety of non-standard devices were used to connect computers to each other with their own ways of presenting data on communication lines, their own cable types, etc. Such devices were able to connect only those types of computers for which they were designed. This situation has created a lot of room for students. The names of many course and diploma projects were devoted to the device pairing.

In the 1980s the state of affairs in local networks began to change dramatically. There are standard technologies for combining computers into a network - Ethernet, Arcnet, Token Ring. Strong impetus for their development gave the PC. These mass products have become ideal elements for building networks. On the one hand, they were powerful enough and capable of working with network software, and on the other hand, they needed to combine their computing power to solve complex problems. Personal computers began to prevail in local networks, while not only as client computers, but also as data storage and processing centers, that is, network servers, displacing mini-computers and mainframes from the usual roles.

Conventional network technologies have turned the process of building a local network from art to routine work. In order to create networks, it was enough to purchase network adapters of the appropriate standard, for example, Ethernet, a standard cable, connect adapters and cables with standard connectors, and install any of the existing network operating systems, for example NetWare, on a computer. Now the network was starting to work, and the connection of a new computer did not cause problems. The connection occurred naturally if the network adapter of the same technology was installed on it.

Local networks compared to the global have made a lot of new technologies in the organization of work of users. Access to shared resources has become much more convenient, since the user could simply study the lists of available resources, and not memorize their identifiers or names. When connecting to a remote resource, it was possible to work with it using commands already known to the user for working with local resources. The consequence and at the same time the driving force of such progress was the emergence of a large number of non-professional users who absolutely did not need to study special (and rather complex) commands for networking. The developers of local networks were able to use all these conveniences when high-quality cable communication lines appeared, with the help of which even first-generation network adapters could provide data rates of up to 10 Mbps.

However, the developers of global networks did not suspect such speeds, since they had to use the communication channels that were available. This was due to the fact that the laying of new cable systems for computing networks thousands of kilometers long would have caused huge capital investments. Only telephone channels that were poorly adapted for high-speed transmission of discrete data were available at that time — 1200 bps was a good achievement for them. For this reason, economical use of bandwidth communication channels became the main criterion for the effectiveness of data transfer methods in global networks. Under such conditions, different procedures of transparent access to remote resources, standard for local area networks, have remained an impermissible luxury for global networks for a considerable time.

At the moment, computer networks are constantly evolving, and quickly enough. The separation between local and global networks is constantly decreasing, largely due to the emergence of high-speed territorial communication channels, which are not inferior in quality to the cable systems of local networks. In global networks, resource access services are formed, just as convenient and transparent as local area services. Such examples in large numbers shows the most popular global network - the Internet.

Converted and local area networks. A passive cable connecting computers to computers has changed various types of communication equipment - switches, routers, gateways. Due to the use of such equipment, it became possible to build large corporate networks that comprise thousands of computers and have a complex structure. The interest in large computers has reappeared. This was due to the fact that after the recession of euphoria about the ease of working with PCs, it became clear that systems that consist of hundreds of servers are more difficult to maintain than a few large computers. Therefore, at the new stage of evolution, mainframes are returning to corporate computing systems. At the same time, they are full-fledged network nodes that support Ethernet or Token Ring, as well as the TCP / IP protocol stack, which have become, thanks to the Internet, the de facto network standard.

Another important trend has emerged, affecting both local and global networks. In them, information, such as voice, video images, and drawings, which were not typical for earlier computing networks, began to be processed. This has led to the need for changes in the work of protocols, network operating systems and communication equipment. The difficulty of transmitting this multimedia information over the network is due to its sensitivity to delays in the case of the transmission of data packets. Delays most often cause distortion of such information in the end nodes of the network. Since the usual services of computer networks, including file transfer or e-mail, form traffic that is insensitive to latency and all network elements were invented for it, the appearance of real-time traffic caused great problems.

Currently, these problems are solved in various ways, for example, using ATM technology specially designed for transmitting different types of traffic. However, despite the great efforts being made in this direction, it is still far from an acceptable solution to the problem, and there is still much to be done in this area to achieve a merger of technologies not only local and global networks, but also technologies of any information networks - computing, telephone, television, etc. Despite the fact that today this idea seems unrealistic to many, experts believe that the prerequisites for such a union already exist. These opinions differ only in estimating the approximate timing of such a union - the terms are from 10 to 25 years. It is believed that the basis for the synthesis will be the packet switching technology used today in computer networks, and not the channel switching technology used in telephony.