• The concept of network technologies, their role in management processes in enterprises. Network and network technology. Network information technologies Exchange of geodetic productions using network technologies

    Network computer technologies are rapidly developing. If previously the main concern of a network administrator was the local computer network of an enterprise or organization, now this network is increasingly becoming geographically distributed. Users must be able to access enterprise network resources from virtually anywhere. At the same time, they want not only to view and send e-mail, but also to be able to access files, databases and other resources on the enterprise network. Within an organization, remotely located branches are often created with their own local networks, which must be connected to the network of the main division using reliable, secure and transparent communications for users. Such networks are called corporate. Taking into account today's realities, users of an enterprise's corporate network also need to be given the opportunity to access the resources of the global Internet, while protecting the internal network from unauthorized access from the outside.

    Thus, a corporate network is a hardware and software system that ensures reliable transfer of information between various applications used in an organization. Often corporate network nodes are located in different cities. The principles by which such a network is built are quite different from those used when creating a local network, even covering several buildings. The main difference is that geographically distributed networks use fairly slow (today it is often tens and hundreds of kilobits per second, sometimes 2 Mbit/s and higher) leased communication lines. If when creating a local network the main costs are for the purchase of equipment and laying cables, then in geographically distributed networks the most significant element of the cost is the rental fee for the use of channels, which grows rapidly with the increase in the quality and speed of data transmission. Otherwise, the corporate network should not impose restrictions on which applications and how they process the information transferred over it. The main problem that has to be solved when creating a corporate network is the organization of communication channels. If within one city you can count on renting dedicated lines, including high-speed ones, then when moving to geographically distant nodes, the cost of renting channels becomes very high, and their quality and reliability often turn out to be very low. A natural solution to this problem is to use already existing wide area networks. In this case, it is enough to provide channels from offices to the nearest network nodes. The global network will take on the task of delivering information between nodes.

    The ideal option for a corporate network would be to create communication channels only in those areas where it is necessary, and transfer over them any network protocols that are required by running applications. At first glance, this is a return to leased communication lines. However, there are technologies for constructing data transmission networks that make it possible to organize channels within them that appear only at the right time and in the right place. Such channels are called virtual. A system that connects remote resources using virtual channels can naturally be called a virtual network. Today, there are two main virtual network technologies - circuit-switched networks and packet-switched networks. The first includes the regular telephone network, ISDN and a number of other more exotic technologies. Packet switching networks are represented by X.25, Frame Relay and, more recently, ATM technologies. Other types of virtual (in various combinations) networks are widely used in the construction of corporate information systems. Circuit-switched networks provide the subscriber with multiple communication channels with a fixed bandwidth per connection. A regular telephone network provides one communication channel between subscribers. If it is necessary to increase the number of simultaneously available resources, additional telephone numbers must be installed. Even if we forget about the low quality of communication, it is clear that the limited number of channels and long connection establishment times do not allow using telephone communications as the basis of a corporate network. For connecting individual remote users, this is quite convenient and often the only available method.

    An alternative to circuit-switched networks is packet-switched networks. When using packet switching, one communication channel is used in a time-sharing mode by many users - much the same as on the Internet. However, unlike networks like the Internet, where each packet is routed separately, packet switching networks require a connection to be established between end resources before information can be transmitted. After establishing a connection, the network “remembers” the route (virtual channel) along which information should be transmitted between subscribers, and remembers it until it receives a signal to break the connection. For applications running on a packet switching network, virtual circuits look like regular communication lines - the only difference is that their throughput and introduced delays vary depending on the network load. Let's consider the main technologies that are used to build corporate networks.

    ISDN

    A widely used example of a circuit-switched virtual network is ISDN(digital network with integration of services). ISDN provides digital channels (64 Kbps) that can carry both voice and data. A basic ISDN (Basic Rate Interface) connection includes two such channels and an additional control channel with a speed of 16 Kbps (this combination is designated as 2B+D). It is possible to use a larger number of channels - up to thirty (Primary Rate Interface, 30B+D). This significantly increases the bandwidth, but leads to a corresponding increase in the cost of equipment and communication channels. In addition, the costs of renting and using the network increase proportionally. In general, the limitations on the number of simultaneously available resources imposed by ISDN lead to the fact that this type of communication is convenient to use mainly as an alternative to telephone networks. In systems with a small number of nodes, ISDN can also be used as the main network protocol. You should just keep in mind that access to ISDN in our country is still the exception rather than the rule.

    X.25

    The classic packet switching technology is the X.25. Today there are virtually no X.25 networks operating at speeds higher than 128 Kbps, which is quite slow. But the X.25 protocol includes powerful error correction facilities, ensuring reliable delivery of information even on poor lines and is widely used where there are no high-quality communication channels. (In our country they are not available almost everywhere.) Naturally, you have to pay for reliability - in this case, the speed of network equipment and relatively large, but predictable delays in the distribution of information. At the same time, X.25 is a universal protocol that allows you to transfer almost any type of data. “Natural” for X.25 networks is the operation of applications using the protocol stack OSI. These include systems that use standards X.400(email) and FTAM(file sharing), as well as some others. Tools are available that allow you to implement the interaction of Unix systems based on OSI protocols. Another standard feature of X.25 networks is communication through regular asynchronous COM ports. Figuratively speaking, the X.25 network “extends” the cable connected to the serial port, bringing its connector to remote resources. Thus, almost any application that can be accessed through a COM port can be easily integrated into an X.25 network. Examples of such applications include not only terminal access to remote host computers, such as Unix machines, but also the interaction of Unix computers with each other (cu, uucp), Lotus Notes-based systems, cc:Mail and MS e-mail Mail, etc. To combine LANs in nodes connected to an X.25 network, there are methods of encapsulating packets of information from the local network into X.25 packets. Some of the service information is not transmitted, since it can be unambiguously restored on the recipient's side. The standard encapsulation mechanism is considered to be that described in RFC 1356. It allows various local network protocols (IP, IPX, etc.) to be transmitted simultaneously through one virtual connection. This mechanism (or the older IP-only RFC 877 implementation) is implemented in almost all modern routers. There are also transmission methods over X.25 and other communication protocols, in particular SNA, used in IBM mainframe networks, as well as a number of proprietary protocols from various manufacturers. Thus, X.25 networks offer a universal transport mechanism for transferring information between virtually any application. In this case, different types of traffic are transmitted over one communication channel, without “knowing” anything about each other. When connecting local networks via X.25, you can isolate separate fragments of the corporate network from each other, even if they use the same communication lines.

    Today there are dozens of public global X.25 networks in the world; their nodes are located in almost all major business, industrial and administrative centers. In Russia, X.25 services are offered by Sprint Network, Infotel, Rospak, Rosnet, Sovam Teleport and a number of other providers. In addition to connecting remote nodes, X.25 networks always provide access facilities for end users. In order to connect to any X.25 network resource, the user only needs to have a computer with an asynchronous serial port and a modem. At the same time, there are no problems with access authorization in geographically remote nodes; If your resource is connected to an X.25 network, you can access it both from your provider's nodes and through nodes on other networks - that is, from almost anywhere in the world. The disadvantage of X.25 technology is the presence of a number of fundamental speed restrictions. The first of them is connected precisely with the developed capabilities of correction and restoration. These tools cause delays in the transmission of information and require a lot of computing power and performance from X.25 equipment, as a result of which it simply “cannot keep up” with fast communication lines. Although there is equipment that has high-speed ports, the actual speed they provide does not exceed 250-300 Kbps per port. At the same time, for modern high-speed communication lines, X.25 correction tools turn out to be redundant and when they are used, equipment power often runs idle. The second feature that makes X.25 networks considered slow is the peculiarities of encapsulation of local network protocols (primarily IP and IPX). All other things being equal, the connection of local networks via X.25 is, depending on the network parameters, 15-40% slower than when using HDLC over a leased line.

    Still, on low-quality communication lines, X.25 networks are quite effective and provide a significant advantage in price and capabilities compared to leased lines.

    Frame Relay

    Frame Relay technology emerged as a means to realize the benefits of packet switching on high-speed communication lines. The main difference between Frame Relay networks and X.25 is that they eliminate error correction between network nodes. The tasks of restoring the flow of information are assigned to the terminal equipment and software of users. Naturally, this requires the use of sufficiently high-quality communication channels. It is believed that to successfully work with Frame Relay, the probability of an error in the channel should be no higher than 10-6-10-7. The quality provided by conventional analog lines is usually one to three orders of magnitude lower. The second difference between Frame Relay networks is that currently almost all of them implement only the mechanism of permanent virtual connections ( PVC ). This means that when you connect to a Frame Relay port, you must determine in advance which remote resources you will have access to. The principle of packet switching - many independent virtual connections in one communication channel - remains here, but you cannot select the address of any network subscriber. All resources available to you are determined when you configure the port. Thus, on the basis of Frame Relay technology, it is convenient to build closed virtual networks used to transmit other protocols through which routing is carried out. A virtual network's "closedness" means that it is completely inaccessible to other users on the same Frame Relay network. For example, in the USA, Frame Relay networks are widely used as backbones for the Internet. However, your private network can use Frame Relay virtual circuits on the same lines as Internet traffic - and be completely isolated from it. Like X.25 networks, Frame Relay provides a universal transmission medium for virtually any application. The main application of Frame Relay today is the interconnection of remote LANs. In this case, error correction and information recovery are carried out at the level of LAN transport protocols - TCP, SPX, etc. Losses for encapsulating LAN traffic in Frame Relay do not exceed two to three percent. The absence of error correction and complex packet switching mechanisms characteristic of X.25 allows information to be transmitted over Frame Relay with minimal delays. Additionally, it is possible to include a prioritization mechanism that allows the user to have a guaranteed minimum information transfer rate for the virtual channel. This capability allows Frame Relay to be used to transmit latency-critical information such as voice and video in real time. This relatively new capability is becoming increasingly popular and is often the main reason for choosing Frame Relay as the backbone of an enterprise network. It should be remembered that today Frame Relay network services are available in our country in no more than one and a half dozen cities, while X.25 is available in approximately two hundred. There is every reason to believe that as communication channels develop, Frame Relay technology will become more common - primarily where X.25 networks currently exist. Unfortunately, there is no single standard that describes the interaction of different Frame Relay networks, so users are locked into one service provider. If it is necessary to expand the geography, it is possible to connect at one point to the networks of different suppliers - with a corresponding increase in costs. There are also private Frame Relay networks operating within the same city or using long-distance (usually satellite) dedicated channels. Building private networks based on Frame Relay allows you to reduce the number of leased lines and integrate voice and data transmission.

    Ethernet/Fast Ethernet

    Ethernet is the most popular local network topology. It is based on the IEEE 802.3 standard. Ethernet has evolved significantly over the years to support new media and features that were not included in the original standard. Available bandwidth can either be shared among multiple users using hubs, or provided entirely to individual PCs using switches. Not long ago, a clear trend has emerged towards providing users of desktop stations with full-duplex communication channels of 10 Mbit/s. This trend was able to take root thanks to the advent of low-cost Ethernet switches, which made it possible to create high-performance, multifunctional networks without high costs.

    Fast Ethernet technology was developed to provide more bandwidth to the devices that needed it, primarily servers and desktop switches. Fast Ethernet is based on the Ethernet standard; This means that implementing this high-speed technology does not require restructuring the existing infrastructure, replacing the management system, or retraining the IT department staff. It is now one of the most popular high-speed technologies - it is inexpensive, stable and fully compatible with existing Ethernet networks. Fast Ethernet networks can use fiber optic (100Base-FX) or copper (100Base-TX) cables. Full duplex communication is supported.

    All information system administrators are faced with the challenge of providing Fast Ethernet channels to connect the most powerful desktop stations and servers without disrupting the work of those users who have enough Ethernet 10Base-T. This is precisely why technology for automatically recognizing the speed of an Ethernet/Fast Ethernet network is needed. With this technology, the same device supports both 10Base-T and 100Base-TX. The same switch will provide support for Ethernet and Fast Ethernet, providing desktop stations with more bandwidth, combining 10 and 100 Mbps hubs, and without introducing any changes to the experience of those users who are completely satisfied with 10 Mbps links. In addition, when working with a switch that automatically detects the data transfer rate, there is no need to configure each of the ports separately. This is one of the most effective ways to selectively increase bandwidth in areas where congestion occurs, while still fully maintaining the potential for further bandwidth expansion in the future.

    Gigabit Ethernet

    Gigabit Ethernet technology fully retains the traditional simplicity and manageability of Ethernet and Fast Ethernet, making it easy to integrate into existing local area networks. The use of this technology makes it possible to increase the bandwidth of the backbone network by an order of magnitude compared to Fast Ethernet. The additional bandwidth allows you to cope with the challenges associated with unplanned changes to the network structure and the addition of new devices to the network, and eliminates the need for constant adjustments to the network. Gigabit Ethernet is ideal for network backbones and server links because it provides high bandwidth at low cost, does not require a change from the traditional Ethernet frame format, and is supported by existing network management systems.

    The emergence of the 802.3ab standard, which allows the use of copper cable as a Gigabit Ethernet medium (though at distances of no more than 100 meters), is another important argument in favor of this technology. It should also be noted that IEEE is working on a new 10 Gbit/s standard.

    ATM

    ATM is a popular technology for local area network backbones. Its use promises significant benefits for large organizations, since it provides close integration between local and geographically distributed networks and is characterized by a high level of fault tolerance and redundancy. To transmit data over the network, communication channels OC-3 (155 Mbit/s) and OC-12 (622 Mbit/s) are used. Just to compare the numbers, these numbers are less than Gigabit Ethernet, but ATM uses alternative methods for allocating bandwidth; By setting one or another level of Quality of Service (QoS), you can guarantee the provision of the bandwidth necessary for the operation of the application. The traffic control capabilities provided by ATM technology enable complete application certainty and service delivery across complex networks. ATM technology has important advantages over existing methods of data transmission in local and global networks, which should lead to its widespread use throughout the world. One of the most important advantages of ATM is providing high speed information transfer (wide bandwidth). ATM eliminates the differences between local and wide area networks, turning them into a single, integrated network. Combining the scalability and efficiency of hardware information transmission inherent in telephone networks, the ATM method provides a cheaper expansion of network capacity. This is a technology solution that can meet future needs, so many users often choose ATM more for its future than today's relevance. ATM standards unify procedures for accessing, switching and transmitting information of various types (data, speech, video, etc.) in one communication network with the ability to operate in real time. Unlike earlier LAN and WAN technologies, ATM cells can be transmitted over a wide range of media - from copper wire and fiber optic cable to satellite links, at any transmission speeds reaching today's limit of 622 Mbit/s. ATM technology provides the ability to simultaneously serve consumers with different requirements for the throughput of a telecommunication system. ATM technology has been gradually making its way into corporate infrastructures for several years now. Users build an ATM network in stages, operating it in parallel with their existing systems. Of course, first of all, ATM technology will have an impact on global networks, and to a lesser extent on trunk communication lines connecting several local area networks. A recent Sege Research survey of 175 users asked which technologies they intended to use on their networks in 1999. ATM has overtaken Ethernet in popularity. More than 40% of users would like to install Ethernet at 100 Mbit/s, and about 45% plan to use ATM at 155 Mbit/s. Quite unexpectedly, it turned out that 28% of respondents intend to use ATM at 622 Mbit/s. A few words about the relationship between ATM and Gigabit Ethernet. Each of these technologies has its own, fairly clearly defined niche. For ATM, these are the backbone networks of a group of buildings integrated into a corporate network, and the backbones of global networks. For Gigabit Ethernet, these are local network backbones and communication lines with high-performance servers. The problems of traffic exchange between Gigabit Ethernet and ATM and the problems of transparent routing are successfully solved. Cisco Systems recently developed a special ATM module for the Catalyst 8500 routing switch. This module allows routing between ATM and Ethernet ports.

    Building a corporate network

    When building a geographically distributed corporate network, all the technologies described above can be used. At the local network level, there is no alternative to Ethernet technologies, including Fast Ethernet and Gigabit Ethernet; Category 5 twisted pair cable is preferable as a physical transmission medium. To connect remote users, the simplest and most affordable option is to use telephone communication. Where possible, ISDN networks may be used. To connect network nodes in most cases, global data networks are used. Even where it is possible to lay dedicated lines, the use of packet switching technologies makes it possible to reduce the number of necessary communication channels and, importantly, ensure compatibility of the system with existing global network equipment. Connecting your corporate network to the Internet makes sense if you need access to relevant services. Using the Internet as a data transmission medium makes sense only when other methods are not available and financial considerations outweigh the requirements for reliability and security. If you will use the Internet only as a source of information, it is better to use the “connection on demand” technology, that is, a connection method where a connection to an Internet node is established only on your initiative and for the right time. This dramatically reduces the risk of unauthorized entry into your network from the outside. The simplest way to provide such a connection is to dial into the Internet via a telephone line or, if possible, via ISDN. Another more reliable way to provide on-demand connectivity is to use a leased line and Frame Relay protocol. In this case, the router on your end should be configured to break the virtual connection when there is no data for a certain time and re-establish it when access to data is required. Widespread connection methods using PPP or HDLC do not provide this opportunity. If you want to provide your information on the Internet (for example, set up a WWW or FTP server), the on-demand connection is not applicable. In this case, you should not only use access restriction using a Firewall, but also isolate the Internet server from other resources as much as possible. A good solution is to use a single point of connection to the Internet for the entire geographically distributed network, the nodes of which are connected to each other using virtual X channels. 25 or Frame Relay. In this case, access from the Internet is possible to a single node, while users in other nodes can access the Internet using an on-demand connection. To transfer data within a corporate network, it is also worth using virtual channels of packet switching networks. The main advantages of this approach are versatility, flexibility, and safety. When building a corporate information system, both X.25 and Frame Relay or ATM can be used as a virtual network. The choice between them is determined by the quality of communication channels, the availability of services at connection points and, last but not least, financial considerations. Today, the costs of using Frame Relay for long-distance communications are several times higher than for X.25 networks. At the same time, higher information transfer speeds and the ability to simultaneously transmit data and voice may be decisive arguments in favor of Frame Relay. In those areas of the corporate network where leased lines are available, Frame Relay technology is more preferable. In addition, telephone communication between nodes is possible via the same network. For Frame Relay, it is better to use digital communication channels, but even on physical lines or voice-frequency channels you can create a quite effective network by installing the appropriate channel equipment. Where it is necessary to organize broadband communications, for example when transmitting video information, it is advisable to use ATM. To connect remote users to the corporate network, access nodes of X.25 networks, as well as their own communication nodes, can be used. In the latter case, the required number of telephone numbers (or ISDN channels) must be allocated, which can be prohibitively expensive.

    In preparing this article, materials from the sites www.3com.ru and www.race.ru were used

    ComputerPress 10"1999

    Today, networks and network technologies connect people in every corner of the world and provide them with access to the greatest luxury in the world - human communication. People can communicate and play with friends in other parts of the world without interference.

    The events taking place become known in all countries of the world in a matter of seconds. Everyone is able to connect to the Internet and post their piece of information.

    Network information technologies: the roots of their origin

    In the second half of the last century, human civilization formed its two most important scientific and technical branches - computer and About a quarter of a century, both of these branches developed independently, and within their framework computer and telecommunication networks were created, respectively. However, in the last quarter of the twentieth century, as a result of the evolution and interpenetration of these two branches of human knowledge, what we call the term “network technology” arose, which is a subsection of the more general concept of “information technology”.

    As a result of their appearance, a new technological revolution occurred in the world. Just as several decades earlier the land surface was covered with a network of expressways, at the end of the last century all countries, cities and villages, enterprises and organizations, as well as individual homes found themselves connected by “information highways.” At the same time, they all became elements of various data transfer networks between computers, in which certain information transfer technologies were implemented.

    Network technology: concept and content

    Network technology is a sufficient set of rules for the presentation and transmission of information, implemented in the form of so-called “standard protocols”, as well as hardware and software, including network adapters with drivers, cables and fiber-optic lines, and various connectors (connectors).

    “Sufficiency” of this set of tools means its minimization while maintaining the possibility of building an efficient network. It should have the potential for improvement, for example, by creating subnets in it that require the use of protocols of various levels, as well as special communicators, usually called “routers.” After improvement, the network becomes more reliable and faster, but at the cost of adding add-ons to the main network technology that forms its basis.

    The term “network technology” is most often used in the narrow sense described above, but it is often broadly interpreted as any set of tools and rules for building networks of a certain type, for example, “local computer network technology.”

    Prototype of network technology

    The first prototype of a computer network, but not yet the network itself, began in the 60-80s. last century multi-terminal systems. Representing a set of monitor and keyboard, located at great distances from mainframe computers and connecting to them via telephone modems or dedicated channels, the terminals left the premises of the computer information center and were dispersed throughout the building.

    At the same time, in addition to the operator of the computer itself on the computer information center, all users of the terminals were able to enter their tasks from the keyboard and observe their execution on the monitor, carrying out some task management operations. Such systems, implementing both time-sharing and batch processing algorithms, were called remote job entry systems.

    Global networks

    Following multi-terminal systems in the late 60s. XX century The first type of networks was created - global computer networks (GCN). They connected supercomputers, which existed in single copies and stored unique data and software, with mainframe computers located at distances of up to many thousands of kilometers, through telephone networks and modems. This network technology has previously been tested in multi-terminal systems.

    The first GCS in 1969 was ARPANET, which worked in the US Department of Defense and united different types of computers with different operating systems. They were equipped with additional modules to implement communication systems common to all computers on the network. It was on it that the foundations of network technologies that are still used today were developed.

    The first example of the convergence of computer and telecommunications networks

    GKS inherited communication lines from older and more global telephone networks, since it was very expensive to lay new long-distance lines. Therefore, for many years they used analog telephone channels to transmit only one conversation at a time. Digital data was transmitted over them at a very low speed (tens of kbit/s), and the capabilities were limited to the transfer of data files and email.

    However, having inherited telephone communication lines, GCS did not take their basic technology, based on the principle of circuit switching, when each pair of subscribers was allocated a channel at a constant speed for the entire duration of the communication session. The GCS used new computer network technologies based on the principle of packet switching, in which data in the form of small portions of packets at a constant speed is issued into a non-switched network and received by their recipients on the network using address codes built into the packet headers.

    Predecessors of local area networks

    Appearance in the late 70s. XX century LSI led to the creation of minicomputers with low cost and rich functionality. They began to really compete with large computers.

    Minicomputers of the PDP-11 family have gained wide popularity. They began to be installed in all, even very small production units to manage technical processes and individual technological installations, as well as in enterprise management departments to perform office tasks.

    The concept of computer resources distributed throughout the enterprise emerged, although all minicomputers still operated autonomously.

    The emergence of LAN networks

    By the mid-80s. XX century technologies for combining minicomputers into networks were introduced, based on switching data packets, as in the GCS.

    They turned the construction of a single enterprise network, called a local (LAN) network, into an almost trivial task. To create it, you only need to buy network adapters for the selected LAN technology, for example, Ethernet, a standard cable system, install connectors (connectors) on its cables and connect the adapters to the minicomputer and to each other using these cables. Next, one of the operating systems intended for organizing a LAN network was installed on the computer server. After that, it began to work, and the subsequent connection of each new minicomputer did not cause any problems.

    The inevitability of the Internet

    If the advent of mini-computers made it possible to distribute computer resources evenly across the territories of enterprises, then the appearance in the early 90s. PC led to their gradual appearance, first in every workplace of any mental worker, and then in individual human dwellings.

    The relative cheapness and high reliability of PCs first gave a powerful impetus to the development of LAN networks, and then led to the emergence of a global computer network - the Internet, which today covers all countries of the world.

    The size of the Internet is growing by 7-10% every month. It represents the core that connects various local and global networks of enterprises and institutions around the world with each other.

    If at the first stage data files and email messages were mainly transmitted via the Internet, today it mainly provides remote access to distributed information resources and electronic archives, to commercial and non-commercial information services in many countries. Its freely accessible archives contain information on almost all areas of knowledge and human activity - from new trends in science to weather forecasts.

    Basic network technologies of LAN networks

    Among them are the basic technologies on which the basis of any specific network can be built. Examples include such well-known LAN technologies as Ethernet (1980), Token Ring (1985) and FDDI (late 80s).

    At the end of the 90s. Ethernet technology has become the leader in LAN network technology, combining its classic version with up to 10 Mbit/s, as well as Fast Ethernet (up to 100 Mbit/s) and Gigabit Ethernet (up to 1000 Mbit/s). All Ethernet technologies have similar operating principles that simplify their maintenance and the integration of LAN networks built on their basis.

    During the same period, their developers began to build network functions into the kernels of almost all computer operating systems that implement the above-mentioned network information technologies. Even specialized communication operating systems like IOS from Cisco Systems have appeared.

    How GCS technologies developed

    GKS technologies on analog telephone channels, due to the high level of distortion in them, were distinguished by complex algorithms for monitoring and data recovery. An example of them is the X.25 technology developed in the early 70s. XX century More modern network technologies are frame relay, ISDN, ATM.

    ISDN is an acronym that stands for Integrated Services Digital Network and allows remote video conferencing. Remote access is provided by installing ISDN adapters in PCs, which work many times faster than any modems. There is also special software that allows popular operating systems and browsers to work with ISDN. But the high cost of equipment and the need to lay special communication lines hinder the development of this technology.

    WAN technologies have progressed along with telephone networks. After the advent of digital telephony, a special technology, Plesiochronous Digital Hierarchy (PDH), was developed, supporting speeds of up to 140 Mbit/s and used by enterprises to create their own networks.

    New Synchronous Digital Hierarchy (SDH) technology in the late 80s. XX century expanded the capacity of digital telephone channels up to 10 Gbit/s, and Dense Wave Division Multiplexing (DWDM) technology - up to hundreds of Gbit/s and even up to several Tbit/s.

    Internet technologies

    Network ones are based on the use of hypertext language (or HTML language) - a special markup language that is an ordered set of attributes (tags) that are pre-implemented by website developers into each of their pages. Of course, in this case we are not talking about text or graphic documents (photos, pictures), which have already been “downloaded” by the user from the Internet, are in the memory of his PC and are viewed through text or images. We are talking about so-called web pages viewed through programs -browsers.

    Developers of Internet sites create them in HTML language (now many tools and technologies have been created for this work, collectively called “website layout”) in the form of a set of web pages, and site owners place them on Internet servers on a rental basis from the owners of their memory servers (the so-called “hosting”). They work on the Internet around the clock, servicing the requests of its users to view the web pages loaded on them.

    Browsers on user PCs, having received access through the server of their Internet provider to a specific server, the address of which is contained in the name of the requested Internet site, gain access to this site. Next, by analyzing the HTML tags of each page being viewed, browsers form its image on the monitor screen in the way it was intended by the site developer - with all the headings, font and background colors, various inserts in the form of photos, diagrams, pictures, etc. .

    In order to understand how it works local network, it is necessary to understand such a concept as network technology.

    Network technology consists of two components: network protocols and the hardware that makes these protocols work. Protocol in turn, is a set of “rules” with the help of which computers on the network can connect to each other and exchange information. With the help of network technologies we have the Internet, there is a local connection between computers in your home. More network technologies called basic, but also have another beautiful name - network architectures.

    Network architectures define several network parameters, which you need to have a little idea about in order to understand the structure of the local network:

    1)Data transfer speed. Determines how much information, usually measured in bits, can be transmitted over a network in a given time.

    2) Format of network frames. Information transmitted through the network exists in the form of so-called “frames” - packets of information. Network frames in different network technologies have different formats of transmitted information packets.

    3) Type of signal coding. Determines how, using electrical impulses, information is encoded in the network.

    4)Transmission medium. This is the material (usually a cable) through which the flow of information passes - the same one that is ultimately displayed on the screens of our monitors.

    5) Network topology. This is a diagram of a network in which there are “edges”, which are cables, and “vertices” - computers to which these cables stretch. Three main types of network designs are common: ring, bus, and star.

    6)Method of access to the data transmission medium. Three methods of accessing the network medium are used: deterministic method, random access method and priority transmission. The most common is the deterministic method, in which, using a special algorithm, the time of use of the transmission medium is divided among all computers located in the medium. In the random network access method, computers compete to access the network. This method has a number of disadvantages. One of these disadvantages is the loss of part of the transmitted information due to collisions of information packets in the network. Priority Access provides, accordingly, the greatest amount of information to the established priority station.

    The set of these parameters determinesnetwork technology.

    Network technology is now widespread IEEE802.3/Ethernet. It has become widespread thanks to simple and inexpensive technologies. It is also popular due to the fact that servicing such networks is easier. The topology of Ethernet networks is usually built in the form of a “star” or “bus”. Transmission media in such networks use both thin and thick coaxial cable, and also twisted pairs and fiber optic cables. The length of Ethernet networks typically ranges from 100 to 2000 meters. The data transfer speed in such networks is usually about 10 Mbit/s. Ethernet networks typically use the CSMA/CD access method, which refers to decentralized random network access methods.

    There are also high-speed network options Ethernet: IEEE802.3u/Fast Ethernet and IEEE802.3z/Gigabit Ethernet, providing data transfer rates of up to 100 Mbit/s and up to 1000 Mbit/s, respectively. In these networks, the transmission medium is predominantly fiber optic, or shielded twisted pair.

    There are also less common, but still widely used network technologies.

    Network technology IEEE802.5/Token-Ring characterized by the fact that all vertices or nodes (computers) in such a network are united in a ring, use the token method of accessing the network, support shielded and unshielded twisted pair, and also fiber optic as a transmission medium. Speed ​​in the Token-Ring network is up to 16 Mbit/s. The maximum number of nodes in such a ring is 260, and the length of the entire network can reach 4000 meters.

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    Local network IEEE802.4/ArcNet is special in that it uses the transfer of authority access method to transfer data. This network is one of the oldest and previously popular in the world. This popularity is due to the reliability and low cost of the network. Nowadays, such network technology is less common, since the speed in such a network is quite low - about 2.5 Mbit/s. Like most other networks, it uses shielded and unshielded twisted pairs and fiber optic cables as a transmission medium, which can form a network up to 6000 meters long and include up to 255 subscribers.

    Network architecture FDDI (Fiber Distributed Data Interface), is based on IEEE802.4/ArcNet and is very popular due to its high reliability. This network technology includes two fiber optic rings, length up to 100 km. This also ensures high data transfer speeds on the network - about 100 Mbit/s. The point of creating two fiber optic rings is that one of the rings carries a path with redundant data. This reduces the chance of losing transmitted information. Such a network can have up to 500 subscribers, which is also an advantage over other network technologies.

    What is network technology? Why is it needed? What is it used for? Answers to these, as well as a number of other questions, will be given within the framework of this article.

    Several important parameters

    1. Data transfer rate. This characteristic determines how much information (measured in most cases in bits) can be transmitted through the network in a certain period of time.
    2. Frame format. Information that is transmitted through the network is combined into information packets. They are called frames.
    3. Signal coding type. In this case, it is decided how to encrypt information in electrical impulses.
    4. Transmission medium. This designation is used for the material, as a rule, it is a cable through which the flow of information passes, which is subsequently displayed on monitor screens.
    5. Network topology. This is a schematic construction of a structure through which information is transmitted. As a rule, a tire, a star and a ring are used.
    6. Access method.

    The set of all these parameters determines the network technology, what it is, what devices it uses and its characteristics. As you can guess, there are a great many of them.

    General information

    But what is network technology? After all, the definition of this concept was never given! So, network technology is a coordinated set of standard protocols and software and hardware that implement them in a volume sufficient to build a local computer network. This determines how the data transmission medium will be accessed. Alternatively, you can also find the name “basic technologies”. It is not possible to consider them all within the framework of the article due to the large number, so attention will be paid to the most popular: Ethernet, Token-Ring, ArcNet and FDDI. What are they?

    Ethernet

    At the moment it is the most popular network technology all over the world. If the cable fails, then the probability that it is the one being used is close to one hundred percent. Ethernet can be safely included in the best network information technologies, due to its low cost, high speed and quality of communication. The most famous type is IEEE802.3/Ethernet. But based on it, two very interesting options were developed. The first (IEEE802.3u/Fast Ethernet) allows for a transmission speed of 100 Mbit/second. This option has three modifications. They differ from each other in the material used for the cable, the length of the active segment and the specific scope of the transmission range. But fluctuations occur in the style of “plus or minus 100 Mbit/second”. Another option is IEEE802.3z/Gigabit Ethernet. Its transmission capacity is 1000 Mbit/s. This variation has four modifications.

    Token-Ring

    Network information technologies of this type are used to create a shared data transmission medium, which is ultimately formed as the union of all nodes into one ring. This technology is based on a star-ring topology. The first one is the main one, and the second one is the additional one. To gain access to the network, the token method is used. The maximum length of the ring can be 4 thousand meters, and the number of nodes can be 260 pieces. The data transfer rate does not exceed 16 Mbit/second.

    ArcNet

    This option uses a bus and passive star topology. Moreover, it can be built on unshielded twisted pair and fiber optic cable. ArcNet is a true old-timer in the world of networking technologies. The network length can reach 6000 meters, and the maximum number of subscribers is 255. It should be noted that the main disadvantage of this approach is its low data transfer rate, which is only 2.5 Mbit/second. But this network technology is still widely used. This is due to its high reliability, low cost of adapters and flexibility. Networks and network technologies built on other principles may have higher speeds, but precisely because ArcNet provides high data yield, this allows us not to discount it. An important advantage of this option is that the access method is used through delegation of authority.

    FDDI

    Network computer technologies of this type are standardized specifications for a high-speed data transmission architecture using fiber optic lines. FDDI has been significantly influenced by ArcNet and Token-Ring. Therefore, this network technology can be considered as an improved data transmission mechanism based on existing developments. The ring of this network can reach a length of one hundred kilometers. Despite the considerable distance, the maximum number of subscribers who can connect to it is only 500 nodes. It should be noted that FDDI is considered highly reliable due to the presence of a primary and backup data path. Adding to its popularity is the ability to quickly transfer data - approximately 100 Mbit/second.

    Technical aspect

    Having considered what the basics of network technologies are and what they are used, now let’s pay attention to how everything works. Initially, it should be noted that the previously discussed options are exclusively local means of connecting electronic computers. But there are also global networks. There are about two hundred of them in the world. How do modern network technologies work? To do this, let's look at the current construction principle. So, there are computers that are united into one network. Conventionally, they are divided into subscriber (main) and auxiliary. The former are engaged in all information and computing work. What the network resources will be depends on them. Auxiliary ones are engaged in the transformation of information and its transmission through communication channels. Due to the fact that they have to process a significant amount of data, servers boast increased power. But the final recipient of any information is still ordinary host computers, which are most often represented by personal computers. Network information technologies can use the following types of servers:

    1. Network. Engaged in the transfer of information.
    2. Terminal. Ensures the functioning of a multi-user system.
    3. Databases. Involved in processing database queries in multi-user systems.

    Circuit Switching Networks

    They are created by physically connecting clients for the time that messages will be transmitted. What does this look like in practice? In such cases, a direct connection is created to send and receive information from point A to point B. It includes the channels of one of many (usually) message delivery options. And the created connection for successful transfer must remain unchanged throughout the session. But in this case, quite strong disadvantages appear. So, you have to wait a relatively long time for a connection. This is accompanied by high data transmission costs and low channel utilization. Therefore, the use of network technologies of this type is not common.

    Message Switching Networks

    In this case, all information is transmitted in small portions. A direct connection is not established in such cases. Data transmission is carried out over the first free available channel. And so on until the message is transmitted to its recipient. At the same time, servers are constantly engaged in receiving information, collecting it, checking it and establishing a route. And then the message is passed on. Among the advantages, it is necessary to note the low cost of transmission. But in this case, there are still problems such as low speed and the impossibility of dialogue between computers in real time.

    Packet switching networks

    This is the most advanced and popular method today. The development of network technologies has led to the fact that information is now exchanged through short information packets of a fixed structure. What are they? Packets are parts of messages that meet a certain standard. Their short length helps prevent network blocking. Thanks to this, the queue at the switching nodes is reduced. Connections are fast, error rates are kept low, and significant gains are made in terms of network reliability and efficiency. It should also be noted that there are different configurations of this approach to construction. So, if a network provides switching of messages, packets and channels, then it is called integral, that is, it can be decomposed. Some of the resources can be used exclusively. Thus, some channels can be used to transmit direct messages. They are created for the duration of data transfer between different networks. When the session for sending information ends, they break up into independent trunk channels. When using packet technology, it is important to configure and coordinate a large number of clients, communication lines, servers and a number of other devices. Establishing rules known as protocols helps with this. They are part of the network operating system used and are implemented at the hardware and software levels.

    Network technology is a coordinated set of standard protocols and software and hardware that implement them, sufficient for building computer networks.

    Protocol is a set of rules and agreements that determine how devices exchange data on a network.

    Currently, the following network technologies dominate: Ethernet, Token Ring, FDDI, ATM.

    Ethernet technology

    Ethernet technology was created by XEROX in 1973. The basic principle underlying Ethernet is a random method of access to a shared data transmission medium (multiple access method).

    The logical topology of an Ethernet network is always bus, so data is transmitted to all network nodes. Each node sees each transmission and distinguishes the data intended for it by the address of its network adapter. At any given time, only one node can carry out a successful transmission, so there must be some kind of agreement between the nodes on how they can use the same cable together so as not to interfere with each other. This agreement defines the Ethernet standard.

    As the network load increases, the need to transmit data at the same time becomes increasingly necessary. When this happens, the two transmissions come into conflict, filling the bus with information garbage. This behavior is known under the term “collision,” that is, the occurrence of a conflict.

    Each transmitting system, upon detecting a collision, immediately stops sending data and action is taken to correct the situation.

    Although most collisions that occur on a typical Ethernet network are resolved within microseconds and are natural and expected, the main disadvantage is that the more traffic on the network, the more collisions there are, the more the network performance drops sharply and collapse may occur. that is, the network is clogged with traffic.

    Traffic– flow of messages in a data network.

    Token Ring Technology

    Token Ring technology was developed by IBM in 1984. Token Ring technology uses a completely different access method. The Token Ring logical network has a ring topology. A special message, known as a Token, is a special three-byte packet that constantly circulates around the logical ring in one direction. When a token passes through a node ready to send data to the network, it grabs the token, attaches the data to be sent to it, and then passes the message back to the ring. The message continues its “journey” around the ring until it reaches its destination. Until the message is received, no node will be able to forward data. This access method is known as token passing. It eliminates collisions and random latency periods like Ethernet.


    FDDI technology

    FDDI (Fiber Distributed Data Interface) technology – fiber optic distributed data interface – is the first local network technology in which the data transmission medium is fiber optic cable. FDDI technology is largely based on Token Ring technology, developing and improving its basic ideas. The FDDI network is built on the basis of two fiber optic rings, which form the main and backup data transmission paths between network nodes. Having two rings is the primary way to increase fault tolerance in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings.

    In normal network operation mode, data passes through all nodes and all cable sections of the primary ring only; the secondary ring is not used in this mode. In the event of some type of failure where part of the primary ring cannot transmit data (for example, a broken cable or node failure), the primary ring is combined with the secondary ring, again forming a single ring.

    Rings in FDDI networks are considered as a common data transmission medium, therefore a special access method is defined for it, very close to the access method of Token Ring networks. The difference is that the token retention time in the FDDI network is not a constant value, as in Token Ring. It depends on the load on the ring - with a light load it increases, and with large congestions it can decrease to zero for asynchronous traffic. For synchronous traffic, the token holding time remains a fixed value.

    ATM technology

    ATM (Asynchronous Transfer Mode) is the most modern network technology. It is designed to transmit voice, data and video using a high-speed, connection-oriented cell switching protocol.

    Unlike other technologies, ATM traffic is divided into 53-byte cells (cells). Using a predefined size data structure makes network traffic more easily quantifiable, predictable, and manageable. ATM is based on transmitting information over a fiber optic cable using a star topology.

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