Network technology is a consistent set of standard protocols and software and hardware that implement them (for example, network adapters, drivers, cables and connectors), sufficient to build computer network. The epithet “sufficient” emphasizes the fact that this set represents the minimum set of tools with which you can build a working network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to standard Ethernet protocols, the use of the IP protocol, as well as special communication devices - routers. The improved network will most likely be more reliable and faster, but at the expense of add-ons to the Ethernet technology that formed the basis of the network.

The term “network technology” is most often used in the narrow sense described above, but sometimes its expanded interpretation is also used as any set of tools and rules for building a network, for example, “end-to-end routing technology,” “secure channel technology,” “IP technology.” networks."

The protocols on which a network of a certain technology is built (in the narrow sense) were specifically developed for joint work, so the network developer does not require additional efforts to organize their interaction. Sometimes network technologies are called basic technologies, bearing in mind that the basis of any network is built on their basis. Examples of basic network technologies Along with Ethernet, such well-known local network technologies as Token Ring and FDDI, or X.25 territorial network technologies and frame relay can serve. To obtain a functional network in this case, it is enough to purchase software and hardware related to the same basic technology - network adapters with drivers, hubs, switches, cable system, etc. - and connect them in accordance with the requirements of the standard for this technology.

Creation of standard local network technologies

In the mid-80s, the situation in local networks began to change dramatically. Standard technologies for connecting computers into a network have been established - Ethernet, Arcnet, Token Ring. Personal computers served as a powerful stimulus for their development. These commodity products were ideal elements for building networks - on the one hand, they were powerful enough to run networking software, but on the other hand, they clearly needed to pool their computing power to solve complex problems, as well as share expensive peripheral devices and disk arrays. Therefore, personal computers began to predominate in local networks, not only as client computers, but also as data storage and processing centers, that is, network servers, displacing minicomputers and mainframes from these familiar roles.

Standard network technologies have transformed the building process local network from art to routine work. To create a network, it was enough to purchase network adapters of the appropriate standard, for example Ethernet, a standard cable, connect the adapters to the cable with standard connectors and install one of the popular network operating systems on the computer, for example, NetWare. After this, the network began to work and connecting each new computer did not cause any problems - naturally, if a network adapter of the same technology was installed on it.

Local networks, in comparison with global networks, have introduced a lot of new things into the way users organize their work. Access to shared resources became much more convenient - the user could simply view lists of available resources, rather than remember their identifiers or names. After connecting to a remote resource, it was possible to work with it using commands already familiar to the user from working with local resources. The consequence and at the same time the driving force of this progress was the emergence of a huge number of non-professional users who did not need to learn special (and quite complex) commands for network work. And local network developers got the opportunity to implement all these conveniences as a result of the emergence of high-quality cable communication lines, on which even first-generation network adapters provided data transfer rates of up to 10 Mbit/s.

Of course, the developers of global networks could not even dream of such speeds - they had to use the communication channels that were available, since laying new cable systems for computer networks thousands of kilometers long would require colossal capital investments. And “at hand” there were only telephone communication channels, poorly suited for high-speed transmission of discrete data - a speed of 1200 bps was a good achievement for them. Therefore, economical use of communication channel bandwidth has often been the main criterion for the effectiveness of data transmission methods in global networks. Under these conditions, various procedures for transparent access to remote resources, standard for local networks, for global networks have long remained an unaffordable luxury.

Modern tendencies

Today, computer networks continue to develop, and quite quickly. The gap between local and global networks is constantly narrowing, largely due to the emergence of high-speed territorial communication channels that are not inferior in quality to local network cable systems. In global networks, resource access services appear that are as convenient and transparent as local network services. Similar examples are demonstrated in large numbers by the most popular global network - the Internet.

Local networks are also changing. Instead of a passive cable connecting computers, a variety of communication equipment appeared in them in large quantities - switches, routers, gateways. Thanks to this equipment, it became possible to build large corporate networks, numbering thousands of computers and having a complex structure. There has been a resurgence of interest in large computers, largely because, after the euphoria over the ease of operation had subsided. personal computers It turned out that systems consisting of hundreds of servers are more difficult to maintain than several large computers. Therefore, in a new round of the evolutionary spiral, mainframes began to return to corporate computing systems, but as full-fledged network nodes supporting Ethernet or Token Ring, as well as the TCP/IP protocol stack, which, thanks to the Internet, became a de facto network standard.

Another very important trend has emerged, affecting equally both local and global networks. They began to process information previously unusual for computer networks - voice, video images, drawings. This required changes to the operation of protocols, network operating systems and communications equipment. The difficulty of transmitting such multimedia information over a network is associated with its sensitivity to delays in the transmission of data packets - delays usually lead to distortion of such information at the end nodes of the network. Since traditional networking services such as file transfer or e-mail generate latency-insensitive traffic, and all network elements were designed with latency in mind, the advent of real-time traffic has created major problems.

Today, these problems are solved in various ways, including with the help of ATM technology specially designed for the transmission of various types of traffic. However, despite significant efforts being made in this direction, an acceptable solution to the problem is still far away, and much remains to be done in this area in order to achieve the cherished goal - the merging of technologies not only of local and global networks, but also the technologies of any information networks - computer, telephone, television, etc. Although today this idea seems like a utopia to many, serious experts believe that the prerequisites for such a synthesis are already exist, and their opinions differ only in assessing the approximate terms of such a merger - the terms are called from 10 to 25 years. Moreover, it is believed that the basis for unification will be the packet switching technology used today in computer networks, and not the circuit switching technology used in telephony, which should probably increase interest in networks of this type.

Topic 4 NETWORK TECHNOLOGIES TO SUPPORT SOLUTION OF MANAGERIAL PROBLEMS AT ENTERPRISES

Any enterprise is a collection of interacting elements (divisions), each of which can have its own structure. The elements are interconnected functionally, i.e. they perform certain types of work within the framework of a single business process, as well as information, exchanging documents, fax messages, written and oral orders. In addition, these elements interact with external systems, and their interaction can be both informational and functional. Thus, in the process of functioning of various enterprises, a very complex multi-level system is involved with developed connections not only between the hierarchical levels of the enterprises themselves, but also with the credit system, the state tax service system, clients, partners and other business participants.

The complexity of this system is aggravated by the fact that it is deployed over large territories, covering a large number of participants belonging to various departments, which affects the peculiarities of their information interaction.

In such conditions, the priority tasks are: organizing effective interaction of all business participants through the use of computing and telecommunications tools that form a network technology for information processing in enterprises and organizations.

Network technology- a set of software, hardware and organizational tools that provide communication and distribution of computing resources of PCs connected to the network.

Network technology is effective tool business, as it provides managers with the necessary service for collective solution of assigned tasks, significantly increases the degree and order of use of resources available on the network, provides them with remote access, allows you to organize a single information space for all participants in business processes.

In terms of creating a single information space The organization of network technology is focused on the following areas:

Integration of various hardware and software systems of all business participants. At the initial stage of development of the data transmission system, the problem of information interaction was solved by connecting individual user terminals to information servers with data transmission over dial-up or dedicated channels and telephone lines. Today there is a need to connect local computer networks of business participants remote from each other through high-speed communication channels.

Creation of an electronic document management subsystem, which includes not only the transfer of electronic documents from one user to another, but also the automation of their processing (accounting, storage, technology for collective development of documents, etc.) and the creation of a convenient graphical environment.

Use of high-performance technical and software, application development based on the introduction of modern client-server technology.

Ensuring data security during the processing and transmission of information in the process of implementing business tasks.

Modern network technologies continue those that emerged in the late 1970s. trend towards the development of distributed data processing. The initial stage in the development of such information processing methods were multi-machine systems, which were a collection of computers of varying performance, integrated into the system using communication channels. The highest stage of distributed data processing technologies has become computer networks of various levels - local and large-scale, which were the basis for organizing network technology to support the solution of management problems in enterprises and organizations.

IN general view A computer network is a system of interconnected and distributed PCs focused on the collective use of hardware, software and information network resources.

Network information resources They are databases of general and individual use, focused on problems solved on the network.

Network hardware resources consists of computers of various types, means of territorial communication systems, communication equipment and coordination of the operation of networks of the same level or different levels.

Network software resources are a set of programs for planning, organizing and implementing collective user access to network-wide resources, automating information processing processes, dynamic distribution and redistribution of network-wide resources in order to increase the efficiency and reliability of meeting user requests.

Purpose of computer networks:

Provide reliable and fast access users to network resources and organize collective exploitation of these resources;

Ensure the ability to quickly move information over any distance in order to obtain timely data for making management decisions.

Computer networks allow you to automate the management of individual organizations, enterprises, and regions. The ability to concentrate large amounts of information in computer networks, the general availability of this data, as well as software and hardware processing tools, and high reliability of operation - all this makes it possible to improve information services to users and dramatically increase the efficiency of using computer technology.

The use of computer networks provides the following opportunities:

Organize parallel data processing by several PCs;

Create distributed databases data located in the memory of various computers;

Specialize individual computers to effectively solve certain classes of problems;

Automate the exchange of information and programs between individual computers and network users;

Reserve computing power and means of data transmission in case of failure of individual network resources in order to quick recovery normal network operation;

Redistribute computing power between network users depending on changes in their needs and the complexity of the tasks being solved;

Combine work in different modes: interactive, batch “request-response” mode, mode of collecting, transmitting and exchanging information.

Thus, it can be noted that a feature of the use of computer networks is not only the approach of hardware directly to the places where information originates and is used, but also the division of processing and control functions into separate components for the purpose of their effective distribution between several personal computers, as well as ensuring reliable user access to computing and information resources and organization of collective exploitation of these resources. At the same time, certain requirements are imposed on computer networks:

1. Performance computer network is assessed from different positions:

Computer network response time, which refers to the time between the moment the request occurs and the moment the response is received. The response time depends on many factors, such as the services used and the degree of congestion of the network or its individual segments, etc.

Network bandwidth determined by the amount of information transmitted through a network or its segment per unit of time. Network throughput characterizes how quickly a computer network can transfer information.

LAN segment- a) a group of devices (for example, PCs, servers, printers, etc.) that are connected using network equipment; 6) a section of a LAN separated from other sections by a repeater, hub, bridge or router. All stations on a segment support the same media access protocol and share its total throughput.

2. Reliability The operation of a computer network is determined by its following characteristics:

- fault tolerance all its components. To increase the reliability of hardware operation, duplication is usually used, when if one of the elements fails, the others will ensure the functioning of the network;

Ensuring the safety of information and protecting it from distortion;

Data security, which is ensured by the protection of information from unauthorized access, implemented through the use of specialized software and hardware.

3. Controllability- this is the ability to monitor the state of computer network nodes, identify and resolve problems that arise during its operation, analyze and plan the operation of the network.

4. Extensibility characterizes the possibility of adding new connections and nodes to a computer network, the possibility of its physical expansion without a significant decrease in performance.

5. Transparency computer network involves hiding the features of the network from the end user in such a way that a specialist can access network resources as ordinary local resources of the personal computer on which he works.

6. Integrability means the ability to connect different types of equipment and software from different manufacturers to a computer network.

As practice shows, by expanding data processing capabilities, best download resources and increasing the reliability of IT operation in general, the cost of processing information in computer networks is no less than one and a half times lower compared to processing similar data on autonomous (local) personal computers.

Currently, three main types of computer networks are most widespread - local, corporate, and global.

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 provided with 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 provides reliable information transfer 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.

An ideal option for a corporate network would be to create communication channels only in those areas where it is necessary, and transmit any network protocols, which 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 you need to increase the number of simultaneously available resources, you have to install additional phone numbers. 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 disconnect 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 service integration). ISDN provides digital circuits (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 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 just have to 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 capabilities, 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, email cc:Mail and MS 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 the transfer various protocols local networks (IP, IPX, etc.) 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 transfer of information between almost 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 global X.25 networks in the world common use, 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 virtually 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 associated 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 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 not be 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 channels on the same lines as Inernet 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 one is comparatively new opportunity is becoming increasingly popular and is often the main argument in favor of choosing Frame Relay as the backbone of a corporate 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, there was a clear trend 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 administrators information systems 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 selectively increasing bandwidth in places where congestion occurs while fully preserving the possibility of further expansion of bandwidth 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 in 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 over 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. If you just compare the numbers, these values ​​are less than for Gigabit Ethernet, but ATM uses alternative methods bandwidth allocation; By setting one or another level of quality of service (Quality of Service, QoS), you can guarantee the provision of the bandwidth necessary for the operation of the application. The traffic management 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 technical solution, able to meet future needs, so many users often choose ATM more for its future than today's relevance. ATM standards unify access, switching and information transfer procedures various types(data, voice, video, etc.) in one communication network with the ability to work 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 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 this 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. Both X.25 and Frame Relay or ATM can be used as a virtual network when building a corporate information system. 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, over the same network it is possible telephone communications between nodes. For Frame Relay it is better to use digital channels communications, however, even on physical lines or voice-frequency channels, you can create a completely 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

The history of the emergence of computer networks is directly related to the development of computer technology. The first powerful computers (the so-called Mainframes) occupied rooms and entire buildings. The procedure for preparing and processing data was very complex and time-consuming. Users prepared punch cards containing data and program commands and transmitted them to the computer center. Operators entered these cards into a computer, and users usually received printed results only the next day. This method of network interaction assumed completely centralized processing and storage.

Mainframe- a high-performance general-purpose computer with a significant amount of RAM and external memory, designed to perform intensive computing work. Typically, many users work with the mainframe, each of whom has only terminal devoid of its own computing power.

Terminal(from Latin terminalis - related to the end)

Computer terminal- input/output device, workplace on multi-user computers, monitor with keyboard. Examples of terminal devices: console, terminal server, thin client, terminal emulator, telnet.

Host(from the English host - host who receives guests) - any device that provides services in the “client-server” format in server mode over any interfaces and is uniquely defined on these interfaces. In a more particular case, a host can be understood as any computer, server connected to a local or global network.

Computer network (computer network, data network) - a communication system for computers and/or computer equipment (servers, routers and other equipment). To transmit information, various physical phenomena can be used, usually various types of electrical signals or electromagnetic radiation.

An interactive mode of operation would be more convenient and efficient for users, in which they can quickly manage the processing of their data from the terminal. But the interests of users were largely neglected in the early stages of the development of computing systems, because batch mode- this is the most efficient mode for using computing power, since it allows you to perform more user tasks per unit of time than any other modes. Fortunately, the evolutionary processes cannot be stopped, and in the 60s the first interactive multi-terminal systems began to develop. Each user received a terminal at his disposal, with the help of which he could conduct a dialogue with the computer. And, although computing power was centralized, data input and output functions became distributed. This interaction model is often called "terminal-host" . The central computer must be controlled operating system, supporting such interaction, which is called centralized computing. Moreover, the terminals could be located not only on the territory of the computer center, but also be dispersed over a large territory of the enterprise. In fact, this was the prototype of the first local area networks (LAN). Although such a machine fully provides data storage and computing capabilities, connecting remote terminals to it is not network interaction, since the terminals, being, in fact, peripheral devices, provide only transformation of the form of information, but not its processing.

Figure 1. Multi terminal system

Local area network (LAN), (local area network, slang local area; English Local AreaNetwork, LAN ) - a computer network that usually covers a relatively small area or a small group of buildings (home, office, company, institute)

Computer (English computer - “calculator”),computer (electronic computer)- a computer for transmitting, storing and processing information.

The term “computer” and the abbreviation “EVM” (electronic computer), adopted in the USSR, are synonymous. However, after the appearance personal computers, The term "computer" was practically forced out of everyday use.

Personal computer, PC (English personal computer,PC ), personal computer a computer intended for personal use, the price, size and capabilities of which satisfy the needs of a large number of people. Created as a computing machine, the computer, however, is increasingly used as a tool for accessing computer networks. .

In 1969, the US Department of Defense decided that in case of war, America needed a reliable information transmission system. The Advanced Research Projects Agency (ARPA) proposed developing a computer network for this purpose. The development of such a network was entrusted to the University of California at Los Angeles, the Stanford Research Center, the University of Utah and the University of California at Santa Barbara. The first test of the technology occurred on October 29, 1969. The network consisted of two terminals, the first of which was located at the University of California, and the second, 600 km away, at Stanford University.

The computer network was called ARPANET; within the framework of the project, the network united four specified scientific institutions, all work was funded by the US Department of Defense. Then the ARPANET network began to actively grow and develop, scientists from different fields of science began to use it.

In the early 70s, a technological breakthrough occurred in the production of computer components - large integrated circuits (LSI) appeared. Their relatively low cost and high functionality have led to the creation of mini- computer (electronic computers), which became real competitors of mainframes. Mini-computer, or mini- computers (not to be confused with modern mini-computers), performed tasks of managing technological equipment, warehouses and other tasks at the enterprise department level. Thus, the concept of distributing computer resources throughout the enterprise emerged. However, all computers of one organization continued to work autonomously.

Figure 2. Autonomous use of several mini-computers in one enterprise

It was during this period, when users gained access to full-fledged computers, that the solution to combining individual computers to exchange data with other nearby computers was ripe. In each individual case this problem was solved in its own way. As a result, the first local computer networks appeared.

Since the creative process was spontaneous, and there was no single solution for connecting two or more computers, there was no question of any network standards.

Meanwhile, the first foreign organizations from Great Britain and Norway were connected to the ARPANET network in 1973, and the network became international. In parallel with ARPANET, other networks of universities and enterprises began to appear and develop.

In 1980, it was proposed to link the ARPANET and CSnet (Computer Science Research Network) together through a gateway using TCP/IP protocols so that all subsets of the CSnet networks would have access to a gateway on the ARPANET. This event led to agreement on the method of internetwork communication between a community of independent computer networks, can be considered the appearance Internet in its modern understanding.

Figure 3. Options for connecting a PC to the first LAN

In the mid-80s, the situation in local networks began to change. Standard technologies for connecting computers into a network have been established - Ethernet, Arcnet, Token Ring, Token Bus, a little later - FDDI. A powerful stimulus for their development was personal computers. These devices have become an ideal solution for creating a LAN. On the one hand, they had sufficient power to process individual tasks, and at the same time, they clearly needed to combine their computing power to solve complex problems.

All standard LAN technologies were based on the same switching principle, which was successfully tested and proved its advantages in transmitting data traffic in global computer networks - packet switching principle .

Internet (pronounced [internet]; English Internet, abbreviated from Interconnected Networks -interconnected networks; slang. no, no) - global telecommunications network of information and computing resources. Serves as a physical basis for World Wide Web Wide WEB) . Often referred to as World Wide Web, Global Network, or just Net.

Standard network technologies have made the task of building a local network almost trivial. To create a network, it was enough to purchase network adapters of the appropriate standard, for example Ethernet , standard cable, connect the adapters to the cable with standard connectors and install one of the popular network operating systems on the computer, for example Novell NetWare. After this, the network began to work, and the subsequent connection of each new computer did not cause any problems - naturally, if it had network adapter the same technology.

Figure 4. Connecting several computers using a “common bus” scheme.

Network card , also known asnetwork card, network adapter, Ethernet adapter, NIC (English networkinterface controller) - a peripheral device that allows the computer to interact with other devices on the network.

Operating system, OS (English operatingsystem) - a basic set of computer programs that provide a user interface, control of computer hardware, work with files, input and output of data, and execution of application programs and utilities.

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

On this moment This is the most popular network technology around 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 Technology, which is due to low cost, high speed and quality of communication. The most famous type is IEEE802.3/Ethernet. But based on it, two very interesting options. 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. Under construction this technology 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. Maximum length rings 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 the main and backup paths data transmission. 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 be 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 transfer is carried out using the first available available channels. 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 should be noted low price transfers. 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 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. Using batch 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.