Network technologies. The concept of network technologies, their role in management processes at enterprises
Network technologies
Network technology is an agreed set of standard protocols and software and hardware that implement them, sufficient for building computer networks.
Protocol- ϶ᴛᴏ a set of rules and conventions that governs how devices communicate on a network.
The following network technologies dominate today: Ethernet, Token Ring, FDDI, ATM.
Ethernet technology
Ethernet technology was created by XEROX in 1973. The basic principle underlying Ethernet is a random access method to a shared data transmission medium (multiple access method).
The logical topology of an Ethernet network is always bus-based; therefore, 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 successfully transmit, so there must be some 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, it becomes increasingly important to transfer data at the same time. When this happens, the two transmissions collide, filling the bus with garbage. This behavior is known as ʼʼcollisionʼʼ, that is, the occurrence of a conflict.
Each transmitting system, upon detecting a collision, immediately stops sending data, and action is taken to correct this situation.
While most of the collisions that occur in a typical Ethernet network resolve within microseconds and are natural and expected, the main drawback is that the more traffic on the network, the more collisions, the network performance drops dramatically and a collapse may occur, that is, the network is clogged with traffic.
Traffic– the flow of messages in the 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 ϶ᴛᴏ special three-byte packet that constantly circulates in one direction around the logical ring. When the 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 sends the message back into the ring. The message continues its ʼʼʼʼʼ journey around the ring until it reaches its destination. Until the message is received, no node will be able to send data. This access method is known as token passing. It eliminates collisions and random wait times like Ethernet.
FDDI Technology
FDDI (Fiber Distributed Data Interface) technology is the first LAN technology in which the data transmission medium is fiber optic cable. FDDI technology is largely based on Token Ring technology, developing and improving its main 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 main way to increase fault tolerance in an FDDI network, and nodes that want to take advantage of this increased reliability potential should 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 kind of failure where part of the primary ring is unable to transmit data (for example, a cable break or node failure), the primary ring is combined with the secondary, again forming a single ring.
Rings in FDDI networks are considered as a common data transmission medium, in connection with this, a special access method is defined for it, very close to the access method of Token Ring networks. The difference is essentially that the token retention time in the FDDI network is not a constant value, as in Token Ring. It depends on the load of the ring - with a small load, it increases, and with large congestion, it can decrease to zero for asynchronous traffic. It is important to note that for synchronous traffic, the token hold 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-switched protocol.
Unlike other technologies, ATM traffic is divided into 53-byte cells (cells). The use of a predefined size data structure makes network traffic more easily quantifiable, predictable, and manageable. ATM is built on the transmission of information over fiber optic cable using a star topology.
Network technologies - concept and types. Classification and features of the category "Network technologies" 2017, 2018.
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network technology - this is an agreed set of standard protocols and software and hardware that implements them (for example, network adapters, drivers, cables and connectors), sufficient to build a computer network. The epithet "sufficient" emphasizes the fact that this set is the minimum set of tools with which you can build a workable network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to the Ethernet standard protocols, the use of the IP protocol, as well as special communication devices - routers. The improved network will likely be more reliable and faster, but at the cost of building on 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 extended interpretation is 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 the basis of which a network of a certain technology is built (in the narrow sense) were specially developed for joint work, therefore, the network developer does not require additional efforts to organize their interaction. Network technology is sometimes referred to as basic technologies, bearing in mind that the basis of any network is built on their basis. Along with Ethernet, well-known local area network technologies such as Token Ring and FDDI, or X.25 area network technologies and frame relay, can serve as examples of basic network technologies. To get a working network in this case, it is enough to purchase software and hardware related to one 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 LAN technologies
In the mid-80s, the situation in local networks began to change dramatically. Standard technologies for connecting computers to a network have been established - Ethernet, Arcnet, Token Ring. Personal computers served as a powerful stimulus for their development. These mass-produced products were ideal elements for building networks - on the one hand, they were powerful enough to run networking software, and on the other, they clearly needed to pool their processing power to solve complex problems, as well as separate expensive peripherals 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 turned the process of building a local network from an art into a chore. To create a network, it was enough to purchase network adapters of the appropriate standard, such as Ethernet, a standard cable, connect the adapters to the cable with standard connectors, and install one of the popular network operating systems, such as NetWare, on the computer. After that, the network began to work and the connection of 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 brought a lot of new things to the way of organizing the work of users. Access to shared resources has become much more convenient - the user could simply view the lists of available resources, and not remember their identifiers or names. After connecting to a remote resource, it was possible to work with it using the commands already familiar to the user for working with local resources. The consequence and at the same time the driving force of such progress was the emergence of a huge number of non-professional users who did not need to learn special (and rather complex) commands for networking at all. And the developers of local networks got the opportunity to realize all these conveniences as a result of the appearance of high-quality cable communication lines, on which even network adapters of the first generation provided data transfer rates up to 10 Mbps.
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 the laying of new cable systems for computer networks thousands of kilometers long would require enormous capital investments. And "at hand" were only telephone communication channels, poorly adapted for high-speed transmission of discrete data - a speed of 1200 bps was a good achievement for them. Therefore, the economical use of the bandwidth of communication channels 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, which are standard for local networks, have long remained an unaffordable luxury for global networks.
Modern tendencies
Today, computer networks continue to develop, and quite rapidly. The gap between local and global networks is constantly shrinking, largely due to the emergence of high-speed territorial communication channels that are not inferior in quality to cable systems of local networks. In global networks, resource access services are emerging 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 such equipment, it became possible to build large corporate networks with thousands of computers and a complex structure. There has been a resurgence of interest in large computers, largely because after the euphoria about the ease of use of personal computers subsided, it became clear that systems with hundreds of servers were more difficult to maintain than a few large computers. Therefore, on a new round of the evolutionary spiral, mainframes began to return to corporate computing systems, but already as full-fledged network nodes that support Ethernet or Token Ring, as well as the TCP / IP protocol stack, which has become the de facto network standard thanks to the Internet.
Another very important trend has emerged, affecting equally both local and global networks. They began to process information that was previously unusual for computer networks - voice, video images, drawings. This required changes to protocols, network operating systems, and communications equipment. The complexity of transmitting such multimedia information over a network is related to its sensitivity to delays in the transmission of data packets - delays usually lead to distortion of such information in the end nodes of the network. Since traditional computer network services such as file transfer or e-mail generate latency-insensitive traffic and all network elements are designed with it in mind, the advent of real-time traffic has led to big 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 the significant efforts made in this direction, it is still far from an acceptable solution to the problem, and much remains to be done in this area. in order to achieve the cherished goal - the fusion of technologies not only of local and global networks, but also of technologies of any information networks - computer, telephone, television, etc. Although today this idea seems to many to be a utopia, serious experts believe that the prerequisites for such a synthesis are already exist, and their opinions differ only in the estimation of the approximate terms of such an association - terms are called from 10 to 25 years. Moreover, it is believed that the basis for the 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 this type of networks.
Material from PIE.Wiki
Modern network technologies have contributed to a new technological revolution. In the United States, the creation of a single network of computers is given the same importance as the construction of expressways in the sixties. Therefore, a computer network is called the "information superhighway". Emphasizing the benefits that the network will bring to all users, Microsoft talks about information "at your fingertips."
HIGH-SPEED DATA TRANSFER CHANNELS
High-speed X.25 and ISDN channels can be used for information transfer. ISDN (Integrated Services Digital Network - Integrated Services Digital Network) allows representatives of different countries to organize video conferences and discuss issues of interest to them without expensive business trips. To implement remote access, digital communication adapters and bridges are inserted into computers, and the slowest adapter for ISDN is many times faster than a modem. Special software has been developed that allows Windows 95 and its Internet browser to work with ISDN. It can be found and obtained free of charge from the World Wide Web server at http://www.microsoft.com. Currently, Russia is building a nationwide digital network with access abroad, which will be able to provide ISDN communication services and provide end users with remote access to local networks of their enterprises and interaction with computer networks, including the Internet at a speed of 64 - 128 Kbps. With. Unfortunately, the implementation of ISDN faces a lot of difficulties, as it requires expensive equipment and requires the laying of special lines.
LOCAL NETWORKS
A computer connected to the network is called a workstation (Workstation), a computer that provides its resources - a server, a computer that has access to shared resources - a client. Several computers located in the same room or functionally performing the same type of work: accounting or planned accounting, registration of incoming products, etc., are connected to each other and combined into a working group so that they can share various resources: programs, documents , printers, fax, etc. The working group is organized so that the computers included in it contain all the resources necessary for normal work. As a rule, a workgroup of more than 10 - 15 computers includes a dedicated server - a fairly powerful computer that hosts all shared directories and special software to control access to the entire network or part of it. Server groups are grouped into domains. A domain user can log on to the network at any workstation in this domain and gain access to all its resources. Typically, in server networks, all shared printers are connected to print servers. From the point of view of organizing the interaction of computers, networks are divided into peer-to-peer (Peer-to-Peer Network) and with a dedicated server (Dedicated Server Network). In a peer-to-peer network, each computer plays an equal role. However, the increase in the number of computers on the network and the growth in the amount of data being transferred leads to the fact that the network bandwidth becomes a bottleneck. Windows 95 is designed primarily to work in peer-to-peer networks, to support the operation of the computer as a client of other networks. Windows 95, like Windows for Workgroups, can act as a server on a network. Ensured compatibility with older MS-DOS and Windows 3.x network drivers. The new operating system allows you to: share hard drives, printers, fax boards, organize peer-to-peer local area networks (LANs); use remote access and turn an office computer into a called server; support 16-bit DOS network drivers. The network administrator can set the overall design of the desktop system, determine what operations will be available to network users, and control the configuration of the desktop system. A network located in a relatively small area is called a local (LAN - Local Area Network). In recent years, there has been a complication of the LAN structure due to the creation of heterogeneous networks that combine different computer platforms. The possibility of video conferencing and the use of multimedia increase the requirements for network software. Modern servers can store binary large objects (BLOBs) containing text, graphics, audio, and video files. In particular, if you need to get a personnel department database over the network, then BLOB technology will allow you to transfer not only personal data: last name, first name, patronymic, year of birth, but also portraits in digital form. Two technologies for using a server There are two technologies for using a server: the file server technology and the client-server architecture. The first model uses a file server that stores most programs and data. At the request of the user, the necessary program and data are sent to him. Information processing is performed at the workstation. In systems with a client-server architecture, data is exchanged between the client application (front-end) and the server application (back-end). Data is stored and processed on a powerful server that also controls access to resources and data. The workstation receives only the results of the query. Developers of information processing applications typically use this technology. The use of large and complex applications has led to the development of a multi-level, primarily a three-level architecture with data hosted on a separate database server (DB). All calls to the database go through the application server, where they are combined. Reducing the number of database calls reduces the license fees for the DBMS. Desktop management interface (DMI) To simplify the installation, security, and administration of networks using a unified set of APIs and remote management tools, Microsoft, IBM, Novell, DEC, HP, Sun, and Synoptics have developed the Desktop Management Interface (DMI) standard. direct interaction interface). The standard provides for the possibility of remote updating of programs recorded in ROM, management of groups and individual clients. The introduction of the standard will reduce the cost of operating local networks by reducing staff and increasing the efficiency of its work.
GLOBAL NETWORKS
A local area network may be part of a global network that is gaining more and more acceptance around the world. The development of mass media and communications contributes to the unification of people living on different continents, according to their interests. Currently, industrialized countries pay great attention to the creation of a unified information environment. The creation of an information superhighway will make it easier in the future to communicate with people who have common interests but are located in different parts of the globe. The prototype of such a superhighway is the Internet, which provides services to millions of users around the world.
TECHNOLOGIES USED IN INTERNET AND INTRANET
Currently, one of the priority areas of work for companies supplying software is the integration of the local network of the enterprise intranet (Intranet), in which the main work of the company takes place, into the global network so that employees of this enterprise can easily create their documents in HTML format ( HyperText Markup Language) and link to other documents. The organization of virtual corporate networks based on the Internet allows you to link together all the branches of suppliers and customers without creating your own network infrastructure. The integration of the corporate Intranet and the global network is based on the use of the same type of methods for storing and presenting information. The computer file system is built on a hierarchical principle, providing for a tree-like data storage structure. Internet Web servers have a hypertext data representation scheme that provides for the creation of links in documents to other documents that contain explanations of various terms, illustrations, audio files, and videos. The standard for constructing such documents is defined by HTML. Software for text-to-speech technology is being developed - translating text into a voice message. In recent years, Microsoft has proposed a number of new technical solutions that provide a user experience on the Internet. Together with Intel Corporation, Microsoft is developing a new protocol that improves the way audio and video information is transmitted over the Internet. A protocol based on ITL and Internet Engineering Task Force (IETF) specifications will include the following protocols: T.120 for document conferencing, H.323 for audio and video conferencing, RTP/RTCP and RSVP for Internet teleconferencing control. It should be noted that a number of telephone companies of the Bell group (RBOC) filed a protest with the Federal Telecommunications Commission (FCC) against the use of audio technologies on the Internet.
Internet value.
It has become customary that in the field of information technology, the innovation process is taking place at an unprecedented pace. “If since 1971 the automotive industry had developed as rapidly as microprocessor technology, then the car of today would have already raced at a speed of 480 thousand km / h and at the same time consumed 1 liter of fuel per 335 thousand km of run” - so figuratively compared the pace of scientific and technological progress in the two leading industries in the United States specialists from Intel, the world leader in the field of microelectronics. To complete the picture, we can add that this car would cost only 75 cents! Against this background, the pace at which the transnational Internet network is being formed over the past three years is noticeable. Specialized publications have already called it the "Network of Networks", and the popular business magazine "Business Week" has defined the near future as the "Internet era". The Internet opens up a new way of human communication, which can be called horizontal. Before its appearance, there was communication and dissemination of information. Basically, vertical: the author writes a book - readers read it. Radio and television transmit something - viewers and listeners listen and watch it. Newspaper prints news - subscribers read them. Feedback was almost non-existent, although the need for it was exceptionally high. This is evidenced by letters to newspapers, applications and responses to radio and television stations, etc. The exchange of information between the readers of a particular book, the listeners of a particular program, was practically impossible. The Internet ensures the dissemination of information for a practically unlimited range of consumers, and they can easily join the discussion without any difficulty. The Internet provides unique opportunities for vertical information communication: between the authorities and citizens, for feedback from the latter to the former. There is no organization behind the widespread introduction of the Internet into our lives, the World Wide Web as a phenomenon develops independently, the engine of the Internet is all of humanity. The main idea of the Internet is the free dissemination of information and the establishment of connections between people. This is the most effective way to overcome racial, religious, and ideological barriers between people, countries, peoples. The Internet is one of the most significant democratic technological advances. With its appearance, information becomes a potential property of the majority of the inhabitants of the planet. All global communications related to the telegraph, telephone, radio, television and computer technology are now being integrated into a single whole - the Internet. We are talking about a mechanism for disseminating information, bringing people together and their interaction, regardless of distance, time, state and many other boundaries.
History of the Internet in Russia
The history of the Russian Internet is counted from the beginning of the 80s, when the Kurchatov Institute was the first in our country to gain access to the world's networks. The Internet in Russia, as well as throughout the world, is increasingly becoming an element of the life of society, of course, becoming more and more like this society. Now the Internet can be accessed from 300-400 thousand computers in Russia and the CIS, and their number is constantly growing. Under favorable conditions, the Russian audience may be much larger, for example, the German one. Most varieties of Internet services are already represented in Russia. Some (news services, for example) have already been mastered and are almost as good as American ones. The most honored Web-servers of Russia already boast several hundred thousand regular readers. This is not bad compared, for example, with business paper press. And if we compare the qualitative indicators of the Internet audience and the TV audience, then in many cases preference can be given to the first. The Russian audience of the Internet, except for the number and absolute level of income, practically does not differ from the American one in other parameters. Typical users of Web services belong to a socially and economically active segment of the population, tend to seek new opportunities for personal and business development, and are generally positive about the ongoing reforms in Russia. In its development, the Russian Internet, in general, repeats the stages of development of the global network. Over the past two years, we have made the leap to almost 2500 new servers. Go to Yahoo, one of the most popular directories on the Internet. In the regions (countries) section, there is a number in front of each item - this is the number of links. And you will see what the Russian section looks like. The growth rate is close to the best in the world, although it is constrained to some extent by communication problems and the relative high cost of graphics in domestic Internet networks. If we talk about the level of information content of the Russian Internet, then, of course, it could be much higher. The Internet is the visiting card of the country. The Russian Internet should unite all Russian-speaking users, be the guardian and distributor of our culture and our language. It is necessary to improve the comfort of the information space in which we live as one of the components of the general level of human life. The main problems of Russian users can be attributed in the first place: a. the lack of a single standard (which, apparently, will never be until Russia becomes the world's leading power in the field of computer technology) for Cyrillic character encoding, which leads to program incompatibility. As a result, those who distribute textual information in Russian on the Internet must present it in several encodings, usually three or four, for the main operating systems: MS Windows, UNIX (KOI-8, OS/2, MacOS), which means an increase in labor costs for the preparation of documents. Otherwise, the user, even having access to the information, will not be able to use it. b. lack of developed telecommunication systems in Russia and poor quality of telecommunication services. The cost of Internet access via dial-up telephone lines at a speed of 14400-28800 bps in Moscow averages 3-5 dollars per hour. In the USA - 1 dollar per hour or less (with incomparable quality). A high-speed and high-quality connection that allows a Russian user to use the full potential of the Internet will cost dozens, and sometimes hundreds of times more than his American counterpart.
Application operation on the Internet
Applications that run on the Internet are built on top of Java technology, which includes the Java programming language, the Java virtual machine, and Web browsers that run Java applications. The Java language is best suited for working with HTML pages. It allows you to go beyond simply browsing Web pages, and makes it possible to organize the interaction of interactive programs with the user. The Java technology extension Java DataBase Connectivity (JDBC) for intranets allows a Java application to access a server directly, which may be located on a local area network. The concept of Cascade Style Sheets (CSS) has been developed, which defines the styles used in the development of HTML pages, their parts and individual elements. It can be found at http//www.w3org/pub/WWW/TR/WD-style. ActiveX ActiveX technology is the next step in the development of OLE, designed to create interactive applications for the Internet and intranets. It supports Java applications and OLE components. ActiveX is based on COM (Component Object Model) and allows page administrators to use sound and video effects when designing documents. ActiveX controls provide Windows applications with Web interaction features. The Distributed Component Object (DCOM) model enables developers to create application components that communicate with each other over the Internet. Plug-in ActiveX is used in Internet Explorer 3.0. Character encoding on the Internet Four encodings are mainly used to encode Cyrillic characters on the Internet: KOI8 (KOI8) - used mainly on computers running UNIX, but not supported by Windows. To solve this problem, it is recommended to install additional KOI fonts and special keyboard drivers like Cyrwin. CP-1251 - used by Microsoft on Windows, widely used on PC IBM-compatible computers. СР-866 - used mainly on computers with MS-DOS. ISO-8859-5 - Applies to UNIX compatible systems. On most servers, the first two encodings are used. The problem of Cyrillic support on the Internet is explained by the fact that the codes of Russian letters in UNIX and Windows operating systems do not match. Difficulties that arise when encoding on KOI8 are discussed in detail on the WWW page at: http://www.nagural.ru/~ache/koi8.html.
The networking of computers has made it possible to organize document management in a new way both in small firms and in large organizations. There is no need to print documents on paper that a team of users is working on. With the right software, a team of users can collaborate on documents, presentations, and databases and e-mail them to other project members, who may work in the same building or in another city, for additions and editing. Sequential distribution allows you to specify the order in which a message will pass between project participants after it has been added and edited. This method of collective work on a document saves a significant part of the working time, since there is no need to waste time on personal meetings for joint work. A modern enterprise cannot be imagined without data sharing and advanced means of guaranteed information protection. Protocols used by e-mail Among the most popular protocols used on the Internet for receiving e-mail are the Simple Mail Transfer Protocol, SMPT, and the Post Office Protocol, POP. SUPPORT FOR NETWORK OPERATING SYSTEMS Microsoft is committed to making Windows the platform of choice for telecommunications and Internet access. Windows 95 contains a large number of network card drivers and network management tools. The unified user interface is virtually independent of the type of network supported. To work with different networks, it is necessary that the operating system supports their protocols, i.e. a set of rules (computer language) used in the transmission of information. The network protocol defines routing methods, addressing methods, and so on. Windows 95 has native support for common network operating systems: Microsoft's Windows NT Advanced Server, Novell NetWare, LAN Manager, LAN Manager for UNIX, IBM's LANServer, 3Com's 3+Open and 3+Share, Banyan's VINES, Digital's Pathworks The operating system allows you to work as part of a heterogeneous network and provides support for a large part of the 32-bit popular network protocols: TCP / IP, IPX / SPX and NetBEUI and ND1S 2.x, 3.x or ODI drivers TCP / IP protocol (Transmission Control Protocol/Internet Protocol) is used when working with global networks such as the Internet and in Microsoft networks.The IPX protocol allows you to connect to NetWare file servers. Windows 95 includes support for various types of network protocols: PPP (Poinl-to-Point Protocol). Serial Line Internet Protocol, NRN (NetWare Remote Node) and the new network protocol Point-to-Point Tunneling Protocol (PPTP), developed by Microsoft in conjunction with 3Com. The protocol allows you to create virtual private networks (VPN) over dial-up lines and send secure network packets over the Internet. PPTP is used in the organization of the "tunnel" during the communication of remote users with their corporate networks via the Internet. There is no need for enterprises to share their own global network infrastructure in order to avoid information leakage. Guaranteed information protection is provided by well-established and proven means of authentication and encryption built into the Windows NT Remote Access Service. The disadvantage of Windows 95 is that a dial-up server running this operating system establishes only one connection at a time. For better performance and flexibility, it is recommended to use Windows NT as the remote access server, which provides up to 256 concurrent connections and parallel routing.
Today, networks and networking technologies connect people in all parts of the world and provide them with access to the greatest luxury in the world - human communication. People communicate and play without interference with friends located in other parts of the world.
The ongoing events become known in all countries of the world in a matter of seconds. Everyone is able to connect to the Internet and post their portion of information.
Network information technologies: their roots
In the second half of the last century, human civilization formed two of its 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 20th century, as a result of the evolution and interpenetration of these two branches of human knowledge, what we call the term “network technology” has arisen, which is a subsection of the more general concept of “information technology”.
As a result of their appearance in the world, a new technological revolution took place. Just as a few decades before the surface of the earth was covered with a network of high-speed highways, at the end of the last century all countries, cities and villages, enterprises and organizations, as well as individual dwellings were connected by "information highways". At the same time, they all became elements of various data transmission networks between computers, in which certain information transfer technologies were implemented.
Network technology: concept and content
Network technology is sufficient to build some complete 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 FOCL, various connectors (sockets).
The "sufficiency" of this set of tools means its minimization while maintaining the possibility of building a workable 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 referred to as "routers". Once improved, the network becomes more reliable and faster, but at the cost of building on top of the core 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".
The prototype of network technology
The first prototype of a computer network, but not yet the network itself, was in the 60-80s. last century multi-terminal systems. Representing a combination of a monitor and keyboard, located at great distances from large computers and connected to them via telephone modems or dedicated channels, the terminals left the premises of the ITC and were dispersed throughout the building.
At the same time, in addition to the operator of the computer itself at the ITC, all terminal users got the opportunity to enter their tasks from the keyboard and monitor their execution on the monitor, also performing some task management operations. Such systems, which implement both time-sharing algorithms and batch processing, were called remote job entry systems.
global networks
Following multi-terminal systems in the late 60s. 20th century was created and the first type of networks - global computer networks (GCN). They connected supercomputers, which existed in single copies and stored unique data and software, with large computers located at distances up to many thousands of kilometers from them, using telephone networks and modems. This network technology has been previously tested in multi-terminal systems.
The first GKS in 1969 was ARPANET, which worked in the US Department of Defense and combined different types of computers with different operating systems. They were equipped with additional modules for the implementation of communication common to all computers included in the network. It was on it that the foundations of network technologies were developed, which are still used today.
First example of 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 through them at a very low speed (tens of kbps), and the possibilities were limited to the transfer of data files and e-mail.
However, having inherited telephone communication lines, GKS did not take their main technology based on the principle of circuit switching, when each pair of subscribers was allocated a channel with 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 rate are issued to an unswitched network and received by their addressees in the network using address codes embedded in the packet headers.
Predecessors of LANs
Appeared in the late 70s. 20th century LSI has led to the creation of minicomputers with low cost and rich functionality. They began to really compete with mainframe computers.
Minicomputers of the PDP-11 family have gained wide popularity. They began to be installed in everything, even very small production units for managing technical processes and individual technological installations, as well as in departments of enterprise management to perform office tasks.
The concept of computer resources distributed throughout the enterprise emerged, although all minicomputers still worked autonomously.
The advent of LAN networks
By the mid 80s. 20th century technologies were introduced for combining mini-computers into networks based on data packet switching, as in the GCS.
They have made building a single enterprise network, called a LAN, 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 mini-computer and to each other using these cables. Next, one of the operating systems was installed on the computer server, designed to organize a LAN - network. After that, it began to work, and the subsequent connection of each new mini-computer did not cause any problems.
The inevitability of the Internet
If the appearance of minicomputers 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 at every workplace of any knowledge worker, and then in individual human dwellings.
The relative cheapness and high reliability of the PC 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 covered all countries of the world.
The size of the Internet grows by 7-10% every month. It is the core connecting various local and global networks of enterprises and institutions around the world with each other.
If at the first stage, data files and e-mail 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 of many countries. Its archives of free access contain information on almost all areas of knowledge and human activity - from new directions in science to weather forecasts.
Basic network technologies of LAN networks
Among them are the basic technologies on which the basis of any particular network can be built. Examples include well-known LAN technologies such as Ethernet (1980), Token Ring (1985) and FDDI (late 80s).
In the late 90s. Ethernet technology has become a leader in LAN-network technology, combining its classic version with up to 10 Mbps, as well as Fast Ethernet (up to 100 Mbps) and Gigabit Ethernet (up to 1000 Mbps). All Ethernet technologies have similar operating principles that simplify their maintenance and the integration of LAN networks built on their basis.
In the same period, network functions that implement the above network information technologies began to be built into the kernels of almost all computer operating systems by their developers. There were even specialized communication operating systems such as Cisco Systems' IOS.
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 recovering data. An example of them is the X.25 technology developed in the early 70s. 20th century More modern network technologies are frame relay, ISDN, ATM.
ISDN is an acronym that stands for Integrated Services Digital Network and enables remote video conferencing. Remote access is provided by installing ISDN adapters in the PC, 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.
Wide area network technologies have progressed along with telephone networks. After the advent of digital telephony, Plesiochronous Digital Hierarchy (PDH) technology was developed, supporting speeds up to 140 Mbps and used by enterprises to create their own networks.
New technology Synchronous Digital Hierarchy (SDH) in the late 80s. 20th century expanded the bandwidth of digital telephone channels to 10 Gbit/s, and Dense Wave Division Multiplexing (DWDM) technology to hundreds of Gbit/s and even up to several Tbit/s.
Internet technologies
Network based on the use of hypertext language (or HTML-language) - a special markup language, which is an ordered set of attributes (tags) that are pre-embedded by the developers of Internet sites into each of their pages. Of course, in this case we are not talking about text or graphic documents (photos, pictures) that have already been “downloaded” by the user from the Internet, are in the memory of his PC and are viewed through text or We are talking about the so-called web pages viewed through programs -browsers.
Internet site developers create them in HTML (now there are many tools and technologies for this work, collectively called "site layout") in the form of a set of web pages, and site owners place them on Internet servers on a lease from the owners of their memory servers (so-called "hosting"). They work around the clock on the Internet, serving the requests of its users to view the web pages uploaded to them.
User PC browsers, having obtained 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. Further, analyzing the HTML tags of each viewed page, browsers form its image on the monitor screen in the form as it was intended by the site developer - with all headings, font and background colors, various inserts in the form of photos, diagrams, pictures, etc. .
Control course work
on Information systems in the economy on topic No. 69:
"Network technologies Ethernet, Token Ring, FDDI and X.25"
Completed: student gr. 720753 Avdeeva D.M.
Checked by: Associate Professor, Ph.D. Ognyanovich A.V.
Introduction…………………………………………………………………………...3
1. The concept of network technologies………………………………………………...5
2. Ethernet technology………………………………………………………..7
3. Token Ring Technology……………………………………………………...12
4. FDDI technology…………………………………………………………….15
5. Protocol X.25……………………………………………………………….19
Conclusion………………………………………………………………………….22
List of sources and literature…………………………………………………23
Introduction
Computer networks, also called computer networks, or data transmission networks, are the logical result of the evolution of the two most important scientific and technical branches of modern civilization - computer and telecommunication technologies. On the one hand, networks are a special case of distributed computing systems in which a group of computers performs a set of interrelated tasks in a coordinated manner, exchanging data automatically. On the other hand, computer networks can be considered as a means of transmitting information over long distances, for which they use data coding and multiplexing methods that have been developed in various telecommunication systems.
The main LAN technologies remain Ethernet, Token Ring, FDDI, Fast and Gigabit Ethernet, Token Ring and FDDI are functionally much more complex technologies than Ethernet on a shared medium. The developers of these technologies sought to endow the network on a shared environment with many positive qualities: to make the media sharing mechanism predictable and manageable, to ensure network fault tolerance, to organize priority service for delay-sensitive traffic, such as voice. In many ways, their efforts have paid off, and FDDI networks have been successfully used as the backbone of campus networks for quite a long time, especially in cases where it was necessary to ensure high reliability of the backbone.
Token Ring is a prime example of token passing networks. Token-passing networks move a small block of data called a token along the network. Ownership of this token guarantees the right to transfer. If the host receiving the token has no information to send, it simply forwards the token to the next end station. Each station can hold the marker for a certain maximum time.
With faster speeds than Ethernet networks, deterministic distribution of network bandwidth between nodes, and better performance (fault detection and isolation), Token Ring networks have been the preferred choice for performance-sensitive applications such as banking systems and systems enterprise management.
FDDI technology can be considered an improved version of Token Ring, since it, like Token Ring, uses a token transfer-based medium access method, as well as a ring topology of connections, but at the same time, FDDI operates at a higher speed and has more perfect failover mechanism.
In the FDDI standards, much attention is paid to various procedures that allow you to determine the presence of a failure in the network, and then make the necessary reconfiguration. FDDI technology extends the failure detection mechanisms of Token Ring technology with redundant links provided by the second ring.
The relevance of this work is due to the importance of studying the technologies of local computer systems.
The aim of the work is to study the characteristics of the Token Ring, Ethernet, FDDI and X.25 networks.
To achieve this goal, the following tasks were set in the work:
To study the concepts of basic network technologies;
Reveal the specifics of the application of technologies;
Consider the advantages and disadvantages of Ethernet, Token Ring, FDDI and X.25;
Analyze the types of network technologies.
The concept of network technologies
In local networks, as a rule, a shared data transmission medium (monochannel) is used and the main role is assigned to the protocols of the physical and link layers, since these levels reflect the specifics of local networks to the greatest extent.
Network technology is an agreed set of standard protocols and software and hardware that implement them, sufficient to build a local area network. Network technologies are called basic technologies or network architectures of local area networks.
Network technology or architecture determines the topology and method of access to the data transmission medium, the cable system or data transmission medium, the network frame format, the type of signal coding, the transmission rate in the local network. In modern local area networks, technologies or network architectures such as Ethernet, Token Ring, FDDI and X.25 are widely used.
The development of computer networks began with the solution of a simpler problem - access to a computer from terminals many hundreds or even thousands of kilometers away from it. The terminals in this case were connected to the computer via telephone networks using special modem devices. The next stage in the development of computer networks was the connection through a modem, not only "terminal - computer", but also "computer - computer". Computers were able to exchange data automatically, which is the basic mechanism of any computer network. Then for the first time appeared on the network the possibility of exchanging files, synchronizing databases, using e-mail, i.e. those services that are currently traditional network services. Such computer networks are called global computer networks.
In essence, a computer network is a collection of computers and network equipment connected by communication channels. Since computers and network equipment can be from different manufacturers, there is a problem of their compatibility. Without the adoption by all manufacturers of generally accepted rules for constructing equipment, the creation of a computer network would be impossible.
For an ordinary user, a network is a wire or several wires with which a computer is connected to another computer or modem to access the Internet, but in reality everything is not so simple. Let's take the most common wire with an RJ-45 connector (these are used almost everywhere in wired networks) and connect two computers, this connection will use the Ethernet 802.3 protocol, which allows you to transfer data at speeds up to 100 Mbps. This standard, as well as many others, is precisely the standard, that is, one set of instructions is used all over the world and there is no confusion, information is transmitted from the sender to the addressee.
The transmission of information over a cable, as some know, is carried out by a stream of bits, which is nothing more than the absence or reception of a signal. Bits, or zeros and ones, are interpreted by special devices in computers in a convenient form and we see a picture or text on the screen, and possibly even a movie. To manually transfer even a small piece of textual information through computer networks, a person would take a very long time, and calculations would stretch over huge stacks of papers. To prevent this from happening, people came up with all these protocols and means of connecting computers into a single whole.
Ethernet technology
Ethernet is the most widely used local area network standard today. The total number of Ethernet networks currently running is estimated at several million.
When they say Ethernet, it usually means any of the variants of this technology. In a narrower sense, Ethernet is a networking standard based on the experimental Ethernet Network that Xerox developed and implemented in 1975.
The access method was tested even earlier: in the second half of the 60s, the radio network of the University of Hawaii used various options for random access to a common radio environment, collectively called Aloha. In 1980, DEC, Intel, and Xerox jointly developed and published the Ethernet version II standard for a coaxial cable network. This latest version of the proprietary Ethernet standard is called the Ethernet DIX standard, or Ethernet P.
Based on the Ethernet DIX standard, the IEEE 802.3 standard was developed, which is largely the same as its predecessor, but there are still some differences. While the IEEE 802.3 standard separates the protocol functions into MAC and LLC layers, in the original Ethernet standard they are combined into a single link layer. Ethernet DIX defines an Ethernet Configuration Test Protocol that is not present in IEEE 802.3. The frame format is somewhat different, although the minimum and maximum frame sizes in these standards are the same.
Often, in order to distinguish between the Ethernet standard defined by the IEEE and the proprietary Ethernet standard DIX, the former is referred to as 802.3 technology, and the proprietary standard is left with the Ethernet name without additional designations. Depending on the type of physical medium, the IEEE 802.3 standard has various modifications - 10Base-5, 10Base-2, 10Base-T, 10Base-FL, lOBase-FB. In 1995, the Fast Ethernet standard was adopted, which in many ways is not an independent standard, as evidenced by the fact that its description is simply an additional section to the main 802.3 standard - section 802.3b. Similarly, the 1998 Gigabit Ethernet standard is described in section 802.3z of the main document.
The Manchester code is used to transfer binary information over the cable for all variants of the physical layer of Ethernet technology that provide a throughput of 10 Mbps. Faster versions of Ethernet use more bandwidth-efficient redundant logic codes. All kinds of Ethernet standards (including Fast Ethernet and Gigabit Ethernet) use the same media separation method, the CSMA/CD method. Let's consider how the general approaches described above to solving the most important networking problems are embodied in the most popular network technology - Ethernet.
Network technology is an agreed set of standard protocols and software and hardware that implements them (for example, network adapters, drivers, cables and connectors) sufficient to build a computer network. The epithet "sufficient" emphasizes the fact that this set is the minimum set of tools with which you can build a workable network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to the Ethernet standard protocols, the use of the IP protocol, as well as special communication devices - routers. An improved network will likely be more reliable and faster, but at the cost of building on top of the Ethernet technology that forms the basis of the network.
The term "network technology" is most often used in the narrow sense described above, but sometimes its broad interpretation is used as any set of tools and rules for building a network, for example, "end-to-end routing technology", "secure channel technology", "IP networking technology". ". The protocols on the basis of which a network of a certain technology is built (in the narrow sense) were specially developed for joint work, therefore, the network developer does not require additional efforts to organize their interaction. Sometimes network technologies are called basic technologies, meaning that the basis of any network is built on their basis. In addition to Ethernet, well-known local area network technologies such as Token Ring and FDDI, or X.25 area network technologies and frame relay, can serve as examples of basic network technologies. To get a working network in this case, it is enough to purchase software and hardware related to one 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.
The basic principle underlying Ethernet is a random method of accessing a shared data transmission medium. A thick or thin coaxial cable, twisted pair, optical fiber or radio waves can be used as such a medium (by the way, the first network built on the principle of random access to a shared medium was the Aloha radio network of the University of Hawaii). The Ethernet standard strictly fixes the topology of electrical connections. Computers are connected to a shared environment in accordance with the typical "common bus" structure. With a time-shared bus, any two computers can communicate. Access to the communication line is controlled by special controllers - Ethernet network adapters. Each computer, and more precisely, each network adapter, has a unique address. Data transfer occurs at a speed of 10 Mbps. This value is the bandwidth of the Ethernet network.
The essence of the random access method is as follows. A computer on an Ethernet network can only transmit data over the network if the network is free, that is, if no other computer is currently communicating. Therefore, an important part of Ethernet technology is the procedure for determining the availability of the medium. After the computer is convinced that the network is free, it starts the transfer, while "capturing" the medium.
The time of exclusive use of the shared environment by one node is limited to the time of transmission of one frame. A frame is a unit of data exchanged between computers on an Ethernet network. The frame has a fixed format and, along with the data field, contains various service information, such as the recipient's address and the sender's address. The Ethernet network is designed so that when a frame enters a shared data transmission medium, all network adapters simultaneously begin to receive this frame. All of them parse the destination address, located in one of the initial fields of the frame, and if this address matches their own address, the frame is placed in the network adapter's internal buffer.
Thus, the destination computer receives the data intended for it. Sometimes a situation may arise when two or more computers simultaneously decide that the network is free and start transmitting information. This situation, called a collision, prevents the correct transmission of data over the network. The Ethernet standard provides an algorithm for detecting and correctly handling collisions. The probability of a collision depends on the intensity of network traffic. After a collision is detected, network adapters that attempted to transmit their frames stop transmitting and, after a random pause, attempt to access the medium again and transmit the frame that caused the collision.
The main advantage of Ethernet networks, which made them so popular, is their cost-effectiveness. To build a network, it is enough to have one network adapter for each computer, plus one physical segment of a coaxial cable of the required length. Other basic technologies, such as Token Ring, require an additional device - a hub - to create even a small network. In addition, fairly simple algorithms for accessing the medium, addressing and transmitting data are implemented in Ethernet networks. The simple logic of the network leads to a simplification and, accordingly, a reduction in the cost of network adapters and their drivers. For the same reason, Ethernet network adapters are highly reliable.
And, finally, another remarkable property of Ethernet networks is their good extensibility, that is, the ease of connecting new nodes. Other basic network technologies - Token Ring, FDDI - although they have many individual features, at the same time have many properties in common with Ethernet. First of all, this is the use of regular fixed topologies (hierarchical star and ring), as well as shared data transmission media. Significant differences between one technology and another are related to the peculiarities of the used method of access to a shared environment. Thus, the differences between Ethernet technology and Token Ring technology are largely determined by the specifics of the media separation methods embedded in them - a random access algorithm in Ethernet and an access method by passing a token in Token Ring.
Token Ring technology
Token Ring is a local area network (LAN) technology of a ring with "token access" - a local area network protocol that resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a marker that moves around the ring. Ownership of a token grants the right to the holder to transmit information on the medium. Ring frames with token access move in a loop.
Stations on a Token Ring Local Area Network (LAN) are logically organized in a ring topology with data being transmitted sequentially from one ring station to another with a control token circulating around the control access ring. This token passing mechanism is shared by ARCNET, the token bus, and FDDI, and has theoretical advantages over stochastic CSMA/CD Ethernet.
The technology was originally developed by IBM in 1984. In 1985, the IEEE 802 committee adopted the IEEE 802.5 standard based on this technology. Recently, even IBM products have been dominated by technologies from the Ethernet family, despite the fact that the company used Token Ring for a long time as the main technology for building local area networks.
This technology offers a solution to the problem of collisions that occurs during the operation of a local network. In Ethernet technology, such collisions occur during the simultaneous transmission of information by several workstations located within the same segment, that is, using a common physical data channel.
If the station that owns the token has information to transmit, it grabs the token, changes one bit of it (as a result of which the token turns into the "beginning of data block" sequence), supplements the information it wants to transmit and sends this information to the next station ring network. When an information block circulates around the ring, there is no token on the network (unless the ring provides an "early token release"), so other stations wishing to transmit information must wait. Therefore, collisions cannot occur in Token Ring networks. If early release of the token is provided, then a new token can be issued after the transmission of the data block is completed.
The information block circulates around the ring until it reaches the intended destination station, which copies the information for further processing. The information block continues to circulate around the ring; it is finally removed after reaching the station that sent the block. The sending station can check the returned block to ensure that it has been viewed and then copied by the destination station.
Unlike CSMA/CD networks (such as Ethernet), token passing networks are deterministic networks. This means that it is possible to calculate the maximum time that will pass before any end station can transmit. This characteristic, along with some reliability characteristics, makes the Token Ring network ideal for applications where latency must be predictable and network stability is important. Examples of such applications are the environment of automated stations in factories. It is used as a cheaper technology and has become widespread wherever there are critical applications for which it is important not so much speed as reliable information delivery. Currently, Ethernet is not inferior to Token Ring in terms of reliability and is significantly higher in performance.
Token Ring networks, like Ethernet networks, use a shared data transmission medium, which consists of cable segments connecting all network stations into a ring. The ring is considered as a common shared resource, and for access to it, not a random algorithm is used, as in Ethernet networks, but a deterministic one, based on the transfer by stations of the right to use the ring in a certain order. The right to use the ring is conveyed using a special frame format called a token or token.
The Token Ring standard was adopted by the 802.5 committee in 1985. At the same time, IBM adopted the Token Ring standard as its core networking technology. Currently, it is IBM that is the main trendsetter in Token Ring technology, producing about 60% of network adapters of this technology.
Token Ring networks operate at two bit rates, 4 Mb/s and 16 Mb/s. The first rate is defined in the 802.5 standard, and the second is a new de facto standard that has emerged as a result of the development of Token Ring technology. Mixing of stations operating at different speeds in the same ring is not allowed.
Token Ring networks operating at 16 Mb/s also have some improvements in the access algorithm compared to the 4 Mb/s standard.
FDDI Technology
Technology Fiber Distributed Data Interface- the first technology of local area networks, which used fiber optic cable as a data transmission medium.
Attempts to use light as a medium carrying information have been made for a long time - back in 1880, Alexander Bell patented a device that transmitted speech over a distance of up to 200 meters using a mirror that vibrated synchronously with sound waves and modulated the reflected light.
In the 1960s, optical fibers appeared that could transmit light in cable systems, similar to how copper wires transmit electrical signals in traditional cables. However, the light loss in these fibers was too great to be used as an alternative to copper strands.
In the 1980s, work also began on the creation of standard technologies and devices for using fiber optic channels in local networks. Work on the generalization of experience and the development of the first fiber optic standard for local networks were concentrated at the American National Standards Institute - ANSI, within the framework of the X3T9.5 committee created for this purpose.
The initial versions of the various components of the FDDI standard were developed by the X3T9.5 committee in 1986 - 1988, and at the same time the first equipment appeared - network adapters, hubs, bridges and routers that support this standard.
Currently, most network technologies support fiber optic cables as one of the physical layer options, but FDDI remains the most established high-speed technology, the standards for which have stood the test of time and are well-established, so that equipment from different manufacturers shows a good degree of compatibility.
FDDI technology is largely based on Token Ring technology, developing and improving its main ideas. The developers of FDDI technology set themselves the following goals as the highest priority:
· increase the bit rate of data transfer up to 100 Mb/s;
· increase network fault tolerance due to standard procedures for restoring it after failures of various kinds - cable damage, incorrect operation of a node, hub, high level of noise on the line, etc.;
Use the potential network bandwidth as efficiently as possible for both asynchronous and synchronous traffic.
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.
The use of two rings is the main way to increase fault tolerance in an FDDI network, and nodes that want to use it must be connected to both rings. In the normal mode of network operation, data passes through all nodes and all sections of the cable of the primary (Primary) ring, therefore this mode is called Thru mode - “through” or “transit”. The secondary ring (Secondary) is not used in this mode.
In the event of some form of failure where part of the primary ring is unable to transmit data (for example, a cable break or node failure), the primary ring is combined with the secondary, forming a single ring again. This mode of network operation is called Wrap, that is, "folding" or "folding" rings. The folding operation is performed by hubs and/or FDDI network adapters. To simplify this procedure, data on the primary ring is always transmitted counterclockwise, and on the secondary - clockwise. Therefore, when a common ring is formed from two rings, the transmitters of the stations still remain connected to the receivers of neighboring stations, which makes it possible to correctly transmit and receive information by neighboring stations.
The FDDI standards place a lot of emphasis on various procedures to determine if a network has failed and then reconfigure as necessary. The FDDI network can fully restore its operability in the event of single failures of its elements. With multiple failures, the network breaks up into several unrelated networks.
Each station in the network constantly receives the frames transmitted to it by the previous neighbor and analyzes their destination address. If the destination address does not match its own, then it broadcasts the frame to its subsequent neighbor. This case is shown in the figure. It should be noted that if the station has captured the token and transmits its own frames, then during this period of time it does not broadcast incoming frames, but removes them from the network.
If the frame address matches the address of the station, then it copies the frame to its internal buffer, checks its correctness (mainly by checksum), passes its data field for further processing to the protocol of the level above FDDI (for example, IP), and then transmits the original frame over the network of the subsequent station. In a frame transmitted to the network, the destination station notes three signs: address recognition, frame copying, and the absence or presence of errors in it.
After that, the frame continues to travel through the network, being broadcast by each node. The station, which is the source of the frame for the network, is responsible for removing the frame from the network after it, having made a full turn, reaches it again. In this case, the source station checks the signs of the frame, whether it reached the destination station and whether it was damaged. The process of restoring information frames is not the responsibility of the FDDI protocol, this should be handled by higher layer protocols.
Protocol X.25
X.25 is a family of network layer protocols for the OSI network model. It was intended for organizing a WAN based on telephone networks with lines with a sufficiently high error rate, therefore it contains advanced error correction mechanisms. Oriented to work with the establishment of connections. Historically, it is the predecessor of the Frame Relay protocol.
X.25 provides multiple independent virtual circuits (Permanent Virtual Circuits, PVCs and Switched Virtual Circuits, SVCs) on a single link, identified in the X.25 network by connection connection identifiers (Logical Channel Identifyer, LCI) or logical channel number (LCN).
Due to the reliability of the protocol and its operation over public telephone networks, X.25 has been widely used both in corporate networks and in worldwide specialized networks for the provision of services, such as SWIFT (bank payment system) and SITA (French Société Internationale de Télécommunications Aéronautiques - a system air transport information service), however, X.25 is currently being replaced by other link layer technologies (Frame Relay, ISDN, ATM) and the IP protocol, remaining, however, quite common in countries and territories with an undeveloped telecommunications infrastructure.
Developed by Study Group VII of the International Telecommunication Union (ITU) as a packet data transfer protocol in telephone networks, it was adopted in 1976 and became the basis of the worldwide PSPDN (Packet-Switched Public Data Networks) system, that is, WAN. Significant additions to the protocol were adopted in 1984, the ISO 8208 X.25 protocol standard is currently in force, and the use of X.25 in local networks has also been standardized (ISO 8881 standard).
X.25 defines the characteristics of the telephone network for data transmission. To initiate communication, one computer calls the other to request a communication session. The called computer can accept or reject the connection. If the call is accepted, then both systems can start transmitting information with full redundancy. Either party may terminate the connection at any time.
The X.25 specification defines a point-to-point interaction between terminal equipment (DTE) and data circuit termination equipment (DCE). DTE devices (terminals and hosts in user equipment) are connected to DCE devices (modems, packet switches and other ports to the PDN network, usually located in the equipment of this network), which are connected to "packet switching exchange" (packet switching exchange) ( PSE or simply switches) and other DCEs inside the PSN and finally to another DTE device.
The DTE may be a terminal that does not fully implement all of the functionality of X.25. These DTEs connect to the DCE through a translation device called a packet assembler/disassembler - PAD. The operation of the terminal/PAD interface, the services offered by the PAD, and the interaction between the PAD and the host are defined respectively by CCITT Recommendations X.28, X3 and X.29.
The X.25 specification constitutes the Layers 1-3 schemas of the OSI reference model. X.25 Layer 3 describes the packet formats and procedures for exchanging packets between Layer 3 peer entities. X.25 Layer 2 is implemented by the Link Access Procedure, Balanced (LAPB). LAPB defines packet framing for a DTE/DCE link. X.25 layer 1 defines the electrical and mechanical procedures for activating and deactivating the physical medium connecting DTE and DCE data. It should be noted that Layers 2 and 3 are also referred to as the ISO standards ISO 7776 (LAPB) and ISO 8208 (X.25 packet layer).
Pass-through between DTE devices is done through a bi-directional link called a virtual circuit. Virtual circuits allow communication between different network elements through any number of intermediate nodes without assigning parts of the physical medium, which is typical for physical circuits. Virtual circuits can be either permanent or switched (temporarily). Permanent virtual circuits are commonly referred to as PVCs; switchable virtual circuits - SVC. PVCs are usually used for the most frequently used data transfers, while SVCs are used for sporadic data transfers. Layer 3 of X.25 is responsible for end-to-end transmission, including both PVCs and SVCs.
After the virtual circuit is established, the DTE sends the packet to the other end of the link by sending it to the DCE using the appropriate virtual circuit. The DCE looks up the virtual circuit number to determine the route of this packet through the X.25 network. The X.25 Layer 3 protocol multiplexes between all DTEs served by a DCE located on the destination side of the network, resulting in the packet being delivered to the destination DTE.
Conclusion
The development of computer technology and information technology served as an impetus for the development of a society built on the use of various information and called the information society.
Information network technologies are focused mainly on providing information services to users.
All network technologies, such as: Ethernet, Token Ring, FDDI or X.25 - can be said to be one of the most significant and striking democratic achievements of the technological process. With their appearance, information and the right to truth and freedom of speech become a potential asset and opportunity for the majority of the inhabitants of the planet, people can unite and interact regardless of time, distance, state and many other borders.
At present, the whole world is covered by the global Internet. It is the Internet that erases all boundaries and ensures the dissemination of information for an almost unlimited circle of people. Allows people anywhere in the world to easily join in the discussion of pressing problems. The main feature and purpose of the Internet is the free dissemination of information and the establishment of communication between people.
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