Interaction is carried out on the basis telephone communication, fiber optic lines ( wired connection) and satellite, radio modem (wireless communications).

The basis of global architecture computer network the model is based Open Systems Interconnection (OSI)–Open Systems Interconnection).

This is due to the variety of computer networks and network software, i.e. with the problem of combining networks of different architectures.

Open system is a system that interacts with other systems in accordance with accepted standards. Exchange between systems occurs via protocols , i.e. a set of rules that determine the interaction of two layers of the same name in the OSI model in various subscriber computers.

The rules defined in the protocol are implemented in a program called driver .

Model OSI has a seven-level structure:

7 ‑ Applied (support for application processes managed
end user).

6 ‑ Representative (syntax and interpretation of transmitted data).

5 ‑ Session (session support - dialogue between remote
processes)

4 ‑ Transport (ensuring interaction of remote processes)

3 ‑ Network (routing, data flow control)

2 ‑ Duct(formation of personnel)

1 ‑ Physical (bit data transfer protocols).

The OSI concept presupposes the standardization of protocols at all levels, however, only levels 1 - 3 lend themselves to this; the rest are more difficult. Therefore, in reality, not all 7 levels are used in networks.

The main idea of ​​this model is that each level is assigned a specific role, including the transport environment. Thanks to this, the overall task of data transmission is divided into individual, easily visible tasks. The necessary agreements for communication between one layer and those above and below are called a protocol.

Protocols physical level are individual for each type of communication equipment used (modem, network adapter, radio modem, etc.). Usually, channel, network And transport levels network interaction is provided by drivers of the corresponding protocols included in the operating system. Protocols functional level(session, representative and application) provide user interface, service and services.

The computer network system effectively manages and coordinates the interaction of user tasks.

Global network INTERNET

An example of a global network is Internet. The logical structure of the Internet is a kind of virtual association that has its own information space. The main cells of the Internet are LAN.

The global Internet network is a collection of large “nodes” interconnected by communication channels. Each “node” is one or more server computers running the UNIX network operating system. These computers are called main or host computers (host). A “node” (or subnetwork of “nodes”) is managed by its owner - an organization called provider . The provider provides clients with access to Internet services.

Providers in Russia are grouped by district, for example, in the Southern Federal District there are 84 providers. Of these, 11 are in Rostov-on-Don. Used to access the Internet Newest technologies(except for the well-known ones - modem, leased line), for example, “Internet from a socket” PLC (Power Line Communication). Special PLC equipment is installed on the existing electrical network in the building, thanks to which customers receive high speed access on the Internet anywhere electrical outlet building.

The global Internet network includes millions of computers and networks running different operating systems, With various formats data on different hardware platforms, therefore its architecture is based on the multi-level principle of message transmission. Basic protocol Internet - TCP/IP (Transmission Control Protocol/Internet Protocol) - transmission control protocol/internet protocol.

The underlying TCP/IP protocol is responsible for

breakdown original message to packets (TCP)

· behind physical delivery of packets to the destination node (IP) and

· assembly of the original message (TCP).

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File Transfer Service Transfer Service FTP files moves copies of files from one Internet node to another in accordance with FTP protocol (File Transfer Protocol - "file transfer protocol"). It does not matter where these nodes are located and how they are connected to each other. Computers that have files for common use, are called FTP servers. For example, to download the file cute4232.exe from GlobalScape's file archive server ftp.cuteftp.com, you must specify the file's URL. When specifying a URL, the FTP protocol is written as follows: ftp://. As a result, the universal resource locator URL takes the form: ftp://ftp.cuteftp.com/pub/cuteftp/cute4232.exe and consists of three parts: ftp:// - access protocol; ftp.cuteftp.com Domain name file archive server; pub/cuteftp/cute4232.exe - file path and file name. WWW- The World Wide Web World Wide Web(WWW) is a hypertext, or more precisely, hypermedia information system for searching Internet resources and accessing them.

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Hypertext is an information structure that allows you to establish semantic connections between text elements on a computer screen in such a way that you can easily transition from one element to another. Hypermedia is what happens if in the definition of hypertext you replace the word “text” with “any type of information”: sound, graphics, video. The WWW system is built on a special data transfer protocol called the HyperText Transfer Protocol (HTTP). WWW pages are hypermedia documents of the World WideWeb system. Created using the hypertext markup language (HTML).

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Tools for developing websites A website is a collection of hypertext documents, which are treated as a single unit and defined by a single URL. To create a website you don’t need to know HTML language. There are many available visual HTML editors, their other name is WYSIWYG mountain editor, which allows you to create websites without knowledge of this language. WYSIWYG stands for: What You See Is What You Get - what you see is what you get. Work in such editors occurs with visual forms, and not with tags. For example, to make a text font bold, you just need to select this text and click the corresponding button in the editor menu. After this, the editor will insert the necessary “l” tags into the HTML code, and the site developer will see the final result on the page. Visual HTML editors: 1. Adobe Dreamweaver- one of the most popular commercial software products, intended for website development. It was originally developed and supported by Macromedia (until 2005). Next versions, starting with Dreamweaver CC (2007), released by Adobe. The editor contains huge selection all kinds of instruments, user-friendly interface, fine settings, allowing you to tailor the program to the needs of the web master, as well as a built-in FTP manager for uploading files to the server. 2. Microsoft Office SharePoint Designer 2007 - a visual HTML editor and web design program from Microsoft. It is one of the components Microsoft package Office 2007, but it also requires separate installation. This package is one of the rather complex editors that allows you to create not only the simplest web pages, but also full-fledged web sites designed for collective work by users. More a new version Microsoft programs Office SharePoint Designer 2010 is maximally tied to the collaboration of a large number of people on one project, which requires installation of the appropriate software on the server where this project is stored. 3. WebPageMaker - simple, fast and convenient editor for creating websites. The user drags pre-prepared texts and graphics to the required places on the page using the mouse. The program includes a large number ready-made templates, which can be used as a basis for a future website. 4 . Nvu is a freely distributed visual HTML editor. The advantage of the Nvu editor is that it is cross-platform: there are versions for Linux, Microsoft Windows and MacOS. 5. KompoZer - a branch of the Nvu editor. KompoZer is a freely distributed web authoring system that combines a web file manager and a visual editor. Compared to Nvu, KompoZer produces shorter markup code. KompoZer is extremely easy to use, which makes it attractive to users who want to create websites without having to pay serious fees. technical knowledge. KornpoZer can be considered as an editor for creating small web projects.

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Purpose and structure global networks

Global computer network, WAN (English Wide Area Network, WAN) - a computer network covering large areas and including big number computers.

Global networks allow you to organize interaction between subscribers over thousands of kilometers. Data transmission in global networks is based on packet switching technology.

Every transferred file is broken into small portions, which are placed in a packet containing the addresses of both the sending and receiving computer.

Packets travel independently across the network: if one packet is lost, it can be easily resent. Since each packet is sent independently of the others and mixed with thousands of similar ones, this, among other things, ensures that data transmission over the Internet is relatively cheap. For example, the cost of delivery email is negligible compared to the cost of sending a message of equal length by fax.

WANs are also called territorial computer networks, serve to provide their services a large number end subscribers scattered over a large area - within a region, region, country, continent or the entire globe.

Due to the large length of communication channels, the construction of a global network requires very large costs, which include the cost of cables and work on their installation, the cost of switching equipment and intermediate amplification equipment that provides the necessary channel bandwidth, as well as operating costs for constant maintenance of in working condition network equipment scattered over a large area.

Typical global subscribers computer network are local enterprise networks located in different cities and countries that need to exchange data with each other. Individual computers also use the services of global networks. Large mainframe computers typically provide access to corporate data, while personal computers used to access corporate data and public Internet data.

WANs are usually created by large telecommunications companies to provide paid services to subscribers. Such networks are called public or public. There are also such concepts as network operator and network service provider.

Network operator(network operator) is the company that supports normal work networks. Service Provider, often also called provider(service provider) - the company that provides paid services network subscribers. The owner, operator, and service provider may be one company, or they may represent different companies.

It is much less common for a global network to be created entirely by some large corporation(such as Dow Jones or Transneft) for their internal needs. In this case, the network is called private. Very common and intermediate option- a corporate network uses the services or equipment of a public wide area network, but supplements these services or equipment with its own. The most typical example here is the rental of communication channels, on the basis of which their own territorial networks are created.

In addition to global computing networks, there are also other types territorial information transmission networks. First of all, these are telephone and telegraph networks that have been operating for many decades, as well as the telex network.

Due to the high cost of WANs, there has been a long-term trend toward a single WAN that can transmit data of any type: computer data, telephone conversations, faxes, telegrams, television images, teletex (data transfer between two terminals), videotex (receiving data stored on the network to your terminal), etc., etc.

Although local and global computer networks are based on the same method - the method packet switching, global networks have quite a lot of differences from local networks..

Global trends are such that everything is subject to integration processes. In the world of finance, mergers and acquisitions are taking place, large industrial groups are creating strategic alliances, even countries and regions are uniting. In this sense, it is not surprising that computer networks and the companies that own these networks also seek to increase their market share and reduce the cost of services provided through consolidation.

Global networks are created by large corporations (telecommunications, less often others for their own needs) to ensure information interaction between computers located in different countries, on different continents.

The company that provides normal functioning global network is calledoperator .

A company that provides paid services to network subscribers is calledprovider .

Global networks are the result of the consolidation of telecommunications companies and the unification of their networks. This is due to the need to expand the range of services provided, the cost of which depends on whether the company has its own communication channels or rents them from competitors.

The functioning of global networks is based onmulti-level message transmission principle . The message is generated at the very high level modelsOSI and sequentially goes through all levels to the lowest. At each level, an additional header is added to the message (which is split into parts shown in Fig. 5.4 as it descends), which is required to receive the message at a similar level on the recipient’s side. On the receiving side, the message sequentially passes from the lower level to the upper one, removing the corresponding headers. That's why top level accepts the original message in its “original” form.

The homogeneity of the information and communication environment of the global network is ensured by the compatibility of software and hardware, which are released in accordance withinternational standards .

The most widespread global networkInternet , the technologies of which have already penetrated into corporate networks, now calledIntranet networks.

Global networks arenodal . This means that the global network includescommunication subnet , to which local networks, individual computers and terminals (means for entering and displaying information) are connected. The subnet consists ofcommunication channels , communication nodes (designed for routing and packet switching) andcommunication node software (KU).

The typical structure of a global network is shown in Fig. 5.5.



Rice. 5.5.Global network structure

LAN - local network; M - Router; MP - multiplexer; KU - communication node; TSS - territorial network communications; RS - work station; PBX - automatic telephone exchange.

To the global network usingrouters And KU local networks are connected.Multiplexer necessary for combination within oneterritorial communication network (TCS) computer and voice traffic fromautomatic telephone exchange (PBX).

Individuals can also connect to the global networkworkstations (PC) and home networks, as well as wireless networks.

Depending on the hardware used, global networks are distinguishedwith dedicated communication channels , circuit switched , packet switched . The most suitable mode of operation of the global network ispacket switching mode .

NOTE

The cost of services in a global packet-switched network is 2-3 times lower than the cost of services in a circuit-switched network, although the total traffic per unit time will be the same.

Networks with dedicated channels are used to organize backbone connections between large local networks. Contact byanalog dedicated lines are made using modems. Contact bydigital allocated channels is carried out using equipment using the principle of time division of channels (TDM). The interconnection of local networks using dedicated channels is carried out by routers and remote bridges. The main disadvantage is the high cost of services.

Circuit switched networks are based on technologyISDN and use analog channels. NetISDN digital and free from the disadvantages of analog communication ( big time connection establishment, low channel quality), but charging is still carried out not for the volume of transmitted traffic, but for the time of the connection.

Packet switched networks are the main means of any information, from television to facsimile. These networks includeX.25 , Frame Relay , ATM , TCP/IP . In global packet-switched networks (excluding TCP/IP), packet routing is used based on the creation of two types of channels -switched virtual circuits (SVC) and permanent virtual channels (PVC). There are two modes for promoting packages -standard and switching modebased on virtual channel number .

Standard The mode is used only to route only the first packet transmitted, which is necessary to establish a connection. It turns out that the first packet lays a virtual channel, setting up intermediate switches, and the remaining packets pass through the virtual channel in switching mode.

As an example, Appendices 5 and 6 consider the global Internet.