Timely exchange of information within team members is an important component of the successful work of any company, regardless of its specifics and scale.

The spread of digital technologies in all industries contributes to the widespread implementation corporate networks at different levels of business, from small firms to holdings.

Design and construction of a corporate network

The popularity of corporate networks is due to a number of their advantages.

Reducing system downtime in the event of hardware, software and technical errors requires a stable, continuous exchange of data between all participants.

Special programs and fine-tuning of access rights to individual documents, functions and sections reduce the risk of information leakage and loss of confidential data. In addition, violators are easy to track using software solutions.

The process of designing a corporate network includes the unification of local networks of departments within the company and the creation of a material and technical base for further planning, organization and management of the core activities of the enterprise.

The construction of a corporate network is based on an agreed and developed architecture of data, platforms and applications, through which information is exchanged between users. Getting a functioning corporate network additionally involves developing tools for maintaining and protecting databases.

Companies creating corporate networks

Among the companies creating corporate networks, it is worth noting:

1. "Altegra Sky" is a Moscow company engaged in providing a full range of services related to the creation internal network, from drawing up the basic architecture to commissioning. The company purchases, installs, commissions all necessary equipment and conducts training events for its clients.


2. Universum is a Moscow-based provider of system integration services and the creation of secure local networks for wide-ranging enterprises. Specialization - installation and fine-tuning of all functional elements of local networks and ensuring uninterrupted operation.


3. Open Technologies is a provider of innovative solutions for data exchange within the company. The company's specialization is creating optimal hierarchical structure, which will provide consistently high speed transfer of documents, images and multimedia using existing server capacity.

Structure, architecture, technologies of enterprise corporate networks

The corporate network of an enterprise is characterized by two elements.

LAN is a local area network that provides stable exchange of necessary data and management of user access rights. To create it you need Hardware– structured cable networks, hereinafter referred to as SCS.

SCS is a telecommunications infrastructure - a collection of all computer devices companies between which data exchange occurs in real time.

Creating a corporate network consists of choosing:

• working group;


• modeling environments;


• software and hardware solutions for its creation;


• configuration and maintenance of the finished architecture.

Building an architecture and choosing a corporate network technology consists of several stages:

• selection of elementary objects included in the corporate data exchange network. As a rule, these are certain products, services of the company and information on them;


• selection of functional, information and resource models for the future network. At this stage, the “internal logic” of the functioning of the future network is determined;


• further, based on the already selected parameters, languages ​​and modeling methods are determined that can solve the assigned problems.

For example, when forming a corporate network for a small manufacturing company, the most accessible modeling languages ​​that do not require hardware power are used. Conversely, creating architecture for large companies with a wide range of activities requires the use of powerful tools.

Corporate local networks via VPN and Wi-Fi

VPN, or Virtual Private Network, is an option for creating a virtual network within an enterprise that uses the capabilities of global network. The peculiarity of building such a network is the ability to access the Internet from anywhere in the world using a registered login and password.

The solution is popular among IT companies, design bureaus and other enterprises that hire employees for remote work. The disadvantage of this method of organizing a local network is the threat of unauthorized access and loss of user data.

Wi-Fi is a more technologically advanced and modern option for creating a corporate network that is not tied to hardware capacity and the physical location of users. Using routers, network access is configured for all employees, and you can “get into” the network from any device.

The main advantage of Wi-Fi is easy integration and scaling of the created network for any number of users. With the help of Wi-Fi, network bandwidth is dynamically redistributed between individual nodes, depending on the level of applied load.

Corporate satellite network

Operation of this type a corporate local network is built on the use of the power of a HUB - a satellite terminal located in network control centers.

Each participant accesses the network using an IP address and a relay satellite that transmits a signal to other users.

This option for organizing a corporate network allows you to:

• quickly connect new users to the existing network;


• remotely monitor its functioning and compliance by participants with the security policy;


• guarantee data safety and fine-tuned privacy.

Satellite networks are the most stable, expensive and technologically advanced way to organize data exchange between employees of the same structure.

Corporate multiservice network

A feature of a multiservice network is the ability to transmit text, graphic, video and audio information using the same communication channels. As a rule, companies providing construction services multiservice networks, create turnkey solutions that allow all necessary types of information to be transmitted via IP addresses.

In technical terms, separate subsystems are created that are designed to transmit certain types of information, while switches, routers and signal amplifiers are used to transmit data. Thus, the network is more stable, tolerates high load levels well and allows peripheral devices to access the central server as quickly as possible.

Corporate computer network

A computer network within a company is an adaptation of Internet technologies for use at the level of an individual company. The main purpose of building such networks is the joint use of information for internal corporate work: simultaneous access and editing of documents, data exchange.

The functioning of a computer network requires the use of an operating system that is compatible with all equipment and software connected to it. It is important to ensure rational distribution of information and provide employees with tools for planning and document management.

The stage of building the architecture of a corporate computer network involves constant communication with future users in order to identify their needs. A successfully built corporate computer network is a convenient software and hardware solution for use in daily work.

Corporate social network

Creating a tool for transmitting messages and exchanging information within one company gives employees the opportunity to maintain contact between departments in real time. At the same time, the product is based on the principle of operation of ordinary social networks with “reduced” functionality, which does not distract the attention of employees from their professional duties.

As a rule, company employees who are in the office or working remotely have access to a corporate social network, while confidential work issues are discussed using secure communication protocols. This ensures prompt and secure communication between company departments without interrupting production and without the threat of data leakage.

Remote access to the corporate network

The basis for remote access to the capabilities of a corporate network is setting up the VPN protocol, which ensures the use of company servers by running a virtual machine.

The technology is based on a terminal server, free subnets and a secure guest network. There is no need for the user to purchase or configure additional programs: access via VPN is carried out in the “Team Viewer” application, compatible with all versions of Windows OS.

This solution is safe due to the possibility fine tuning access rights to data stored on company servers.

Security of corporate networks: threats and protection

Unauthorized access to data stored on corporate servers and the threat of their loss are two main dangers from which it is necessary to protect the enterprise network.

For these purposes the following are used:

• antivirus systems;


• prompt blocking of unauthorized access manually;


• fine tuning VPN networks, cutting off unauthorized users by entering a login and password.

Permanent protection is achieved using firewalls, monitoring the functioning of all network elements in real time.

Read our other articles:

Lecture No. 26

Subject: Corporate networks. Purpose. Structure. Main functions.

1. THE CONCEPT OF “CORPORATE NETWORKS”. THEIR MAIN FUNCTIONS.

Corporate network- a system that ensures the transfer of information between various applications used in the corporation's system.

The corporate network is geographically distributed, i.e. uniting offices, divisions and other structures located at a considerable distance from each other. Often corporate network nodes are located in different cities and sometimes countries. The principles by which such a network is built are quite different from those used when creating a local network, even covering several buildings. The main difference is that geographically distributed networks use fairly slow leased communication lines. If when creating a local network the main costs are for the purchase of equipment and laying cables, then in geographically distributed networks the most significant element of the cost is the rental fee for the use of channels.

Applications mean system software- Database, postal systems, computing resources, file service, and facilities, with which the end user works.

The main tasks of a corporate networkthere is interaction between system applications located in different nodes and access to them by remote users.

The corporate network makes the transition to geographically remote nodes, which allows the use of existing global networks. For this purpose, organizations are provided with channels from offices to the nearest network nodes. A frequently used network is the Internet.

When using the Internet as the basis for a corporate data network, it turns out that the Internet is interweb , in which all information passes through many completely independent nodes connected through the most diverse channels and data networks. The Internet binds users to one protocol - IP.

But when connecting corporate networks to the Internet, problems arise security and problem virus infection. There are protections for this:

1. Firewall is a router, PC, host or a group of hosts created specifically to protect a network or subnet from misuse of protocols and services by hosts outside that subnet.

Router - a network device, based on information about the network topology and certain rules, making decisions about forwarding network layer packets between different network segments.

Host - any computer that has full two-way access to other computers on the Internet.

1. A set of anti-virus programs.

Corporate networkis a complex system that includes a variety of components: different types of PCs, system and application software, network adapters, hubs, switches and routers, and a cable system.

The main task system integrators and administrators this is the functioning of an expensive system in processing information flows circulating between employees of the enterprise and allowing them to make timely and rational decisions.

2. CORPORATE NETWORK STRUCTURE

Used to connect remote userstelephone communications and modems.

To unite network nodes, they are usedglobal data networks, where it is possible to lay dedicated lines, the use of packet switching technologies makes it possible to reduce the number of necessary communication channels.

Connecting your corporate network to the Internet is necessary if you need access to relevant services. If you will only use the Internet as a source of information, it is better to use technology"connection on demand"(dial-on-demand).

To transfer data within a corporate network, you should also usevirtual channelspacket switching networks.

A corporate network is a rather complex structure that uses various types of communications, communication protocols and methods of connecting resources

Data transmission network equipment classes:

1. peripheral (used to connect end nodes to the network),
2. main or support , which implements the basic functions of the network (channel switching, routing, etc.).

Periphery equipment for two classes.

• routers serve to unite homogeneous LANs through global data networks;
  • gateways implement the interaction of applications running in different types networks.

Introduction

One of the basic human needs is the need for communication, which becomes possible when people understand each other. To do this, they study languages, master the culture of communication, and use modern means and methods of communication. Communication in a broad sense refers to the process, path and means of transmitting an object or message from one place to another. Communications can be organized using different transmission media, for example, water and air communications, gas pipelines, railways and highways, etc.
Computer networks provide invaluable assistance to people, the emergence of which marked a new era in the history of communications development. With the advent of computer networks, people began to talk about computer communications, meaning the exchange of all kinds of information using computers. They are increasingly entering our lives, in some cases displacing, and in others complementing existing ones. Being far from each other, you exchange letters by mail - in computer network this type of communication is known as email. To discuss some important problem, you organize a meeting, meeting, conference. A corresponding type of communication exists in a computer network. This is a teleconference. Computer communications are in many ways reminiscent of traditional ones, but at the same time, mail delivery time is significantly reduced, communications are organized more quickly, the ability to communicate with a larger circle of people expands, and prompt access to global information repositories appears.
Computer communications are provided using computer networks: local, regional, corporate, global.
At the lecture you will learn how they differ from each other and what their hardware is, namely: what components ensure the network operates, what communication channels are used, what a modem and network adapter are, what role protocols play in computer networks, and much more.

Computer networks. Basic information.

Telecommunication(from Greek tele - “afar”, far ~ and Lat. communicato - “communication”) - this is the exchange of information at a distance.
Radio transmitter, telephone, teletype, fax machine, telex and telegraph are the most common and familiar examples of telecommunications technology to us today.
Later, another means was added to them - computer communications, which are now becoming increasingly widespread. They promise to supplant fax and teletype communications, just as the latter supplanted the telegraph.

Computer communications– exchange of information at a distance using computer networks.

Nowadays, computer networks are becoming increasingly important in the life of mankind, and their development is very promising. Networks can unite and make available the information resources of both small enterprises and large organizations occupying premises remote from each other, sometimes even in different countries.

Computer networks– a system of computers connected by information transmission channels.

The purpose of all types of computer networks is determined by two functions:
- ensuring the sharing of hardware and software network resources;
- providing shared access to data resources.
For example, all participants in a local network can share one common printing device - a network printer or, for example, resources hard drives one dedicated computer - file server. Software can be shared in the same way. If the network has special computer, allocated for shared use by network participants, it is called a file server.

Networks by dimension are divided into local, regional, corporate, global

the local network(LAN - Local Area Network) - a connection of computers located at short distances from each other (from several meters to several km). PCs in such networks are located in the same room, in the same enterprise, in nearby buildings.
Local networks do not allow shared access to information among users located, for example, in different parts of the city. They come to the rescue regional networks, connecting computers within one region (city, country, continent).

regional net(MAN - Metropolitan Area Network) - combining PCs and local networks to solve a common problem on a regional scale. Regional A computer network connects computers located at a considerable distance from each other. It may include computers within a large city, economic region, or individual country. Typically, the distance between subscribers of a regional computer network is tens to hundreds of kilometers.
Many organizations interested in protecting information from unauthorized access (for example, military, banking, etc.) create so-called corporate networks. A corporate network can unite thousands and tens of thousands of computers located in different countries and cities (an example is the Microsoft Corporation network)

corporatenetworks - association of local networks within one corporation.

The needs of forming a single world information space led to the creation of the global computer network Internet.

global networks(WAN - Wide Area Network) – a system of interconnected local networks and user PCs located at remote distances for the common use of world information resources .
Information networks create a real opportunity for quick and convenient user access to all information accumulated by humanity throughout history.

Based on the type of transmission medium, networks are divided into:

Wired (coaxial cable, twisted pair, fiber optic);
- wireless with information transmission via radio channels or in the infrared range.
According to the method of organizing the interaction of network computers divided into peer-to-peer and dedicated server (hierarchical networks).
All computers in a peer-to-peer network have equal rights. Any network user can access data stored on any computer.
The main advantage of peer-to-peer networks is the ease of installation and operation. The main disadvantage is that in peer-to-peer networks it is difficult to resolve information security issues. Therefore, this method of organizing a network is used for networks with a small number of computers and where the issue of data protection is not fundamental.
In a hierarchical network, when setting up a network, one or more servers are allocated in advance - computers that manage data exchange over the network and resource distribution. Any computer that has access to the server's services is called a network client or workstation.

The general scheme for connecting computers into local networks is called network topology. There are only 5 main types of network topologies:

1. BUS topology. In this case, the connection and data exchange is carried out through a common communication channel called a common bus. The bus type structure is simpler and more economical since it does not require additional device and uses less cable. But it is very sensitive to cable system faults. If the cable is damaged in even one place, then problems arise for the entire network. The location of the fault is difficult to locate.

2. STAR topology. In this case, each computer is connected with a separate cable to general device called a hub, which is located at the center of the network. The star cable system is more resistant to faults in the cable system. A damaged cable is a problem for one specific computer; it does not affect the operation of the network as a whole. No effort is required to isolate the fault. The disadvantages of a star topology include the higher cost of network equipment due to the need to purchase a hub. In addition, the ability to increase the number of nodes in the network is limited by the number of hub ports. Currently, this structure is the most common type of connection topology in both local and global networks.

3. RING topology. In networks with a ring topology, data in the network is transmitted sequentially from one station to another along the ring, usually in one direction. If the computer recognizes the data as intended for it, then it copies it to its internal buffer. In a network with a ring topology, it is necessary to take special measures so that in the event of a failure or disconnection of any station, the communication channel between the remaining stations is not interrupted. The advantage of this topology is ease of management, the disadvantage is the possibility of failure of the entire network if there is a failure in the channel between two nodes.

4. Mesh topology. The mesh topology is characterized by a computer connection scheme in which physical communication lines are established with all adjacent computers. In a network with a mesh topology, only those computers between which intensive data exchange occurs are directly connected, and for data exchange between computers that are not directly connected, transit transmissions through intermediate nodes are used. The mesh topology allows the connection of a large number of computers and is typically characteristic of global networks. The advantages of this topology are its resistance to failures and overloads, because There are several ways to bypass individual nodes.
5. Mixed topology. While small networks typically have a typical star, ring, or bus topology, large networks typically have random connections between computers. In such networks, it is possible to distinguish separate arbitrary subnetworks that have a standard topology, which is why they are called networks with a mixed topology.

The operating principles of various electronic networks are approximately the same:

1. The network consists of interconnected PCs
In most cases, the network is built on the basis of several powerful computers, called servers. Servers and, accordingly, second-order (regional), third-order (corporate), fourth-order (local) networks are usually connected to global network servers, and users of individual computers are connected to them - subscribers(clients) networks. Note that networks of not all intermediate levels (for example, corporate) are required.

2. PCs are interconnected by communication channels
The main purpose of creating any computer network is to ensure the exchange of information between objects (servers and clients) of the network. To do this, it is necessary to communicate between computers. Therefore, the mandatory components of any network are all kinds of communication channels (wired and wireless), for which they use different physical media. In accordance with this, networks distinguish between such communication channels as telephone and fiber optic lines, radio communications, space communications, etc.
The purpose of communication channels in a computer network is easy to understand if you compare them with the transport channels of a freight or passenger transportation system. Transportation of passengers can occur by air, by railways or by water (sea or river) routes. Depending on the transportation environment, the vehicle is chosen. Information is transported through computer networks. The environments in which network computers communicate determine the means by which computers are connected. If this is an environment that requires telephone communication, then the connection is made through a telephone cable. Connecting computers using electrical cables, radio waves, fiber optic cables, etc. is widely used.

Let's look at the main types of channels. Some of them are mutually exclusive, some may describe one channel from different angles.
There are channels digital and analog.
TO analog channels can be considered an ordinary telephone channel. To use it, you need a special device - a modem that converts digital information to analog. Analogue channels are highly susceptible to interference and have low bandwidth (several tens of kilobytes per second). Now there is a trend to replace all analog channels with digital ones, not only in computer networks, but also in telephone networks.
Channels are also divided into dedicated And switched.
Using dial-up line, the connection is formed for the duration of the data transfer, and at the end of this transfer it is disconnected. Dial-up is communication via a regular telephone line.

Dedicated the line works differently:
The connection is permanent and always allows you to transfer data from one computer to another. Leased lines differ from switched lines in high speed (up to tens of Megabits per second) and at a high price rent.
Channels are divided by physical device on electric wired, optical and radio channels.
Wired channels represent a connection with an electrical cable, possibly complexly arranged. All such channels use data transmission using electrical impulses.

Optical channels communications are based on light guides. The signal is transmitted using lasers.

Radio channels operate on the same principle as radio and television.
These are all different communication channels. The efficiency of communication in computer networks significantly depends on the following main characteristics (parameters) of communication channels:
- throughput (data transfer rate), measured by the number of bits of information transmitted over the network per second (bits per second is called baud);
Average throughput – measured on average over a certain period of time (for large file)
Guaranteed bandwidth – the minimum bandwidth that the channel provides (for video files)
- reliability - the ability to transmit information without distortion and loss;
- cost;
- expansion possibilities (connecting new computers and devices).

To transmit information over communication channels, it is necessary to convert computer signals into signals from physical media.
For example, when transmitting information via a fiber optic cable, the data presented in the computer will be converted into optical signals, for which special technical devices are used - network adapters.

Network adapters (network cards) - technical devices that perform the functions of pairing computers with communication channels.
If the communication channel – telephone line, then a modem is used to receive and transmit information.

Modem– (modulator – demodulator) – device for conversion digital signals PC to audio (analog) signals of the telephone line and vice versa.
The main characteristic of the modem is the speed of receiving and transmitting information (measured in bits per second). Modern modems have a data transmission and reception speed of 33600 bits per second, 57600 bits per second.

3. The network operates using protocols
In order for information transmitted by one PC to be understood by another PC, it was necessary to develop uniform rules called protocols.

Protocol– a set of agreements on the rules for generating and transmitting messages, on methods of exchanging information between PCs, on the rules of operation of various equipment on the network

There are 2 types of Internet protocols: basic and application protocols.

basic protocols responsible for physical sending electronic messages of any type between Internet computers (IP and TCP). These protocols are so closely related that they are most often referred to as the TCP/IP protocol;

applied higher-level protocols responsible for the functioning of specialized Internet services: HTTP protocol (transfer of hypertext messages), FTP protocol (file transfer), email protocols, etc.
In a technical sense, TCP/IP is not one, but two network protocols. TCP is a transport layer protocol. It controls how information is transferred. The IP protocol is addressable. It determines where data transfer occurs.

4. The operation of a PC on a network is ensured by network programs, usually organized according to the client-server model:

server- a program that provides services, client– a program that consumes server services - programs

IP-addresses

The information exchanged between PCs is divided into packages. A PACKET is a “piece” of information containing the address of the sender and recipient.
A. Many packets form a stream of information that is received by the user's PC
B. Then the “scattered packets” arriving from the network are collected into a single “bundle” by the client program of your PC (for example, the Microsoft browser Internet Explorer)
C. In order for the packet to find its recipient, each PC is assigned an IP address (upon registration with the provider). An IP address contains 4 bytes (32 bits) separated by dots or 4 numbers from 0 to 255. It is easy to calculate that the total number of different IP addresses is more than 4 billion: 232 = 4294967296.

The lP address is “read” from right to left. Typically, the rightmost digit indicates a specific computer, and the remaining digits indicate network and subnet numbers (i.e., local area networks).
Sometimes this may not be the case, but in any case, if the address is represented in binary form, then some of the rightmost bits identify a specific computer, and the rest indicate the networks and subnets to which the computer belongs.

Example. 192.45.9.200. Network address - 192.45; subnet address - 9; computer address - 200.
The packet contains the recipient's address and the sender's address, and is then thrown into the network.
Routers determine the route that packets take.

Domain name system

Computers can easily communicate with each other using a numeric IP address, but it is not easy for a person to remember a numeric address, and for convenience, the Domain Name System (DNS) was introduced.
Domain name system assigns a unique numerical IP address to each computer Domain name. Domain addresses are assigned by the Internet Network Information Center (InterNIC).

Domain (domain– region, district) – defines a set of PCs belonging to any part of the Internet, within which computers are united according to one characteristic.

Domain address defines an area representing a range of host computers. Unlike a digital address, it is read in reverse order. First comes the name of the computer, then the name of the network on which it is located.
A computer name includes at least two levels of domains. Each level is separated from the other by a dot. To the left of the top-level domain are subdomains for the general domain.
In the Internet address system, it is common to represent domains as geographic regions. They have a name consisting of two letters.
Example. Geographic domains of some countries: France - fr; Canada- sa; USA - us; Russia - ru; Belarus - by.
There are also domains divided by thematic signs. Such domains have three-letter abbreviation.
Example. Educational establishments - edu. Government agencies - gov. Commercial organizations – com:

tutor.sp tu.edu . Here edu- a common domain for schools and universities. Tutor- subdomain sp tu , which is a subdomain edu.

World Wide Web

The most popular Internet service is the World Wide Web (abbreviated WWW or Web), also called the World Wide Web. The presentation of information on the WWW is based on the capabilities of hypertext links. Hypertext- this is text that contains links to other documents. This makes it possible, when viewing a document, to easily and quickly move to other information related to it in meaning, which can be text, image, sound file or have any other form accepted on the WWW. At the same time, linked documents can be scattered across the globe.
Numerous intersecting connections between WWW documents and the computer web span the planet - hence the name. Thus, there is no dependence on the location of a specific document.
The World Wide Web service is designed for access to a special kind of electronic documents, which are called Web documents or, more simply, Web pages. A Web page is an electronic document that, in addition to text, contains special formatting commands, as well as embedded objects (drawings, audio and video clips, etc.).
Browse web pages using special programs, called browsers, so the browser is not just a WWW client used to interact with remote Web servers, it is also a means of viewing Web documents. For example, if a Web page was saved to your hard drive, you can view it using a browser without an Internet connection. This type of browsing is called offline browsing.
Unlike printed electronic documents, Web pages are not absolute, but relative formatting, that is, they are formatted at the time of viewing in accordance with the screen and browser they are viewed on. Strictly speaking, the same Web page when viewed in different browsers may look different - it depends on how the browser reacts to the commands that its author has built into the Web page.
Each Web document (and even each object embedded in such a document) on the Internet has its own unique address - it is called uniform resource locator URL (Uniformed Resource Locator) or, for short, URL. By contacting this address, you can obtain the document stored there.
There are many, many Web documents stored on the Internet. Over the past seven years, WWW content has doubled every year and a half. Apparently, in the coming years this rate will decrease somewhat, but will remain quite high, according to at least to the 10 billion mark. Due to such a huge number of Web documents, there is an important problem of searching and selecting them on the Web today - we will look at it separately, but for now let’s get acquainted with how a URL formally looks like.
Example URL: http://klyaksa.net/htm/exam/answers/images/a23_1.gif
Here is the URL to the picture located on one of the Web pages of the portal www.klyaksa.net.
A document URL has three parts and, unlike domain names, is read from left to right. The first part indicates the name of the application protocol through which this resource is accessed. For the World Wide Web service, this is the HyperText Transfer Protocol (HTTP). Other services have different protocols. The protocol name is separated from the rest of the address by a colon and two forward slashes.
The second element is the domain name of the computer on which the document is stored. We are already familiar with the structure of a domain name - its elements are separated by dots. The domain name is followed by a slash.
The last element of the address is the path to access the file containing the Web document on the specified computer. With the file access path recorded in operating system We are already familiar with Windows, but there is an important difference. In Windows, it is customary to separate directories and folders with the backslash character "\", while on the Internet it is recommended to use a regular forward slash "/". This is due to the fact that the Internet began on computers running in the operating room. UNIX system, and there it is customary to divide directories this way.
Each hyperlink on the Internet is associated with the Web address of some document or object (a file with a picture, sound recording, video clip, etc.). When you click on a hyperlink, a request is sent to the Network for the supply of the object to which the hyperlink points. If such an object exists at the specified address, it is downloaded and played. If it does not exist in nature (for example, it ceased to exist for some reason), an error message is displayed - then you can return to the previous page and continue working.

Basic Internet services

1. Electronic mail (E-mail).
Electronic mail (E-mail - Electronic mail, English mail - "mail") is the most common and, until recently, the most popular use of the Internet. According to estimates by the International Telecommunication Union, the number of users by email exceeds 50 million. The popularity of e-mail is explained not only by its capabilities, but also by the fact that it can be used with any type of Internet access, even the cheapest.
When using email, each user is assigned a unique email address, which is usually formed by appending the username to the name of the computer itself. The username and computer name are separated by the special symbol @. For example, if the user's login name is emsworth on the computer blandings.corn, then his email address will look like [email protected].

3. Teleconferencing service (Usenet)
Another widely used service provided by the Internet is Usenet news- Usenet news, which is also often called newsgroups (they have nothing to do with television, and the prefix “tele” means “remote”, “operating at a long distance”). They provide the opportunity to read and post messages to public (open) discussion groups.
Usenet is a virtual, imaginary network through which news is transmitted between computers - news servers using a special protocol NNTP (Network News Transfer Protocol).

4. File Transfer Service (FTP) deals with the reception and transmission of large files. The FTP service has its own servers on the global network where data archives are stored. These archives may be commercial or restricted, or may be publicly available.

5. Access to a remote computer (Telnet)
If we recall the history of the development of computers, there was a time when the computer itself was large and stood in a special computer room. The terminals (i.e., displays with keyboards) that allowed the computer to be used were located in another room. The displays were alphanumeric, so the dialogue with the computer consisted of entering symbolic commands, in response to which the computer printed the corresponding data on the screen.
When creating a remote access system, it was decided to preserve this method of dialogue with a computer.
The remote access program is called Telnet.
For its functioning, like all Internet services, it is necessary to have two parts - a server program installed on a remote computer, and a client program installed on the remote computer. local computer.
To connect to a remote system, you must be a registered user, that is, have a login name and password. To establish a connection, you must specify the name of the remote computer. After a successful connection, you can do the same operations on the remote computer as on the local computer, i.e. browse directories, copy or delete files, run various programs, having an alphanumeric interface.

6. IRC (Internet Relay Chat) service designed for direct communication between several people in real time. This service is also called chat conferencing or simply chat.

7. ICQ service. Its name comes from the expression I seek you - I am looking for you. The main purpose is to enable communication between two people, even if they do not have a permanent IP address.
8. World Wide Web (WWW) service- this is one information space, consisting of hundreds of millions of interconnected electronic documents stored on Web servers. Individual documents are called Web pages. Groups of thematically linked Web pages are called Web sites or Web sites.

Transmission with the establishment of a virtual channel differs from transmission with the establishment of a logical connection in that the connection parameters include a route laid out in advance by the network, along which all packets within the network pass. of this connection. The virtual circuit for the next session may take a different route.

Packets can travel in a network in three main ways: datagram transmission, connection-based transmission, and virtual circuit transmission.

In datagram transmission, an individual packet is treated as an independent transmission unit (datagram), no connection is established between nodes, and all packets travel independently of each other. Transmission with the establishment of a logical connection involves the establishment communication sessions with the definition of a procedure for processing a certain number of packets within one session.

Since computers and network equipment can be from different manufacturers, the problem of their compatibility arises. Without the adoption by all manufacturers of generally accepted rules for constructing equipment, the creation of a computer network would be impossible. Therefore, the development and creation of computer networks can only occur within the framework of approved standards for:

Interaction software user with a physical communication channel (via network card) within one computer;

Interaction of a computer through a communication channel with another computer.

There are three levels in the implementation of communications: hardware, software and information. In terms of hardware and software levels communications– this is the organization of a reliable connection channel and the transmission of information without distortion, the organization of information storage and effective access to it.

Modern computer software has a multi-level modular structure, i.e. The program code written by the programmer and visible on the monitor screen (top-level module) goes through several levels of processing before turning into an electrical signal (low-level module) transmitted to the communication channel.

When computers interact through a communication channel, both computers must fulfill a number of agreements (on the magnitude and shape of electrical signals, the length of messages, methods of reliability control, etc.).

In the early 80s of the twentieth century, a number of international organizations developed a standard model of network interaction - model of open systems interaction (OSI – Open System Interconnection). In the OSI model, all network protocols are divided into seven layers: physical, channel, network, transport, session, representative and application.

Formalized rules that determine the sequence and format of messages exchanged between modules located at the same level, but on different computers are called protocols.

Modules that implement neighboring layer protocols and are located on the same computer also communicate with each other in accordance with clearly defined rules and using standardized message formats. These rules are called interface and define a set of services provided by this layer to the neighboring layer.

A hierarchically organized set of protocols for the interaction of computers on a network is called stack of communication protocols, which can be implemented in software or hardware. Lower-level protocols are typically implemented using a combination of software and hardware, while higher-level protocols are implemented purely in software.

The protocols of each level are independent from each other, i.e. a protocol at any layer can be changed without having any effect on the protocol at another layer. The main thing is that the interfaces between the layers provide the necessary connections between them.

The OSI standard uses special names to designate units of data that protocols at different levels deal with: frame, packet, datagram, segment.

The OSI model has published, publicly available specifications and standards adopted by agreement among many developers and users. If two networks are built in compliance with the rules of openness, then they have the opportunity to use hardware and software different manufacturers adhering to the same standard, such networks are easily interfaced with each other, easy to learn and maintain. Example open system is a global computer network called the Internet.

In local networks, the following main methods are used for computers to access communication lines for data transmission: priority, marker and random. Priority access was implemented in the 100G-AnyLAN standard, and token access in Token Ring technology. These methods are currently not widely used due to the complexity of the equipment that implements them.

Ethernet is the most common standard for data transmission in local networks today, implemented at the data link level of the OSI model, according to which computer access to the communication line is provided randomly. The standard uses a multiple access method with carrier sensing and collision detection. It is used in networks with a “common bus” topology.

Recently, it has become widespread radio-ethernet(the corresponding standard was adopted in 1997) for organizing a wireless local network (WLAN - Wireless LAN). Radio networks are convenient for mobile means, but also find application in other areas (chains of hotels, libraries, airports, hospitals, etc.).

Radio Ethernet uses two main types of equipment: a client (computer), an access point, which plays the role of a link between the wired and wireless network. Wireless network can operate in two modes: “client/server” and “point-to-point”. In the first mode, several computers can connect to one access point via a radio channel; in the second mode, communication between end nodes is established directly without a special access point.

The most famous modification of radio-Ethernet is WiFi (Wireless Fidelity) a technology that provides transmission speeds of up to 11 Mbit/s, and uses a multiple access method with carrier sensing and collision avoidance (the corresponding standard was adopted in 2001). For communication, omnidirectional and narrow directional antennas are used (the latter for point-to-point connections). An omnidirectional antenna guarantees communication over distances of up to 45 meters, and a highly directional antenna – up to 45 km. Can serve up to 50 clients at the same time.

Unlike wired Ethernet, it is important for radio networks that the radio signals from different sending nodes do not overlap at the input of the receiving node. Otherwise, a collision will occur in the network. To prevent collisions in radio-Ethernet, it is necessary to strictly observe the radio signal ranges of individual nodes.

Using Internet methods packet switching made it quite fast and flexible. Unlike circuit switching, packet switching does not need to wait for a connection to be established with the receiving computer; packets travel independently of each other. This allows various services (email, www, IP telephony, etc.) to transmit information.

The Internet is based on the idea of ​​connecting many independent networks of almost arbitrary architecture. An open network architecture means that individual networks can be designed and developed independently, with their own unique interfaces exposed to users and/or other network service providers, including Internet services.

The key to the rapid growth of the Internet has been a free, open access to basic documents, especially protocol specifications. It played an important role in the development of the Internet commercialization, which includes not only the development of competitive, private network services, but also the development of commercial products (hardware and software network software) that implement Internet technologies.

The basis of Internet data transmission is the puncture stack TCP/IP (Transmission Control Protocol/Internet Protocol) which provides:

- independence from the network technology of a separate network – TCP/IP defines only the transmission element – datagram and describes the way it moves through the network;

- universal connectivity of networks, by assigning each computer a logical address used 1) by the transmitted datagram to identify the sender and recipient, 2) by intermediate routers to make routing decisions;

- confirmation - The TCP/IP protocol provides confirmation of the correctness of information flow during data exchange between the sender and the recipient;

- support for standard application protocols – email, file transfer, remote access, etc.

The TCP/IP stack defines 4 levels of interaction, each of which takes on a specific function in organizing reliable operation of the global network

The TCP/IP protocol software module is implemented in the computer operating system as a separate system module (driver). The user can independently configure the TCP/IP protocol for each specific case (number of network users, capacity of physical communication lines, etc.).

The main task of TCP is the delivery of all information to the recipient’s computer, control of the sequence of transmitted information, and resending of undelivered packets in the event of network failures. Reliability of information delivery is achieved as follows.

On the sending computer, TCP breaks down a block of data coming from the application layer into individual segments, assigns numbers to segments, adds a header, and passes the segments to the internetworking layer. For each sent segment, the sending computer expects a special message to arrive from the receiving computer - a receipt confirming the fact that the computer received the required segment. The waiting time for the corresponding receipt to arrive is called timeout time.

Setting the timeout time and the sliding window size is very important for network performance. The TCP protocol provides a special automatic algorithm for determining these values, taking into account the throughput of physical communication lines.

The purpose of the TCP protocol is to determine what type of application programs the data received from the network belongs to. To distinguish application programs, special identifiers are used - ports. The assignment of port numbers is carried out either centrally if the application programs are popular and publicly available (for example, a remote access service FTP files has port 21, and the WWW service has port 80), or locally - if the application developer simply associates any available, randomly selected number with this application.

TCP protocol can work as a UDP protocol (User Datagram Protocol), which, unlike TCP, does not provide reliable packet delivery and protection against failures in information transmission (does not use receipts). The advantage of this protocol is that it requires a minimum of settings and parameters for transmitting information.

IP protocol is the core of the entire TCP/IP stack architecture and implements the concept of transmitting packets to the desired address (IP address). Appropriate level of interaction ( Internet level, see Fig.4.1 ) provides the ability to move packets across the network using the route that is currently optimal.

IP addressing of computers on the Internet is based on the concept of a network consisting of hosts. Host represents a network object that can send and receive IP packets, for example, a computer, work station or router. Hosts are connected to each other through one or more networks. The IP address of any of the hosts consists from the address (number) of the network (network prefix) and the host address in this network.

In accordance with the convention adopted at the time of the development of the IP protocol, the address is represented by four decimal numbers separated by dots. Each of these numbers cannot exceed 255 and represents one byte of a 4-byte IP address. The allocation of only four bytes to address the entire Internet network is due to the fact that at that time the mass distribution of local networks was not expected. ABOUT personal computers and there was no talk of workstations at all. As a result, 32 bits were allocated for the IP address, of which the first 8 bits indicated the network, and the remaining 24 bits indicated the computer on the network. The IP address is assigned by the network administrator during the configuration of computers and routers. For convenience, they are represented as four decimal digits separated by a comma, for example, 195.10.03.01. There are five classes of IP addresses - A,B,C,D,E. Depending on the class of IP address on the network, there will be a different number of addressable subnets and the number of computers in a given subnet.

Since it is extremely inconvenient to use digital network addressing when working on the Internet, symbolic names are used instead of numbers - domain names. A domain is a group of computers united by one name. Symbolic names give the user the opportunity to better navigate the Internet, since remembering a name is always easier than a digital address.

In addition, all countries in the world have their own symbolic name indicating the top level domain of that country. For example, de – Germany, us – USA, ru – Russia, by – Belarus, etc.

IN structural components Internet networks include:

- routers– special devices that connect separate local networks to each other by directly addressing each of the subnets using IP addresses. The forwarding of packets between subnets according to destination addresses is called routing;

- proxy server(from the English proxy - “representative, authorized”) is a special computer that allows local network users to receive information stored on computers on the Internet. First, the user connects to the proxy server and requests a resource (for example, e-mail) located on another server. The proxy server then either connects to the specified server and obtains the resource from it, or returns the resource from its own memory. The proxy server also allows you to protect the client computer from certain network attacks;

- DNS server – a special computer that stores domain names.

To protect the local network from unauthorized access (hacker attacks, viruses, etc.), software and hardware systems are used - firewalls. On the network, it filters the flow of information in both directions and blocks unauthorized access to a computer or local network from the outside. The firewall allows you to control the use of ports and protocols, “hide” unused ports to prevent attacks through them, and also deny/allow access of specific applications to specific IP addresses, i.e. control everything that can become a tool of a hacker and unscrupulous companies. Firewalls generally operate at the network level and filter packets, although protection can also be organized at the application or data link level. Packet filtering technology is the cheapest way to implement a firewall, because... in this case, it is possible to scan packets of various protocols at high speed. The filter analyzes packets at the network level and is independent of the application used.

Firewall It is a kind of software firewall, a means of controlling incoming and outgoing information. Firewall programs are built into standard operating systems.

Provider is an Internet access provider - any organization that provides individuals or organizations with access to the Internet. Providers are generally divided into two classes:

Internet Access Providers (ISP);

Online Service Providers (OSP).

An ISP can be a company that pays for a high-speed connection to one of the companies that are part of the Internet (AT&T, Sprint, MCI in the USA, etc.). These can also be national or international companies that have their own networks (such as WorldNet, Belpak, UNIBEL, etc.)

OSPs, sometimes simply called "interactive services", can also have their own networks. They provide additional information services available to customers who subscribe to these services. For example, Microsoft OSPs offer users access to Internet services from Microsoft, America Online, IBM and others. ISPs are the most common.

Typically, a large provider has its own POP (point-of-presence) in cities where local users connect.

To interact with each other, different providers agree to connect to so-called NAP access points (Network Access Points), through which information flows of networks belonging to a separate provider are combined.

There are hundreds of large providers operating on the Internet; their backbone networks are connected via NAP, which provides a single information space for the global Internet computer network.

The main Internet services include:

- electronic mail (e-mail);

- WWW (World Wide Wed, The World Wide Web) ;

- FTP (File Transfer Protocol);

- UseNet newsgroups, the corresponding NNTP protocol (Network News Transport Protocol) is intended for replication of articles in the distributed discussion system UseNet;

- Telnet remote terminal service provides the ability to work on a remote computer on a network that supports the Telnet service;

- IP-telephony service (IP-Telephony)– allows you to use the Internet as a means of exchanging voice information and transmitting faxes in real time using voice signal compression technology. To ensure the operation of IP telephony, the H.323 protocol stack is used, which splits the data stream into packets and assembles packets into correct sequence, determining packet losses, ensuring synchronization and continuity of data flow. Voice data is transmitted via UDP without waiting for a receipt.

In addition to the most popular protocols indicated, others are also used on the Internet - network file system(NSF), network monitoring and management (SNMP), remote procedure execution (RPC), network printing, etc.

There are several organizations responsible for the development of the Internet:

- Internet Society (ISOC)– a professional community that deals with the growth and evolution of the Internet as a global communication infrastructure;

- Internet Architecture Board (IAB) – An ISOC-managed organization responsible for technical control and coordination of work for the Internet. The IAB coordinates the direction of research and new developments for the TCP/IP protocol and is the final authority in defining new Internet standards. It includes: Internet Engineering Task Force (IETF) – an engineering group that deals with the immediate technical problems of the Internet and Internet Research Task Force (IRTF)– coordinates long-term projects using TCP/IP protocols;

- Internet Corporation for Assigned Names and Numbers (ICANN) – an international non-profit organization for providing local and regional networks with a specific IP address . This organization has a special information center - InterNIC (Internet Network Center);

- World Wide Web Consortium, W3C (W3 consortium) – a coordinating organization to promote the Internet as a medium for implementing positive social and economic transformations in society.

A corporate network (CN) is an organization’s infrastructure that supports the solution of current problems and ensures its implementation missions. It unites the information systems of all corporation facilities into a single space and is created as a system-technical basis information system, as its main system-forming component, on the basis of which other subsystems are constructed.

Creating a corporate network allows you to:

Create a unified information space;

Promptly receive information and generate consolidated reports at the enterprise level;

Centralize financial and information data flows;

Promptly collect and process information;

Reduce costs when using server solutions and moving from workgroup solutions to enterprise-level solutions;

Process multimedia data streams between departments;

Reduce communication costs between departments and organize a single number space;

Ensure high-quality communication at high speeds;

Organize a video surveillance system.

Basic requirements for modern corporate networks:

- scalability means the possibility of increasing server capacity (performance, volume of stored information, etc.) and territorial expansion of the network;

- network reliability– is one of the factors determining the continuity of the organization’s activities;

- performance– the growth in the number of network nodes and the volume of processed data places ever-increasing demands on the throughput of the communication channels used and the performance of devices that ensure the functioning of the CIS;

- economic efficiency – saving money on the creation, operation and modernization of network infrastructure with the constant growth in the scale and complexity of corporate networks;

- Information Security - ensures the stability and security of the business as a whole, and protects the storage and processing of confidential information online.

The following basic principles for building a corporate network are distinguished:

- comprehensive nature - the network extends to the entire corporation;

- integration – the corporate network provides the ability for its users to access any data and applications, subject to policy information security;

- global character – The CS provides information about the life of the organization regardless of politics and state borders;

- adequate performance characteristics– the network has the property of being manageable and has a high level of failure-free operation, survivability, and serviceability while supporting applications that are critical for the corporation’s activities;

Maximum usage standard solutions, standard standardized components.

A corporate network can be viewed from various perspectives:

- structures ( system technical infrastructure );

- system functionality(services and applications);

- performance characteristics to (properties and services).

From a system-technical point of view, it is an integral structure consisting of several interconnected and interacting levels: computer network, telecommunications, computer and operating platforms, middleware, applications.

From a functional point of view, the CS is an effective medium for transmitting relevant information necessary to solve the problems of the corporation.

From the point of view of system functionality, the CS looks like a single whole, providing users and programs with a set of useful services ( services), system-wide and specialized applications, which has a set of useful qualities and contains services, guaranteeing the normal functioning of the network.

Typically, the CS provides users and applications with a number of universal services - DBMS service, file service, information service (Web service), e-mail, network printing and others.

TO system-wide applications include automation tools for individual work, used by various categories of users and aimed at solving typical office tasks - word processors and spreadsheet processors, graphic editor etc.

Specialized Applications are aimed at solving problems that are impossible or technically difficult to automate using system-wide applications, and define application functionality within the corporation.

The corporate network ensures that new applications can be deployed and run efficiently while preserving investments in it, and in this sense must have the properties of openness, performance and balance, scalability, high availability, security and manageability. These properties determine performance characteristics created information system.

System-Wide Services– this is a set of tools that are not directly aimed at solving applied problems, but are necessary to ensure the normal functioning of the CIS. Information security, high availability, centralized monitoring and administration services must be included in the CS.

CS is a mixed topology network that includes several local networks.

Speed ​​and ease of local network deployment;

Low costs for purchasing equipment;

Low cost of operation and no subscription fee;

Preserving investments in the local network when moving or changing offices.

The main disadvantage of such networks is that the data transfer speed decreases with increasing distance.

Using the Internet as a transport medium for data transmission when building an enterprise CS (Fig. 4.4) provides the following advantages:

Low subscription fee;

Ease of implementation.

Figure 4.4 – Using the Internet as a transport medium
data transmission

The disadvantages of such a network include low reliability and security, and the lack of a guaranteed data transfer speed.

Consolidating local enterprise networks into a single corporate network based on leased data transmission channels (Fig. 4.5) brings the following advantages:

High quality provided data transmission channels;

High level of services provided by the provider;

Guaranteed data transfer speed.

Figure 4.5 – Consolidation of local networks into a single network based on leased data transmission channels

A properly designed and implemented corporate network, the choice of reliable and productive equipment determines the performance of the CIS, the possibility of its effective and long-term operation, modernization and adaptation to rapidly changing business conditions and new tasks.

The infrastructure components of the corporate network are:

Cable system that forms the physical medium for data transmission;

Network equipment that provides data exchange between terminal equipment (workstations, servers, etc.).

When creating corporate networks, the main task is to build building-scale networks ( local) and groups of closely located buildings ( campus), integration using communication channels of geographically remote units. The Internet or a city network can act as a unifying means.

When building local and campus networks, we use switches, and when building geographically distributed networks – routers. Switches provide high-speed exchange within a local network, transmitting information only to destination nodes. Switches operate with channel protocol addresses, which, as a rule, are Ethernet/Fast Ethernet/Gigabit Ethernet, which ensures “transparent” operation of the network, and switches can perform their basic functions without time-consuming configuration. When transmitting information, routers operate logical addresses - for example, IP, IPX protocol addresses, etc., which allows them to process information using a hierarchical representation of the structure of a network that has a significant scale or consists of disparate and heterogeneous segments.

Wireless office networks serve as an alternative to traditional cable systems. Their main difference from cable systems is that data between computers and network devices is transmitted not through wires, but through a highly reliable wireless channel. By using a wireless network built in accordance with the Wi-Fi specification, the flexibility and scalability of the local network is ensured, the ability to easily connect new equipment, workstations, and mobile users, regardless of the type of computer used. The use of wireless network technologies allows you to receive additional services: Internet access in a conference room or meeting room, organization of a Hot-Spot access point, etc.

Advantages of using wireless networks:

Speed ​​and ease of wireless network deployment;

Network scalability, the ability to build multi-cell networks;

Preservation of investments in the local network when changing the location of the office;

Rapid restructuring, changing the configuration and size of the network;

Mobility of users within the network coverage area.

In Fig. Figure 4.6 shows an office network consisting of several wireless cells, in the center of which there are access points connected by a single wired channel or wireless bridges. Such a network provides the highest performance, scalability, and free movement of users within the radio visibility zones of access points.

To organize uninterrupted operation and ensure data security in the CS, it is necessary to have a network administration service. Administration is a management process, the activity of managing an assigned area of ​​work through administrative management methods.

Figure 4.6 – Wireless network in an organization

Administration of a computer network involves information support for users and allows minimizing the influence of the human factor on the occurrence of failures in its operation.

System Administrator– an employee who ensures the organization’s network security, creating optimal performance of the network, computers and software. Often, the functions of a system administrator are performed by companies engaged in IT outsourcing.

The administrator decides on network planning, selecting and purchasing network equipment, monitors the progress of network installation and ensures that all requirements are met. After installing the network equipment, he checks it and installs network software on servers and workstations.

The administrator's responsibilities include monitoring the use of network resources, registering users, changing user access rights to network resources, integrating diverse software used on file servers, database management system (DBMS) servers, workstations, timely copying and backup of data and restoring normal operation of network equipment and software after failures.

In large organizations, these functions may be distributed among several system administrators ( security administrators, users, Reserve copy , databases and etc.).

Web server administrator – installs, configures and maintains web server software.

Database Administrator– specializes in database maintenance and design.

Network Administrator– develops and maintains networks.

System engineer(or system architect) – is engaged in building corporate information infrastructure at the application level.

Network Security Administrator– deals with information security issues.

When administering a network connected to the Internet and on which Internet services are installed, the following problems arise:

Organization of a network based on TCP/IP protocols;

Connecting a local or corporate network to the Internet;

Routing of information transmission in the network;

Obtaining a domain name for an organization;

Exchange of email within the organization and with recipients outside of it;

Organization of information services based on Internet and Intranet technologies;

Network security.