Coursework: Wireless Telecommunication Systems. Basic information about telecommunication systems Telecommunication systems

An important sphere of human activity is the information infrastructure, due to which many necessary areas are developing. At first, the telegraph network was used for this, after which telephones, radio, television, and computers began to appear. Any information created in electronic form can arrive at the destination without a specialist.

Communication of the subjects of the country, international communication works on the basis of multichannel telecommunication systems. For this, analog and digital devices are used. With their help, audio, video, multimedia are transmitted. Therefore, people have access to the Internet, cellular and many other services. This is why it is necessary to train specialists to work in this area.

Features of the profession

If a graduate graduates with a degree in multichannel telecommunication systems, who will he work with? You can get a job at an enterprise for the vacancy "technician". The duties of the employee include providing a certain territory with communications, television, radio broadcasting.

The technician works with what is required for the transmission systems to function. Reconstruction of lines and installation of the latest equipment is in progress. The main place in the technical equipment belongs to fiber-optic technology, with the help of which the transmission speed and network quality are increased.

Employee training

The profession of "multichannel telecommunication systems" of future specialists is taught using applied disciplines. They need to understand the installation and operation of cable and digital systems data transmission.

The lectures study the technologies of software and hardware data encryption to protect information. With an advanced training profile, it is required to master the training program of management activities and management of the organization. Colleges and institutes of different cities of Russia teach in the specialty "multichannel telecommunication systems".

What can graduates do?

Specialists should operate multichannel telecommunication systems. Mandatory work on information security networks. An important activity is participation in the organization's production work.

Employees perform the work of several employee positions. They produce the convergence of telecommunication technologies and services. One of the main areas is the promotion of network services. If a graduate graduated from training in the specialty "multichannel telecommunication systems", who should he work and where? Technicians are required in government and commercial enterprises.

Responsibilities of specialists

Technicians perform installation and maintenance. Monitoring and diagnostics of systems is mandatory. The employees eliminate the consequences of accidents and equipment defects, determine the methods for restoring functioning.

At the enterprises of technology, measurements of equipment indicators are carried out. They carry out the installation and professional maintenance of computer networks. The employee takes responsibility for the administration of network equipment, installation, access settings.

The technician interacts with network protocols. He monitors the functioning of network equipment. In their professional activities, they use proven information security tools. Other responsibilities include:

• analysis of systems operation to identify problems;
• ensuring secure administration;
• participation in work planning;
• monitoring of new systems;
• marketing research.

Professionals build and operate information transmission systems, operate at automatic stations. Graduates in the specialty "multichannel telecommunication systems" are employed in line-equipment shops, radio relay departments, communication centers. The technician acquires the necessary skills.

Salary and prospects

If a graduate has received the specialty "multichannel telecommunication systems", the salary at first will be about 20,000 rubles. At the same time, the employee must know and be able to install and connect telephone equipment, set up a mini-automatic telephone exchange, the Internet.

The employee needs to constantly improve, increasing the level of knowledge and skills. Such an employee will always be in demand, which will increase personal income. To get a lot of money, you need to have rich experience in servicing communication systems, installing equipment, generating documentation. You can work in specialized state and commercial enterprises.

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Ministry of Education of the Russian Federation

Far Eastern State Technical University

(DVPI named after V.V. Kuibyshev)

Department of Design and Production of Radio Equipment

Telecommunication systems

Performed by D.R. Rakipova

student of group Pi (b) -21

Checked by T.A. Sebto

Main questions

1. What are telecommunication systems?

2. What is an information system?

3. What is its role?

4. What characteristics of information systems do you know?

5. What classifications of information systems do you know?

6. What is a communication channel?

7. What types of communication channels are there?

8. What is an information network?

9. How can you organize access to information networks?

telecommunication information network communication

Introduction

Conclusion

Basic concepts

Bibliography

Introduction

Without exaggeration, the 21st century can be called the age of information technology. The concept of information technology includes many aspects. One of the most important parts of this area is the direct transfer of information through information networks.

Telecommunication technologies are the principles of organizing modern analog and digital systems and communication networks, including computer and INTERNET networks.

Telecommunications means are a set of technical devices, algorithms and software that allow you to transmit and receive speech, information data, multimedia information using electrical and electromagnetic oscillations over cable, fiber-optic and radio-technical channels in various wavelengths. These are devices for converting information, its coding and decoding, modulation and demodulation, these are modern Computer techologies processing.

1. Characteristics and classification of information networks

Modern telecommunication technologies are based on the use of information networks.

A distinctive feature of the communication network is the large distances between points in comparison with the geometric dimensions of the areas of space occupied by the points.

Computing network - an information network that includes computing equipment. Computing network components can be computers and peripheral devices that are sources and receivers of data transmitted over the network. These components constitute the data terminal equipment (DTE or DTE - Data Terminal Equipment). Computers, printers, plotters and other computing, measuring and executive equipment of automatic and automated systems can act as OOD. The actual transfer of data occurs using media and means, united under the name of the data transmission medium.

The preparation of the data transmitted or received by the DTE from the data transmission medium is carried out by a functional block called the Data Circuit-Terminating Equipment (DCE or DCE). The DCE can be a structurally separate unit or a unit built into the DTE. The DTE and DCE together constitute a data station, which is often referred to as a network node. An example of a DCE is a modem.

Computing networks are classified according to a number of characteristics.

Computer networks are distinguished depending on the distance between the nodes to be connected:

Territorial? covering a significant geographic area; among territorial networks, regional and global networks can be distinguished, having, respectively, regional or global scales; regional networks are sometimes called MAN (Metropolitan Area Network) networks, and the common English name for territorial networks is WAN (Wide Area Network);

Local (LAN)? covering a limited area (usually within the distance of stations no more than a few tens or hundreds of meters from each other, less often by 1 ... 2 km); local area networks stand for LAN (Local Area Network);

Corporate (enterprise scale)? a set of interconnected LANs covering the territory where one enterprise or institution is located in one or more closely located buildings. Local and corporate computer networks are the main type of computer networks used in computer-aided design (CAD) systems.

The unique global Internet is especially distinguished (the World Wide Web (WWW) information service implemented in it is translated into Russian as The World Wide Web); it is a network of networks with its own technology. In the Internet, there is the concept of intranets (Intranets) - corporate networks within the Internet.

Distinguish between integrated networks, non-integrated networks and subnets. An integrated computer network (internetwork) is an interconnected collection of many computer networks, which are called subnets in the internetwork.

In automated systems of large enterprises, subnets include the computing facilities of individual project departments. Internets are needed to combine such subnets, as well as to combine technical means of computer-aided design and manufacturing systems into a single integrated automation system (CIM - Computer Integrated Manufacturing). Typically, internets are adapted for different types of communication: telephony, e-mail, video transmission, digital data, etc., in which case they are called integrated service networks. The development of internetworks consists in the development of heterogeneous subnetting tools and standards for building subnets that are initially adapted for interfacing. Subnets in internets are combined according to the selected topology using interworking blocks.

2. Layered architecture of information networks

In the general case, for the functioning of computer networks, it is necessary to solve two problems:

Transfer the data for the intended purpose in the correct form and in a timely manner;

The data received by the user must be recognizable and have the proper form for their correct use.

The first problem is related to routing tasks and is provided by network protocols (low-level protocols).

The second problem is caused by the use of different types of computers in networks, with different codes and language syntax. This part of the problem is solved by introducing high-level protocols.

Thus, the complete end-user-centric architecture includes both protocols.

Developed reference model of interaction open systems(OSI) supports the concept that each layer provides services to the higher layer and is based on the lower layer and uses its services. Each level performs a specific function of data transmission. Although they must work in strict order, each of the levels allows several variations. Consider the reference model. It consists of 7 layers and is a layered architecture that is described by standard protocols and procedures.

The lower three layers provide network services. Protocols that implement these layers must be provided at every node in the network.

The top four layers provide services to the end users themselves and are thus associated with them and not with the network.

Physical layer. This part of the model defines the physical, mechanical, and electrical characteristics of the communication lines that make up the LAN (cables, connectors, fiber optic lines, etc.). We can assume that this level is responsible for Hardware... Although the functions of other levels can be implemented in the corresponding microcircuits, they still belong to software. The function of the physical layer is to ensure that symbols entering the physical medium at one end of the channel reach the other end. When using this downstream symbol transport service, the task of the channel protocol is to ensure reliable (error-free) transmission of data units over the channel. Such blocks are often called loops, or frames. The procedure usually requires: synchronization on the first character in the frame, recognizing the end of the frame, detecting erroneous characters, if any, and correcting such characters in some way (usually this is done by requesting a retransmission of a frame in which one or more erroneous characters are detected ).

Channel level. The data link layer and the physical layer below it provide an error-free transmission channel between two nodes in the network. This layer defines the rules for using the physical layer by network nodes. The electrical representation of the data on the LAN (data bits, data coding methods and markers) are recognized at this and only at this level. This is where errors are detected (recognized) and corrected by re-transmission requests.

Network layer. The function of the network layer is to establish a route for data transmission over the network or, if necessary, through multiple networks from the transmission node to the destination node. This layer also provides for flow or congestion control to prevent overflow of network resources (storage in nodes and transmission channels), which can lead to interruption. When performing these functions at the network layer, the service of the lower layer is used - a data transmission channel that ensures the error-free arrival of a data block inserted into the channel at the opposite end along the network route.

The main task of the lower levels is to transfer data blocks along the route from the source to the receiver, delivering them in a timely manner to the desired end.

Then the task of the upper levels is to actually deliver the data in the correct form and recognizable form. These upper levels do not know about the existence of the network. They provide only the service required of them.

Transport layer. Provides reliable, consistent data exchange between two end users. For this purpose, the transport layer uses a network layer service. It also controls the flow to ensure that blocks of data are received correctly. Due to differences in endpoints, data in a system can be transmitted at different rates, so if flow control is not in place, slower systems can be overwhelmed by faster ones. When more than one packet is in process, the transport controls the order in which the message components pass. If a duplicate of a previously received message arrives, then this layer recognizes this and ignores the message.

Session level. The functions of this layer are to coordinate communication between two applications running on different workstations. It also provides services to the superior presentation layer. This happens in the form of a well-structured dialogue. These functions include creating a session, controlling the transmission and reception of message packets during a session, and terminating a session. This layer also manages negotiations as needed to ensure correct communication. The dialogue between the user of the session service (ie, the presentation layer parties and the upstream layer) may consist of normal or accelerated data exchange. It can be duplex, i.e. simultaneous two-way transmission, when each side has the ability to transmit independently, or half-duplex, i.e. with simultaneous transmission in one direction only. In the latter case, special labels are applied to transfer control from one side to the other. The session layer provides a synchronization service to overcome any errors it finds. With this service, synchronization marks must be inserted into the data stream by the users of the session service. If an error is detected, then the session connection must be returned to a certain state, users must return to the set point of the dialog flow, discard some of the transferred data, and then restore the transfer starting from this point.

Presentation layer. Manages and transforms the syntax of data blocks that end users exchange. This situation can occur in heterogeneous PCs (IBM PC, Macintosh, DEC, Next, Burrogh), which need to exchange data. Purpose - transformation of syntactic data blocks.

Application level. Application protocols provide appropriate semantics or meaning to the information exchanged. This layer is the boundary between the PP and the processes of the OSI model. A message intended to be transmitted over a computer network enters the OSI model at a given point, passes through layer 1 (physical), is forwarded to another PC, and travels from layer 1 in reverse order until it reaches the IP on another PC through its application layer. Thus, the application layer provides a mutual understanding of the two application programs on different computers.

3. Varieties of communication channels

Data transmission medium is a set of data transmission lines and interaction units (i.e. network equipment not included in data stations) intended for data transmission between data stations. Data transmission media can be public or dedicated for specific user.

Channel (communication channel) - means of one-way data transmission. An example of a channel might be a frequency band allocated to a single transmitter in radio communications.

Data transmission channel - means of two-way data exchange, including the equipment for the termination of the data channel and the data transmission line. By the nature of the physical data transmission medium (PD), data transmission channels are distinguished on optical communication lines, wired (copper) communication lines, and wireless.

Communication channels can be divided into:

1. Wire communication lines

In computer networks, wired communication lines are represented by coaxial cables and twisted pairs of wires. Twisted pairs sometimes referred to as a balanced line in the sense that the two wires of the line carry the same signal levels (with respect to ground), but with different polarities. When received, a signal difference is perceived, called a paraphase signal. The common mode noise is then self-compensated.

2. Optical communication lines

Optical communication lines are implemented in the form of fiber-optic communication lines (FOCL). The structure of the FOCL is a quartz core with a diameter of 10 microns, covered with a reflective cladding. FOCLs are the backbone of high-speed data transmission, especially over long distances.

3. Wireless communication channels

In wireless channels, information is transmitted based on radio wave propagation.

The higher the carrier frequency, the greater the capacity (number of channels) of the communication system, but the smaller the maximum distances at which direct transmission between two points without repeaters is possible. The first of the reasons gives rise to the tendency to master new higher frequency ranges.

Radio channels are included in the required part of in satellite and radio relay communication systems used in territorial networks, in cellular systems mobile communications, they are used as an alternative to cable systems in local networks and when connecting networks of individual offices and enterprises into corporate networks.

4. Satellite data transmission channels

Satellites in communication systems can be located in geostationary (36 thousand km) or low orbits. With geostationary orbits, delays in signal transmission are noticeable (there and back about 520 ms). It is possible to cover the surface of the entire globe with four satellites. In LEO systems, a specific user is served alternately by different satellites. The lower the orbit, the smaller the coverage area and, therefore, either more ground stations are needed, or the space between satellite connection, which naturally makes the satellite heavier. The number of satellites is also much larger (usually several dozen).

The structure of satellite data transmission channels can be illustrated by the example of the well-known VSAT (Very Small Aperture Terminal) system. The ground part of the system is represented by a set of complexes, each of which includes a central station (CS) and subscriber stations (AP). The CS communicates with the satellite via a radio channel (bandwidth 2 Mbit / s) through a directional antenna with a diameter of 1 ... 3 m and transceiver equipment. APs are connected to the central station according to the "star" scheme using multichannel equipment or via a radio channel via a satellite. Those APs that are connected via a radio channel (these are mobile or hard-to-reach objects) have their own antennas, and a different frequency is allocated for each AP. The DS broadcasts its messages on one fixed frequency, and receives them on the AP frequencies.

4. Organization of access to information networks

The structure of territorial networks

The global Internet is the largest and only network of its kind in the world. It occupies a unique position among global networks. It would be more correct to regard it as an amalgamation of many networks that retain their independent significance. Indeed, the Internet has neither a clear ownership nor a national identity. Any network can have a connection to the Internet and, therefore, be considered part of it if it uses the TCP / IP protocols accepted for the Internet or has converters to TCP / IP protocols. Almost all national and regional networks have Internet access.

A typical territorial (national) network has a hierarchical structure.

The upper level is federal nodes, interconnected by backbone communication channels. Trunk channels are physically organized on fiber-optic lines or on satellite communication channels. The middle level is regional nodes that form regional networks. They are connected to federal nodes and, possibly, to each other by dedicated high- or medium-speed channels, such as T1, E1, B-ISDN channels or radio relay lines. The lower level is local nodes (access servers) connected to regional nodes, mainly dial-up or dedicated telephone communication channels, although there is a noticeable tendency towards a transition to high- and medium-speed channels. It is to local nodes that local networks of small and medium-sized enterprises are connected, as well as computers of individual users. Corporate networks of large enterprises are connected to regional nodes with dedicated high- or medium-speed channels.

Main types of access

1. Telecommunication technology service. The main services provided by telecommunication technologies are:

Email;

File transfer;

Teleconferences;

Referral services (bulletin boards);

Video conferencing;

Access to information resources (information bases) of network servers;

Mobile cellular communications;

Computer telephony;

The specificity of telecommunications is manifested primarily in application protocols. Among these, the best known are the Internet-related protocols and the ISO-IP (ISO 8473) protocols, which belong to the seven-layer open systems model. Internet application protocols include the following:

Telnet is a terminal emulation protocol, or, in other words, an implementation protocol remote control it is used to connect the client to the server when they are placed on different computers, the user through his terminal has access to the server computer;

FTP - file exchange protocol (remote node mode is implemented), the client can request and receive files from the server, the address of which is specified in the request;

HTTP (Hypertext Transmission Protocol) - a protocol for communication between WWW servers and WWW clients;

NFS is a network file system that provides access to files of all UNIX machines on the local network, i.e. node file systems appear to the user as a single file system;

SMTP, IMAP, POP3 - e-mail protocols.

These protocols are implemented using the appropriate software. For Telnet, FTP, SMTP on the server side, fixed protocol port numbers are allocated.

2. Email.

Electronic mail (E-mail) is a means of exchanging messages for electronic communications (off-line). You can forward text messages and archived files. The latter can contain data (for example, program texts, graphic data) in various formats.

3. File exchange.

File exchange - access to files distributed across different computers. On the Internet, at the application level, FTP protocol... Access is possible in off-line and on-line modes. In off-line mode, a request is sent to the FTP server, the server generates and sends a response to the request. In on-line mode, interactive browsing of FTP-server directories, selection and transfer of the necessary files is carried out. An FTP client is required on the user's computer.

4. Teleconferences and message boards.

Teleconferences - access to information allocated for group use in individual conferences (newsgroups). Global and local teleconferences are possible. Including content in newsgroups, sending out new submissions, and fulfilling orders are the main functions of teleconferencing software. E-mail and on-line modes are possible.

The largest teleconferencing system is USENET. In USENET, information is organized hierarchically. Messages are sent either like an avalanche or through mailing lists. In on-line mode, you can read the list of messages, and then the selected message. In off-line mode, a message is selected from the list and an order is sent to it.

Teleconferences can be with or without a moderator. Example: A team of authors working on a book on mailing lists.

There are also audio conferencing (voice teleconferencing) facilities. The call, connection, conversation occurs for the user as in a regular telephone, but the connection goes through the Internet.

The electronic "bulletin board" BBS (Bulletin Board System) is a technology similar in functionality to a teleconference that allows you to centrally and promptly send messages to many users. Software BBS combines e-mail, teleconferencing and file sharing. Examples of programs that have BBS facilities are Lotus Notes, World-group.

5. Access to distributed databases.

In client / server systems, the request must be generated in the user's computer, and the organization of data retrieval, their processing and the formation of a response to the request belong to the computer server. In this case, the necessary information can be distributed across different servers. On the Internet there are special database servers called WAIS (Wide Area Information Server), which can contain collections of databases under the control of various DBMS.

A typical scenario for working with a WAIS server:

Selecting the required database;

Formation of a query consisting of keywords;

Sending a request to the WAIS server;

Receiving from the server headers of documents corresponding to the given keywords;

Selecting the desired header and sending it to the server;

Getting the text of the document.

Unfortunately, WAIS is currently not being developed, therefore it is used little, although indexing and searching by indices in large arrays of unstructured information, which was one of the main functions of WAIS, is an urgent task.

6. Information system WWW.

WWW (World Wide Web - World Wide Web) is a hypertext information system of the Internet. Its other short name is Web. This more modern system provides users with more options.

First, it is hypertext - a structured text with the introduction of cross-references, reflecting the semantic connections of parts of the text. Reference words are highlighted with color and / or underlining. Selecting a link brings up the text or picture associated with the link word. You can search for the desired material by keywords.

Secondly, the presentation and acquisition of graphical images is facilitated. Web-accessible information is stored on Web servers. The server has a program that constantly monitors the arrival of requests from clients on a specific port (usually port 80). The server satisfies the requests by sending the client the content of the requested Web pages or the results of the requested procedures. WWW client programs are called browsers.

There are text and graphical browsers. Browsers have commands for paging, moving to the previous or next document, printing, clicking on a hypertext link, etc. For the preparation of materials and their inclusion in the WWW database, a special HTML language(Hypertext Markup Language) and software editors that implement it, such as Internet Assistant as part of Word or Site Edit, document preparation is provided as part of most browsers.

An HTTP protocol based on TCP / IP has been developed for communication between Web servers and clients. The web server receives the request from the browser, finds the file that matches the request, and passes it to the browser for viewing.

Conclusion

Intranet and Internet technologies continue to evolve. New protocols are being developed; old ones are being revised. NSF has made the system much more complex by introducing its backbone network, several regional networks, and hundreds of university networks.

Other groups also continue to join the Internet. The most significant change was not due to the addition of additional networks, but due to additional traffic... Physicists, chemists, and astronomers work and exchange more data than computer scientists, who make up the majority of the early Internet traffic users. These new scientists led to a significant increase in the download of the Internet when they started using it, and downloads steadily increased as they used it more and more.

To accommodate the growth in traffic, the capacity of the NSFNET backbone has been doubled, resulting in a current capacity of approximately 28 times the original capacity; another increase is planned to bring this ratio to 30.

At the moment, it is difficult to predict when the need for additional bandwidth increases will disappear. The growth in demand for network exchange was not unexpected. The computer industry has taken great pleasure in the constant demands for more processing power and more memory for data over the years. Users are just beginning to understand how to use the network. In the future, we can expect a constant increase in the need for interaction. Therefore, higher bandwidth interoperability technologies will be required to accommodate this growth.

The expansion of the Internet lies in the complexity created by the fact that several autonomous groups are part of a unified Internet. The original designs for many subsystems assumed centralized management. It took a lot of effort to fine-tune these projects to work under decentralized governance.

So, for the further development of information networks, higher-speed communication technologies will be required.

Basic concepts

Communication network is a system consisting of objects that perform the functions of generating, transforming, storing and consuming a product, called points (nodes) of the network and transmission lines (links, communications, connections) that transfer the product between points.

Information network - a communication network in which information is the product of generation, processing, storage and use.

Computing network - an information network that includes computing equipment.

Data transmission medium is a set of data transmission lines and interaction units (i.e. network equipment not included in data stations) intended for data transmission between data stations.

Data transmission line - means that are used in information networks to propagate signals in the desired direction.

Channel (communication channel) - means of one-way data transmission.

Data transmission channel - means of two-way data exchange, including channel termination equipment and data transmission line.

Bibliography

1. Semenov Yu.A. Internet protocols and resources. M .: Radio and communication, 1996.

2. Lazarev V.G. Intelligent Digital Networks: A Handbook. / Ed. Academician N.A. Kuznetsova. - M .: Finance and Statistics, 1996.

3. Finaev V.I. Information exchanges in complex systems: Tutorial... Taganrog: Publishing house TRTU, 2001.

4. A.V. Pushnin, V.V. Yanushko. Information networks and telecommunications. Taganrog: Publishing house TRTU, 2005.128 p.

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Classification of networks

The classification of fuel assemblies is based on the most characteristic functional, informational and structural features.

By the degree of territorial dispersal network elements (subscriber systems, communication nodes) distinguish between global (state), regional and local computer networks (GVS, RVS and LAN).

By the nature of the functions implemented networks are divided into computing (the main functions of such networks are information processing), information (for obtaining reference data at the request of users), information and computing, or mixed, in which computing and information functions are performed in a certain, non-constant ratio.

By control method FAs are divided into networks with centralized(the network has one or more governing bodies), decentralized(each speaker has facilities for network management) and mixed management, in which, in a certain combination, the principles of centralized and decentralized control are implemented (for example, under centralized control, only tasks with the highest priority are solved, associated with the processing of large amounts of information).

On the organization of information transfer networks are divided into networks with information selection and information routing. In networks with selection of information, built on the basis of a mono-channel, the interaction of the AS is made by the selection (selection) of the data blocks (frames) addressed to them: all the frames transmitted in the network are available to all the AS of the network, but only the AS they are intended for take a copy of the frame. In networks with routing information multiple routes can be used to transfer frames from sender to receiver. Therefore, with the help of communication systems of the network, the problem of choosing the optimal (for example, the shortest in terms of delivery time of the frame to the addressee) route is solved.

By the type of organization of data transmission information routing networks are divided into circuit (channel) switching, message switching and packet switching networks. There are networks in operation that use mixed data transmission systems.

By topology, those. configurations of elements in TVS, networks are divided into two classes: broadcast and sequential. Broadcast configurations and much of the sequential configurations (ring, star with smart center, hierarchical) are characteristic of LANs. For wide area and regional networks, the most common is an arbitrary (mesh) topology. Hierarchical configuration and "star" have also found application.

IN broadcast configurations at any given time, only one workstation (subscriber system) can operate for frame transmission. The rest of the PCs on the network can receive this frame, i.e. such configurations are typical for LAN with information selection. The main types of broadcast configuration are common bus, tree, star with a passive center. The main advantages of a LAN with a common bus are simplicity of network expansion, simplicity of used control methods, no need for centralized control, minimal cable consumption. A tree LAN is a more advanced version of a bus network. A tree is formed by connecting several buses with active repeaters or passive multipliers (“hubs”), each branch of the tree is a segment. The failure of one segment does not lead to the failure of the rest. In a LAN with a star topology, there is a passive connector or an active repeater in the center - fairly simple and reliable devices.

In sequential configurations typical for networks with information routing, data transmission is carried out sequentially from one PC to a neighboring one, and different types of physical transmission medium can be used in different parts of the network.

The requirements for transmitters and receivers are lower than in broadcast configurations. Sequential configurations include: arbitrary (cellular), hierarchical, ring, chain, star with an intelligent center, snowflake. In the LAN, the most widespread are the ring and the star, as well as mixed configurations - star-ring, star-bus.

In a LAN with a ring topology, signals are transmitted in only one direction, usually counterclockwise. Each PC has up to a full frame of memory. When moving a frame around the ring, each PC receives a frame, analyzes its address field, takes a copy of the frame, if it is addressed to this PC, and retransmits the frame. Naturally, all this slows down the data transfer in the ring, and the duration of the delay is determined by the number of PCs. The removal of a frame from the ring is usually performed by the sending station. In this case, the frame makes a full circle around the ring and returns to the sending station, which perceives it as a receipt - confirmation of the receipt of the frame by the addressee. The removal of a frame from the ring can also be carried out by the receiving station, then the frame does not complete a full circle, and the sending station does not receive a confirmation receipt.

The ring structure provides a fairly broad functionality of the LAN with high efficiency of using a mono channel, low cost, simplicity of control methods, and the ability to monitor the operability of a mono channel.

In broadcast and most sequential configurations (except for the ring), each segment of the cable must provide signal transmission in both directions, which is achieved: in half-duplex communication networks - using one cable for alternating transmission in two directions; in duplex networks - using two unidirectional cables; in broadband systems - the use of different carrier frequencies for simultaneous transmission of signals in two directions.

Global and regional networks, like local ones, can, in principle, be homogeneous (homogeneous), in which software-compatible computers are used, and heterogeneous (heterogeneous), including software-incompatible computers. However, given the length of the hot water supply and the DCS and the large number of computers used in them, such networks are often heterogeneous.

The main function of telecommunication systems (TCS), or data transmission systems (SPD) is to organize prompt and reliable exchange of information between subscribers. The main indicator of TCS efficiency - information delivery time - depends on a number of factors: the structure of the communication network, the throughput of communication lines, methods of connecting communication channels between interacting subscribers, information exchange protocols, methods of subscribers access to the transmission medium, methods of packet routing.

Types of networks, lines and communication channels. TVS uses communication networks - telephone, telegraph, television, satellite. The following are used as communication lines: cable (ordinary telephone lines, twisted pair, coaxial cable, fiber-optic communication lines (FOCL, or light guides), radio relay, radio lines.

Among cable lines optical fibers have the best performance. Their main advantages: high throughput (hundreds of megabits per second) due to the use of electromagnetic waves in the optical range; insensitivity to external electromagnetic fields and the absence of its own electromagnetic radiation, low labor intensity of laying an optical cable; spark, explosion and fire safety; increased resistance to aggressive environments; low specific gravity (the ratio of the linear mass to the bandwidth); wide areas of application (creation of public access highways, computer communication systems with peripheral devices of local networks, in microprocessor technology, etc.).

Disadvantages of FOCL: signal transmission is carried out in only one direction; connecting additional computers to the optical fiber significantly attenuates the signal; the high-speed modems required for optical fibers are still expensive; the light guides connecting the computers must be equipped with converters of electrical signals into light signals and vice versa.

The following are used in fuel assemblies types of communication channels:

simplex, when the transmitter and receiver are connected by a single communication line, through which information is transmitted only in one direction (this is typical for television communication networks);

half duplex, when two communication nodes are also connected by one line, along which information is transmitted alternately in one direction, then in the opposite direction (this is typical for information and reference, request-response systems);

duplex, when two communication nodes are connected by two lines (forward link and reverse), along which information is simultaneously transmitted in opposite directions.

Switched and dedicated communication channels. TKS distinguishes between dedicated (non-commutated) communication channels and those with commutation for the duration of information transmission over these channels.

Using dedicated channels communication transceiver equipment of communication nodes is permanently connected to each other. This ensures a high degree of readiness of the system to transfer information, more high quality communication, support for a large amount of graphics. Due to the relatively high costs of operating networks with dedicated communication channels, their profitability is achieved only if the channels are fully loaded.

For switched channels communications created only for the duration of the transmission of a fixed amount of information are characterized by high flexibility and relatively low cost (with a small volume of traffic). Disadvantages of such channels: loss of time for switching (establishing communication between subscribers), the possibility of blocking due to the busyness of certain sections of the communication line, lower quality of communication, high cost with a significant volume of traffic.

Analog and digital coding of digital data. Data transfer from one TCS node to another is carried out by sequential transmission of all message bits from the source to the destination. Physically information bits are transmitted as analog or digital electrical signals. Analog are called signals, which can represent an infinite number of values ​​of a certain quantity within a limited range. Digital(discrete) signals can have one or a finite set of values. When working with analog signals, a sine-wave analog carrier signal is used to transmit encoded data, and when working with digital signals, a two-level discrete signal... Analog signals are less sensitive to distortion due to attenuation in the transmission medium, but data encoding and decoding is easier for digital signals.

Analog coding It is used when transmitting digital data over telephone (analog) communication lines, which dominate in regional and global TVS and are initially focused on the transmission of acoustic signals (speech). Before transmission, digital data, usually coming from a computer, is converted into analog form using a modulator-demodulator (modem), which provides a digital-to-analog interface.

There are three ways to convert digital data to analog form, or three modulation methods:

amplitude modulation, when only the amplitude of the carrier of sinusoidal oscillations changes in accordance with the sequence of transmitted information bits: for example, when transmitting a unit, the amplitude of oscillations is set to large, and when transmitting zero, it is low, or there is no carrier signal at all;

frequency modulation, when, under the influence of modulating signals (transmitted information bits), only the frequency of the carrier of sinusoidal oscillations changes: for example, when transmitting zero, it is low;

phase modulation, when, in accordance with the sequence of transmitted information bits, only the phase of the carrier of sinusoidal oscillations changes: when passing from signal 1 to signal 0 or vice versa, the phase changes by 180 degrees.

The transmitting modem converts (modulates) the sine wave carrier signal (amplitude, frequency, or phase) so that it can carry the modulating signal, i.e. digital data from a computer or terminal. The inverse transformation (demodulation) is performed by the receiving modem. In accordance with the implemented modulation method, modems are distinguished with amplitude, frequency and phase modulation. The most widespread are frequency and amplitude modulations.

Digital coding digital data is performed directly by changing the levels of signals carrying information.

For example, if in a computer digital data is represented by signals of 5V levels for code 1 and 0.2V for code 0, then when these data are transmitted to the communication line, the signal levels are converted to + 12V and -12V, respectively. Such coding is carried out, in particular, using asynchronous serial adapters RS-232-C when transferring digital data from one computer to another over short (tens and hundreds of meters) distances.

Synchronization of TCS elements. Synchronization is part of the communication protocol. In the process of communication synchronization, synchronous operation of the receiver and transmitter equipment is ensured, in which the receiver samples the incoming information bits (i.e., the signal level in the communication line is measured) strictly at the moments of their arrival. Synchronization signals set the receiver to the transmitted message even before it arrives, maintain synchronization of the receiver with the incoming data bits.

Depending on the methods for solving the synchronization problem, there are synchronous transmission, asynchronous transmission, and auto-tuning transmission.

Synchronous transmission differs in the presence of an additional communication line (except for the main one, through which data is transmitted) for the transmission of synchronizing pulses (SI) of a stable frequency. Each SI adjusts the receiver. The delivery of data bits to the communication line by the transmitter and the sampling of information signals by the receiver are performed at the moments of the appearance of the SI. In synchronous transmission, synchronization is very reliable, but this comes at a high price - the need for an additional communication line.

Asynchronous transmission does not require an additional communication line. Data transmission is carried out in small, fixed-length blocks (usually bytes). Synchronization of the receiver is achieved by sending an additional bit before each transmitted byte - a startbit, and after the transmitted byte - another additional bit - a stopbit. A startbit is used for synchronization. This synchronization method can only be used in systems with low data rates.

Auto-tuning transmission, also does not require an additional communication line, it is used in modern high-speed data transmission systems. Synchronization is achieved by using self-synchronizing codes(SK). The coding of the transmitted data using the SC is to ensure regular and frequent changes (transitions) of the signal levels in the channel. Each transition of the signal level from high to low or vice versa is used to trim the receiver. The best ones are considered to be those that ensure the transition of the signal level at least once during the time interval required to receive one information bit. The more frequent the signal level transitions, the more reliably the receiver synchronizes and the more confidently the received data bits are identified.

The most common are the following self-timing codes:

NRZ-code (non-return-to-zero code);

RZ code (return to zero code);

Manchester code;

Bipolar code with alternating level inversion (e.g. AMI code).

Rice. Message encoding schemes using self-synchronizing codes

In fig. the schemes for coding message 0101100 using these CKs are presented.

To characterize and comparatively assess the UK, the following indicators:

level (quality) of synchronization;

Reliability (confidence) of recognition and selection of received information bits;

The required rate of change in the signal level in the communication line when using the SC, if the line capacity is specified;

The complexity (and, therefore, the cost) of the equipment that implements the IC.

Digital communication networks (DSS). In recent years, digital communication networks that use digital technology have become increasingly widespread in TVS.

Reasons for the spread of digital technology in networks:

Digital devices used in DCS are manufactured on the basis of highly integrated integrated circuits; compared with analog devices they are distinguished by great reliability and stability in operation and, in addition, in production and operation, as a rule, they are cheaper;

Digital technology can be used to transmit any information over one channel (acoustic signals, television video data, facsimile data);

Digital techniques overcome many of the transmission and storage limitations that are inherent in analog technologies.

In the DSN, when transmitting information, the analog signal is converted into a sequence of digital values, and when receiving, the reverse conversion is performed.

An analog signal appears as a constant change in amplitude over time. For example, when talking on the phone, which acts as a transducer of acoustic signals to electrical signals, mechanical vibrations of the air (alternating high and low pressure) are converted into an electrical signal with the same amplitude envelope characteristic. However, the direct transmission of an analog electrical signal via a telephone line is associated with a number of disadvantages: signal distortion due to its nonlinearity, which is increased by amplifiers, signal attenuation during transmission through the medium, susceptibility to the influence of noise in the channel, etc.

In the CSS, these disadvantages are surmountable. Here, the form of an analog signal is represented in the form of digital (binary) images, digital values ​​representing the corresponding values ​​of the envelope of the amplitude of sinusoidal oscillations at points at discrete levels. Digital signals are also susceptible to attenuation and noise as they pass through the channel, however, at the receiving point it is necessary to note only the presence or absence of a binary digital pulse, and not its absolute value, which is important in the case of an analog signal. Consequently, digital signals are accepted more reliably, they can be completely restored before they fall below the threshold value due to attenuation.

Conversion of analog signals to digital is carried out by various methods. One of them - pulse code modulation(PCM), proposed in 1938 by A.Kh. Reeves (USA). When using PCM, the transformation process includes three stages: display, quantization, and encoding (Figure 12.2).

Rice. 12.2. Converting an analog signal to an 8-element digital code

First stage (display) based on Nyquist mapping theory. The main point of these theories is: "If an analog signal is displayed at a regular interval with a frequency of at least twice the maximum frequency of the original signal in the channel, then the display will contain information sufficient to restore the original signal." When transmitting acoustic signals (speech), the electrical signals representing them in the telephone channel occupy a frequency range from 300 to 3300 Hz. Therefore, the DSN adopted a display frequency of 8000 times per second. The mappings, each called a Pulse Amplitude Modulation (IAM) signal, are stored and then transformed into binary images.

At the quantization stage each IAM signal is assigned a quantized value corresponding to the nearest quantization level. And DSS the entire range of changes in the amplitude of the IAM signals is divided into 128 or 256 quantization levels. The more quantization levels, the more accurately the amplitude of the IAM signal is represented by the quantized level.

At the coding stage each quantized mapping is assigned a 7-bit (if the number of quantization levels is 128) or 8-bit (with 256-step quantization) binary code. In fig. 12.2 shows the signals of an 8-element binary code 00101011 corresponding to a quantum signal with a level of 43. When encoding with 7-element codes, the data transfer rate over the channel should be 56 Kbit / s (this is the product of the display frequency and the bit width of the binary code), and when encoding 8- element codes - 64 Kbps.

In modern DSN, another concept of converting analog signals into digital ones is used, in which not the IAM signals themselves are quantized and then encoded, but only their changes, and the number of quantization levels is assumed to be the same. Obviously, this concept allows for the conversion of signals with greater accuracy.

Satellite communication networks. The advent of satellite communication networks triggered the same revolution in information transmission as the invention of the telephone.

The first communications satellite was launched in 1958, and the first commercial communications satellite was launched in 1965 (both in the United States). These satellites were passive, later amplifiers and transceiver equipment began to be installed on the satellites.

The following methods are used to control data transmission between the satellite and terrestrial PTSs:

1. Conventional multiplexing - with frequency division and time division. In the first case, the entire frequency spectrum of the radio channel is divided into subchannels, which are allocated between users for the transmission of any schedule.

The costs of this method: with irregular transmission, subchannels are used irrationally; a significant portion of the original channel bandwidth is used as a divider to prevent sub-channels from interfering with each other. In the second case, the entire time spectrum is divided between users, who, at their discretion, dispose of the provided time slices (slots). It is also possible for the channel to be idle due to its irregular use.

2. The usual discipline "primary / secondary" with using survey / selection methods and tools. As the primary body that implements such a discipline of satellite communications control, one of the terrestrial RTS is more often used, and less often - a satellite. The polling and selection cycle takes a significant amount of time, especially if there are a large number of speakers in the network. Therefore, the response time to the user's request may be unacceptable for him.

3. Primary / Secondary Management Discipline without polling, with the implementation of the method of multiple access with time slicing (TDMA). Here the slots are assigned to the primary RTS called reference. Receiving requests from other PTSs, the reference station, depending on the nature of the traffic and channel occupancy, satisfies these requests by assigning stations to specific slots for transmitting frames. This method is widely used in commercial satellite networks.

4. Peer-to-peer management disciplines. They are characterized by the fact that all users have an equal right to access the channel and there is a rivalry between them for the channel. In the early 70s, N. Abramson from the University of Hawaii proposed a method of effective competition for a channel between uncoordinated users, called the ALOHA system. There are several variants of this system: a system that implements the random access method (random ALOHA); peer-to-peer priority slot system (slot ALOHA), etc.

TO main advantages satellite communication networks include the following:

Large bandwidth due to the operation of satellites in a wide range of gigahertz frequencies. The satellite can support several thousand voice communication channels. For example, one of the currently used commercial satellites has 10 transponders, each of which can transmit 48 Mbps;

Providing communication between stations located at very long distances, and the ability to serve subscribers in the most difficult-to-reach points;

The independence of the cost of information transmission from the distance between interacting subscribers (the cost depends on the duration of the transmission or the volume of the transmitted schedule);

The ability to build a network without physically implemented switching devices, due to the broadcasting of satellite communications. This opportunity is associated with a significant economic effect that can be obtained compared to using a conventional non-satellite network based on multiple physical lines communication and communication devices.

Flaws satellite communication networks:

The need to spend money and time to ensure the confidentiality of data transmission, to prevent the possibility of data interception by “foreign” stations;

The presence of a delay in the reception of a radio signal by a ground station due to the large distances between the satellite and the RTS. This can cause problems related to the implementation of channel protocols, as well as the response time;

Possibility of mutual distortion of radio signals from ground stations operating at adjacent frequencies;

Exposure of signals on the Earth-satellite and satellite-Earth sections to the influence of various atmospheric phenomena.

To solve the problems with the allocation of frequencies in the 6/4 and 14/12 GHz bands and the placement of satellites in orbit, active cooperation of many countries using satellite communications technology is required.

By purpose, telecommunication systems are grouped as follows:

TV broadcasting systems;

Communication systems (including personal calls);

Computer networks.

By the type of information transmission medium used:

Cable (traditional copper);

Fiber optic;

Essential;

Satellite.

By the method of information transfer:

Analog;

Digital.

Communication systems are subdivided by mobility into:

Fixed (traditional subscriber lines);

Movable.

Mobile communication systems are subdivided according to the principle of coverage of the service area:

For microcellular - DECT;

Cellular - NMT-450, D-AMPS, GSM, CDMA;

Trunking (macro, zonal) - TETRA, SmarTrunk;

Satellite.

TV broadcasting systems

Television broadcasting systems (TV) by the method of signal delivery and coverage area are divided into:

TV reception networks;

- "cable" (systems of collective television reception (SKTP));

Technologies of wireless high-speed distribution of multimedia information MMDS, MVDS and LMDS;

Satellite.

Mobile communication systems

Cellular mobile communication systems (PCS), personal radio call networks (PRN) and satellite communication systems are designed to transmit data and provide mobile and stationary objects with telephone communications. Data transmission to a mobile subscriber dramatically expands its capabilities, since, in addition to telephone, it can receive telex and facsimile messages, various types of graphic information, etc. An increase in the amount of information requires a reduction in the time for its transmission and reception, as a result of which there is a steady increase in production mobile facilities radio communications (pagers, cellular radiotelephones, satellite user terminals).

The main advantage of the MTS: mobile communication allows the subscriber to receive communication services at any point within the coverage areas of terrestrial or satellite networks; thanks to advances in communication technology, small universal subscriber terminals (AT) have been created. SPS provide consumers with the opportunity to access the public telephone network (PSTN), transfer of computer data.

Mobile networks include: cellular mobile networks (SSMS); trunking communication networks (STS); personal radio call networks (PRN); personal satellite (mobile) communication networks.

Cellular mobile networks

Among modern telecommunication means, the most rapidly developing networks are cellular radiotelephone communications. Their implementation made it possible to solve the problem of economical use of the allocated radio frequency band by transmitting messages on the same frequencies, but in different zones (cells) and to increase throughput telecommunication networks. They got their name in accordance with the cellular principle of communication organization, according to which the service area is divided into cells (cells).

The cellular communication system is complex and flexible technical system, allowing a wide variety of configuration options and a set of functions performed. It can provide transmission of speech and other types of information. For voice transmission, in turn, ordinary two-way and multi-way telephone communication (conference communication - with more than two subscribers participating in a conversation at the same time), voice mail can be implemented. When organizing a regular telephone conversation, the modes of auto-dialing, call waiting, call forwarding (conditional or unconditional), etc. are possible.

Modern technologies allow to provide JSSS subscribers with high quality of voice messages, reliability and confidentiality of communication, miniature radiotelephones, protection from unauthorized access.

Trunking networks

Trunking networks are somewhat similar to cellular networks: they are also terrestrial radiotelephone mobile networks that provide mobility of subscribers within a sufficiently large service area. The main difference is that STSs are simpler in terms of construction principles and provide subscribers with a smaller set of services, but due to this they are cheaper than cellular services. STSs have a much lower capacity than cellular ones and are fundamentally focused on departmental (corporate) mobile communications. The main application of the STS is corporate (official, departmental) communication, for example, the operational communication of the fire service with the number of exits (channels) "to the city" significantly less than the number of system subscribers. The main requirements for STS are: provision of communication in a given service area, regardless of the location of mobile subscribers; the possibility of interaction between individual groups of subscribers and the organization of circular communication; efficiency of communication management, including at various levels; providing communication through control centers; the possibility of priority establishment of communication channels; low energy costs of the mobile station; confidentiality of conversations.

Name trunking communication comes from the English trunk (trunk) and reflects the fact that the trunk of communication in such a system contains several physical (usually frequency) channels, each of which can be provided to any of the subscribers of the system. This feature distinguishes the STS from the previous two-way radio communication systems, in which each subscriber had the opportunity to access only one channel, but the latter had to serve a number of subscribers in turn. Compared to such systems, STS have a significantly higher capacity (throughput) with the same quality of service indicators.

Paging networks

Personal radio call networks (PRN) or paging networks (paging - call) are one-way mobile communication networks that transfer short messages from the center of the system (from a paging terminal) to miniature subscriber receivers (pagers).

Personal radio calling networks provide services of a convenient and relatively cheap type of mobile communication, but with significant limitations: one-way communication, not in real time and only in the form of short messages. SPRs are quite widespread in the world - in general, of the same order as cellular networks, although their prevalence in different countries differs significantly.

Mobile satellite networks

Along with the already publicly available SPS (personal radio call and cellular), satellite communication networks are developing more and more actively. The following areas of application of mobile satellite communications are relevant:

Expansion of cellular networks;

The use of satellite communications in areas where the deployment of an ATP is impractical, for example, due to the low population density;

The use of satellite communications in addition to the existing cellular, for example, to ensure roaming in case of incompatibility of standards, or in any emergency situations;

Fixed wireless communication in areas with a low population density in the absence of SPS and wire communication;

When transmitting information on a global scale (waters of the World Ocean, breaks in ground infrastructure, etc.).

In particular, when moving a subscriber out of the service area of ​​local cellular networks, satellite communication plays a key role, since it has no restrictions on binding the subscriber to a specific location. In many regions of the world, the demand for mobile services can only be effectively met through satellite systems.

Fiber optic networks

Fiber optic communication line (FOCL) is a type of transmission system in which information is transmitted through optical dielectric waveguides known as "optical fiber". A fiber-optic network is an information network, the connecting elements between the nodes of which are fiber-optic communication lines. Fiber optic network technologies, in addition to fiber optics issues, also cover issues related to electronic transmission equipment, its standardization, transmission protocols, network topology issues and general issues of network construction.

FOCL advantages: wide bandwidth, low attenuation of the light signal in the fiber, low noise level, high noise immunity, low weight and volume, high security against unauthorized access, galvanic isolation of network elements, explosion and fire safety, cost-effectiveness of fiber-optic cables (FOC), durability operation, remote power supply.

Disadvantages of FOCL: the cost of interface equipment (the price of optical transmitters and receivers is still quite high), installation and maintenance of optical lines (the cost of installation, testing and support of fiber-optic communication lines also remains high), the requirement for special fiber protection.

The advantages from the use of fiber-optic communication lines are so significant that, despite the listed disadvantages of optical fiber, further prospects for the development of fiber-optic communication technology in information networks are more than obvious.

Telecommunication networks represent the most sophisticated equipment in the world. One has only to think about the telephone network, which includes more than 2 billion fixed and mobile phones with universal access. When one of these phones makes a request, the telephone network is able to communicate with any other phone in the world. In addition, many other networks are linked to the telephone network. This suggests that the complexity of the global telecommunications network exceeds the complexity of any other system in the world.

Telecommunication services have a significant impact on the development of the global community. If we know the telephone density of a country, then we can estimate the level of its technical and economic development. In underdeveloped countries, the density of fixed (fixed) telephones does not exceed 10 telephones per 1000 inhabitants; in developed countries, for example in North America and Europe, it is approximately 500 - 600 phones per 1000 inhabitants. Economic and cultural development developing countries depend (in addition to many other factors) on the availability of efficient telecommunications services. The local area network (LAN) to which our computer is connected is connected to the LANs of other sites located throughout our university. This is necessary for the effective collaboration of different departments. We communicate daily with people in other organizations via email, telephones, facsimiles and mobile phones. This happens on an organizational, national and international scale.

Telecommunications play significant role in many areas Everyday life ... Each of us daily uses not only telecommunication services, but also services that rely on telecommunications. Here are some examples of services that depend on telecommunications: banking, ATMs, electronic commerce; aviation, railway, ticket booking; sales, wholesale and order processing; payments by credit card in stores; booking hotel rooms by travel agencies; procurement of materials by industry; government operations.

Test questions:

1. The concept of a network. What are the capabilities of the network?

2. In what year did the first network appear, what was it called and where?

3. Name the main components of the network.

4. List the indicators of computer networks.

5. Describe the levels of the open systems interoperability reference model.

6. Give definitions to the concepts of "protocol", "interface", "transparency", "network operating system".

7. What components include technical support computer networks? Describe them.

8. Name the types of networks.

9. Give the classification of networks.

10. Describe the benefits of local area networks.

11. Describe the main hardware components of the LAN.

12. How do the file-server and client-server models differ from each other?

13. Describe the cables used in most networks.

14. What technologies are used to transmit coded signals over cable?

15. What is a transceiver? What is it for?

16. What are the advantages and types of wireless networks.

17. Describe the methods of access to the LAN

18. Give the concept of a telecommunication system.

19. List the types of telecommunication systems.

20. Describe mobile networks.

Topic 9. Internet network

What is Telecommunications?

Telecommunication is the transmission of signs, signals, messages, written text, images, sounds or information of any kind by means of wired, radio-optical or other electromagnetic systems. Telecommunication occurs when technologies are used to exchange information between communication participants. Transmission takes place either electrically via physical media such as cables or using electromagnetic radiation. Similar transmission paths are often subdivided into communication channels, which has the advantage of multiplexing. The term is often used in the plural, telecommunications, as it encompasses many different technologies.

Early means of communication at a distance included visual signals such as beacons, smoke signals, semaphore telegraph, signal flags, and optical heliographs. Other forms of long-distance communication used in the past are audible messages such as coded drum beats, horns, and loud whistles. Long-distance communication technologies of the 20th and 21st centuries typically used electrical and electromagnetic technologies such as telegraph, telephone and TTY, network communications, radio, microwave transmission, fiber optic lines, and communication satellites.

The wireless revolution took place in the first decade of the 20th century thanks to the pioneering work in radio communications by Guglielmo Marconi, the 1909 Nobel laureate in physics. Other notable early inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone and Samuel Morse (inventors of the telegraph), Alexander Graham Bell (inventor of the telephone), Edwin Armstrong and Lee de Forest (inventors of radio), as well as Vladimir Zworykin, John Loughy Byrd and Philo Farnsworth (inventors and designers of television).

Origin of the name "Telecommunications"

The word "telecommunications" is a combination of the Greek prefix tele- (τηλε-), which means "far" or "from afar" and the Latin - "communicare" - "to share", "to connect". Its modern use is borrowed from French because it was used in that sense in 1904 by the French engineer and novelist Edouard Estaunier. The word "communication" entered the English language at the end of the 14th century. It comes from the Old French "comunicación", which, in turn, comes from the Latin "communicationem" (in the nominative case "communicatio"), the noun from the stem of the past participle "communicare" - "to divide", "to divide"; "communicate", "transmit", "report"; "join", "unite", "make common" from "communis" - common.

The history of the development of telecommunications

Lighthouses and pigeons

In the Middle Ages, signal towers were usually used on highlands as a means of relaying the signal. These signaling circuits had the disadvantage of being able to transmit only one bit of information, so that the meaning of a message such as "enemy spotted" had to be agreed upon in advance. One famous example of their use was during the Spanish Armada, when a chain of signal towers (beacons) transmitted the signal from Plymouth to London.

In 1792, Chappe, a French engineer, built the first stationary visual telegraphy (or semaphore line) system between Lille and Paris. However, the semaphore was in need of skilled operators and expensive towers, located at intervals of ten to thirty kilometers. As a result of competition from the electric telegraph, the last commercial semaphore line ceased operations in 1880.

Pigeons have sometimes been used as mail carriers in various cultures throughout human history. Pigeon mail is believed to have originated with the Persians and was used by the Romans as an aid. Frontinois mentions the use of carrier pigeons by Julius Caesar as messengers in the conquest of Gaul. The Greeks also transmitted the names of the winners of the Olympic Games to different cities by means of carrier pigeons. At the beginning of the 19th century, the Dutch government used this postal system on the islands of Java and Sumatra. And in 1849, Paul Julius Reuter organized a pigeon mail for the delivery of exchange information between Aachen and Brussels, which operated for a year, until telegraph communication appeared between these cities.

Telegraph and telephone

Sir Charles Wheatstone and Sir William Fothergill Cook invented the electric telegraph in 1837. It is also believed that the first commercial electric telegraph was built by Wheatstone and Cook and opened on April 9, 1839. Both inventors viewed their device as "an improvement of the (by that time already existing) electromagnetic telegraph", and not as a new device.

Samuel Morse independently developed the version of the electric telegraph shown on September 2, 1837. The code he developed was an important step forward over Wheatstone's signaling method. The first transatlantic telegraph cable was successfully laid on 27 July 1866, enabling the first transatlantic data transmission.

The conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci was the inventor of the first device that allowed electrical transmission of voice over a line as early as 1849. However, Meucci's device had little practical value as it relied on an electrophonic effect and thus required placing the receiver in the mouth of users in order to "hear" what was being said. The first commercial telephone services appeared in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London.

In 1832, James Lindsay demonstrated a wireless telegraphy session to his students in class. By 1854, he was able to demonstrate transmission across the Firth of Tay from Dundee to Woodhaven, Scotland, two miles (3 km) away, using water as the transmission medium. In December 1901, Guglielmo Marconi established a wireless link between St. John's, Newfoundland, Canada and Poldhu, Cornwall, England, which earned him the 1909 Nobel Prize in Physics (which he shared with Karl Brown). Although, short-range radio communication had already been demonstrated back in 1893 by Nikola Tesla in front of the National Electric Light Association.

On March 25, 1925, John Logie Byrd was able to demonstrate the transmission of moving images at the Selfridges department store in London. Byrd's device was based on the Nipkow disc and became known as mechanical television. It formed the basis for experimental broadcasts made by the British Broadcasting Corporation, beginning September 30, 1929. However, most of the 20th century televisions were based on the cathode ray tube invented by K. Brown. The first example of such a promising television was produced and demonstrated to his family by Farnsworth on September 7, 1927.

Computers and the Internet

On September 11, 1940, George Stibitz submitted a problem for his complex number calculator in New York using a teletypewriter, and received in return the results of calculations at Dartmouth College in New Hampshire. This configuration of a centralized computer (PC) with remote simple terminals remained popular in the 1970s. However, already in the 1960s, research began on packet switching, a technology that sends a message in pieces to its destination in an asynchronous manner without going through a centralized computer. The four-node network, launched on December 5, 1969, was the prototype for the ARPANET, which had grown to 213 nodes by 1981. The ARPANET eventually merged with other networks and the Internet was born. While the development of the Internet was the focus of the Internet Engineering Task Force (IETF), which published a series of working proposals, other networking developments such as the local area network (LAN), Ethernet (1983), and the ring protocol marker (1984) took place in industrial laboratories. ...

Information Technology

Modern telecommunications are based on a number of key concepts that have gone through a path of progressive development and improvement over a hundred years.

Basic elements of telecommunications

Telecommunication technologies can be primarily divided into wired and wireless methods. Although, in general, a basic telecommunications system consists of three main parts, which are always present in one form or another:

A transmitter that receives information and converts it into a signal.

A transmission medium, also called a physical channel that carries a signal. An example of this is the "free space channel".

A receiver that receives a signal from a channel and converts it back into information useful to the receiver.

For example, in a broadcasting station, the high power amplifier of the radio station is the transmitter and the transmitting antenna is the interface between the power amplifier and the "free space" channel. Free space is the transmission medium and the receiver antenna is the interface between the “free space channel” and the receiver. The radio receiver then receives a radio signal where it is converted from electricity to sound that people can hear.

Sometimes there are telecommunication systems "Duplex" - systems with two-way communication, combining in one box both a transmitter and a receiver, that is, transceivers. For example, a cell phone is a transceiver. Electronic circuit the transmitter and receiver electronics inside the transceiver are actually completely independent of each other. This can be easily explained by the fact that radio transmitters contain power amplifiers that operate with electrical powers of the order of a few watts or kilowatts, but radio receivers deal with radio signals that are in the order of a few microwatts or nanowatts. Therefore, transceivers must be carefully designed and wired to isolate the high-power part of the circuit from the low-power part so that no interference is generated.

Telecommunications over fixed lines are called point-to-point because communication is between one transmitter and one receiver. Telecommunications carried out by radio transmission are called broadcast communications because they are carried out between one powerful transmitter and numerous low-power but sensitive radio receivers.

Telecommunications in which multiple transmitters and multiple receivers have been designed to share the same physical channel are called multiplex systems. Sharing physical channels using multiplexing often results in very significant cost savings. The multiplex systems are located in telecommunication networks and the multiplexed signals are switched by nodes with the required receiving terminal.

Analog and digital communication

Communication signs can be transmitted either by analog or digital signals. There are analog communication systems and digital communication systems. In an analog system, the signal changes continuously as the information changes. In a digital system, information is encoded as a set of discrete values ​​(for example, a set of ones and zeros). During propagation and reception, the information contained in analog signals inevitably degrades due to unwanted physical noise. The transmitter output is virtually silent. Typically, noise in a communication system can be expressed as adding or subtracting random interference from the desired signal. This form of noise is called additive noise, given that the noise can be negative or positive at different points in time. Noise that is not additive is noise that is much more difficult to describe and analyze.

On the other hand, if the addition of the annoying effect of noise does not exceed a certain threshold, then the information contained in the digital signal will not be distorted. Noise immunity is a key advantage of digital signals over analog signals.

Telecommunication networks

A telecommunication network is a collection of transmitters, receivers and communication channels that exchange messages. Some digital communications networks contain one or more routers that work together to transmit information to the exact user for whom it is intended. An analog communications network consists of one or more switches that establish communication between two or more users. For both types of networks, repeaters may be needed to amplify or recreate the signal over long distances. This is to combat attenuation that can make the signal indistinguishable from noise. Another advantage of digital systems over analog systems is that their output value is easier to store in memory as two voltage states (high and low) than continuously changing values ​​over a range of states.

Channels of connection

The term "channel" has two different meanings... In one sense, a channel is a physical medium that carries a signal between a transmitter and a receiver. For example, atmosphere for sound communications, fiber optic for some types of optical communications, coaxial cable for communications using voltages and electric currents in them, and free space for communications using visible light, infrared waves, ultraviolet light and radio waves. This last channel is called the "free space channel". The transmission of radio waves from one place to another does not depend on the presence or absence of an atmosphere between them. Radio waves travel through a perfect vacuum as easily as they travel through air, fog, clouds, or any other gaseous medium.

Another meaning of the term "channel" is considered in the field of telecommunications, in the sense of a communication channel, which is part of the transmission medium so that the entire medium can be used to transmit several data streams at the same time. For example, one radio station can broadcast radio waves in free space around 94.5 MHz (megahertz), while another radio station can simultaneously broadcast radio waves around 96.1 MHz. Each radio station will transmit radio waves over a frequency band of about 180 kHz (kilohertz), centered on the frequencies indicated above, which are called “carrier frequencies.” Each station in this example is 200 kHz apart from neighboring stations, and the difference is between 200 kHz and 180 kHz (20 kHz) is an engineering tolerance that takes into account deficiencies in the communication system.

In the above example, the “free space channel” has been divided into communication channels according to frequencies, and each channel has been assigned a separate frequency band for transmitting radio waves. This system of dividing the medium in channels according to frequency is called "frequency division multiplexing". Another term for the same principle is called "wavelength division multiplexing", which is most commonly used in optical communications where multiple transmitters share the same physical medium.

Another way of dividing the communication medium into channels is to give each sender a repeating amount of time (a "time slot", for example, 20 milliseconds out of every second) and allow each sender to send messages only within that time slot allocated to that sender. This technique of dividing the medium into communication channels is called time division multiplexing (TDM) and is used in fiber optic communication.Some radio communication systems use TDM within a dedicated FDM channel.Therefore, these systems use a hybrid of TDM and FDM.

Modulation

Shaping a signal to transmit information is called modulation. Modulation can be used to represent a digital message as an analog signal. This type of modulation is commonly referred to as "keying", a term inherited from the Morse code in telecommunications and is subdivided into several keying techniques (these include phase shift keying, frequency shift keying, and amplitude shift keying). Bluetooth, for example, uses phase shift keying to exchange information between different devices. In addition, there is a manipulation that combines phase and amplitude changes called (in the lingo of the field) Quadrature Amplitude Shift Keying (QAM) and is used in high-bandwidth digital radio systems.

Modulation can also be used to carry low frequency analog signals at higher frequencies. This is useful because analog low frequency signals cannot be efficiently transmitted across free space. Therefore, information from the analog low frequency signal must be embedded in the high frequency signal (known as the "carrier wave") before transmission. There are several different modulation schemes available to accomplish this, the two most basic modulation techniques being amplitude modulation (AM) and frequency modulation (FM). An example of this process is to "embed" the DJ's voice into a 96 MHz carrier wave using frequency modulation (the voice will then be "caught" by the radio on "96 FM"). In addition, modulation has the advantage that it can use frequency division multiplexing (FDM).

Telecommunications in society

Telecommunications have an important social, cultural and economic impact on modern society. In 2008, revenues in the telecommunications industry were $ 4.7 trillion, or just under 3% of the gross world product (at an official rate).

Impact of information technology on the economy

Microeconomics

At the microeconomic level, companies have used telecommunications to develop global business empires. This is a matter of course in the case of Amazon.com, but according to academician Edward Lehnert, even the average Walmart retailer has benefited from better telecommunications infrastructure compared to the competition. In cities around the world, homeowners use their phones to order and organize a variety of home services, from pizza deliveries to electricians. Even in relatively poor sectors of society, the use of telecommunications for their own benefit was noted. In Narsingdi District of Bangladesh, isolated villagers use Cell Phones for ordering goods directly from wholesalers in order to purchase goods at a better price. In Cote d'Ivoire, coffee makers track hourly changes in coffee prices on their mobile phones and sell them at the best price.

Macroeconomics

At the macroeconomic level, Lars-Hendrik Roller and Leonard Waverma have proposed a causal relationship between good telecommunications infrastructure and economic growth. Few dispute the existence of a correlation, although some argue that it is wrong to view this relationship as causal.

With the economic benefits of using good telecommunications infrastructure, there is growing concern about unequal access to telecommunication services around the world, called the digital divide. In 2003, a study by the International Telecommunication Union (ITU) showed that about 1/3 of the countries have less than one mobile phone for every 20 people and 1/3 of the countries have less than one landline phone for every 20 people. In terms of Internet access, roughly half of all countries have less than one Internet connection for every 20 people. Based on this information and data on educational attainment, ITU has developed an indicator that measures the overall ability of citizens to access information and communication technologies... According to this indicator, Sweden, Denmark and Iceland are among the top three, while the African countries of Nigeria, Burkina Faso and Mali are at the bottom of this rating.

The role of communications in the modern world

Telecommunications play a significant role in public relations. In view of the fact that such devices as a telephone were initially of practical value (for example, the ability to run a business or order services), their social aspect was not taken into account at all. This continued until the late 1920s, and in the 1930s, the social aspects of the device became an important topic in the promotion of phones. New promotions now appealed to consumer emotions, highlighting the importance of social conversation and the desire to stay connected with family and friends.

Since then, the role that telecommunications play in public relations has become more and more important. In recent years, the popularity of sites social networks has risen sharply. These sites allow users to communicate with each other, as well as share photos, events, and see the statuses and profiles of other users. Profiles can include age, interests, sexual preferences, and relationship status. Thus, these sites can play an important role in everything from organizing social movements to courtship.

Before the rise of social networking sites, technologies such as short message service (SMS) and the telephone also had a significant impact on social interaction. In 2000, the market research group Ipsos MORI reported that 81% of users aged 15 to 24 in the United Kingdom used short messaging to coordinate public relations and 42% for flirting.

The importance of telecommunications in human life

Culturally, telecommunications have empowered citizens to gain access to music and movies. With the help of television, people can watch movies that they have not seen before in their own home without having to go to a video store or movie theater. With the help of radio and the Internet, people can listen to music they have never heard before without visiting a music store.

Telecommunications has also changed the way news is received. According to a 2006 study by the nonprofit Pew Internet and the American Life Project, out of just over 3,000 Americans surveyed, the majority cited TV, radio or newspapers as their source of news.

Telecommunications have also had a significant impact on advertising. TNS Media Intelligence reported that in 2007, 58% of advertising spending in the United States was spent on media-dependent telecommunications services.

International Telecommunication Union

Many countries have passed legislation that complies with the requirements of the International Telecommunication Regulations established by the International Telecommunication Union (ITU), which is “the UN's lead agency for information and communication technologies.” In 1947, in Atlantic City, the ITU conference decided to “grant international protection to all frequencies registered in the new international frequency list and used in accordance with the Radio Regulations. "According to the ITU Radio Regulations adopted in Atlantic City, all frequencies indicated in the international frequency registration, considered by the Council and registered in the International Frequency Register" are eligible for international protection from harmful interference. "

With a global perspective, political debate and legislation were adopted regarding the management of telecommunications and broadcasting. In the history of broadcasting, there have also been discussions regarding equating to conventional communications such as print, modern telecommunications such as broadcasting. With the outbreak of World War II, there was an explosive growth in international propaganda broadcasting. Countries, their governments, rebels, terrorists and militias used all possible methods of telecommunications and broadcasting to promote their propaganda. Patriotic propaganda of political movements and colonization began in the mid-1930s. In 1936, the BBC conducted propaganda programs in the Arab world, in part contrasting its broadcasts with similar broadcasts from Italy, which also had colonial interests in North Africa.

Modern insurgents, such as those that fought in the last war in Iraq, often use intimidating phone calls, SMS messages, and the dissemination of sophisticated video attacks against coalition troops involved in the anti-terrorist operation. "The Sunni rebels even have their own television station, Al-Zawraa, which, while banned by the Iraqi government, continues to broadcast from Erbil, Iraqi Kurdistan, even after changing satellite hosting several times under pressure from the coalition."

Modern media

Telecommunications equipment sales

According to the data compiled by Gartner Ars-tecnika, major consumer telecommunications equipment has been sold worldwide in millions of units:

Telephone

In the telephone network, one subscriber connects to another subscriber by means of switches on different telephone exchanges... The switches form an electrical connection between two users and the settings of these switches are determined electronically when the caller dials the number. Once the connection is established, the caller's voice is converted into an electrical signal using a small microphone in the caller's handset. This electrical signal is sent through the network to the user at the other end, where it is converted back into the sound of a small speaker in the called party's handset.

Landline telephones in most residential buildings are analog, meaning the speaker's voice directly determines the signal voltage. Although calls over short distances can be handled end-to-end as analog signals, telephone service providers increasingly end-to-end conversion of incoming signals to digital signals for transmission. The advantage of this approach is that the digitized speech data can be transmitted together with data from the Internet and can be fully reproduced when communicating over long distances (as opposed to analog signals, which will inevitably be distorted by noise).

Mobile phones have had a significant impact on telephone networks. The number of mobile subscribers currently exceeds the number of fixed-line subscribers. Mobile phone sales in 2005 were 816.6 million, given that this figure is almost equally split between the markets of Asia / Pacific (204 million), Western Europe (164 million), CEBVA (Central Europe, the Middle East and Africa) (153.5 million), North America (148 million) and Latin America (102 million). With new subscriptions in the five years since 1999, Africa is outperforming other markets with 58.2% growth. Increasingly, these telephones are served by systems in which voice messages are transmitted in digital form, such as GSM or W-CDMA, and the number of analog systems, such as AMPS, is decreasing.

Also, there have been fundamental changes in telephone communications, which remained behind the scenes. Beginning with the activities of TAT-8 in 1988, the 1990s saw widespread adoption of fiber-based systems. The advantage of fiber-optic communications is that it offers dramatic increases in bandwidth. Actually, TAT-8 was able to support 10 times more phone calls than the most modern copper cable laid at that time, and modern fiber optic cables are able to support 25 times more phone calls than TAT-8 supported. This increase in throughput is due to a number of factors: First, optical fibers are physically much smaller than competing technologies. Secondly, they do not suffer from crosstalk, which means that several hundred of them can be easily assembled together in a single cable. Finally, improvements in multiplexing have led to exponential growth in single fiber throughput.

Many modern fiber optic networks communicate using a protocol known as Asynchronous Transfer Mode (ATM). ATM protocol allows for shared data transmission. It is suitable for public switched telephone networks because it establishes a path for data through the network and associates a traffic agreement with that path. A traffic agreement is essentially an agreement between a client and a network about how the network should process data; if the network cannot meet the traffic agreement, then the connection to that network is rejected. This is important because telephone connections must be guaranteed to maintain a constant bit rate so that the caller's voice can be transmitted completely without delays or drops. There are competitors to ATM, such as Multi-Protocol Label Switching (MPLS), which perform a similar task and are expected to supplant ATM in the future.

Radio and television

In a broadcasting system, a high power central broadcasting tower transmits a high frequency electromagnetic wave to multiple low power receivers. The high frequency wave sent by the tower is modulated by a signal containing a visual or sound information... The receiver, in turn, is tuned to receive and amplify the high-frequency wave and, using a demodulator, extract a signal containing visual or audio information. The broadcast signal can be either analog (the signal changes continuously with the information) or digital (the information is encoded as a set of discrete values).

The broadcast media industry has entered a critical turning point in its development with the transition from analogue to digital broadcasting in many countries. This move was made possible by the production of cheaper, faster and more functional integrated circuits. The main advantage of digital broadcasting is that it does away with a number of disadvantages that are typical for traditional analogue transmissions. In the television picture, this is manifested by the elimination of problems such as snowy pictures, ghosting and other distortions. This is due to the nature of analog transmission, which means distortion caused by noise will be noticeable in the end result. Digital transmission overcomes this problem as digital signals are restored to discrete values ​​upon receipt and therefore small disturbances do not affect the final result. In a simplified example, if the binary message 1011 was transmitted with the amplitude of the signals:, and the received signals have the amplitudes:, then when decoding we get in the binary message 1011 - an ideal reproduction of what was sent. From this example, you can see the problem of digital transmission, which is that if the noise is large enough, it can significantly change the decoded message. By using forward error correction, the receiver can correct several bit errors in the received message, but too much noise will result in poorly understood output signals and hence transmission disruption.

In digital television broadcasting, there are three competing standards that are likely to be adopted around the world. These are ATSC, DVB and ISDB standards. All three standards use MPEG-2 for video compression. ATSC uses Dolby Digital AC-3 for audio compression, ISDB uses Advanced Audio Coding (MPEG-2 Part 7) and DVB does not have a standard for audio compression, but generally uses MPEG-1 Part 3 Layer 2. The choice of modulation also varies from scheme to scheme. In digital audio broadcasting, the standards are much more unified in virtually all countries that choose to adopt the Digital Audio Broadcasting standard (also known as the Eureka 147 standard). The exception is the United States, which has selected HD Radio. HD Radio, unlike Eureka 147, is based on a transmission method known as IBOC, which allows digital information to be transmitted by conventional AM or FM analog transmitters.

However, despite the anticipation of a “digital” transition, analog television is still being broadcast in most countries. An exception is the United States, where analogue television broadcasts have ceased (all but very low power television stations) since June 12, 2009 after a double grace period. In Kenya, analogue television broadcasting also ceased in December 2014, following multiple date postponements. For analogue television, there are three standards used for broadcasting color television. They are known as PAL (German design), NTSC (North American design), and SECAM (French design). It is important to understand that these methods of transmitting color television have nothing to do with black and white television standards, which also vary from country to country. For analog radio, the transition to digital radio is hampered by the fact that analog receivers are significantly cheaper than digital receivers. The choice of modulation for analog radio is typically between amplitude (AM) or frequency (FM) modulations. To achieve stereo reproduction, an amplitude modulated subcarrier for stereo FM is used.

Internet

The Internet is a worldwide network of computers and computer networks that communicate with each other using the Internet Protocol. Any computer on the Internet has a unique IP address that can be used by other computers to direct information to it. Therefore, any computer on the Internet can send a message to any other computer using its IP address. These messages carry with them the IP address of the sending computer, allowing two-way communication. The Internet is the exchange of messages between computers.

It is estimated that 51% of information transmitted over two-way telecommunications networks in 2000 was transmitted over the Internet, while most of the rest (42%) was transmitted through a landline telephone. By 2007, the Internet clearly dominated and captured 97% of all information in telecommunications networks (most of the rest (2%) - via mobile phones. As of 2008, approximately 21.9% of the world's population has access to the Internet with the most high access (measured as a percentage of population) in North America (73.6%), Oceania / Australia (59.5%) and Europe (48.1%) Leading broadband access: Iceland (26.7%) %), South Korea (25.4%) and the Netherlands (25.3%).

The Internet works in part because of the protocols that govern how computers and routers communicate with each other. The nature of computer network communication lends itself to consideration from the standpoint of a layered approach, when some protocols in the protocol stack run more or less independently of other protocols. This allows the lower layer protocols to be tuned to a specific state on the network until the way the higher layer protocol works changes. Practical example why this is important is that it allows the Internet browser to execute the same code in the same way, regardless of whether the computer is connected to the Internet via an Ethernet or Wi-Fi connection. Protocols are often spoken of in terms of their place in the OSI Reference Model, which emerged in 1983 as the first step in an unsuccessful attempt to create a universally accepted set of network protocols.

The Internet is characterized by a change in the physical environment and channel protocol several times along the entire route passing by packets. This is because the Internet does not place any restrictions on what physical medium and what communication protocols can be used. This leads to the adoption of information and protocols that are most appropriate for the situation on the local network. In practice, in most cases of intercontinental communication, a protocol with asynchronous mode transmission (ATM) or its more modern equivalent - based on fiber. This is because most intercontinental Internet communications use the same infrastructure as the public switched telephone network.

At the network level, standardization takes place with the Internet Protocol (IP) required for logical addressing. For the World Wide Web, these "IP addresses" are derived from "human readable" form using the DNS domain name system (eg 72.14.207.99 originating from www.google.com). On the this moment The most widely used version of the Internet Protocol is version four, but the transition to version six is ​​inevitable.

At the transport layer, most communications accept either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). TCP is used when it is necessary for every message sent to be accepted by another computer, while UDP is used when it is simply desirable. In the case of TCP, packets are retransmitted if they are lost and reordered before being presented to higher layers. With UDP, packets are not sequenced and are not retransmitted if lost. Both TCP and UDP packets carry port numbers to indicate which application or process should handle the packet. Since some application layer protocols use specific ports, network administrators can control traffic according to specific requirements. For example, to restrict access to the Internet by blocking traffic destined for a specific port, or to affect the operation of some applications by assigning priority.

Above the transport layer, there are certain protocols that are sometimes used and freely placed in sessions and presentation layers, primarily the protocols: Secure Sockets Layer (SSL) and Transport Layer Security (TLS). These protocols ensure that data transferred between two parties remains completely confidential. And finally, at the application level, many of the users of Internet protocols are aware of such as HTTP (web browser), POP3 (email), FTP (file transfer), IRC (Internet chat), BitTorrent ( general access to files) and XMPP (instant messaging).

Voice over Internet Protocol (VoIP) allows data packets to be used for synchronous voice communications. Data packets are marked as voice packets and can be prioritized for real-time transmission, synchronous conversation is less prone to competing with other types of data traffic that can be delayed (i.e. file or email transfer) or pre-buffered (i.e. there is audio and video) without distortion. This prioritization works well when the network has sufficient bandwidth for all VoIP calls occurring simultaneously, and the network has a prioritization option enabled. private corporate network but the Internet as a whole cannot be configured in this way, and therefore there is a big difference in the quality of VoIP calls over the private network and over the public Internet.

Local and global computer networks

Despite the growth of the Internet, the characteristics of local area networks (LANs) - computer networks that do not go beyond a few kilometers - remain different. This is because networks of this size do not require all the functions associated with larger networks and are often more cost effective and efficient without them. While not connected to the Internet, they also have privacy and security benefits. However, the purposeful lack of a direct Internet connection does not provide guaranteed protection against hackers, military forces, or economically powerful powers. These threats exist if there are any methods to connect to the local network remotely.

Wide area networks (WANs) are private computer networks that can span thousands of kilometers. Again, some of their benefits include privacy and security. Initially, local and global networks were intended for the armed forces and intelligence services, which must keep their data safe and secret.

In the mid-1980s, several communication protocols emerged to fill the gaps between the data link and application layers of the OSI reference model. These include Appletalk, IPX, and NetBIOS, with IPX installed, which dominated in the early 1990s due to its popularity with MS-DOS users. TCP / IP, which exists and at the moment, was usually used only in large government and research institutions.

As the popularity of the Internet increased and its traffic had to be routed to private networks, TCP / IP protocols replaced existing LAN technologies. Additional technologies, such as DHCP, that allow IP / TCP-based computers to self-configure on the network. Such functions are also implemented in the AppleTalk / IPX / NetBIOS protocol suites.

Asynchronous Transfer Modes (ATM) or Multi-Protocol Label Switching (MPLS) are typical data link protocols for more large networks such as WANs; Ethernet and Token Ring are typical link layer protocols for local area networks. These protocols differ from older protocols in that they are simpler, for example, they omit functions such as guaranteed quality maintenance, as well as elimination of collisions. Both of these differences allow for more economical systems.

Despite the modest popularity of IBM Token Ring in the 1980s and 1990s, virtually all LANs today use wired or wireless Ethernet equipment. At the physical layer, most wired Ethernet implementations use twisted-pair copper cables (including common 10BASE-T networks). However, some early implementations used heavier coaxial cables, and in recent implementations (especially in high-speed ones) optical fiber has been used. When using optical fiber, a distinction must be made between multimode fibers and singlemode fibers. Multimode fibers can be viewed as a thicker fiber that is cheaper to manufacture, but has the disadvantage of a narrower usable bandwidth and worse attenuation, and therefore poorer long-haul performance.

Information transfer rate

The effective volume of information exchanged around the world through two-way networked telecommunications increased from 281 petabytes of information in 1986 to 471 petabytes in 1993, from 2.2 exabytes in 2000 to 65 exabytes in 2007 (adjusted for optimal compression) ... This information equivalent is roughly equivalent to two newspaper pages per person per day in 1986 and six whole newspapers per person per day by 2007. Given this growth, telecommunications are playing an increasing role in the development of the world economy and the global telecommunications sector amounted to about 4.7 trillion in 2012. dollars. The volume of the global telecommunications market will amount to $ 1.5 trillion in 2010, which corresponds to 2.4% of the world's gross domestic product (GDP).