Traditionally, the following types of public telephone networks are distinguished: city, rural, zonal and long-distance. City telephone networks (GTS) provide telephone communications in the territory of a more or less large city and its immediate suburbs. Rural telephone networks (RTN) provide telephone communications within rural administrative areas. The networks of these two types are united by a common name local telephone networks.

Zonal telephone networks is a complex of structures that are designed for communication between subscribers of several different local telephone networks located on the territory of one telephone zone. In such a zone, a single seven-digit number is used. zone numbering. The territories of telephone zones often coincide with the territories of regions, territories and other administrative entities.

Intercity telephone network - this is a complex of structures that are designed to organize communications between subscribers of local telephone networks located in different telephone zones.

All these networks together form the public telephone network (PSTN), which is part of the country's Interconnected Communications Network. A mandatory requirement for the PSTN is full connectivity between all local, national and regional telephone networks. Moreover, connectivity between telephony islands must be provided (and was provided for many years ago) so that any subscriber can connect to any other subscriber, receiving the ability to transmit data, switch it and protect it at the national and regional levels.

In addition to the PSTN, there are also institutional, departmental, corporate telephone networks that provide internal telephone communications to enterprises, institutions, corporations, and organizations. Such networks can be completely autonomous, but most often they have access to the public telephone network.

A more detailed classification of networks and a description of their structure are given in the course “Communication Networks”.

Switching

Word switching(switching) means “turning on and off”. For Electrical Engineer switching element - This is a device that, when operating, can go into any of two states: ON and OFF. This is true both for optical switching elements and for transistors, with the help of which logic gates and flip-flops for Boolean operations, binary memory, etc. are built. By the way, it is on this basis, with the help of finite state machines, Karnaugh maps and other means, that switching circuits are created.

The Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) has defined switching How “a connection of one (specific) of the many inputs of a system with one (specific) of its many outputs, organized on request and provided to this input-output pair for the time required for the exchange of information between them.” In other words, the connection is created according to the called user's line number dialed by the calling user and is maintained until one of them hangs up. As long as this connection exists, speech, data or video information can be transmitted over it.

Thus, having received the request dial-up communication, the network establishes a connection between the calling and called users (people, computers or modems), which is completely and completely available to them, but only for the duration of the connection. During this entire time, no connection resources are used to service other requests, and natural pauses in conversation or data transmission cannot be filled by other conversations or other data. When communication ends, the connection is destroyed, after which the network resources from which it was composed can be used to create other connections.

Taking into account the information about communication networks given in the previous paragraph and the concepts introduced at the beginning of this paragraph, we can say that commutation is a process serial connection several permanently existing channels independently of one another into one composite channel, created only for the duration of communication so that users at the end points of this switched channel can communicate with each other, i.e. exchange information. The components of the switched channel are selected from among those that are free, available, and located in the desired direction.

Note that both of the above definitions apply only to channel switching. There is also a concept packet switching, which is only mentioned in this book, and then a little later.

Channel switching can be analog and digital.

Analog switching is the process in which a connection between the endpoints of a switched channel is established through operations on an analog signal (possibly sampling it, but not converting it to digital form). Analog switching is covered in the next two chapters of the textbook.

Digital switching is the process in which a connection between the endpoints of a switched channel is established using operations on a digital signal without converting it to analog signal. The remaining eight chapters cover various aspects of digital circuit switching.

Switching methods

The multichannel electrical communications course examines the classical methods of channel multiplexing - space division, time division and frequency division. If you need to connect two channels multiplexed using the same method, then obvious reasons, it is preferable to switch these channels using the same method as their multiplexing. Hence the three classic switching methods:

Spatial switching- connection of spatially separated channels using electromechanical, electronic, digital or optical technology using switching elements built on the basis of the same technology.

Time switching provides the possibility of commutation
work in space, but when spatially commuting
the physical path reaches its receiver at the switch
tion field, the receiver is commanded to select only those
data that corresponds to a specific time frame
nalu. If the receiver and transmitter are assigned different times
channels, temporary switching is required, which we will talk about later
we discuss in chapter 4.

Frequency switching Typically used for commutation
tions of television channels and radio channels are not included in this textbook.
is being considered.

Switching nodes and stations represent a set of technical means designed to process calls received via subscriber and connecting lines of the network, to provide the initiators of these calls with basic and additional communication services, as well as for accounting and charging for services. This definition covers switching nodes and stations of all types used in the Interconnected Communications Network of the Russian Federation, namely: city automatic telephone exchanges (ATS), private telephone exchanges (PBX), hubs (K), nodes of incoming (UVS) and outgoing (UIS) city messages telephone networks, special service nodes (USS), long-distance exchanges (AMTS), automatic switching nodes (ASK), central (CS), node (US) and terminal (OS) rural telephone exchanges and other information distribution devices.

In general, a switching node (station) contains a switching field designed to connect incoming and outgoing channels (lines) during the exchange of information; control devices that ensure the establishment of a connection through a switching field, as well as the reception and transmission of control information; sets (station terminations) of incoming and outgoing lines; code receivers and transmitters; devices for monitoring and diagnostics of subscriber lines and equipment of the switching center itself; power supplies; crossover equipment and some auxiliary devices.

X. Bezir simplifies the above by defining switching station as a set of station terminations of lines, switching devices and control devices of one network node, the task of which is to establish, maintain and destroy connections between incoming and outgoing information channels specified by the corresponding addresses.

Switching nodes and stations are classified according to the method of servicing connections (manual, semi-automatic, automatic), by the place occupied in the communication network (terminal, intermediate, transit, central, node), by the principle of switching (analog, digital), by type of equipment (electromechanical , quasi-electronic, electronic).

Created for the production and special needs of government agencies. They can serve as a data transmission medium (LAN) and organize internal telephone communications.

Often, departmental telephone communication networks use direct telephones that provide a connection to only one subscriber, without the ability to dial a number. In such cases, there may be no call switching at all or it may be performed manually by the dispatcher (called on a single line).

Often, departmental communication networks have access to a public communication network for some subscribers. Departmental communication networks are also used to provide communication services to the public and other users.

The concept of departmental communication networks was part of the Federal Law of February 16, 1995 No. 15-FZ “On Communications” (as amended on July 17, 1999), which included Article 8. “Departmental communication networks, dedicated communication networks of physical and legal entities»

In 2003, the Russian Federation adopted a new law on communications No. 126-FZ, where there is no concept of “departmental communications”, but there is Article 16 describing communication networks special purpose - as special-purpose communication networks designed for the needs of government authorities, the needs of national defense, state security and law enforcement. Article 14 also talks about dedicated communication networks. .

Vladimir Putin signed the Federal Law “On Amendments to the Federal Law “On Communications” on March 2, 2016, which was adopted by the State Duma on February 19, 2016 and approved by the Federation Council on February 26, 2016.

In order to expand the possibilities of using communications for the needs of government authorities, the needs of national defense, state security and law enforcement Federal law it is established that special-purpose communication networks can be connected to a public communication network without being transferred to the category of a public communication network on the basis of agreements on the connection of telecommunication networks concluded by communication operators and owners of special-purpose communication networks.

At the same time, the Federal Law introduces the concept of “owner of a special-purpose communication network,” which means the federal executive body, its territorial body, or a division of the federal government that manages the special-purpose communication network, including through the relevant control centers, and owns it with the right of operational management. executive body exercising certain powers of the specified federal body.

The owner of a special-purpose communication network can be allocated a numbering resource from the numbering resource of a public communication network.

The Federal Law specifies that special-purpose communication networks cannot be used for the paid provision of connection services and traffic transmission services (along with the already provided ban on the use of special-purpose communication networks for the paid provision of communication services).

The Federal Law establishes that public communication network operators are obliged to provide connection services to owners of special-purpose communication networks in accordance with the rules for connecting telecommunication networks and their interaction, approved by the Government of the Russian Federation.

Along with this, the Federal Law provides for the right of the federal executive body in the field of communications to withdraw in whole or in part the numbering resource allocated to the owner of special-purpose communications, as well as the grounds for such withdrawal.

In accordance with the Federal Law, the Government of the Russian Federation is vested with the authority to establish the procedure for the specified withdrawal and, by definition, the federal executive body authorized to exercise control over the use of the numbering resource allocated to the owner of the special-purpose communication network.

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LETTER from the Ministry of Communications of the Russian Federation dated 28-03-95 54 ON THE PROCEDURE FOR CONNECTING TO PUBLIC COMMUNICATION NETWORKS AND THE PROCEDURE FOR REGULATING PASSAGE... Relevant in 2018

4. Technical requirements when connecting to public communication networks

4.1. Technical conditions for connection

4.1.1. Technical conditions for connecting a communication network to a public communication network are issued by the public network operator to the operator of the connected network upon written request. If the provision of services that the connected network intends to provide to users is subject to licensing in accordance with current legislation, a copy of the license issued by the Ministry of Communications of the Russian Federation is attached to the request.

Refusal to issue technical conditions for connection to a network operator that has the appropriate license is not permitted.

4.1.2. Technical conditions for connection must reflect:

the specific way in which connections between networks are established;

technical parameters at network connection points (signal levels, signal spectra, transmission speeds, signaling types, signal codes, cable types, etc.);

method of accounting for traffic from the connected communication network (outgoing and incoming);

interaction of control systems and technical operation, including the method of organizing interaction between the control centers of the connected network and the public network;

interaction of synchronization systems;

a list of construction and installation works that must be performed to carry out the connection, including, if necessary, the expansion of switching capacity and interstation channel banks of the public network in all necessary areas for passing traffic from/to the connected network in accordance with the current VNTP and other regulatory and technical documentation , containing requirements for communication networks;

stages of connection work.

4.1.3. It is not allowed to include in the technical conditions for connection the construction of objects and structures and the installation of equipment that are not related to the transmission of traffic from/to the connected network other than on a compensatory basis.

4.2. Connection to the public telephone network

4.2.1. Joining at the local level

4.2.1.1. The connected network, depending on the ratio of its capacity (at the end of the license period) and the capacity of the local public communication network, can be connected to the latter as an institutional PBX, district PBX, a hub area of a zoned urban local network, or a terminal or hub PBX of a rural local network.

Networks with a capacity of less than 1000 numbers are included in public city networks only as corporate PBXs or city PBX hubs.

In some cases, subject to mandatory approval by the Ministry of Communications of the Russian Federation, the connected network may contain a switching node through which connections between subscribers of the public communications network pass.

4.2.1.2. Communication networks providing telematics services are usually included in telephone networks at the level of subscriber installations. It is allowed to include networks providing telematic services and information and reference services as special services of local telephone networks. A specific decision on the method of connection is made by the operator of the public communications network, if the license of the operator of the connected network does not contain specific instructions on the method of connection.

4.2.1.3. The numbering allocated to the connected network (its switching stations and subscriber installations with access to the public communications network) is determined by the operator of the latter when issuing technical conditions for connection.

4.2.1.4. Subject to availability technical feasibility It is permitted to organize direct channel bundles between switching stations of the connected network and automatic telephone exchanges of the public network located in the same numbering zone, while maintaining the unity of numbering of subscribers of the connected network.

4.2.2. Connection at intrazone level

4.2.2.1. With this method of connection, the connected network is included in the PBX of the public communication network as a local network and is assigned an intra-zone access code ab. The code is selected in accordance with the current numbering plan for the public communications network.

4.2.2.2. The numbering allocated to the connected network is determined by the operator of the public communication network with mandatory agreement with the Giprosvyaz Institute (assigned to the given region) when issuing technical conditions for connection.

4.2.2.3. If technically possible, it is permitted to organize direct channel bundles between switching stations of the connected network and international telephone exchanges of the public network while maintaining the unity of numbering of subscribers of the connected network.

4.2.2.4. To connect at the intrazone level, the connected network, according to the license (for the last year of its validity), must have an installed capacity of at least the average capacity of the local network in the numbering zone in question, but in any case not less than 30,000 numbers.

If the network capacity is more than 60,000 numbers, it can be allocated more than one intrazone ab code.

4.2.3. Intercity connection

4.2.3.1. With this connection method, the connected network is included in the public long-distance communication network as a numbering zone and is assigned a long-distance access code ABC.

4.2.3.2. The intercity code allocated to the connected network is determined by the Ministry of Communications of the Russian Federation in accordance with the numbering plan for the public communications network of the Russian Federation.

4.2.3.3. Connection of a communication network to a public network at the intercity level is allowed only for existing networks that have an installed capacity of their own local switching stations of at least 300 thousand numbers with a utilization rate of at least 50%.

4.2.3.4. In certain technically justified cases, simultaneous connection of communication networks to the public network at the intercity and local levels is permitted. In this case, connection at the local level is carried out separately in each numbering zone of the public network where such connection is carried out, in accordance with these Regulations and the principles of constructing a public telephone network.

4.2.4. Connection at the level of subscriber installations is carried out in accordance with the current rules for the provision of services by local telephone networks of the Russian Federation.

4.3. Connection to public telegraph networks

4.3.1. As public telegraph networks, these Regulations consider the public telegraph network with message switching and subscriber telegraph networks - the AT-50 network (national) and the Telex network (international), in the future - the unified AT/Telex network.

4.3.2. Connection to public subscriber telegraphy networks (AT-50, Telex) is permitted for departmental and other subscriber telegraphy networks, data transmission networks and telematic services.

4.3.3. Connection to the public telegraph network with message switching (TG-OP) is allowed for telegraph networks whose operators are licensed to provide the Telegram service or provide the specified service under an agreement with the operators of the TG-OP network.

The procedure for connecting other networks and equipment to the TG-OP network for transmitting non-telegraph traffic is determined by a separate regulation approved by the Ministry of Communications of the Russian Federation.

4.3.4. Connection to public telegraph networks is carried out, as a rule, at the level of subscriber installations (AT-50, Telex) or end points (TG-OP). In this case, specific connection points and numbering of the corresponding telegraph network allocated to the connected network or service are established by regional (zonal) operators of public telegraph networks.

4.3.5. In some cases, if the connected network has the appropriate technical means, connection to public telegraph networks is allowed at the level of channel switching stations (substations) (AT-50, Telex) or message switching centers (hubs) (TG-OP). In this case, specific connection points and numbering of the corresponding telegraph network allocated to the connected network or service are established by the Ministry of Communications of the Russian Federation.

4.3.6. Transit transmission of public telegraph network traffic through connected networks is not permitted, with the exception of public data networks designated by the Ministry of Communications of the Russian Federation as transport networks for the transmission of telegraph traffic.

4.4. Connection of personal radio call networks to the public telephone network

The connection of personal radio call networks to the public telephone network is carried out in accordance with the concept adopted by the State Committee for Electric Networks of Russia.

4.5. Connection of mobile radio networks to the public telephone network

The connection of mobile radio communication networks to the public telephone network is carried out in accordance with the concept adopted by the State Committee for Electric Networks of Russia.

4.6. Connection of trunking networks to the public telephone network

The connection of trunking networks to the public telephone network is carried out in accordance with the concept adopted by the State GKES of Russia.

The public communication network is intended for the paid provision of telecommunication services to any user of communication services on the territory of the Russian Federation and includes telecommunication networks that are defined geographically within the service territory and numbering resource and are not defined geographically within the territory of the Russian Federation and the numbering resource, as well as networks communications determined by the technology for implementing the provision of communication services.

A public communications network is a complex of interacting telecommunication networks, including communications networks for the distribution of television and radio broadcasting programs.

The public communications network has connections to the public communications networks of foreign countries.

1.3 Dedicated communication networks

Dedicated communication networks are telecommunication networks intended for the provision of paid telecommunication services to a limited circle of users or groups of such users. Dedicated communication networks can interact with each other. Dedicated communication networks do not have connections to the public communication network, as well as to the public communication networks of foreign countries.

Technologies and means of communication used to organize dedicated communication networks, as well as the principles of their construction, are established by the owners or other owners of these networks.

A dedicated communications network may be connected to a public communications network with transfer to the category of a public communications network if the dedicated communications network meets the requirements established for a public communications network. In this case, the allocated numbering resource is withdrawn and a numbering resource is provided from the numbering resource of the public communication network.

The provision of communication services by operators of dedicated communication networks is carried out on the basis of appropriate licenses within the territories specified therein and using the numbering assigned to each dedicated communication network in the manner established by the federal executive body in the field of communications.

1.4 Technological communication networks

Technological communication networks are designed to support the production activities of organizations and control technological processes in production.

Technologies and means of communication used to create technological communication networks, as well as the principles of their construction, are established by the owners or other owners of these networks.

If there are free resources of a technological communication network, part of this network can be connected to a public communication network with transfer to the category of a public communication network for the provision of paid communication services to any user on the basis of an appropriate license. Such affiliation is permitted if:

The part of the technological communication network intended for connection to the public communication network may be technically, or programmatically, or physically separated by the owner from the technological communication network;

The part of the technological communication network connected to the public communication network meets the requirements for the functioning of the public communication network.

A part of a technological communication network connected to a public communication network is allocated a numbering resource from the numbering resource of a public communication network in the manner established by the federal executive body in the field of communications.

The owner or other possessor of a technological communication network, after connecting a part of this communication network to a public communication network, is obliged to keep separate records of the costs of operating the technological communication network and its part connected to the public communication network.

Technological communication networks can be connected to technological communication networks of foreign organizations only to ensure a single technological cycle.

Communication network- a set of technical means and distribution media that ensure the transmission and distribution of information from many sources to many recipients.

Communication networks built on the basis of telecommunications are called telecommunication networks. Information transmission is carried out by multi-channel transmission systems, distribution - by switching stations.

In the literature, communication networks are classified according to their purpose, the nature of the formation and allocation of channels, types of switching, equipment and placement conditions, and degree of automation. Let us consider in more detail the classification characteristics of communication networks.

The classification of communication networks can be presented in the form of a diagram shown in Figure 2.

1.By purpose Communication networks are divided into two large groups:
- v Public communication networks
- v Limited-use communication networks.

A public communication network is created to provide communication services to the population, various institutions, enterprises and organizations. From the laws of the Russian Federation: a public communication network is intended for the provision of paid telecommunication services to any user of communication services on the territory of the Russian Federation and includes telecommunication networks that are defined geographically within the service territory and numbering resource and not geographically defined within the territory of the Russian Federation and numbering resource , as well as communication networks determined by the technology for implementing the provision of communication services

When building limited-use communication networks, specific requirements are implemented due to the nature of the activities of a particular department in whose interests it is created this network, and also provides for the possibility of subscribers connecting to the public network. Such networks include internal communication networks and long-distance communication networks. These are special purpose communication networks, dedicated communication networks.

Intra-industrial or technological communication networks: telecommunication networks of federal executive authorities, as well as enterprises, institutions and organizations, created to manage intra-industrial activities and technological processes that do not have access to the public communication network.

2. By the nature of formations and allocation of communication channels communication networks are divided into
v Primary
v Secondary.

Primary network- a set of standard physical circuits, standard transmission channels and network paths, formed on the basis of network nodes, network stations, terminal devices of the primary network and transmission lines connecting them. In this case, a typical physical circuit and a typical channel are understood as a physical circuit and a transmission channel, the parameters of which comply with accepted standards.

Network path- a standard group path or several series-connected standard group paths with path formation equipment switched on at the input and output.

Secondary communication network- a set of lines and communication channels formed on the basis of the primary network, stations and switching nodes or stations and switching nodes, providing a certain type of communication.

The main task of the primary network is the formation of standard channels and group communication paths, the task of the secondary network is the delivery of messages of a certain type from the source to the consumer.

The primary network, in turn, is classified according to territorial characteristics:

v backbone primary network connects with channels various types all regional, regional and republican centers of the country;
v intrazonal primary network is part of the primary network, limited to the territory of one zone, coinciding with the administrative boundaries of the region, territory, republic. In some cases, an intrazonal network may cover several areas and, conversely, there may be several intrazonal networks within one territorial unit;
v local primary networks - part of the network limited to the territory of a city or rural area. They provide the output of message transmission channels directly to the station and further to subscribers.
v zonal primary networks are a combination of intrazonal and local primary networks into one network.

The hierarchy of primary communication can be seen in Figure 3.

Figure 3 - Primary network hierarchy

3. Separation of primary and secondary communication networks based on territory coverage.

Depending on the territory served, networks can be local, corporate, national, or global (territorial). And also rural, urban, intra-regional, local, intercity (backbone for the primary network), international.

Local communication network- a communication network located within a certain territory (enterprise, firm, etc.).

Corporate communication network- a communication network that unites the networks of individual enterprises (firms, organizations, joint-stock companies, etc.) on the scale of one or several states.

Intraregional or zonal communication network, - long-distance telecommunications network within the territory of one or more constituent entities of the Federation.

Backbone communication network- intercity telecommunication network between the center of the Russian Federation and the centers of the constituent entities of the Federation, as well as between the centers of the constituent entities of the Federation.

Intercity communication network - a communication network that provides communication between subscribers located on the territory of different constituent entities of the Russian Federation or different administrative regions of one constituent entity of the Russian Federation (except for districts within the city).

International communication network - a set of international stations and channels connecting them, providing international communications to subscribers of various national networks.

Local communication network - a telecommunication network formed within an administrative or otherwise defined territory, not related to regional communication networks; local networks are divided into rural and urban.

Rural communication network - a communication network that provides telephone communication in the territory of rural administrative districts.

Urban communication network - a network that serves the needs of a large city. The function of a metropolitan network is to act as a backbone for communications local networks the whole city.

National communications network - a communication network of a given country, providing communication between subscribers within that country and access to the international network.

Global (territorial) network communications unites networks located in different geographical areas of the globe. One example of such a network could be Internet.

4 . By service area Communication networks are divided into long-distance, international, local (rural, urban).

The main definitions are written in subparagraph 3.

5. Separation of networks according to the type of information transmitted. Based on the type of information transmitted, digital, analog and mixed communication networks are distinguished.

Analog communication is the transmission of a continuous signal.

Digital communication is the transmission of information in discrete form ( digital form). A digital signal is analog in its physical nature, but the information transmitted with its help is determined by a finite set of signal levels. For processing digital signal Numerical methods are used.

The existence of mixed networks is typical during the transition from analog communication networks to digital ones.

6. Based on equipment and placement conditions, communication networks are divided into
v Mobile
v Stationary

Mobile refers to communication networks, the elements of which (CC, linear communication facilities) are located on the transport base and can be moved. One of the common types mobile networks is a military field communications network.

Fixed communication networks are created on the basis of communication nodes located in stationary structures. Fixed networks may, if necessary, include moving elements, for example, when replacing stationary elements that have failed for a short time, temporarily placing subscribers on moving objects, or the need to temporarily strengthen certain network elements.

7. According to the degree of automation, communication networks are divided into:
- v Manual
- v automated
- v Automatic.

On manual In communication networks, all or the vast majority of basic operations are performed by humans.

Automated are called networks in which the overwhelming number of functions for performing a certain volume of operations are carried out by a technical device.

Such networks are assessed by the degree of automation, which is determined by the coefficient Ka, equal to the ratio of the volume of operations performed by technical devices to the total volume of operations performed:

Where ns- the total volume of operations performed over a certain time, na- the number of operations performed by the machines.

Automatic networks provide for the performance of all functions for the transmission and switching of messages by automatic machines.

8. By type of switching networks are divided into switched, partially switched and non-switched.

For switched and partially switched Communication networks are characterized by the use of various switching options.

Long-term called switching, in which a permanent connection is established between two points on the network.

Operational called switching, in which a temporary connection is organized between two points on the network.

The combination of operational andlong-term switching assumes that in some sections of the information direction of the communication network long-term switching can be used, and in others operational switching.

Switched communication network- this is a secondary network that provides a connection at the request of the subscriber or in accordance with given program through the telecommunication channel of terminal devices of the secondary network using switching stations and switching nodes for the duration of message transmission. Transmission channels in switched networks are public channels. On partially switched communication networks, the use of all long-term and operational switching systems is provided. Really existing and projected communication networks in the near future belong to the class of partially switched ones.

TO non-switched communication networks These include secondary networks that provide long-term (permanent and temporary) connections of end devices (terminals) through a telecommunication channel using stations and switching nodes. Non-switched networks include the core communication network.

9.Separation networks by type of connection. Depending on the type of communication, communication networks are divided into telephone, videotelephone, telegraph, facsimile, data transmission, audio and television broadcasting networks.
v Telephone network- this is the most common type operational communications. Network subscribers can be: individuals, so legal - enterprises and organizations. It is used both for transmitting analog messages, as well as digital and text or graphic messages, so not only people, but also various hardware can be subscribers of the telephone network.

The operating principle of the telephone network is based on transmission sound signal via electrical wires. The first telephone exchange opened in 1877 in Connecticut (USA). Telephone operators manually connected subscribers to each other. In 1833 it was already opened telephone connection between Boston and New York. The first telephone lines were free, and only young men could work as telephone operators.

Today, the telephone network is a collection of switching nodes, the role of which is performed by automatic telephone exchanges (automatic telephone exchanges), and connecting and communication channels.

v Broadcasting- organization and distribution of various messages to the population using systems, networks, and electrical communications. Broadcasting is a mass medium.

There is the following classification: sound and TV broadcasting - depending on the type of messages.

Sound broadcasting is the process of circular transmission of various audio information to a wide range of geographically dispersed listeners through a special set of technical means.

The primary television signal is also generated by the scanning method. The spectrum of the video signal depends on the nature of the image, and the energy spectrum is concentrated in the band f=0...6 MHz.

Moreover, color television is compatible with black and white television, i.e. a color image is received by black and white television and vice versa, color televisions perceive a black and white image.

v Telegraph networks designed for transmitting (receiving) open text messages(telegrams) or pre-encrypted (cryptograms). To organize telegraph communication, terminal devices such as telegraph machines and personal computers are used.
v Fax networks are intended for transmitting (receiving) messages in the form of printed, handwritten, graphic and other still images of flat originals with reproduction of their copies at the receiving point. In networks of this type of communication, special terminal devices are used - fax machines.
v Data network-- a system consisting of end devices (terminals) connected by data transmission channels and switching devices (network nodes), and intended for the exchange information messages between all end devices.
10. Separation of networks by degree of security. Based on this criterion, communication networks are divided into protected (encrypted telephone networks, encrypted telegraph communications, etc.) and unprotected. In turn, secure networks can use equipment with guaranteed and temporary durability
11. Separation of networks by type of connection(equipment used). Based on the type of communication (equipment used), communication networks can be divided into wired (cable, airborne, fiber-optic) and radio networks (radio relay, tropospheric, satellite, meteor, ionospheric, etc.).

Wired communication lines include overhead communication lines (metal conductors, the laying of which is carried out openly, by tensioning them between supports-pillars with fixation on insulators) and cable communication lines (metal conductors, isolated from each other and from the environment, the laying of which is carried out openly , on the surface of something, or underground, under water, in sewer structures).

Advantages of wired communication networks:

v absence of mutual interference when laying together a large number of lines in a limited area (subject to certain laying rules);
v low level of self-interference in lines and channels of wired communication, which determines relatively high quality communications that ensure reliability, timeliness and reliability of message transmission;
v relative secrecy of message transmission;
v in wired communications it is more difficult than in radio communications to deliberately interfere with the exchange of messages, etc.

Disadvantages of wired communication networks:

v the need for significant financial and material costs due to the need to organize and carry out expensive earthworks (especially in cities), the need to use expensive materials (non-ferrous metals, etc.);
v impossibility (increased complexity) of laying and operating lines in hard-to-reach areas (in wetlands, in the mountains);

susceptibility of wire lines to damage due to natural and man-made emergency situations, as well as the possibility of their intentional damage.

Means wireless communication(including radio communications) in modern world play one of the leading roles in the process of transmitting and processing information. Some 100 years have passed since the first experiments in wireless telecommunications, but during this time the means and technologies of radio communications (wireless communications), such as component scientific and technological progress have penetrated into many areas of modern society.

Modern wireless communications, despite their small size and weight, are often quite complex. technical devices, requiring qualified specialists to design such systems and maintain their high performance characteristics.

The advantages of wireless communication lines are obvious: they are cost-effective (no need to dig trenches to lay cables and rent land); low operating costs; high throughput and quality of digital communications; rapid deployment and change of network configuration; easy overcoming of obstacles - railways, rivers, mountains, etc.

Wireless communications in the radio range are limited by congestion and shortage of frequency range, insufficient secrecy, susceptibility to interference, including intentional interference and from adjacent channels, and increased power consumption. In addition, radio communications require lengthy approval and registration with the assignment of frequencies by the Gossvyaznadzor authorities (in our country the state authorized body), rent for the channel, and mandatory certification of radio equipment by the State Commission for Radio Frequencies.

Serious disadvantages of wireless communications are: relatively low throughput; poor signal transmission through walls, possibility of data interception or unregistered entry if additional security mechanisms are not used.

12. Also, all networks can be divided by type of topology.

The simplest communication network consists of two nodes and one branch (Fig. 4.)

Figure 4 - The simplest network communications

Such a network is called degenerate. More complex networks are characterized by spatial structure (or topology).

v The first topology is a common bus (SH) (Fig. 5)

Figure 5 - Common bus topology

This principle is used to build computer networks and technological information transmission networks in railway transport.

Advantages: simplicity (since one communication channel is used).

v Ring topology (Fig. 6)

Figure 6 - Ring topology

IN ring topology information is transmitted in a circle, as a rule, this is a wired connection at the road level, computer networks, and the transmission of a circular call.

Advantages: simplicity and higher reliability compared to a common bus.

The disadvantage is the installation of additional communication channels.

v Star or radial topology (Fig. 7)

Figure 7 - Radial topology

CUS - central communication center;

1, 2, 3 - peripheral communication nodes.

Based on the principle of star-shaped (radial) topology, wired, fiber-optic and radio communication systems are built.

Advantages: simplicity and good reliability.

v Fully connected topology (Fig. 8).

Figure 8 - Fully connected topology

The principle of fully connected topology is used in especially critical types of communications, as well as in some types of radio communications.

Advantages: high reliability, since even with the output of several communication channels, the network can function normally.

Disadvantages: high cost and length of communication channels.

v Tree or node topology (Fig. 9.)

Figure 9 - Tree topology

Many railway transport systems are built according to the principle of tree (nodal) topology.

Advantages: small number of channels with a large number of nodes.

13. Networks are differentiated based on the method of message delivery circuit-switched and storage networks (message-switched and packet-switched networks).

Circuit switched networks-- for transmission between terminal devices, a physical or logical channel is allocated, through which continuous transmission of information is possible throughout the entire communication session. The transmission route in such systems is usually determined when a communication session is established and does not change until the end. A circuit-switched network is, for example, a telephone network. In such networks, it is possible to use nodes of a very simple organization, up to manual switching, but the disadvantage of such an organization is the inefficient use of communication channels or an increase in connection waiting time if the flow of information is inconsistent and unpredictable.

Packet switched networks-- messages between nodes in such a network are transmitted in short bursts - packets that are switched independently and combined at the network node closest to the recipient. The vast majority are built according to this scheme. computer networks. This type of organization very effectively uses data transmission channels between network nodes, but requires more complex equipment of the nodes (implementing the division of messages into packets, their routing, temporary storage of packets, monitoring the fact of delivery to the recipient node and restoring messages from packets at the end node of the network), which predetermined its use in large information and telecommunication networks, an example of which is the Internet.