The basis of the theory and technology of telecommunications is the transmission of various kinds of messages (information) over a distance. Under information understand the totality of information about any objects, events, processes of someone's activity, etc. The information presentation form is called message . It can be speech or music, handwritten or typewritten text, drawings, drawings, television images.
For transmission over communication channels, each message is converted into an electrical signal. Signal is a physical process that displays transmitted message (physical medium messages). Physical quantity by change, which ensures the display of messages, is called the informational or representing parameter of the signal.
The transfer of messages from one point in space to another is carried out by the telecommunication system. Telecommunication system (telecommunication system) - a set of technical means that ensures the transmission of messages from a source to a recipient over a distance (Figure 1.1).
The telecommunication system as a whole solves two problems:
1) message delivery - functions of the telecommunication system;
2) the formation and recognition of messages - the functions of the terminal equipment.
transmission path called a set of devices and lines that ensure the transmission of messages between users.
Transmission channel (communications) – part of the transmission path between any two points. The transmission channel does not include terminal devices.
Figure 1.1 - Structural diagram of the telecommunication system (telecommunication system)
The principle of telecommunication signaling is shown in Figure 1.2.
Figure 1.2 - The principle of transmission of telecommunication signals
At the input and output of the message transmission path, terminal devices are switched on that provide the conversion of messages into electrical signals and the reverse conversion. These devices are called primary converters and the signals generated by them are also called primary . For example, when transmitting speech primary converter is a microphone, when transmitting an image - a cathode-ray tube, when transmitting a telegram - the transmitting part of the telegraph apparatus.
The message source generates the message a(t) , which is converted into an electrical signal s(t) . Signals are reconverted in a telecommunications system and transported in a form other than the original.
Telecommunication network (telecommunication network) - a set of communication lines (channels) of switching stations, terminal devices, in a certain territory, ensuring the transmission and distribution of messages (Figure 1.3).
Figure 1.3 - Generalized structural scheme telecommunication networks (telecommunication network)
At the input and output of the communication network, terminal devices are switched on that provide the conversion of messages into electrical signals and the reverse conversion. End devices are connected to the exchange subscriber lines. Switching stations are interconnected by connecting lines. Switching stations connect incoming lines to outgoing lines at the appropriate address.
IN general view, the message transmitted from the source to the recipient consists of two parts: address and information. Based on the contents of the address part, the switching station determines the direction of communication and selects a specific recipient of the message. The information part contains the message itself.
The set of procedures and processes, as a result of which the transmission of messages is ensured, is called communication session , and the set of rules in accordance with which a communication session is organized is called protocol .
Telecommunication systems are classified by purpose, by the type of signal used, by the method of connection, by the degree of integration of the tasks to be solved, and by the method of information exchange (Fig. 1.7).
By appointment distinguish between telephone networks, facsimile networks, networks data transmission and teletex.
By type of applied signal communication systems are divided into analog and digital.
Analog networks use a continuous signal. Its peculiarity is that two signals can differ from one another as little as desired. Digital networks use a signal that consists of various elements. These elements are 1 and 0. The unit is usually denoted by an impulse or a segment harmonic oscillation with a certain range. Zero is indicated by the absence of transmitted voltage. The combination of 1 and 0 makes up a message - a code combination.
By connection method systems are divided into circuit-switched, message-switched, and packet-switched networks.
In circuit-switched networks, subscriber connections are made by the type of automatic telephone exchange. Their main disadvantage is big time connection due to busy channels or the called subscriber. The exchange of information in networks with message switching is carried out according to the type of telegram transmission. The sender composes the text of the message, indicates the address, category of urgency and secrecy, and this message is recorded in a memory device (storage). When the channel is released, the message is automatically transmitted to the next intermediate node or directly to the subscriber. At the intermediate node, the message is also written to the memory and, when the next section is released, it is transmitted further. The advantage of such networks is that there is no refusal to receive a message. The disadvantage is the relatively large delay time of the message due to its storage in the memory. Therefore, such networks are not used to transmit information that requires real-time delivery. In packet-switched networks, information is exchanged in the same way as in message-switched networks. However, the message is divided into short packets that quickly find their way to the destination. As a result, the packet delay time will be less.
By degree of integration tasks to be solved, there are integrated digital networks and digital networks of integral service.
In digital integrated networks, integration is carried out at the level technical devices. One device solves several problems. For example, it solves the problem of channel compaction and switching. In integrated service digital networks, integration occurs at the service level. Telephony, teletex, data and other signals are transmitted digitally using the same devices. In such networks, there is no division into primary and secondary networks.
How information is exchanged networks are divided into synchronous, asynchronous and plesiochronous.
In synchronous networks, control signal generators at the final and waypoints are constantly synchronized regardless of whether information is transmitted or not. In asynchronous networks, synchronization occurs only for the duration of a message.
The plesiochronous method of operation allows for the absence of constant adjustment of the local oscillators. Reception of messages is ensured through the use of highly stable local oscillators with autotuning to single frequency signals at fairly long time intervals.
Telephone network It is designed to transmit voice (acoustic) messages over a distance.
Data networks designed to exchange information between computers. Data networks like telegraph networks use discrete signals. Unlike telegraphy, data transmission networks provide a high speed and quality of message transmission. A given probability of delivery is guaranteed at any practically necessary message rate. This is achieved through the use additional devices improving the quality of message transmission, which are structurally combined with transmitters and receivers of data transmission systems, forming transceiver devices, which are called data transmission equipment (ADD).
Fax network designed to convey not only content, but also appearance the document itself.
The terminal device of facsimile networks is a digital facsimile machine that operates over the telephone network at speeds of 2.4-4.8 kbps or over data networks at speeds of 4.8; 9.6; and 48 kbps. It carries out entropy coding information with a compression ratio of about 8, which allows you to transfer a page of text in 2 minutes. at a speed of 2.4 kbps and, respectively, for 30 s at a speed of 9.6 kbps.
Teletex – it is an alphanumeric transmission system business correspondence, which is built on the subscriber principle. The main idea of teletex is to combine all the capabilities of a modern typewriter with the transmission of messages, while maintaining the content and form of the text. This system is a bit like a telex (subscriber telegraph), but differs from it in a large set of characters (256 due to an 8-element code), a higher transmission speed (2400 bps), high reliability, the ability to edit documentation prepared for transmission, and others. Additional features. The transmission of information in the teletex system is carried out via telephone networks.
An important feature and fundamental advantage of teletex compared to telex is the absence of the need for additional work on the keyboard during text transmission. This advantage is achieved due to the fact that the text prepared on the terminal device is stored in its random access memory, from where the information is transmitted via a communication channel. received message can be reproduced on the display screen or printed.
The teletex system has much in common with the data transmission system, namely: the digital transmission method, the transmission rate of 2.4 kbps, the methods used to improve error control and connection management.
The discrepancy between these systems lies in the fact that teletex uses a spoken language, while data transmissions use formalized languages.
Services are being created on the basis of teletex and fax networks. Email, those. telecommunication network letter-post transmission services that provide a “hard copy” of the original.
Separate use of the above secondary networks hinders the development of telecommunications systems. The introduction of digital networks makes it possible to ensure the transmission of signals on a single digital basis various services, i.e. organize integrated service digital network. A digital integrated service network is understood as a set of architectural and technological methods and hardware and software tools for delivering information territorially. remote users, which makes it possible to digitally provide users with various services. This network allows the transmission of telephone, telegraph and other signals using a single universal terminal. This terminal must contain a telephone, a display and a keypad for typing. A subscriber of such a network can watch the image on the display and talk to other party on the phone.
We will repeatedly return to issues related to the organization of the activities of the telecommunications sector in the Russian Federation, to consider them from different angles. Here we will consider the most general provisions.
The basics of activities in the field of communications are regulated by the Federal Law "On Communications", which defines the powers of state authorities, as well as the rights and obligations of persons participating in the organization of the provision of communication services and using them. According to this Law, a communication network is a technological system that includes means and communication lines and is intended for telecommunications or postal communications.
The fundamentals of activity and management methods of communication organizations are related to the form of ownership of networks and communication facilities, which may be in federal ownership, the property of the constituent entities of the Russian Federation, municipalities, legal and individuals. Due to the fact that communication forms an infrastructure, its development is interconnected with the development and development of territories and settlements, as well as the entire economic mechanism of the country. The functioning and development of the industry is also based on land legislation, since many telecommunications facilities often require land acquisition. General view about communication networks of the Russian Federation gives fig. 4.4.
Communication network management is understood as a set of organizational and technical measures that are aimed at ensuring the smooth and coordinated functioning of all its elements and traffic regulation. Traffic is the load created by the flow of calls from users arriving at the means of communication and measured by the time these means are occupied. For example, if 10 clients during an astronomical hour talked on the phone for 12 minutes each, then during this hour they created a load on the station's instruments of 120 minutes, or 2 hours of classes, or 2 Earl. Taking into account the magnitude of the load per hour the greatest load, as well as the normalized quality of service (the number of failures in connections or waiting time) determines the volume of switching and other equipment on communication networks.
When managing the networks that make up the Unified Energy System of the Russian Federation, the Federal Executive Authority in the field of communications, currently this is the Ministry information technologies and Communications, as well as the Federal Communications Agency, determine the procedure for the interaction of networks both in normal and emergency conditions, and also establish requirements for their construction and management, numbering, used means of communication, organizational and technical conditions for stable operation, means of protecting networks and information from unauthorized access. Telecom operators must create network management systems that meet these requirements.
Any communication network is a complex technological system that combines facilities, means and communication lines that are subject to technical operation and are intended for transmission. electrical signals(traffic). Communication facilities are buildings or other objects specially constructed or adapted to accommodate communication facilities. Communication lines are transmission lines, physical circuits and line-cable communication structures. Communication channels are organized in communication lines for the transmission of signals carrying information. Line-cable communication facilities are engineering infrastructure facilities for placing communication cables (for example, city cable ducts or collectors). Communication means are technical and software tools for generating, receiving and processing, storing, transmitting, delivering telecommunication messages and postal items, including terminal devices and means for measuring, controlling and repairing the main and additional equipment(for example, an electronic switch or a tower with antennas installed on it). Radio-electronic means are also distinguished, i.e. technical equipment for receiving and transmitting radio waves. For their operation, the radio frequency spectrum is allocated, the radio frequency ranges are distributed by the International Telecommunication Union (ITU). Within the country, a special commission issues permission to the operator to use a specific frequency band, and also establishes the conditions for its use.
Communication networks common use(SSOP) are a complex of interacting telecommunication networks, including communication networks for the distribution of television and radio broadcasting programs, and are designed to provide telecommunication services to any user in the territory of the Russian Federation. These networks can be tied to a territory, a numbering resource, and also differ in the technology of providing services (for example, cellular mobile communication systems, city telephone networks, etc.). The SSTNs are connected to the corresponding networks of other states, which makes it possible to serve international traffic.
Telecommunications organizations are legal entities for which the activity in the field of communications is the main one. A legal entity providing communication services on the basis of an appropriate license is called a communication operator. User of communication services - a person who orders or uses communication services. Depending on the place where users receive communication services, there are three sectors: corporate (services at the workplace), residential
and mobile (services on the road). The user is called a subscriber if an agreement has been concluded with him for the provision of communication services when a subscriber code is allocated for these purposes or unique code identification. Communication services can be provided by a legal entity that is not the owner of the network, but leases part of the network resources from any communications operator. Such a company is called a service provider (service provider), or provider (for example, Internet providers).
The Law "On Communications" defines a communication service as the activity of receiving, processing, storing, transmitting and delivering telecommunication messages and postal items. However, this activity can also be defined as the process of producing a service. At the same time, a service in the market sense of the word is a benefit (product) that the client receives and which is expressed in the fact that with its help he solves his problems and satisfies his needs, and the way the product is produced, the client most often not interested.
Communication services are characterized by one-time consumption, and their cost depends on the type and quality of communications. In addition to services, the user receives/consumes applications, which, unlike services, are provided in the form of a reusable final product (for example, a program for working on the Internet, CD with information, etc.). Historically, services were provided by the telecommunications industry, while the information technology industry was originally focused on the provision of applications (obviously, therefore, the concept of an application is not presented in the Federal Law "On Communications").
Information service - meeting the information needs of users by providing information products. Accordingly, the user of information services is a person who applies to an information system or an intermediary to obtain the information he needs and uses it. Providers of information services (content, applications) are often referred to as content providers.
The unity of the SSOP is technically and economically ensured on the basis of interconnection and traffic transmission services. Connection service - the activity of a telecom operator aimed at meeting the needs of other telecom operators in organizing the interaction of telecommunication networks, in which conditions are created to make the network "transparent" for the transfer of information (traffic pass) between users of the services of interacting networks. The connection service is paid. Traffic passing service - an activity, as a result of which one operator passes the traffic of another operator through its network to other networks of interacting operators. This service is also paid, in connection with which the operators enter into a relationship that is called mutual settlements.
Some operators, in accordance with the Law "On Communications", are obliged to provide universal communication services, i.e. such, the provision of which to any user on the territory of the country is carried out with a certain quality and at a reasonable price regulated by the state. Currently, universal services include: local telephone services, telegram services and some postal services. Legal basis representations of these services are discussed in Chap. 8.
Dedicated communication networks (VSN) are designed to provide paid services communications to a limited circle (groups) of users and can interact with each other. Each network is allocated a numbering resource, i.e. a set of numeric codes that can be used to identify subscribers. Until the VSS is connected to the SSOP, the technologies and means of communication, the principles of building networks and other parameters of management and economic activity are established by the owners of these networks. VSS can join the public network if it meets the requirements of the latter. At the same time, its numbering resource is withdrawn, and in return a part of the public network numbering resource is provided.
Technological communication networks are designed to provide production activities organizations, management production processes in other sectors of the national economy, which may go beyond the borders of the country. Just as in the previous case, the owners establish the principles for organizing these networks. It is allowed to attach a part technological network to the SSOP under certain conditions: 1) if this part can be technologically, physically or programmatically separated from the main network; 2) if the relevant organizational and technological requirements are met.
Special Purpose Communication Networks (SSSN) are intended for the needs of government controlled and security, defense, law enforcement. These needs can also be met at the expense of the ESE resources in accordance with the current legislation. To do this, control centers for special-purpose communication networks ensure their interaction with other ESE networks. As a rule, CCTS cannot be used for commercial purposes, they are financed from the budget.
The postal network is a set of postal facilities and postal routes of postal operators united under the auspices of the Federal State Unitary Organization Russian Post. Organizations of the federal postal service are state unitary organizations and state institutions created on the basis of federally owned property. Postal facilities are separate subdivisions of postal organizations (post offices, railway post offices, mail transportation departments at railway stations and airports, postal communication centers), as well as their structural subdivisions (postal exchange offices, post offices and other departments). All of them provide reception, transportation, delivery (delivery) of postal items, and also carry out postal money transfers.
In order to ensure the integrity, stable operation and security of the unified telecommunication network of the Russian Federation and the use of the radio frequency spectrum, activities in the field of communications are regulated by the state (the Ministry of Information Technologies and Communications of the Russian Federation, the Russian Communications Agency, the Russian Federation Agency for Informatization, as well as a number of commissions and other federal bodies in within their jurisdiction). The main directions of activity regulation in accordance with the current legislation: development and implementation public policy and implementation of coordination in the creation and development of communication networks, satellite communication systems, including the use of civil television and radio broadcasting systems in the country; development and adoption of regulations relating to the activities and development of the industry, taking into account the proposals of all interested organizations; performance of the functions of the Communications Administration in the implementation of international activities; control over the execution of licenses and compliance with mandatory requirements, primarily by the so-called self-regulatory organizations; use of the radio frequency spectrum based on a permit procedure for access to it, convergence of the terms of use with international ones, urgency and payment, transparency and openness of procedures for the distribution and use of the spectrum.
To imagine the size of the communication network, we note that today more than 3000 organizations have received licenses for the right to provide communication services, more than 90 thousand service points for the population and organizations are operating. Currently, more than 37 million devices are installed in the fixed communication network, and the owners cell phones have already become more than 85 million people. The Internet audience is more than 15 million people. By early 2005, communications industry revenues reached $47 billion.
One of the largest organizations in the industry is OJSC Svyazinvest, which, after reorganization in 2002-2003. has the structure shown in Fig. 4.5.
Features of management in the communications industry are due to at least two circumstances: first, the network nature of the relationship of economically independent entities; secondly, the features of the product: the predominance of the non-material component in the communication service, its heterogeneity (heterogeneity), non-transformability into property, non-permanence, since the production processes and consumption of the service almost always coincide in time. The last circumstance imposes special requirements throughout the service delivery process. If, in the manufacture of a table, the legs can be made at one time, and the table top at another, and at night the factory may not work, then in telecommunications, individual elements and the network as a whole must be in constant readiness to create a communication channel that functions reliably throughout the entire time of communication between the sender of information and its recipient. At the same time, it is never known in advance where there will be a need to create such a channel, how many channels and in what directions they will be in demand at the same time. It is clear that managing such a system is extremely difficult. Therefore, in addition to the usual management of the organization, interaction management is required. various operators(organizations) of communication, as well as the management of communication networks in general (see Section 11.1-11.3).
From this short description management in the telecommunications industry follows how complex the communication system is. Thus, it is legitimate to ask what purpose a system of such complexity serves.
CHAPTER 1 BASICS OF TELECOMMUNICATIONS
1. 1. Typical data transmission system
Any data transmission system (DTS) can be described in terms of its three main components. These components are the transmitter (or so-called "information source"), the data link and the receiver (also called the "receiver" of information). In two-way (duplex) transmission, the source and destination can be combined so that their equipment can transmit and receive data at the same time. In the simplest case, SPT between points A and B (Fig. 1. 1) consists of the following main seven parts:
> Data terminal equipment at point A.
> Interface (or junction) between data terminal equipment and data link equipment.
> Data channel equipment at point A. > Transmission channel between points A and B. > Data channel equipment at point B. > Interface (or junction) of data channel equipment.
> data terminal equipment at point B.
Data terminal equipment(DTE) is a generic term used to describe a user terminal or part of it. OOD
Rice. 1.1. Typical data transmission system: but - block diagram of the data transmission system;
b - real data transmission system
may be the source of information, its recipient, or both at the same time. The DTE transmits and/or receives data through the use of a data link facility (DCE) and a transmission channel. The corresponding international term is often used in the literature - DTE (Data Terminal Equipment). Often the DTE can be Personal Computer, mainframe (mainframe computer), terminal, data collector, cash register, global signal receiver navigation system or any other equipment capable of transmitting or receiving data.
The data link equipment is also referred to as data communication equipment (DTE). Widely used international term DCE (Data Communication Equipment), which we will use in what follows. The function of a DCE is to enable the transfer of information between two or more DTEs over a certain type of channel, such as telephone. To do this, the DCE must provide a connection to the DTE on the one hand, and to the transmission channel on the other. On fig. one. 1, but DCE may be an analog modem if used analog channel, or, for example, a channel/data service unit (CSU/DSU - Channel Seruis Unit/ Data Service Unit), if a digital channel type E1/T1 or ISDN is used. Modems developed in the 1960s and 1970s were purely signal-converting devices. However, in last years modems have acquired a significant number of complex features, which will be discussed below.
Word modem is an abbreviation for the device that performs the MOD/DEModulation process. Modulation is the process of changing one or more parameters of the output signal according to the law of the input signal. In this case, the input signal is usually digital and is called a modulating signal. The output signal is usually analog and often called the modulated signal. Currently, modems are most widely used to transfer data between computers across public switched telephone network(PSTN, GTSN - General Switched Telephone Network)
An important role in the interaction between DTE and DCE is played by their interface, which consists of incoming / outgoing circuits in DTE and DCE, connectors and connecting cables. In domestic literature and standards, the term is also often used. joint
The DTE connects to the DCE at one of the C2 interfaces When a DCE connects to a communication channel or distribution medium, one of the C1 interfaces is used
1. 2. Communication channels
1. 2. 1. Analog and digital channels
Under communication channel understand the totality of the propagation medium and technical means of transmission between two channel interfaces or junctions of type C1 (see Figure 1-1). For this reason, the C1 junction is often referred to as a channel junction.
Depending on the type of transmitted signals, there are two large classes of communication channels digital and analog
A digital channel is a bit path with a digital (pulse) signal at the input and output of the channel A continuous signal is received at the input of an analog channel, and a continuous signal is also taken from its output (Fig. 1 2) As you know, signals are characterized by the form of their representation
Fig 1 2 Digital and analog transmission channels
Signal parameters can be continuous or take only discrete values. Signals can contain information either at each moment of time (continuous in time, analog signals), or only at certain discrete times (digital, discrete, pulse signals).
Digital channels are PCM, ISDN, T1 / E1 type channels and many others. Newly created SPDs are trying to build on the basis of digital channels, which have a number of advantages over analog ones.
Analog channels are the most common due to their long history of development and ease of implementation. A typical example of an analog channel is a voice frequency channel (HF), as well as group paths for 12, 60 or more voice frequency channels. The PSTN telephone circuit typically includes multiple switches, splitters, group modulators, and demodulators. For the PSTN, this channel (its physical route and a number of parameters) will change with each next call.
When transmitting data, there must be a device at the input of the analog channel that would convert the digital data coming from the DTE into analog signals sent to the channel. The receiver must contain a device that would convert back received continuous signals into digital data. These devices are modems. Similarly, when transferring digital channels data from the DTE has to be converted to the form adopted for this particular channel. This conversion is handled by digital modems, often referred to as ISDN adapters, E1/T1 channel adapters, line drivers, and so on (depending on the particular type of channel or transmission medium).
The term modem is widely used. This does not necessarily imply any modulation, but simply indicates certain operations for converting signals coming from the DTE for their further transmission over the channel in use. Thus, in a broad sense, the terms modem and data link equipment (DCE) are synonymous.
1. 2. 2. Switched and dedicated channels
Switched channels are provided to consumers for the duration of the connection at their request (call). Such channels fundamentally contain switching equipment telephone exchanges(ATS). Ordinary telephones use switched PSTN circuits. In addition, dial-up channels provide integrated services digital network(ISDN - Integrated Services Digital Network).
Leased (leased) channels are leased from telephone companies or (very rarely) laid by the most interested organization. Such channels are fundamentally point-to-point. Their quality is generally higher than the quality of switched channels due to the lack of influence of the switching equipment of the automatic telephone exchange.
1. 2. 3. Two- and four-wire channels
As a rule, channels have a two-wire or four-wire termination. For brevity, they are called, respectively, two-wire and four-wire.
Four-wire channels provide two wires for transmitting a signal and two more wires for receiving. The advantage of such channels is practically complete absence influence of signals transmitted in the opposite direction.
Two-wire channels allow you to use two wires for both transmitting and receiving signals. Such channels make it possible to save on the cost of cables, but require the complication of channel-forming equipment and user equipment. Two-wire channels require solving the problem of separating the received and transmitted signals. Such decoupling is implemented using differential systems that provide the necessary attenuation in opposite directions of transmission. The imperfection of differential systems (and nothing is perfect) leads to distortion of the amplitude-frequency and phase-frequency characteristics of the channel and to a specific interference in the form of an echo signal.
1. 3. Seven-layer OSI model
In order to interact, people use a common language. If it is not possible to talk directly to each other, aids are used to convey messages. One of these means is the postal system (Fig. 1. 3). In its composition, certain functional levels can be distinguished, for example, the level of collection and delivery of letters from mailboxes to the nearest mail communication nodes and in the opposite direction, the level of sorting letters in transit nodes, etc. e. Various standards adopted in the postal service for the size of envelopes, the procedure for issuing addresses, etc. make it possible to send and receive correspondence from almost anywhere in the world.
A similar picture takes place in the field of electronic communications, where the market for computers, communication equipment, information systems and networks is unusually wide and diverse. For this reason, the creation of modern information systems becomes impossible without the use of common approaches during their development, without unification of the characteristics and parameters of their constituent components.
The theoretical basis of modern information networks is determined by the Basic Reference Model of Open Systems Interconnection (OSI - open systems interconnection) International Standards Organization (ISO - International Standards Organization). It is described by the ISO 7498 standard. The model is international standard for data transfer. According to the reference
Table 1. 1. Functions of the levels of the open systems interaction model
| Level | Functions |
| 7. Applied | Interface with application processes |
| 6. Representative | Representation negotiation and interpretation of transmitted data |
| 5. Session | Support for dialogue between remote processes; ensuring connection and disconnection of these processes; implementation of data exchange between them |
| 4. Transport | Ensuring end-to-end data exchange between systems |
| 3. Networked | Routing; segmentation and consolidation of data blocks; data flow management; error detection and reporting |
| 2. Channel | Data link management; framing: media access control; data transmission over the channel; channel error detection and correction |
| 1. Physical | Physical interface with data link; bit modulation and line coding protocols |
The OSI interaction model distinguishes seven levels that form the area of open systems interaction (Table 1. 1).
The main idea of this model is that each level has a specific role. Thereby common task data transmission is split into separate specific tasks. Level functions, depending on its number, can be performed by software, hardware or firmware. As a rule, the implementation of the functions of the higher levels is of a software nature, the functions of the link and network levels can be performed both in software and in hardware. The physical layer is usually implemented in hardware.
Each level is defined by a group of standards that include two specifications: protocol and provided for the higher level service. A protocol is a set of rules and formats that define the interaction of objects of the same model level.
Closest to the user is the application layer. Its main task is to provide already processed (accepted) information. This is usually handled by system and user application software, such as a terminal program. When transferring information between different computing systems, the same code representation of the alphanumeric characters used should be used. In other words, the applications of the interacting users must work with the same code tables. The number of characters represented in the code depends on the number of bits used in the code, that is, on the basis of the code. The most widely used codes are given in Table. one. 2.
Rice. 13. Functional levels of the postal system
Table 1. 2. Main characteristics of common character codes
All kinds of national extensions of the listed codes are often used, for example, the main and alternative Cyrillic encodings for the ASCII code. In this case, the code base is increased to 8 bits.
The functions of modern modems belong to the levels "farthest" from the user - physical and channel.
1. 3. 1. Physical layer
This layer defines the interfaces of the system with the communication channel, namely the mechanical, electrical, functional and procedural parameters of the connection. The physical layer also describes the procedures for transmitting signals to and from the channel. It is designed to carry a stream of binary signals (sequence of bits) in a form suitable for transmission over the specific physical medium used. As such physical environment transmissions can be a voice frequency channel, a connecting wire line, a radio channel, or something else.
The physical layer performs three main functions: establishing and disconnecting connections; signal conversion and interface implementation.
Establishing and disconnecting a connection
When using switched channels at the physical level, it is necessary to carry out a preliminary connection of the interacting systems and their subsequent disconnection. When using dedicated (leased) channels, this procedure is simplified, since the channels are permanently assigned to the corresponding communication directions. In the latter case, the exchange of data between systems that do not have direct connections is organized by switching flows, messages, or data packets through intermediate interacting systems (nodes). However, the functions of such switching are already performed for more than high levels and have nothing to do with the physical level.
In addition to the physical connection, interacting modems can also "negotiate" on a mode of operation that suits them both, that is, modulation method, transmission rate, error correction and data compression modes, etc. d. After the connection is established, control is transferred to a higher link layer.
Signal conversion
To match the sequence of transmitted bits with the parameters of the used analog or digital channel, it is necessary to convert them into an analog or discrete signal, respectively. The same group of functions includes procedures that implement the interface with a physical (analogue or digital) communication channel. This joint is often called environment-dependent interface and it can correspond to one of the guested C1 channel joints. Examples of such joints C1 can be: 26557-85) - for dedicated voice frequency channels, S1-TG (GOST 22937-78) - for telegraph communication channels, S1-ShP (GOSTs 24174-80, 25007-81, 26557-85) - for primary broadband channels, C1 -FL (GOSTs 24174-80, 26532-85) - for physical communication lines, C1-AK - for acoustic coupling of DCE with a communication channel and a number of others.
The signal conversion function is main function modems. For this reason, the first modems that lacked intelligence and did not perform hardware compression and error correction were often referred to as signal conversion devices(OOPS).
Interface Implementation
The implementation of the interface between DTE and DCE is the third essential function physical level. Such interfaces are regulated by the relevant recommendations and standards, which, in particular, include V. 24, RS-232, RS-449, RS-422A, RS-423A, V. 35 and others. Such interfaces are defined by domestic GOSTs as converter joints C2 or joints independent of the environment.
Standards and recommendations for DTE-DCE interfaces define general characteristics (transmission rate and sequence), functional and procedural characteristics (nomenclature, category of interface circuits, rules for their interaction); electrical (values of voltages, currents and resistances) and mechanical characteristics (dimensions, distribution of contacts in circuits).
At the physical level, a certain class of faults is diagnosed, for example, such as a wire break, power failure, loss of mechanical contact, etc. P.
A typical protocol profile when using a modem that supports only physical layer functions is shown in Figure 2. one. 4. It is assumed that the computer (DTE) is connected to the modem (DCE) via the RS-232 interface, and the modem uses the V modulation protocol. 21.
Fig 1 4 Protocol profile for a modem with physical layer functions only
The noise immunity of a communication channel consisting of two modems and a transmission medium between them is limited and, as a rule, does not meet the requirements for the reliability of transmitted data. For this reason physical layer considered as an unreliable system
1. 3. 2. Link layer
The link layer is often referred to as the data link control layer. The means of this layer implement the following main functions
> formation of data blocks of a certain size from the transmitted sequence of bits for their further placement in the information field of frames, which are transmitted over the channel,
> encoding the contents of the frame with an error-correcting code (usually with error detection) in order to increase the reliability of data transmission,
> restoration of the original data sequence on the receiving side,
> providing code-independent data transmission in order to implement for the user (or application processes) the possibility of arbitrary choice of data representation code;
> data flow control at the link level, that is, the rate of their issuance to the recipient DTE;
> elimination of the consequences of losses, distortions or duplication of frames transmitted in the channel.
HDLC is recommended as a standard for layer 2 protocols by ISO. (High Level Data Link Control). It has become extremely widespread in the world of telecommunications. Based on the HDLC protocol, many others have been developed, which are, in essence, some adaptation and simplification of a number of its capabilities in relation to a specific application area. This subset of HDLC includes commonly used SDLC protocols. (Synchronous Data Link Control), LAP (Link Access Procedure), LAPB (Link Access Procedure Balanced), LAPD (Link Access Procedure D-channel), LAPM (Link Access Procedure for Modems), LLC (Logical Link Network), LAPX (Link Access Procedure eXtention) and a number of others. For example, the LAPB and LAPD protocols are used in ISDN digital networks. (Integrated Services Digital Network)," LAPM is the basis for the V error correction standard. 42, LAPX is a half-duplex variant of HDLC and is used in terminal networks and systems operating in the Teletex standard, and the LLC protocol (Link Logic Control) implemented in almost all networks with multiple access (for example, in wireless local networks). On fig. one. 5 shows the HDLC protocol family and its applications.
Rice. one. 5. HDLC protocol family
Fig 1 6. Protocol profile for a modem with physical and link layer functions
A possible protocol profile for a modem that supports the functions of the physical and link layers is shown in fig. one. 6. It is believed that the computer is connected to the modem via the RS-232 interface, and the modem already implements the V 34 modulation protocol and hardware error correction according to the V 42 standard
Rice. 17 Protocol profile for DCE with multiple access
In some networks based on point-to-multipoint circuits, the signal received by each DCE is the sum of the signals transmitted from a number of other DCEs. The links in such networks are called multiple access circuits or monochannels, and the networks themselves are called multiple access networks. Such networks are some satellite networks, terrestrial packet radio networks, as well as local wired and wireless networks.
The corresponding layers of the OSI model in multi-access transmission are somewhat different from those used in point-to-point DTN. The second level should provide upper levels virtual channel for error-free transmission of packets, and the physical layer must provide a bit path. There is a need for an intermediate layer to manage the multiple access channel so that frames can be transmitted from each DCE without constantly colliding with the rest of the DCEs. This layer is called the MAC media access control layer. (Medium Access Control). It is usually considered the first sub-level of level 2, i.e. e. level 2. 1. Traditional link layer in this case becomes the LLC logical link control layer (Logical Link Control) and is sublevel 2. 2. In fig. one. 7 shows the relationship of the second layer and the LLC and MAC sublayers.
1. 4. Fax
1. 4. 1. Sending a fax image
Fax communication is a type of documentary communication designed to transmit not only the content, but also the appearance of the document itself. The essence of the facsimile transmission method is that the transmitted image (original) is divided into separate elementary areas, which are scanned at a scanning speed of 60, 90, 120, 180 or 240 lines / min. The brightness signal proportional to the reflection coefficient of such elementary areas is converted into digital form and transmitted over a communication channel using one or another modulation method. On the receiving side, these signals are converted into image elements and reproduced (recorded) on the receiving form.
The block diagram of facsimile communication is shown in fig. one. 8. The image (original) to be transmitted is scanned with a light spot of the required size. The spot is formed by a light-optical system containing a light source and an optical device. The spot is moved along the surface of the original by a scanning device (RU). Part luminous flux incident on the elementary area of the original is reflected and fed to a photoelectric converter (PC), in which it is converted into an electrical video signal. The amplitude of the video signal at the output of the photoconverter is proportional to the magnitude of the reflected light flux. Next, the video signal is fed to the input of an analog-to-digital converter (ADC), where it is converted into a digital code. From the exit ADC digital the code is fed to the input of a signal conversion device (SCD), that is, a modulator, where, by using one of the modulation protocols, the spectrum of the digital video signal is transferred to the frequency range of the communication channel used.
Rice. one. 8. Structural diagram of facsimile communication
At the receiving side, the modulated signal coming from the communication channel sequentially enters the UPS and DAC for demodulation and digital-to-analogue conversion, respectively. Next, the video signal enters the playback device (VU), where, as a result of the action of the scanning device, a copy of the transferred image is reproduced on the form. The process of obtaining the final facsimile copy is the reverse of the scanning process is called replication. To ensure the synchronism and in-phase sweeps on the transmitting and receiving sides, synchronization devices (CS) are used.
Thus, the facsimile machine (fax) is very similar to a photocopier, in which the original and the copy are separated by many kilometers.
Modern fax modems incorporate all the components of fax machines with the exception of scanning and reproducing devices. They "know how" to communicate with ordinary faxes, while the received information about the transmitted image is output to a computer, where the fax transmission program is converted into one of the common graphic formats. In the future, the document obtained in this way can be edited, output to a printer or transferred to another correspondent who has a fax machine or a computer with a fax modem.
1. 4. 2. Fax Standards
As recommended Standardization Sectors of the International Telecommunication Union(ITU-T- International Telecommunications Union - Telecommunications) Depending on the type of modulation used, there are four groups of faxes. The first facsimile standards belonging to group 1 were based on the analog method of information transmission. A page of text by group 1 faxes was transmitted in 6 minutes. Group 2 standards have improved this technology in the direction of increasing the transmission speed, resulting in the transmission time of one page being reduced to 3 minutes.
The group 3 fax standard was originally defined by ITU-T Recommendation T. 4 1980. This standard has been reissued twice, first in 1984 and again in 1988. The 1990 revision of this standard approved the coding schemes developed for group 4 facsimile machines, as well as the higher transmission rates specified by the V standards. I 7, V. 29 and V. 33. The radical difference between Group 3 fax machines and earlier ones is the all-digital transmission method with speeds up to 14400 bps. As a result, using data compression, a group 3 fax sends a page in 30-60 seconds. When communication quality deteriorates, group 3 faxes go into emergency mode, slowing down the transmission speed. According to the group 3 standard, two degrees of resolution are possible: standard, providing 1728 horizontal dots and 100 vertical dpi; and high, doubling the vertical dot count, which gives a resolution of 200x200 dpi and halves the speed.
Fax machines of the first three groups are focused on the use of analog PSTN telephone channels. In 1984, ITU-T adopted the Group 4 standard, which provides for resolutions up to 400x400 dpi and faster speeds at lower resolutions. Group 4 faxes produce very high quality resolution. However, they need the high speed links that ISDN networks can provide and cannot operate over PSTN links.
Virtually all fax machines currently sold are based on the Group 3 standard. one. 8 illustrates the operation of just such faxes.
1. 5. Flow control
1. 5. 1. The need for flow control
In any system or data transmission network, situations arise when the load entering the network exceeds the capacity to service it. In this case, if no measures are taken to limit the incoming data (graphics), the queue sizes on the network lines will grow indefinitely and eventually exceed the sizes of the buffers of the corresponding communication means. When this happens, units of data (messages, packets, frames, blocks, bytes, characters) arriving at nodes for which there is no free buffer space will be discarded and retransmitted later. As a result, there is an effect when as the incoming load increases, the real throughput decreases, and transmission delays become extremely large.
The means of dealing with such situations are flow control methods, the essence of which is to limit incoming traffic to prevent congestion.
A flow control scheme may be needed in the transmission section between two users (transport layer), between two network nodes (network layer), between two neighboring DCEs exchanging data over a logical channel (link layer), and also between terminal equipment and data channel equipment, interacting via one of the DTE-DCE interfaces (physical layer).
Transport layer flow control schemes are implemented in file transfer protocols such as ZModem; flow control schemes network layer- as part of the protocols of H. 25 and TCP/IP; link layer flow control schemes - as part of reliability protocols such as MNP4, V. 42; flow control at the physical layer is implemented within the set of functions of the corresponding interfaces, such as RS-232. These three levels of control schemes are directly related to the hardware and software of modems, and their specific implementations will be discussed in the relevant sections of the book.
1. 5. 2. Window method
Consider a class of flow control methods commonly used by the link, network, and transport layer protocols called windowed flow control. A window is the largest number of information units that can remain unacknowledged in a given transmission direction.
Windowing is used during transmission between a transmitter and a receiver if an upper bound is placed on the number of data units that have already been transmitted by the transmitter but have not yet been acknowledged by the receiver. Upper bound, specified as a positive integer and is the window or window size. The receiver notifies the transmitter that it has received a data unit by sending a special message to the receiver (Fig. 1. nine). Such a message called an acknowledgment, authorization, or receipt. Confirmation can be positive - ACK (ACK knowledge), signaling the successful reception of the corresponding information unit, and negative - NAK (Negative Acknowledgment), indicating that the expected portion of data was not received. After receiving the receipt, the transmitter may send another unit of data to the receiver. The number of tickets in use must not exceed the size of the window.
Rice. one. 9. Window flow control
Receipts are either contained in special control packets or added to regular information packets. Flow control is used when transmitting one at a time virtual channel, a group of virtual channels, the entire flow of packets that appear in one window and are addressed to another node can be controlled. The transmitter and receiver can be two network nodes or a user terminal and an input node of the communication network. The units of data in a window can be messages, bursts, frames, or characters.
There are two strategies: end-to-end window management and node-by-node management. The first strategy relates to flow control between input and output network nodes for some transfer process and is often implemented as part of file transfer protocols. The second strategy relates to flow control between each pair of serial nodes and is implemented as part of link layer protocols such as SDLC, HDLC, LAPB, LAPD, LAPM, and others.
1. 6. Classification of modems
There is no strict classification of modems and, probably, cannot exist due to the wide variety of both the modems themselves and the scope and modes of their operation. Nevertheless, a number of features can be distinguished, according to which a conditional classification can be carried out. Such features or classification criteria include the following: scope;
functional purpose; type of channel used; constructive execution; support for modulation protocols, error correction and compression data. Many more detailed technical features can be distinguished, such as the modulation method used, the DTE interface, and so on.
1. 6. 1. By scope
Modern modems can be divided into several groups:
> for switched telephone channels;
> for dedicated (leased) telephone channels;
> for physical trunks:
Modems low level(line drivers) or short distance modems (short range modes)",
- baseband modems (. baseband modes);
> for digital systems transmissions (CSU/DSU);
> for cellular communication systems;
> for packet radio networks;
> for local radio networks.
The vast majority of manufactured modems are designed for use on dial-up telephone channels. Such modems must be able to work with automatic telephone exchanges (ATS), distinguish their signals and transmit their dialing signals.
The main difference between modems for physical lines and other types of modems is that the bandwidth of physical lines is not limited to 3, 1 kHz, typical for telephone channels. However, the bandwidth of the physical line is also limited and depends mainly on the type of physical medium (shielded and unshielded). twisted pair, coaxial cable, etc.) and its length.
From the point of view of the modems used for signaling for physical lines, they can be divided into low level modems(line drivers) using digital signals, and modems from the "main band" (baseband), which use modulation methods similar to those used in modems for telephone channels.
Modems of the first group usually use digital methods bipulse transmission, allowing the formation of pulsed signals without a constant component and often occupying a narrower frequency band than the original digital sequence.
Modems of the second group often use different kinds quadrature amplitude modulation, allowing you to radically reduce the required to transmit a frequency band. As a result, on the same physical lines, such modems can achieve transmission rates up to 100 Kbps, while low-level modems provide only 19, 2 Kbps.
Modems for digital transmission systems resemble low-level modems. However, unlike them, they provide connection to standard digital channels, such as E1 / T1 or ISDN, and support the functions of the corresponding channel interfaces.
Modems for cellular communication systems are compact in design and support special modulation and error correction protocols that allow efficient data transmission in cellular channels with a high level of interference and constantly changing parameters. Among these protocols, ZyCELL, ETC and MNP10 stand out.
Packet radio modems are designed to transmit data over the air between mobile users. At the same time, several radio modems use the same radio channel in a multiple access mode, for example, carrier sense multiple access, in accordance with ITU-T AX. 25. The radio channel is close in its characteristics to a telephone channel and is organized using standard radio stations tuned to the same frequency in the VHF or KB range. The packet radio modem implements modulation and multiple access techniques.
Local radio networks are a rapidly developing promising network technology that complements ordinary local area networks. Their key element is specialized radio modems (local radio network adapters). Unlike the previously mentioned packet radio modems, these modems provide data transmission over short distances (up to 300 m) at a high speed (2-10 Mbps), comparable to the transmission rate in wired local networks. In addition, radio local area network radios operate in a certain frequency range using complex waveforms, such as pseudo-random hopping signals.
1. 6. 2. By transmission method
According to the transmission method, modems are divided into asynchronous and synchronous. Speaking of synchronous either asynchronous method transmissions usually involve transmission over a communication channel between modems. However, transmission over the DTE-DCE interface can also be synchronous or asynchronous. The modem can work with the computer in asynchronous mode and simultaneously with remote modem- in synchronous mode or vice versa. In this case, it is sometimes said that the modem synchronous-asynchronous or it works in synchronous-asynchronous mode.
Typically, synchronization is implemented in one of two ways, related to how the sender and receiver clocks work:
independently of each other (asynchronously) or in concert (synchronously). If Since the transmitted data is made up of a sequence of individual characters, then, as a rule, each character is transmitted independently of the others, and the receiver is synchronized at the beginning of each received character. For this type of communication, asynchronous transmission is usually used. If the transmitted data is a continuous sequence of characters or bytes, then the sender and receiver clocks must be synchronized over a long period of time. In this case, synchronous transmission is used.
The asynchronous transfer mode is mainly used when the transferred data is generated at random times, for example by the user. In such a transmission, the receiving device must resynchronize at the beginning of each received character. To do this, each transmitted character is framed with an additional start and one or more stop bits. This asynchronous mode is often used when transferring data over the DTE-DCE interface. When transmitting data over a communication channel, the possibilities of using the asynchronous transmission mode are largely limited by its low efficiency and the need to use simple modulation methods, such as amplitude and frequency modulation. More advanced modulation methods, such as OFM, QAM, etc., require maintaining constant synchronism of the reference clock generators of the sender and receiver.
With the synchronous transmission method, a large number of characters or bytes are combined into separate blocks or frames. The entire frame is transmitted as a single bitstring without any delay between the eight-bit elements. In order for the receiving device to provide different levels of synchronization, the following requirements must be met.
> The transmitted bit sequence must not contain long sequences of zeros or ones so that the receiving device can stably allocate clock frequency synchronization.
> Each frame must have reserved sequences of bits or characters marking its start and end.
There are two alternative methods of organizing synchronous communication: character- or byte-oriented, and bit-oriented. The difference between the two is how the start and end of a frame are determined. With the bit-oriented method, the receiver can determine the end of the frame with an accuracy of a single bit, but a byte (character).
In addition to high-speed data transmission over physical channels, the synchronous mode is often used for transmission over the DTE - DCE interface. In this case, additional interface circuits are used for synchronization, through which a clock frequency signal is transmitted from the sender to the receiver.
1. 6. 3. By intellectual capabilities
By intellectual capabilities, modems can be distinguished:
without control system;
> supporting a set of AT commands;
> with support for V commands. 25bis;
> with proprietary command system;
> supporting network management protocols.
Most modern modems are endowed with a wide range of intellectual capabilities. The de facto standard has become a set of AT commands developed at one time by Hayes and allowing the user or application process to fully control the modem's characteristics and communication parameters. For this reason, modems that support AT commands are called Hayes-compatible modems. It should be noted that AT commands support not only PSTN modems, but also packet radio modems, external ISDN adapters, and a number of other modems with narrower scopes.
The most common set of commands that allow you to control the connection establishment and autocall modes are the ITU-T V. 25bis.
Specialized modems for industrial applications often have a proprietary command set different from the AT command set. The reason for this is the large difference in operating modes and functions between general purpose modems and industrial (network) modems.
Industrial modems often support the SMNP Network Management Protocol (Simple Manager Network Protocol), allowing an administrator to manage network elements (including modems) from a remote terminal.
1. 6. 4. By design
By design, modems are distinguished:
> external;
> internal;
> portable;
> group.
External modems These are stand-alone devices connected to a computer or another DTE via one of the standard DTE-DCE interfaces. An internal modem is an expansion card that plugs into the appropriate slot on the computer. Each of the design options has its advantages and disadvantages, which will be discussed below.
Portable modems are intended for use by mobile users in conjunction with computers of the Notebook class. They are small in size and high in price. Their functionality, as a rule, is not inferior to the capabilities of full-featured modems. Often portable modems are equipped with a PCMCIA interface.
Group modems are a collection of individual modems combined into a common unit and having common block power supply, control and display devices. The standalone modem of the group modem is a card with a connector installed in the unit and is designed for one or small number channels.
1. 6. 5. By supporting international and proprietary protocols
Modems can also be classified according to the protocols they implement. All protocols that regulate certain aspects of the functioning of modems can be classified into two large groups:
international and corporate.
International level protocols are developed under the auspices of the ITU-T and accepted by it as recommendations (formerly ITU-T was called International Advisory Committee on Telephony and Telegraphy - CCITT, international abbreviation - CCITT). All ITU-T recommendations for modems are in the V series. Proprietary protocols are developed by individual modem companies in order to outperform the competition. Often, proprietary protocols become de facto standard protocols and are accepted in whole or in part as ITU-T recommendations, as has happened with a number of Microcom protocols. The most active in the development of new protocols and standards are those well-known firms like AT&T, Motorola, U. S. Robotics, ZyXEL and others.
From a functional point of view, modem protocols can be divided into the following groups:
> Protocols that define the rules for the interaction of a modem with a communication channel (V. 2, v. 25):
> Protocols governing the connection and algorithms for the interaction of the modem and DTE (V. 10, v. 11, v. 24, v. 25, v. 25bis, v. 28);
> Modulation protocols that define the main characteristics of modems designed for dial-up and leased telephone channels. These include protocols such as V. 17, V. 22, V. 32, V. 34, HST, ZyX and many others;
> Error protection protocols (V. 41, V. 42, MNP1-MNP4);
> Communication compression protocols such as MNP5, MNP7, V. 42bis;
Rice. one. 10. Classification of modem protocols
> Protocols that define the procedures for diagnosing modems, testing and measuring the parameters of communication channels (V. 51, V.52, V.53, V.54, V.56).
> Protocols for negotiating communication parameters at the stage of its establishment (Handshaking) e.g. v. 8.
The prefixes "bis" and "ter" in the names of the protocols denote, respectively, the second and third modification of the existing protocols or the protocol associated with the original protocol. In this case, the original protocol, as a rule, remains supported.
Some clarity among the variety of modem protocols can be introduced by their conditional classification, shown in Fig. one. 10. CHAPTER 8 DATA COMPRESSION PROTOCOLS
1.1 Composition and structure of the national communication system.
1 .2 ESE architecture. Status of networks, services, telecommunication systems.
1.3 Classification of services, users and services.
1.4 Nomenclature and types of services provided.
1.5 Main trends in the development of telecommunication networks.
1.6 Stages of development of the ESE of Russia.
1.7 General requirements for telecommunication networks.
Section 1 is devoted to the conceptual and target foundations for the construction, development
and general organizational and technical provisions unified network telecommunications
Russian Federation. IN this section the purpose, composition and structure of the National Communications System of the Russian Federation are considered from a systemic standpoint. Special attention paid to the architecture of the Unified Telecommunication Network (UTN), the principles of its construction, the categories of networks that are part of the UT. The purpose of the primary network, secondary networks, telecommunication systems and telecommunication services is considered. The classification of users of the network, services and telecommunication services is given. Considerable attention is paid to the range of telecommunications services provided to the population of the country at the present time and in the near future. The main trends in the development of telecommunications in the world are indicated, which largely determines the process of development of the ESE. important place in the section takes consideration
stages of development of the ESE, which determine the technical policy pursued by the Ministry of Information Technologies and Communications of the Russian Federation. Significant Attention
is given to the requirements for communication networks, which determine the policy for the development of communications, design and operation of telecommunication networks. To control the level of assimilation of the studied material,
test questions. To increase the level of knowledge and promptly obtain
For reference information, a list of references and a glossary are provided.
1.1 Composition and structure of the nationwide communication system
The existence of modern society is unthinkable without the exchange of information. Information, understood in the broad sense of the word as a reflection of the diversity of the surrounding world, performs the following main functions in society: communicative, or the function of human communication; cognitive, the purpose of which is to obtain new information ; managerial, the purpose of which is to form the expedient behavior of the controlled system. To intensify information processes in the communication of people in the first half of the last century, the development of means electrical communication, providing acceleration in the first place of such forms of information movement as transmission and distribution. Over a century and a half, the means of communication have changed many times, new types of electrical communication have appeared, but their main function in society - the intensification of communication processes - has been preserved. The need for intensification of information processes associated with the management and cognitive activities of people led to the creation of computer technology. Computer technology has made it possible to accelerate such forms of information movement as processing, search, storage, perception, display, distribution, etc. processes in society. Expedient information activity of people, information and means of information activity are the main components of the information system of society. If the purpose of information activity is communication using means of communication, then the information system created for this purpose is called a communication system. In accordance with the system approach, when creating any system, the integration of components into a system, their interactions, connections and relationships should be aimed at achieving a common goal. In particular, within the framework of the communication system, the principles of interaction of communication facilities should be agreed upon, their parameters should be indicated, the procedure for using these facilities should be established, the methods of operation, the proportions and prospects for their development should be determined, the goals of assigning all elements and subsystems with the overall goal of the system functioning should be agreed.
In our country, in order to most fully meet the needs of the population, public authorities and administration, defense and security of law and order, as well as business facilities in the services of electrical and postal communications, a communication system of the Russian Federation (SS RF).Communication system RF (Communication RF) unites all communication systems of the country in terms of organizational, technological, methodological and other features into a single communication system and is a set of networks, communication services and other means of support located and functioning on the territory of the Russian Federation. The means of the SS of the Russian Federation together with the means of CT (computer technology) constitute the technical basis for the informatization of society. The structure of the RF communication system is shown in fig. 1.1
Rice. 1.1 Composition of the RF communication system
The SRF includes federal communications and technological communications systems. Main Components federal communications are federal telecommunications (FES) and federal postal service(FPS).
Telecommunications- any transmission or reception of signs, signals, written text, images, sounds via wire, radio, optical and other electromagnetic systems.
Postal service– reception, processing, transportation and delivery of postal items, as well as transfer of funds.
Federal Telecommunications includes public communication systems, special purpose communication systems and dedicated communication systems.
Public communication systems- an integral part of the RF SS, open for use by all individuals and legal entities, the services of which cannot be denied to these individuals.
Dedicated communication systems- these are telecommunication systems of individuals and legal entities that do not have access to public communication systems.
Special purpose communication systems designed to meet the needs of public administration, defense, security and law enforcement in the Russian Federation. Such communication systems can not be used to provide services to the public. Technological communication systems- these are telecommunication systems of enterprises, institutions and organizations created to manage in-house activities and technological processes that do not have access to public systems. If there are free resources in technological communication systems, these network resources can be connected to a public communication system and used to provide possible services to any user. Dedicated communication systems also can be connected to the public telecommunications system if they comply with its requirements. At present, the Federal Telecommunications includes the following public telecommunication systems: telephone communication (STFS); telegraph communications (STgS); facsimile communication (SPS); newspaper transmission (SNG); data transmission (SPD); distribution of sound broadcasting programs (SPRAP); distribution of television broadcasting programs (SRPTV). In the process of development of the RF SS, the composition of telecommunication systems is undergoing significant changes due to the integration of a number of systems and the formation of new ones. This process is primarily due to the introduction of new technologies and new technical solutions in telecommunication networks. As a first step in the integration of individual telecommunication systems, it is possible to combine telecommunication systems that provide the transmission of documentary messages into a documentary telecommunication system (SDES). Further development of integration is associated with the creation of a system with the integration of services (N - ISDN and B - ISDN) and intelligent telecommunication systems, as well as communication systems of the new (next) generation - NGN. Telephone system(TC) is designed to meet the needs of the population, institutions, organizations and enterprises in the transmission of telephone, facsimile messages and data at a speed of no more than 64 kbps. The TS system provides access to technological telephone networks, the international telephone network, as well as communication with mobile subscribers and the Internet. Telegraph communication system provides transmission of documentary messages presented in the form of alphanumeric text. Data communication system provides data transfer to a wide range of enterprises and institutions of the country, the population, as well as to meet the needs of automated control systems. Fax system provides the transmission of still, both color and black-and-white, grayscale and line art in the form of photographs, drawings, graphs, handwritten texts, etc. in any language and with any alphabet printed on forms of standard sizes. Newspaper transmission system is designed to transfer original prints of newspapers received from publishers to decentralized printing points. Signal distribution system for sound broadcasting programs designed to transmit broadcast programs to the population of the country. Television signal distribution system programs is intended for the implementation of television broadcasting.
Means of providing the RF SS
All means that ensure the normal functioning of the RF SS can be divided into means technical, software, methodological, informational and organizational support.Technical support of the RF SS- a set of devices and communication systems, electronic and computers and systems, linear and civil structures, combined into a single complex of technical means of communication of the country. Software- a set of operating systems, translators, compilers, application software packages and operational documents that ensure the functioning of the RF SS. Methodological support- a set of methods, models, algorithms, rules, standards, instructions that regulate the interaction of technical means and people with technical means in the process of functioning of the RF SS. Information Support includes: description of equipment; reference data (for example, telephone directories); messages for radio and television programs; accounting and archival information necessary for planning and development of the RF SS; current information about the functioning of the system and other information. Organizational support includes: instructions, guidance materials, orders, staffing tables, as well as documents defining goals, rights, duties, modes of operation, interaction of employees and organizational units at various stages of functioning and development of the Communications System of the Russian Federation. Experience and developments in the creation of large organizational and technical systems show that reassessment of the role of any means of support can nullify all efforts to create an effective communication system. In accordance with the principles of the integrity of the system methodology, at all stages of the development of the system, it must be considered as a whole, i.e. take into account all its components, their connections and relationships that significantly affect the achievement of the goal, its systemic properties.
