Information transfer systems (SPI) are used to transfer messages from one subscriber to another. Messages can be discrete and continuous. Discrete messages are sequences of characters, and the number of different characters is finite. Examples of discrete messages are telegraph messages, telecode, etc. Sources of information that create discrete messages are called discrete. Continuous messages are continuous functions of time. Sources of information that create continuous messages are called continuous. Examples of continuous messages are speech, music, the value of some parameter that changes over time, etc.

SPNs intended for transmission of discrete messages are called discrete or digital, and SPNs intended for transmission of continuous messages are called continuous or analog.

Channels, in which discrete messages are transmitted are called discrete, and channels in which continuous messages are transmitted are called continuous. Transmission of continuous messages is also possible in discrete form. To do this, it is necessary to transform continuous messages from the source of continuous information into discrete ones, and discrete messages will be transmitted through the channel, that is, the channel will be discrete.

Replacing continuous messages with discrete always done with the specified precision. To do this, one should expand the continuous message in a series (1.8) in terms of orthogonal functions, i.e., represent the message in the following form:

where the expansion coefficients are orthogonal functions forming a system of orthogonal functions. Two functions (or two signals) are called orthogonal if they satisfy the integral relation (1.9)

Here, the energy of the function (signal) Definition (2.2) is valid for any systems of orthogonal functions, as

limited in time (finite), and for those with infinite length. The expansion coefficients are found according to the equality (1.10)

If the system of orthogonal functions consists of complex functions, then the expansion is written, as for real functions, in the form (2.1), and the orthogonality condition and the expansion coefficients are determined as follows:

Comparing (2.3), (2.5) with the definition of correlation functions, for example, with (1.21), one can see that the expansion coefficients are the correlation coefficients between the message and the functions.The series (2.1) in the general case contains an infinite number of terms. Setting the required accuracy, you can always leave a finite number of expansion terms, discarding those that have little effect on (2.1). In this case, we obtain

is determined by the discarded terms of expansion (2.1). The selection can ensure that the ride, where the ride is the specified value of the root mean square error.

Representation (2.6) means that a message with a given degree of accuracy is completely determined by a finite set of expansion coefficients. Then it is necessary to replace a finite set of expansion coefficients with a finite set of symbols that must be transmitted over a discrete channel.

The choice of a system of orthogonal functions and a method for translating the expansion coefficients into symbols is determined by the properties

message and the required accuracy of its reproduction. For instance; if the message spectrum is limited in width, then it is expedient from a practical point of view to represent it in the form of a Kotelnikov series, in which

The function is called a function of samples, In this case, the message is replaced by a sequence of samples that follow each other with an interval Quantizing the samples by amplitude, we get a finite number of different values.When quantizing by amplitude, a quantization error occurs, which is smaller, the more quantization levels are. Based on the required fidelity of the message, you can find the required number of quantization levels. After quantization, we find that the message is determined by a finite set of quantized samples. Replacing one or another quantized sample with its own symbol, we get the opportunity to transmit a continuous message in the form of a discrete one.

With other properties of the message, it may turn out to be more expedient from a practical point of view, another expansion in terms of orthogonal functions. For example, if you break a message into segments of duration, then on each segment the message can be represented as a Fourier series, in which

The exponent (2.9) is a periodic function with a period In addition to those mentioned above, a large number of other systems of orthogonal functions are known, many of which have found application in SPI.

It should be noted that systems of orthogonal functions are widely used in mathematics to solve various problems. Orthogonal functions used in SPI for message transmission will be called orthogonal signals. Accordingly, the constellations of such signals are orthogonal signaling systems. The use of orthogonal signaling systems for representing continuous messages in the form of series is one example of the use of signaling systems in the SPI. From (2.2), (2.4) it follows that the signals of such systems must satisfy the only condition, orthogonality.

Multichannel information transmission systems. The need for information exchange between many subscribers has led to the construction of multichannel information transmission systems. Each multichannel SPI operates in its own frequency range, which is determined by its purpose. Subscribers included in the multichannel "SPI work in a common frequency band, within which each of them is provided with a channel for information transmission.

The formation of a multichannel SPI from many subscribers can be carried out by two methods of combining subscribers. One.

of these we will call the centralized union and the other autonomous. With centralized integration, the exchange of information between two subscribers is carried out through the central stations in Fig. 2.1, a and b). When transmitting information over long distances from subscribers of one zone, it is first combined in its own central station and in Fig. 2.1, a), then it is sent over the line to the central station of another zone, after which it is divided according to the subscribers of this zone. In fig. 2.1, and the arrows show the path of information passing between subscribers. Let's call such multichannel SPI multichannel centralized linear systems (MCLS). The MCLS includes radio relay lines, radio telemetry systems, etc.

The centralized association of subscribers can also be used to exchange information between subscribers within one zone (Fig. 2.1, b). This requires one CA. The arrows in Fig. 2.1, b shows the path! passing; information between subscribers From fig. 2.1, b it can be seen that the transmission of information is carried out along the radius vectors that go out and enter the central station. For this reason, such multichannel SPI can be called multichannel centralized radial systems (MCRS). Examples of ICRC are radio communication systems for civil services, air traffic control systems, command radio control systems, etc.

In those cases when linearity or radiality will not be noted, multichannel DSS with centralized compaction will be called multichannel centralized systems (MSC).

Another method of combining subscribers is autonomous, in which subscribers exchange information directly with each other (Fig. 2.1, c). There is no need for a central station. We will call such SPI multichannel autonomous systems (MAC). Examples of MAC are grass-roots radio communication systems (military, rural), command radio control systems, etc.

MSC allows to establish a more efficient exchange of information between many subscribers, better use the allocated frequency bands and time. However, the presence of the CA makes the MSC more vulnerable than the MAC, since the failure of the CA

leads to the failure of the entire MDC. The presence of a CA in many cases complicates the entire SPI and increases its cost. In addition, in some cases, in accordance with the tactical and technical requirements, the use of the CA is simply impossible. For these reasons, MCC and MAC will organically complement each other when creating a Unified Automated Communication System (EASC).

It should be noted that in some cases multichannel SPI can be built both with a centralized union of subscribers and with an autonomous one. In such cases, the merger method should be carried out taking into account the tactical, technical and economic requirements. In addition, it is possible to use both centralized and autonomous combining together.

Methods of compaction and separation of channels and subscribers. Depending on the purpose, each SPI is allocated a certain frequency range, which is hereinafter referred to as a common frequency band (common for all subscribers). The use of a common frequency band by subscribers is determined by the methods of compression (placement of signal spectra of all subscribers in the common band) and separation (separation of subscriber signals). Since this or that compaction method uniquely determines the separation method (the opposite is also true), in what follows we will classify the compaction and separation methods according to the separation methods.

There are three possible methods for dividing the information of different subscribers, transmitted over the channels dedicated to them. Frequency division (PD) method (see, for example,) is that each subscriber is assigned his own subscriber frequency band (frequency channel) within the overall frequency band of the system. In this case, the subscriber frequency bands do not overlap, but the subscriber signals do overlap in time. The time division (BP) method is that each subscriber works in its own subscriber time interval (time channel), during which other subscribers do not transmit information. The subscriber spectra occupy the entire total frequency band and completely overlap. The method of code division (CD) is that the division is carried out according to the form of signals used by a particular subscriber, and the subscribers work in a common frequency band at the same time.

Frequency division was the first to find application, since it was known earlier than other methods and was quite simply implemented in practice. The development of pulse modulation techniques has led to the emergence of time division. Attention to code separation was drawn by the work of Costas in 1959. However, it should be noted that the basics of separating information according to the form of signals (the basics of linear selection) were developed by D.V. Ageev in 1935.

Frequency-division and time-division SPIs have been studied in great detail. Methods for calculating and designing such SPI have been created, although research is still being carried out on their

improvement. The situation is different in the case of a code division SPI. Since the code division is based on the difference of signals, the construction of such SPI and their characteristics are determined by the choice of signals and their properties. Usually, the number of subscribers is large enough, therefore, the choice of signals for SPI with CD is reduced to the definition of signal systems with given properties. The development of SPI with CR and led to research in the field of the theory of signal systems, the main results of which will be presented in the future.

SPI with KR are address systems, since the subscriber's signals play the role of his address. Address SPIs can be divided into two classes - synchronous address systems (SAS) (see, for example,) and asynchronous address systems (AAS) (see, for example). The former are used mainly for centralized consolidation of subscribers, and the latter for stand-alone.

In the CAS, information transmission is carried out in such a way that the information carriers satisfy the orthogonality condition (2.2), i.e., if the subscribers use signals with spectra, then for the equalities

Note that the orthogonality conditions (2.10), (2.11) are special cases of linear independence of signals. If equality (2.10) is satisfied, then (2.11) is also true. If the signals are linearly independent, then they are separated without mutual interference. In practice, orthogonal signals are commonly used.

Since the orthogonality is violated with time offsets, it is necessary to have time synchronization to ensure orthogonality. Thus, in the CAS, the transmission of information by different subscribers is carried out by orthogonal signals, subject to time synchronization between them. The presence of synchronization leads to the fact that mutual interference does not arise in the SAS.

It should be noted that in an SPI with PD, mutual interference always exists in principle, since signals with a finite duration have infinitely long spectra, and crossover filters pass all frequencies with a finite attenuation. For these two reasons, a part of the signal energy of an arbitrary channel in the PDS with PD enters any channel, creating mutual interference. By choosing signals (by reducing "out-of-band" emissions) and filters (by increasing attenuation outside the passband), placing channels in frequency, it is possible to reduce mutual interference to an acceptable

In AAS, equalities (2.10), (2.11) do not hold, therefore in such systems there is mutual interference between users, which is sometimes called “non-orthogonality noise”. Due to mutual interference, the number of simultaneously operating subscribers in the AAS with the same noise immunity will be less than in synchronous ones. But when building an AAS, there is no need to ensure the synchronization of subscribers in time and frequency. This is a significant advantage of AAS over synchronous systems, especially in cases where it is impossible to provide time synchronization of subscribers scattered over a large area, for this reason AAS has been developed.

In SAS and AAS, to ensure the operation of a large number of subscribers, it is necessary to have at least the same number of different signals. Since the signals cannot be selected arbitrarily, then for such SPI it is necessary to use signal systems with certain properties. Further material is mainly devoted to the choice of signal systems. The solution to the issues of choosing signal systems is largely determined by the purpose of the SPI and its characteristics. The main characteristics of the SPI are noise immunity and efficiency. By the noise immunity of an SPI we mean its ability to resist interference, and by its efficiency we mean the use of the total frequency band, time and power of the transmitter.

Since any SPI consists of channels (in the limiting case of one), it is first necessary to consider the noise immunity and efficiency of one channel, i.e., a single-channel SPI. Let us do this using the example of a discrete SPI designed for transmitting discrete messages.

Telecommunication systems (TS) are usually understood as structures and means designed to transmit large amounts of information (usually in digital form) through specially laid communication lines or radio air. At the same time, it is assumed that a significant number of system users will be served (from several thousand). Telecommunication systems include such information transmission structures as television broadcasting (collective, cable, satellite, cellular), public switched telephone networks (PSTN), cellular communication systems (including macro- and microcellular), paging systems, satellite communication systems and navigation equipment, fiber data transmission networks.

It should be noted that the main requirement for communication systems is the absence of the fact of interruption of communication, but some deterioration in the quality of the transmitted message and waiting for the establishment of communication are allowed.

Types of telecommunication systems

By purpose, telecommunication systems are grouped as follows:

• - TV broadcasting systems;
• - communication systems (including a personal call);
• - computer networks.

By the type of information transmission medium used:

• - cable (traditional copper);
• - fiber optic;
• - etheric;
• - satellite.

By the method of information transfer:

• - analog;
• - digital.

Communication systems are subdivided by mobility into:

• - fixed (traditional subscriber lines);
• - movable.

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

• - for microcellular - DECT;
• - cellular - NMT-450, D-AMPS, GSM, CDMA;
• - trunking (macrocellular, zonal) - TETRA, SmarTrunk;
• - satellite.

TV broadcasting systems

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

• - television reception networks;
• - "cable" (systems of collective television reception (SKTP));
• - technologies of wireless high-speed distribution of multimedia information MMDS, MVDS and LMDS;
• - satellite.

Television reception networks, historically the very first vehicles, deliver a signal to the consumer through repeaters (relay communication lines) covering the territory of Russia (densely populated regions). The distance between repeaters is about 40-80 km.

At the present stage, the development of collective television reception technology is associated with the creation of cable television systems (CTS), each of which can serve up to several tens of thousands of subscribers. The use of such systems makes it possible to resolve the issues of ensuring high-quality program delivery in areas with difficult reception conditions, as well as to ensure the transmission of additional information to subscribers - teletext information, satellite broadcasting channels.

Collective television reception systems, depending on the volume of subscribers covered, are divided as follows:

• - collective television reception systems;
• - large systems of collective television reception;
• - cable television systems.

It is assumed that SKT are designed to serve subscribers of one entrance or building, KSCTP - several buildings, SKT - a large residential area. The distinctive features of SCT should also include the technical and economic feasibility of using other types of programs (satellite, local video studios, etc.) along with on-air reception in standard TV and radio broadcasting channels. It should be noted that a prerequisite for the successful development of SKT is the choice of such a construction scheme, in which it is possible to use KSPKTP and SKTP as the lower links of distribution networks without significant alterations, otherwise the implementation of SKT in areas with existing development is associated with large additional capital costs.

Satellite television systems have received a new development in the direction of creating inexpensive installations for individual reception of satellite television programs. The broadcasting of television programs through satellite television broadcasting systems (STV) has proven to be economically viable for small areas. For a number of energy parameters, a suitable frequency range is in the 12 GHz region: at these frequencies, precipitation losses are relatively small (in Europe, the change in attenuation due to precipitation does not exceed 3.3 dB for 99.9% of the time, antenna sizes (diameter 2 m) with a narrow radiation pattern, a relatively cheap element base has been developed.

Geostationary satellites are used to broadcast live television programs. Satellites for the transmission of television programs are divided into:

• - satellites for long-distance communications for telephone communications, information transmission and transmission of television programs;
• - satellites for the redistribution of television programs, for example, to cable networks;
• - satellites for transmitting television and radio programs directly to individual receivers, TV satellites: in the English designation DBS (direct broadcast satellite), in the German designation SDE (direct reception satellite);

Mobile communication systems

Cellular mobile communication systems (PCS), personal radio call networks (PRN) and satellite communication systems are designed to transmit data and provide mobile and stationary objects with telephone communications. Data transmission to a mobile subscriber dramatically expands its capabilities, since, in addition to telephone messages, it can receive telex and facsimile messages, various types of graphic information, etc. radio communications (pagers, cellular radiotelephones, satellite user terminals).

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

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

Cellular mobile networks

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

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

Modern technologies make it possible to provide CCC subscribers with high quality of voice messages, reliability and confidentiality of communications, miniature radiotelephones, protection from unauthorized access.

Trunking networks

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

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

If we use an analogy with cellular communication, then in the simplest case, an STS is one cell of the cellular system, but with a somewhat specific (narrow) set of services. A cellular network is always built in the form of a set of cells, which are connected to a common switching center (CC), with the handover from cell to cell as the subscriber moves. If it is necessary to increase the capacity of the cellular network, additional fragmentation of the cells is carried out with an appropriate modification of the frequency plan (frequency distribution among the cells). In a STS, which is known to operate with a limited capacity, they usually strive to maximize the coverage area. In practice, the radius of a STS cell can reach 40-50 km and more. This results in a higher transmitter power, compared to cellular communication, a higher energy consumption of a power source, large dimensions and weight of subscriber equipment.

Even if the STS is built in the form of several cells (multi-zone system), this is done primarily with the aim of expanding the coverage area, and not for the sake of increasing capacity; at the same time, the sizes of the cells (zones) remain large enough. The centralized control of the plurality of zones remains limited, as does the handover from zone to zone, which (if at all) leads to a short interruption of communication.

To increase the bandwidth, restrictions are usually imposed on the duration of the call, and the specificity of corporate communications is reflected in the system of user priorities, taken into account when providing a communication channel in a queue, and in uniting subscribers into groups with the possibility of dispatching all subscribers of the group at the same time. The same specificity leads to higher, on average, in comparison with cellular communications, requirements for the promptness and reliability of communication. In addition to speech information, some other types of information can be transmitted to the STS, in particular, digital - control, telemetry, burglar alarms, etc.

The general trend in the development of professional mobile radio communication systems is the transition from analog standards to unified international digital standards that ensure confidentiality and improved communication quality, more efficient use of the frequency range, roaming for all subscribers and the ability to transfer data at high speed.

Paging networks

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

In the simplest case, the PRL consists of a paging terminal (PT), a base station (BS) and pagers. The terminal, which includes the operator panel and the system controller, performs all system control functions. The BS consists of a radio transmitter and an antenna-feeder device, and provides the transmission of paging signals to the entire coverage area of ​​the system, the radius of which can be up to 100 km. Pagers receive the messages that are addressed to them. In more complex cases, the PRS can have several radio transmitters, as evenly distributed as possible within the coverage area, which makes it possible to more reliably provide communication for the entire area.

There are four types of messages that can be transmitted in the LMS: tone, numeric, alphanumeric, and speech. Tones were the only message type in early pager models. The digital message may contain a phone number to call. The most common transmission of a text message is up to 100-200 characters long. The message is displayed on the pager display, which can have from one to eight lines, up to 12-20 characters per line, long messages are displayed in parts. The transmission of voice messages has not yet received wide distribution. Calling a subscriber, i.e. message addressing can be carried out in one of three ways: individually, to several subscribers (general call) or to a group of subscribers (group call (GW)). In the first case, the call is addressed to a specific subscriber by his individual number, in the second - to several subscribers with sequential transmission of their individual numbers, in the third - the call is addressed simultaneously to a group of subscribers using a common group number. Messages to be transmitted are also entered into the system in one of three ways: by voice over the telephone network and by the paging operator; through a telephone network with tone dialing - the message is typed on the keypad of the telephone set and goes directly to the paging terminal, bypassing the operator; from a computer (via the telephone network) with a set of messages on the computer and access directly to the PT.

The disadvantages of paging communication include the transmission of a message out of real time: the message is not transmitted at the time of its issuance by the sender, but in the order of the queue with similar messages from other senders; in practice, the delay from the moment a message is received to its transmission on the air is small - usually it does not exceed a few minutes. It should also be borne in mind that if a message is sent to a pager that is in the “shadow” zone at the time of transmission, the message will be lost (not received by the subscriber).

Asynchrony (sequence) of message transmission, combined with the brevity of the latter, which are usually transmitted only in one direction, provides a very efficient use of the communication channel, at least two orders of magnitude more efficient (in terms of the number of subscribers served) than in cellular communication. even taking into account the reuse of frequencies in the latter. As a result, paging turns out to be technically simpler and more economical than cellular communication, i.e., ultimately, it is much cheaper for the subscriber.

In addition to messages intended for specific subscribers or groups of subscribers, paging systems usually organize a kind of general information channel containing operational information about exchange news, weather, traffic conditions, etc. In pagers, as a rule, a number of additional services are provided: clock, calendar, the ability to adjust the type and volume of the sound signal, storing previously received messages in the memory with the ability to re-read them, etc.

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

Mobile satellite networks

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

• - expansion of cellular networks;
• - the use of satellite communications in areas where the deployment of an ATP is impractical, for example, due to the low population density;
• - the use of satellite communications in addition to the existing cellular, for example, to ensure roaming in case of incompatibility of standards, or in any emergency situations;
• - fixed wireless communication in areas with low population density in the absence of SPS and wire communication;
• - when transmitting information on a global scale (waters of the World Ocean, breaks in ground infrastructure, etc.).

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

Satellite communication is quite organically combined with cellular. Almost all MSSS provide for a fairly high degree of integration with cellular communications; in particular, in addition to AT, intended for satellite systems, it is planned to create dual-mode terminals designed to operate in a satellite system and in any of the cellular standards.

For a subscriber, the use of a satellite terminal does not require special knowledge. The number is dialed by the user using the keypad, just like when using a regular telephone. The system automatically allocates a free channel and assigns it to the interlocutors for the duration of the conversation. As a rule, multiplexing (temporary, private or code) is used, which has proven itself in multichannel communication.

Of course, the equipment (not only subscriber's) of satellite communication networks is more expensive than that of CCC, and, accordingly, the subscription fee is much higher. Some inconvenience is presented by the delay of the speech signal due to the remoteness of the base (satellite) station (about 36,000 km), which is fractions of a second.

Various MSSS have their own characteristics, mainly due to the characteristics of their orbital constellations, but in the field of user characteristics and services provided, they have much in common (both with each other and with terrestrial cellular systems). All types of information are transmitted in digital form at speeds from 1200 to 9600 bit / s. The telephone mode is organized using the AT's built-in signal rate converters. In addition to full-duplex telephony, Personal ATs allow you to connect to a computer and support a variety of services such as faxing, email and voice mail, paging and priority service, encryption, and location tracking.

Fiber optic networks

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

FOCL advantages

Wide bandwidth - due to the extremely high carrier frequency of 1014 GHz. This gives the potential for transmission over one optical fiber of a stream of information of several terabits per second. High bandwidth is one of the most important advantages of optical fiber over copper or any other media.

Low attenuation of the light signal in the fiber. Industrial optical fiber currently produced by domestic and foreign manufacturers has an attenuation of 0.2-0.3 dB at a wavelength of 1.55 microns per kilometer. Low attenuation and low dispersion allow building sections of lines without retransmission up to 100 km or more.

Low noise in fiber optic cable allows to increase the bandwidth by transmitting various signal modulations with low code redundancy.

High noise immunity. Since the fiber is made of a dielectric material, it is immune to electromagnetic interference from surrounding copper cabling systems and electrical equipment that can induce electromagnetic radiation (power lines, electric motor installations, etc.). Multi-fiber cables also do not have the EM crosstalk problem inherent in multi-pair copper cables.

Light weight and volume. Fiber optic cables (FOC) are lighter and lighter than copper cables for the same bandwidth. For example, a 900-pair telephone cable with a diameter of 7.5 cm can be replaced with a single fiber with a diameter of 0.1 cm. times less than the telephone cable in question.

High security against unauthorized access. Since the FOC practically does not radiate in the radio range, it is difficult to eavesdrop on the information transmitted over it without disrupting reception and transmission. Monitoring systems (continuous control) of the integrity of the optical communication line, using the properties of high sensitivity of the fiber, can instantly disable the "compromised" communication channel and give an alarm. Sensor systems using the interference effects of propagated light signals (both through different fibers and different polarizations) have a very high sensitivity to vibrations and small pressure drops. Such systems are especially necessary when creating communication lines in government, banking and some other special services that impose increased requirements for data protection.

Galvanic isolation of network elements. This advantage of optical fiber lies in its insulating property. Fiber helps avoid electrical ground loops that can occur when two network devices on a bare network, connected by copper cable, are grounded at different points in a building, such as on different floors. In this case, a large potential difference can occur, which can damage the network equipment. For fiber, this problem simply does not exist.

Explosion and fire safety. Due to the absence of sparking, optical fiber increases the safety of the network in chemical, oil refineries, when servicing high-risk technological processes.

Efficiency of FOC. The fiber is made of silica based on silica, a widespread and therefore inexpensive material, unlike copper. Currently, the cost of fiber in relation to copper pair is 2: 5. At the same time, FOC makes it possible to transmit signals over much longer distances without retransmission. The number of repeaters on long lines is reduced with the use of FOC. With the use of soliton transmission systems, distances of 4000 km have been achieved without regeneration (that is, only with the use of optical amplifiers at intermediate nodes) at a transmission rate above 10 Gbit / s.

The duration of the service life. Fiber degrades over time. This means that the attenuation in the laid cable gradually increases. However, due to the perfection of modern technologies for the production of optical fibers, this process is significantly slowed down, and the service life of the FOC is approximately 25 years. During this time, several generations / standards of transceiving systems may change.

Remote power supply. In some cases, a remote power supply of the information network node is required. Optical fiber cannot function as a power cable. However, in these cases it is possible to use a mixed cable, when, along with optical fibers, the cable is equipped with a copper conductive element. Such a cable is widely used both in Russia and abroad.

Despite numerous advantages over other methods of information transmission, fiber-optic networks also have disadvantages, mainly due to the high cost of precision mounting equipment and the reliability of laser radiation sources. Many of the shortcomings are likely to be leveled out with the advent of new competitive technologies in fiber-optic networks.

Disadvantages of FOCL

The cost of interface equipment. Electrical signals must be converted to optical signals and vice versa. The price of optical transmitters and receivers is still quite high. When creating an optical communication line, highly reliable specialized passive switching equipment, optical connectors with low losses and a large resource for connection-disconnection, optical splitters, and attenuators are also required.

Installation and maintenance of optical lines. The cost of installation, testing and support of fiber-optic communication lines also remains high. If the fiber optic cable is damaged, then it is necessary to splice the fibers at the break point and protect this section of the cable from the external environment. Manufacturers, meanwhile, are bringing to the market more and more sophisticated tools for installation work with FOCs, reducing their price.

Requirement for special fiber protection. Is the optical fiber strong? In theory, yes. Glass, as a material, can withstand colossal loads with a tensile strength above 1 GPa (109 N / m2). This would seem to mean that a single amount of fiber with a diameter of 125 microns will withstand the weight of a weight of 1 kg. Unfortunately, this is not achieved in practice. The reason is that optical fiber, no matter how perfect it is, has microcracks that initiate breaking. To increase reliability, the optical fiber is coated with a special varnish based on epoxy acrylate during manufacture, and the optical cable itself is strengthened, for example, with kevlar-based threads. If it is required to meet even more severe breaking conditions, the cable can be strengthened with a special steel cable or fiberglass rods. But all this entails an increase in the cost of an optical cable.

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

Various means and systems of communication and telecommunications are used for the transmission and distribution of electronic data.

Here are the types of communication and the types of information used in them. This:

1. postal (alphanumeric and graphic information),
2. telephone (voice transmission (including alphanumeric data),
3. telegraph (alphanumeric messages),
4. facsimile (alphanumeric and graphic information),
5. radio and radio relay (speech, alphanumeric and graphic information),
6. satellite communication (also video information).

Communication in an organization is subdivided into:
wired and wireless,
internal (local) and external,
simplex, duplex and half duplex.

Duplex mode- this is when you can simultaneously speak and hear the interlocutor.
Half duplex transmission(Half-Duplex) is a method of bidirectional data transmission (in two directions over one channel), in which information can be transmitted only in one direction at a time. This is a dual frequency simplex, or half duplex. From the end-user perspective, it is equivalent to a simplex.
Simplex mode- this is when subscribers talk to each other in turn.

Communication line- physical wires or cables connecting points (nodes) of communication with each other, and subscribers - with the nearest nodes.

Channels of connection is formed in various ways.
The channel can be created for the period of connection of two subscribers of telephone or radio communication and conducting a voice communication session between them. In radio communication, this channel can represent a data transmission medium in which several subscribers can work simultaneously, and in it several communication sessions can be carried out simultaneously.

Wherein:
1) wire communication includes: telephone, telegraph communication and data transmission systems;
2) wireless connectivity includes:
a) mobile radio communications (radio stations, cellular and trunk communications, etc.);
b) stationary radio communications (radio-relay and space (satellite) communications);
3) optical fixed communication over air and fiber-optic communication cables.

Communication cables

Twisted pair- insulated conductors twisted in pairs to reduce interference between them. There are five categories of twisted pairs: the first and the second are used for low-speed data transmission; the third, fourth and fifth - at transfer rates up to 16, 25 and 155 Mbit / s.

Coaxial cable- a copper conductor inside a cylindrical shielding protective shell made of thin copper conductors, insulated from the conductor by a dielectric. Transfer rates up to 300Mbps. The significant cost and complexity of the gasket limits its use.
The characteristic impedance of the cable (the ratio between the amplitudes of the incident voltage and current waves) is 50 ohms.

Fiber optic cable consists of transparent fibers of an optically transparent material (plastic, glass, quartz) with a diameter of several microns, surrounded by a solid filler and placed in a protective sheath. The refractive index of these materials changes in diameter in such a way that the beam deflected to the edge returns back to the center.
Information transfer is carried out by converting electrical signals into light signals using, for example, an LED. This provides resistance to electromagnetic interference and a range of up to 40 km.

Telephone communications- the most common type of operational and managerial communication.
It officially appeared on February 14, 1876, when Alexander Bell (USA) patented the invention of the first telephone.
The range of audio signals transmitted through domestic telephone channels is 300 Hz – 3.4 kHz.

Automatic telephone communication It is formed with the help of switching nodes, the role of which is performed by automatic telephone exchanges (ATS), and communication channels (lines) connecting these nodes.
Together with subscriber lines (a telephone line from a subscriber to the nearest automatic telephone exchange), it constitutes a telephone network. The telephone network has a hierarchical structure - terminal (intra-departmental, local, district, etc.), city, regional (regional, territorial, republican), state and international automatic telephone exchanges. PBXs are connected to each other using connecting lines.

Telephone exchange(Automatic telephone exchange) - a building with a complex of technical means intended for switching telephone channels.
At the automatic telephone exchange, the telephone channels of the subscribers are connected for the duration of their negotiations, and then, at the end of the negotiations, their disconnection. Modern vehicles are automatic technical devices (including computers).

Office PBX, as a rule, provide not only internal communication of units with each other with the ability to access external networks, but also various types of industrial communication (dispatch, technological, loud-speaking and director) for communication of the director with subordinates, holding meetings and conferences, as well as the functioning of security systems and fire alarm.
The peculiarity of modern automatic telephone exchanges is the possibility of using computer equipment and technology; organization of connection with radiotelephones and pagers. In institutions, radiotelephones are used to overcome high levels of electromagnetic fields and partitions, forming infrared communication channels.

Local, intra-office, or office telephone systems (PBX or EATX) are widely used in organizations. In addition to a wide range of service capabilities, they can significantly reduce the number of city telephone numbers, as well as not load city lines and automatic telephone exchanges for local calls. Increasingly, mini- and micro-office PBXs are being used.

Wireless communication channels

There are three main types of wireless networks:

1. radio networks of a free radio frequency range (the signal is transmitted over several frequencies at once);
2. microwave networks (long-distance and satellite communications);
3. infrared networks (laser, transmitted by coherent beams of light).

Modern wireless networks include:

• radio relay communication;
• paging communication;
• cellular and cellular communications;
• trunk communication;
• satellite communications;
• television, etc.

Radio relay communication formed by the construction of long lines with transmitting and receiving stations and antennas.
It provides narrow-band, high-frequency data transmission at a distance between the nearest antennas within line-of-sight (approximately 50 km). The data transfer rate in such a network reaches 155 Mbit / s.

Trunking or trunked communication- (trunk, communication channel) - a communication channel organized between two stations or network nodes for transmitting information of a group of users in one radio channel (up to 50 or more subscribers) with a range of 20 to 35, 70 and 100 km.
This is a professional mobile radio communication (PMR) with automatic distribution of a limited number of free channels among a large number of mobile subscribers, which allows efficient use of frequency channels, significantly increasing the capacity of the system.

Cellular radiotelephone communication(cellular mobile communications, SPS) appeared in the late 1970s. It is also called mobile. Industrial ATP systems have been in operation in the United States since 1983, and in Russia since 1993.
The principle of the organization of the SPS is to create a network of equidistant antennas with its own radio equipment, each of which provides around itself a zone of stable radio communication (eng. "Cell" - honeycomb).

The LMS uses frequency division (FDMA), time (TDMA) and code division (CDMA) techniques.
FDMA- frequency division, TDMA- multi-access with time division of channels (used in mobile systems of GSM standard), CDMA- code division of channels (signals from other users are perceived by a subscriber of such a network as "white noise" that does not interfere with the operation of the receiving device).

Another wireless communication method is optical communication lines(laser or optical communication) using a point-to-point topology.
The method of sound transmission using a modulated light beam was proposed at the beginning of the 20th century, and the first commercial devices appeared in the mid-1980s.This communication has a high bandwidth and noise immunity, does not require permission to use the radio frequency range, etc.
Such laser systems support any data transfer protocol. The original signal is modulated by an optical laser emitter and is transmitted into the atmosphere in the form of a narrow light beam by the transmitter and the optical system of the lenses.

On the receiving side, this light beam drives the photodiode, which regenerates the modulated signal.

While propagating in the atmosphere, the laser beam is exposed to microscopic particles of dust, vapors and liquid droplets (including precipitation), temperature, etc. These effects reduce the communication range, from a few to 10-15 km. The distance also depends on the power of the transmitting devices, which ranges from tens to hundreds of mW and is due to the need to ensure stable communication. The system provides more than 99.9% communication reliability.

Satellite connection

It is formed between special ground stations for satellite communications and a satellite with antennas and transmitting and receiving equipment.

It is used for the purpose of circular information support for a large number of subscribers, as a broadband broadcasting system (television, sound broadcasting, newspaper transmission), for organizing long-distance virtual trunk communication lines, etc. set of services, incl. multimedia, radio navigation, etc.

The satellites are located in one of three orbits.
A satellite using a geostationary orbit (eng. "Geostationary Earth Orbit", GEO), is located at an altitude of 36 thousand km from the Earth, and is motionless for the observer. It covers significant areas (territories) of the planet.
Mean Earth Orbit, MEO) the habitats of satellites are characterized by an altitude of 5-15 thousand km, and in low orbits (English "Low Earth Orbit", LEO) the altitude of the satellites does not exceed 1.5 thousand km. In this case, they cover small, local areas.

Satellite communication stations are divided into: stationary, portable (transportable) and portable.

According to the types of transmitted signals, communication facilities are divided into analog and digital or discrete.
To analog include continuous signals (electrical vibrations), as a rule, smoothly changing the amplitude of their values ​​during a session of information transmission, for example, speech on a telephone channel.
When transmitting any information over data transmission networks, they are converted into digital form. For example, coded pulse trains are transmitted over the telegraph. The same happens when transferring information between computers via any telecommunications. Such signals are called discrete (digital).
When transmitting information from a computer, an eight-bit binary code is used as a code.

Methods of data transmission over communication networks

Currently, there are many ways to transfer data. But in all methods, data transmission occurs according to the principle of electrical signals. Electrical signals - this, translating into a computer language, bits , which are digital or analog signals that turn into electrical impulses.

The totality of all types of data transmission is called data link... It includes such means of data transmission as: Internet networks, fixed lines, points of reception and transmission of data. Data transmission channels are divided into two types: analog and discrete.
The main difference is that analog type is a continuous signal and discrete, in turn, is an intermittent stream of data.

To ensure the best performance, all devices work with devices in a discrete form. In a discrete form, digital codes are used that are converted into electrical signals. And to transmit discrete data using an analog signal, you need modulation discrete signal.

When using the information on the device, the reverse transformation of the signal occurs. The inverse transformation of the signal is called demodulation... Thus, there are two signal conversion processes: modulation and demodulation. In the process of modulation, information is a sinusoidal signal with a certain frequency.

To transform data, the following are used modulation methods:

1. Amplitude data modulation;
2. Frequency modulation data;
3. Phase modulation of data.

To transmit data of discrete type over a digital channel, a system is used coding... Basically, there are two types of encoding.

1. Potential coding;
2. Pulse coding.

It is worth noting that the coding methods presented above are used on high-quality channels of information transmission. And it is more reasonable to resort to modulation only when signal distortion occurs during data transmission.

In most cases, modulation is used in working with large information networks. Since most of the information is transmitted via analog line... This is due to the fact that these lines were developed long before the appearance of digital signals.

Also, each type of channel has its own way data synchronization... There are two main types of data synchronization: asynchronous and synchronous ... Synchronization is used to make accurate data transfer from source to consumer.

Synchronization requires additional hardware. For example, to carry out the synchronization process, an additional line is needed to transmit clock pulses to the communication channel. Synchronization enables continuous and clear data transmission. The data transfer process begins with the appearance of clock pulses.

The main feature of asynchronous data transmission is that no additional communication channel is required. In this type, during transmission, bytes are used that accompany the transmitted byte of information.

1. Simplex (unidirectional);
2. Half duplex;
3. Duplex (bi-directional).

Before sending information to the computer network, the sender divides the information into small blocks, which are most often called data packages... At the final point of departure, all packages are collected in a single sequential list. Then there is a process of converting all the parts into a single source material.

To work properly, the data packet must contain information such as:

1. Transferred files;
2. Links to the file, information about the file;
3. File control codes. They are a list of information about a file.

Additional operations to increase the efficiency of the communication channel.
There are three types switching computing system:

1. Channel switching;
2. Packet switching;
3. Switching messages.

Channel switching serves to create a continuous channel from serially connected lines. After this channel is formed, all information and files can be transferred at high speed.
Switching messages serves to work with mail files and servers. This operation includes a number of possibilities such as: transmission, reception, storage. A large number of messages are usually transmitted in blocks. When sending a group of messages, the block moves from one communication node to another and eventually reaches the addressee. If a block transmission error occurs (communication failure, technical problems, etc.), then the entire message block will begin to be transmitted again. Until the moment when the entire block of messages reaches the recipient, it will be impossible to make a new transfer.

The process of transferring packets of messages is completely identical to the process of transferring messages. Due to its smaller size, the packet with information quickly passes through the communication nodes. Therefore, the channel is busy only when transmitting packet data, and upon completion it is released for further downloads. This type of data transmission is a recognized standard for the Internet.

Modern communication networks have digital data transmission technology, which will make it possible to transmit any type of information over this channel. And the latest modern materials and high quality installation allow you to achieve high connection speeds.

Give a formulation of what an information and communication system is. Draw a generalized structure of the information and communication system (ICS) and describe the tasks that it should solve.

Information system is an information processing system, including associated resources such as human, technical and financial, for the provision of information and the dissemination of information.

The information system is called a complex that includes computing and communication equipment, software, linguistic tools and information resources, as well as system personnel and provides support for the dynamic information model of some part of the real world to meet the information needs of users.

Information system, IS (Information System - IS) is a system designed to implement and maintain an information model of any area of ​​human activity.

Information and communication system- a set of computing facilities and communication equipment designed for processing, storing and transmitting information.

Generalized structure of IKS:

The generalized structural diagram of the information system includes the following main elements:

Local networks;

Channels and means of communication;

Switching nodes;

Servers for storing and processing information;

Operator workplaces;

User workplaces;

Subscriber terminals.

Input and display devices for various information.

Classification of systems and access networks. Give a general description of these systems (purpose, information transfer rate, etc.).

By the way of information processing: digital, analog.

By bandwidth: narrowband, broadband, ultra-wideband.

By localization of subscribers: fixed, mobile communications.

By geographic extent: personal, local, urban, global.

By the type of information transmitted: speech, data, video.

By applied tasks: communication systems, control, monitoring.

Technologies of wired subscriber access can be divided into five main groups according to the criterion of the transmission medium and categories of users:

LAN (Local Area Network)- a group of technologies designed to provide corporate users with services of access to the resources of local area networks and using structured cable systems of categories 3, 4 and 5, coaxial cable and fiber-optic cable as a transmission medium.

DSL (Digital Subscriber Line)- a group of technologies designed to provide PSTN users with multimedia services and using the existing PSTN infrastructure as a transmission medium.

KTV (cable TV)- a group of technologies designed to provide users of CATV networks with multimedia services (by organizing a return channel) and using fiber-optic and coaxial cables as a transmission medium.

OAN (Optical Access Networks)- a group of technologies designed to provide users with broadband services, access lines to multimedia services and using fiber-optic cable as a transmission medium.

ACS (shared access networks)- a group of hybrid technologies for organizing access networks in apartment buildings; As a transmission medium, the existing infrastructure of the PSTN, radio transmission networks and power supply networks is used in the houses.

3. What organizations are solving the issues of standardization in the field of information transmission systems. What does standardization give in the field of communication systems?

Technology or solution + widespread market adoption = "standard"

Some critical mass is needed for the standard to be adopted.

Who develops the standards?

Anyone with sufficient resources (time, finances, power, authority, etc.), for example:

State - GOST-R, DSTU, etc.

International of Electronic and Electrical Engineers (IEEE), ETSI

Society of Automotive Engineers (SAE)

Qualcomm (CDMA), Motorola (iDEN, TETRA, FLEX), Intel (PC architecture), Microsoft (OS), etc.

Why are standards good?

From a market point of view:

Ensuring compatibility of both individual products and systems

Due to competition, prices are reduced

A standard solution is rarely the best solution

The main goal of standardization is to ensure the compatibility of equipment from different manufacturers within a single communication network. In the field of telecommunications, such a leading international standardization organization is the Telecommunications Standardization Sector of the International Telecommunications Union (ITU - T).

ITU - T xDSL modems are indexed "G". It is the recommendations of this series that standardize almost all transmission systems operating over cable communication lines.

The leading national organizations for the development and implementation of telecommunication standards in the world are the American National Standards Institute (ANSI) and the European Telecommunication Standards Institute (ETSI).

In addition to these three organizations, the ADSL Forum (ADSLF) and the Universal ADSL Working Group (UAWG) are actively working in the field of xDSL technology standardization.

4. Point out the main advantages (at least five) of digital communication systems in comparison with analog systems. Provide arguments for how these benefits are achieved?

The main advantages of digital systems:

1) High quality of information transmission (a digital signal can take fixed values. For example, if during analog data transmission signals of a weak level are more susceptible to interference, then in digital form the signal level is set by a code and the possibility of error with the same noise and modulation type depends only on the degree of difference between the levels of symbols that transmit the code. In digital communication, the task is only to distinguish between fixed levels. in analog communication, any deviation in reception will be an error. and a digital signal, even if it deviated from the original level, but this deviation is not large enough to " guess "(define) the character, then it will be accepted without error).

2) Stability of characteristics (unlike a digital one, an analog filter deals with an analog signal, its properties are not discrete, so the transfer function depends on the internal properties of its constituent elements.).

3) High noise immunity (the possibility of using noise-immune coding).

4) Control of the quality of information transmission (the ability to select the transmission rate depending on the quality of the channel. (The number of positions of the multi-level code) a large number of positions - more speed, but the probability of error is higher due to a decrease in the "distance" between the positions).

5) Cost-effectiveness (transmission and switching of signals in digital form allow the implementation of equipment on a single hardware platform. This allows you to dramatically reduce the complexity of manufacturing equipment, significantly reduce its cost, energy consumption and dimensions. In addition, the operation of systems is greatly simplified and their reliability increases.) ...

5. Describe departmental information and communication systems. Draw a generalized structure of the system of the Call Service Center of the "102" service of the Ministry of Internal Affairs and indicate what tasks it solves?

The ever-growing requirements for the promptness and accuracy of response in extreme situations put forward new conceptual tasks for the technical equipment of public security services.

There is a need to transfer large volumes of digital information from the scene of an emergency, to provide prompt access to databases, to identify a person by fingerprints, photo and video materials, etc. Narrowband departmental digital information transmission systems cannot fully cope with the transmission of large amounts of information, which is often necessary in extreme situations.

One of the new directions in the development of departmental telecommunication networks is the creation of call service centers (CSC), which make it possible to increase the efficiency of the emergency services of the Ministry of Internal Affairs of Ukraine.

Block diagram of VSS:

The basis of the station equipment of the service "102" is a software and hardware complex based on IP technologies (AVAYA), which provides for intelligent routing of calls arriving at the center, a distributed architecture of operator workstations and management of multimedia contacts over an IP network.

The hardware and software IP complex combines several devices at once:

fully functional telephone exchange;

LAN switch / hub;

router and firewall;

Internet access and VPN support;

application server (call-center, CRM integration).

Tasks : with the introduction of call centers, new possibilities for receiving and processing alarm messages appear: receiving and accounting for each call from the "102" service, ensuring the interaction of emergency services with the population and among themselves, registering all the necessary information on incidents, as well as immediately notifying the relevant departments and services.

6. How are the tasks of information protection in departmental information and communication systems solved? What types of threats to information in ICS do you know?

Data security at risk we will understand the potentially existing possibility of accidental or deliberate action or inaction, as a result of which data security may be compromised.

Explanation - All channels of data leakage can be divided into indirect and direct. Indirect channels do not require direct access to the technical means of the information system. The direct ones accordingly require access to the hardware and data of the information system.

AND information security- security of information and supporting infrastructure from accidental or deliberate influences of a natural or artificial nature, fraught with harm to the owners or users of information.

Data security- such a state of stored, processed and received data, in which it is impossible to accidentally or intentionally receive, change or destroy.

Data protection- a set of targeted actions and measures to ensure data security.

Thus, data protection is the process of ensuring data security, and security is the state of the data, the end result of the protection process. Data protection is carried out using methods (methods) of protection.

Method (method) of data protection- a set of techniques and operations that implement data protection functions. For example, encryption and password methods. Based on protection methods, means of protection(e.g. encryption / decryption devices, password analysis programs, burglar alarms, etc.).

Data security system(SODB) - a set of data protection tools and mechanisms. Defense mechanism- a set of security tools that function together to perform a specific task to protect information.

7. What channels of information leakage do you know and what are the main reasons for their occurrence?

Taking into account the physical nature of information transfer paths, technical leakage channels can be classified into the following groups:

Electromagnetic;

Visual-optical;

Vibroacoustic;

Material (paper, photo, magnetic media

With regard to automated systems (AS), the following leakage channels are distinguished:

Electromagnetic channel.

The cause of its occurrence is the electromagnetic field associated with the flow of electric current in the hardware components of the speaker.

The electromagnetic field can induce currents in closely spaced wire lines (pickups).

The electromagnetic channel, in turn, is divided into the following channels:

Radio channel (high-frequency radiation);

Low frequency channel;

Network channel (pickup to the power supply network);

Grounding channel (pickup on ground wires);

Linear channel (pickup on the communication line between computer systems).

Vibroacoustic channel.

It is associated with the propagation of sound waves in the air or elastic vibrations in other media that occur during the operation of the information display devices of the AU.

Visual channel.

It is connected with the ability of an intruder to visually observe the operation of the AC information display devices without entering the premises where the system components are located. In this case, photo and video cameras, etc. can be considered as a means of highlighting information.

Information channel. It is associated with access (direct and telecommunication) to the elements of the AU, to information carriers, to the most input and output information (and results), to software (including operating systems), as well as connection to communication lines.

The information channel can be divided into the following channels:

Channel of switched communication lines;

Channel of leased lines of communication;

Local area network channel;

Machine media channel;

Terminal and peripheral channel.

8. Draw the structure of the Shannon protected channel model. What assumptions and assumptions are made in this model?

In this K. Shannon's scheme, the model of a passive adversary (intruder) is used, observing only the cipher-text ( Cryptogram) (passive attack based on knowledge of cipher text), probabilistic model of cryptographic transformation - cryptosystem ( Encipherer - Decipherer) - used to protect transmitted information ( Message) from breach of confidentiality.

Assumptions that are accepted in K. Shannon's model:

- the transfer of information from the source to the receiver occurs without errors (ideal communication channel);

- the concept of perfect security is introduced provided that the probabilistic distribution of keys

(Key) on the set of keys uniformly (ideally random key);

- there is no feedback between the receiver and the source of the message;

- the source of information is described using Shannon's information theory;

- all calculations used in the process of information processing (including cryptographic transformation) are performed without errors (error-free calculation model).

9. What is the concept of the Weiner branch channel expressed?

Branch channel model - a model of a system for transmitting information over a communication channel with a branch, which includes a formal description of the method for reliable transmission of discrete messages to a legitimate recipient in the presence of a diversion channel of information leakage. This means that the legitimate receiver must be able to function normally, and the diversion channel receiver must not be able to receive reliable information.

The diversion channel model makes it possible to take into account the capabilities of the intruder both in intercepting messages and setting up interference that disrupts the operation of the main channel.

10. What is the Seven-Layer Open Systems Interconnection (OSI) Model? What are the levels of this model and what tasks are solved at each level? At what levels are the tasks of information protection solved?

The OSI Basic Reference Model is the most general description of the structure for building standards that ensure the interaction of application processes of systems working with each other.

The figure schematically depicts the OSI principle. Before being sent, the transmitted message is “descended” to the levels of the model, and at each level the service information intended for the corresponding level on the receiving side is attached to it. The receiving side sequentially "picks up" the received message. At the same time, each level, working with the information intended for it, extracts a message from its "package" and transfers it to the next level.

Physical layer (Physical Layer )

Provides the transmission of a bit stream over a physical medium. This level is related to: Characteristics of physical media of data transmission, such as bandwidth, noise immunity, characteristic impedance and others; Characteristics of electrical signals transmitting discrete information, for example, the steepness of the pulse edges, the voltage or current levels of the transmitted signal, the type of coding, the signal transmission rate. In addition, the types of connectors and the purpose of each contact are standardized here.

-Physical characteristics of interfaces and transmission media

-Presentation of beats.

-Speed ​​of data transfer.

-Bit sync.

Data Link Layer)

Converts unreliable physical layer media into a more reliable channel for delivering data to the next network layer. The bit stream coming from the physical layer is split into frames. The correctness of transmission of each frame is ensured.

-Frame synchronization.

-Physical addressing.

-Flow control.

-Correction of errors.

Network Layer

Responsible for delivering a packet from source to destination between different networks with an arbitrary topology (while the channel is responsible for delivering data between any nodes of the same network with a corresponding typical topology).

-Logical addressing.

-Routing.

Transport Layer

Responsible for delivering the entire message from process to process. He ensures that the complete message arrives at individual packet loss and in the correct order, providing both error correction and process-to-process flow control.

-Addressing processes.

-Segmentation and assembly.

-Connection management.

Session Layer

Establishes, maintains, and synchronizes communication sessions (interactions) between endpoint computers. It provides dialog control and provides synchronization tools where service marks are inserted inside long messages. They allow, in case of refusal, to return back to the last mark and continue the transfer not from the beginning, but from the point at which it broke off.

-Dialogue control.

-Synchronization.

Presentation Layer

Deals with the form of presentation of information transmitted over the network, without changing its content. Various data formats are converted to some standardized form for transmission over the network. At this level, data encryption and decryption can be performed.

-Broadcasting (encoding).

-Encryption.

-Compression.

Application Layer

It is a set of various protocols through which users (a person or a program) gain access to the network and its shared resources. P attachments to a neuter user (various programs for accessing network services) use application-level protocols. The data unit of this level is usually called message.

-Email services.

-File transfer and access.

-Remote registration (login).

-Access to WWW.

Security protocols exist at all levels of the model. For instance:

The transport layer uses the SSL TLS (Secure Sockets Layer) and TLS protocols using symmetric encryption and asymmetric cryptography to authenticate exchange keys.

At the network level, the IP-Security (IPSec) suite of protocols is currently used, which solves the issues of encryption, authentication and information security during the transport of IP packets over the network.

At the data link layer, WEP (Wired Equivalent Privacy) protocol, developed to protect information in wired communication channels, has been used for a long time in Wi-Fi wireless data transmission technologies. But more recently, the improved WPA and WPA2 protocols have been used.

Physical layer technologies such as, for example, FHSS and OFDM create significant difficulties for unauthorized access to information.

Similar information.

Basic concepts of information transfer

Information is a collection of information about the world around us. A person receives this information in the process of interacting with the outside world, studying various phenomena through books, radio, television and other means of communication. Any exchange of information presupposes one or another language, the signs of which and the rules of application to the recipient and sender of information. A collection of characters containing some information is called a message. Material carriers of messages and therefore information can be a magnetic tape or disk with records, paper with text, mechanical vibrations of a certain medium, vibrations of e-mail. current and voltage, electromagnetic waves, optical radiation, etc. All possible message carriers are called signals in a broad sense.

The most commonly used signals are e-oscillations. current and voltage, em. waves and mechanical vibrations of an elastic medium carrying messages. If information from some source is perceived directly by the human senses, then they talk about the direct transmission of the message. If the information cannot be directly perceived by the human senses, then they resort to converting the message into some signals. Thus, a signal is a certain physical process that uniquely displays information and is suitable for transmitting it over a distance. A common property of any signals is informational content, which is determined by the degree of novelty of the message. Signals that do not carry new information to the recipient are not informative for him.

A person receives the greatest information through sight and hearing. Therefore, the transmission of information by means of light and sound signals is widespread. Such methods of transferring information are called direct. However, these methods have limited capabilities due to the scattering and absorption of the energy of light and sound vibrations in space and the limited sensitivity of the human sensory organs. Electrical and electromagnetic signals are used to transmit information over long distances.

Classification of communication systems

By the physical nature of the signal, communication systems are divided into: 1) acoustic 2) electrical 3) electromagnetic 4) optical

According to the technical implementation, communication systems are divided into: 1) telephone 2) telegraph 3) radio engineering 4) television 5) satellite 6) fiber-optic 7) computer 8) facsimile

According to the direction of information flow, they can be: 1) one-way 2) two-way 3) branched network

By the type of use of communication lines, communication systems are divided into: 1) wired 2) cable 3) radio waves 4) fiber-optic

By the method of information processing, communication systems are divided into: 1) analog 2) digital

Radio communication Radio wave range and its classification

At the heart of radio communication is the use of em. waves (EMW) freely propagating in space. The speed of EMW propagation provides almost instantaneous transmission of various messages over long distances. From the entire spectrum of EMEs, EMs are used in radio communications. whose frequency waves are in the range from 3 · 10 3 to 3 * 10 12 Hz. If the inventor of radio communications Popov used radio waves with λ = 200-500m, now the optical range of the em is also used. hesitation. Officially, radio waves include em. waves with λ> 5 * 10 -5, i.e. with frequency ν<6*10 12 Гц. Под длиной волны понимают расстояние, проходимое волной за один период колебания: λ=c*T=c/f, где c=3*10 8 м/c - скорость распространения э.м. волны. Согласно международному регламенту связи радиоволны разделены на 12 диапазонов. Столбцы в таблице – 1) f, Гц 2) λ, м 3) нумерация и наименование радиодиапазонов (международный регламент) 4) наименование частот (международный регламент) 5) Внерегламентные термины. Данные таблицы: 1-ая строка:

1) 3 2) 10 8 3) 1 decameter 4) extremely low (ELF) 5) very long waves (VLF) 2nd line: 1) 30 2) 10 ** 7 3) 2 megameter 4) ultra-low (ELF) 5 ) ADD. 3rd line: 1) 300 2) 10 ** 6 3) 3 Hectometer 4) Infra-low (NPH) 5) SDV 4th line: 1) 3 * 10 ** 3 2) 10 ** 5 3) 4-meter 4) very low (VLF) 5) SDV 5th line: 1) 3 * 10 ** 4 2) 10 ** 4 3) 5 km 4) low (LF) 5) long 6th line: 1) 3 * 10 ** 5 2) 10 ** 3 3) 6 hectometer 4) average (MF) 5) average (SV) 7th row: 1) 3 * 10 ** 6 2) 10 ** 2 3) 7 Hectometer 4) high (HF) 5) short (HF) 8th line: 1) 3 * 10 ** 7 2) 10 3) 8m 4) very high (VHF) 5) VHF 9th line: 1) 3 * 10 ** 8 2) 1 3) 9 decimeter 4) ultrahigh (UHF) 5) VHF 10th line: 1) 3 * 10 ** 9 2) 10 ** - 1 3) 10 centimeter 4) ultrahigh (microwave ) 5) VHF 11th line: 1) 3 * 10 ** 10 2) 10 ** - 2 3) 11mm 4) extremely high (EHF) 5) VHF 12th line: 1) 3 * 10 ** 11 2) 10 ** - 3 3) 12 decimeter 4) hyperhigh (HHF) 5) submillimeter waves 13th line: 1) 3 * 10 ** 12 2) 10 ** - 4 3) Infrared rays 14th line: 1) 3 * 10 ** 13 2) 10 ** - 5 3) infrared rays 15th row: 1) 3 * 10 ** 14 2) 10 ** - 6 3) visible rays 16th s line: 1) 3 * 10 ** 15 2) 10 ** - 7 3) visible and ultraviolet rays 17th line: 1) 3 * 10 ** 16 2) 10 ** - 8 3) X-rays 18th line: 1) 3 * 10 ** 17 2) 10 ** - 9 3) X-rays 19th line: 1) 3 * 10 ** - 18 2) 10 ** - 10 3) X-rays.

The division of radio waves is carried out taking into account the peculiarities of receiving and the conditions of their propagation over the earth's surface. It must be remembered that there is no sharp boundary between the properties of radio waves lying in adjacent ranges. Emission and reception of EMW is performed using transmitting and receiving antennas. In the simplest case, the excitation of radio waves is carried out in the transmitting antenna when a high frequency current flows through it. i A = I m * cos (ωt-φ). Γ where I m is the current amplitude; ω = 2πf - vibration frequency; t is time; φ - early. phase.

When such a current flows in the antenna, the energy of the high-frequency oscillations is converted into the energy of the EMW excited in space. The efficiency of this conversion depends on the frequency of the supply current. The higher the frequency of the current in the antenna, the greater the radiated power. Em. Low-power optical oscillations are excited by light-emitting diodes, and those of medium and high power are excited by optical quantum generators (lasers).