entranceModern telecommunications systems. Types of telecommunication systems
Network classification
The basis of the classification of TVS is the most characteristic functional, information and structural features.
According to the degree of territorial dispersal Network elements (subscriber systems, communication sites) distinguish global (state), regional and local computing networks (DHW, RVS and LAN).
By the nature of the functions implemented Networks are divided into computational (the main functions of such networks - information processing), information (for reference data on user requests), information and computational, or mixed, in which, in a certain, non-permanent ratio, computing and information functions are performed.
By way of control TVs divide on the network with centralized (there is one or more managers on the network), decentralized (Each speakers has a network management tools) and mixed control In which the principles of centralized and decentralized management are implemented in a certain combination (for example, under centralized management, only tasks with the highest priority are solved related to the processing of large amounts of information).
On the organization of information transfer Networks are divided into networks with information breeding and information routing. In networks with information breeding, Monocanal-based under construction, the interaction of the AC is made by selecting (selection) of the data blocks addressed to them (frames): All network speakers are available all frames transmitted in the network, but a copy of the frame is removed only by the speakers with which they are intended. On networks with information routing Several routes can be used to transfer frames from the sender to the recipient. Therefore, using communication systems, the task of selecting the optimal one is solved (for example, the shortest possible shipping time of the frame) of the route.
By type of data transfer Networks with information routing are divided by network switching networks (channels), message commutation and packet switching. In operation there are networks that use mixed data transmission systems.
On topology, those. Configurations of elements in TVS, networks are divided into two classes: broadcast and consistent. Broadcast configurations and a significant part of consecutive configurations (ring, a star with an intelligent center, hierarchical) are characteristic of LAN. For global and regional networks, an arbitrary (cellular) topology is the most common. We also found the use of hierarchical configuration and "star".
IN broadcast configurations At any time, only one workstation (subscriber system) can work at the frame transfer. The remaining PC networks can receive this frame, i.e. Such configurations are characteristic of LAN with the selection of information. The main types of broadcast configuration are total tire, wood, star with passive center. The main advantages of the LAN with a common bus are simplicity of network expansion, simplicity of control methods used, no need for centralized control, minimum cable consumption. LAN with a tree type topology is a more developed version of the network with a tire topology. The tree is formed by connecting multiple tires with active repeaters or passive multiplayers ("hubs"), each branch of the tree is a segment. The refusal of one segment does not lead to the failure of the rest. In the LAN with the Topology type "Star" in the center there is a passive connector or an active repeater - there are approximately simple and reliable devices.
In consecutive configurations characteristic of network routing networks, data transmission is carried out sequentially from one PC to the neighboring, and in different parts of the network can be used different types physical transmitting medium.
Lower requirements for transmitters and receivers are presented here than in broadcast configurations. Serial configurations include: arbitrary (cellular), hierarchical, ring, chain, star with intelligent center, snowflake. In the LAN, a ring and star, as well as mixed configurations - star-ring, star-tire were the greatest distribution.
In the LAN with an annular topology, the signals are transmitted only in one direction, usually counterclockwise. Each PC has a memory to a whole frame. When you move the frame over the ring, each PC takes a frame, analyzes its address field, removes a copy of the frame if it is addressed to this PC, relays the frame. Naturally, all this slows down the data transmission in the ring, and the delay duration is determined by the PC number. Removing the frame from the ring is usually made by the sender station. In this case, the frame makes the full circle over the ring and returns to the sender station, which perceives it as a receipt - confirmation of the receipt of the frame to the addressee. The removal of the frame from the ring can be carried out and the recipient station, then the frame does not make a complete circle, and the sender station does not receive a confirmation receipt.
The annular structure provides quite wide functionality LAN with high efficiency of using monocanal, low cost, simplicity of management methods, the ability to control the operation of monocanal.
In the broadcast and most serial configurations (with the exception of the ring), each cable segment must provide signals in both directions, which is achieved: in half-duplex communication networks - using one cable for alternately in two directions; in duplex networks - with the help of two unidirectional cables; In broadband systems - the use of different carrier frequency for simultaneous signal transmission in two directions.
Global and regional networks, as well as local, in principle, may be homogeneous (homogeneous), which use software-compatible computer, and inhomogeneous (heterogeneous), including software-incompatible computers. However, given the length of the DHW and RVS and the large number of computers used in them, such networks are more often inhomogeneous.
The main function of telecommunication systems (TKS), or data transmission systems (SPD) is to organize the operational and reliable exchange of information between subscribers. The main indicator of the effectiveness of TKS - the time of delivery of information - depends on a number of factors: communication network structures, bandwidth Communication lines, ways to connect communication channels between interacting subscribers, information exchange protocols, subscriber access methods to a transmitting environment, packet routing methods.
Types of networks, lines and communication channels. The TVS uses communication networks - telephone, telegraph, television, satellite. As a link line applies: cable (conventional telephone communication lines, twisted pair, coaxial cable, fiber optic communication lines (Will, or fiber), radio relay, radio.
Among cable lines Communications The best indicators have fibers. Their main advantages: High throughput (hundreds of megabits per second), due to the use of electromagnetic waves of the optical range; insensitivity to external electromagnetic fields and the absence of own electromagnetic emissions, low laboriousness of the optical cable laying; spark, explosion and fire safety; increased resistance to aggressive media; a small specific mass (radiation ratio to the bandwidth); Wide applications (creation of collective access highways, computer communication systems with peripheral devices of local networks, in microprocessor technique, etc.).
Disadvantages of WOLS: signal transmission is carried out only in one direction; Connection to the fiber of additional computers significantly loosens the signal; High-speed modems required for light guides are still expensive; Filters connecting computers must be supplied with electrical signal transducers in light and back.
In TVS found the use of the following types of communication channels:
Simplex, When the transmitter and receiver are associated with one line of communication, in which the information is transmitted only in one directions (this is typical for television communication networks);
half duplex, When two bond nodes are also connected by a single line, in which the information is transmitted alternately in one direction, then in the opposite (this is typical for information and reference, request-response systems);
duplex When two communication nodes are connected by two lines (direct communication line and reverse), for which the information is simultaneously transmitted in opposite directions.
Switched and dedicated communication channels. The TCC distinguishes the dedicated (non-commutable) communication channels and switched to the time of transmitting information on these channels.
Using dedicated channels Communication Transmitting equipment of communication nodes is constantly connected to each other. This ensures a high degree of system readiness to transfer information, higher quality communication, support for large graphics. Due to relatively large spending on the operation of networks with dedicated communication channels, their profitability is achieved only if there is enough to fully load the channels.
For switched channels The relationships created only at the time of transmitting a fixed amount of information are characterized by high flexibility and a relatively small cost (with a small traffic volume). Disadvantages of these channels: loss of switching time (establishing a connection between subscribers), the ability to block due to the employment of individual links of the communication line, lower quality of communication, the big value with a significant amount of traffic.
Analog and digital coding of digital data. Sending data from one TKS node to another is carried out by serial transmission of all bits of the message from the source to the destination item. Physically information bits are transmitted as analog or digital electrical signals. Analog called signals Which may represent countless values \u200b\u200bof some values \u200b\u200bwithin a limited range. Digital (discrete) signals May have one or end set of values. When working with analog signals, an analog sinusoidal signal is used to transmit the encoded data, and when working with digital signals - two-level discrete signal. Analog signals are less sensitive to distortion due to attenuation in the transmitting medium, but the data encoding and decoding are simply carried out for digital signals.
Analog coding It is used in transmitting digital data on telephone (analog) communication lines dominant in regional and global TVS and initially focused on transmitting acoustic signals (speeches). Before transferring digital data from usually from computer, converted to an analog form using a demodulator modulator (modem) that provides a digital-analog interface.
Three methods of converting digital data into an analog form or three modulation methods are possible:
amplitude modulation, When only the amplitude of the carrier sinusoidal oscillations changes in accordance with the sequence of transmitted information bits: for example, when transmitting an amplitude unit of oscillations is set large, and when the carrier is transmitted, it is not available at all;
frequency modulation, When only the frequency of carrier sinusoidal oscillations changes under the action of modulating signals (transmitted information bits): for example, when transmitted zero - low;
phase modulation When only the phase of carrier sinusoidal oscillations changes in accordance with the sequence of transmitted information bits: when moving from the signal 1 to the signal 0 or vice versa, the phase varies 180 degrees ..
The transmitting modem converts (modulo) the signal carrier of sinusoidal oscillations (amplitude, frequency, or phase) so that it can carry the modulating signal, i.e. Digital data from computer or terminal. Reverse transformation (demodulation) is carried out by the receiving modem. In accordance with the realizable modulation method, modems with amplitude, frequency and phase modulation are distinguished. Frequency and amplitude modulation obtained the greatest distribution.
Digital coding Digital data is done directly by changing the levels of signals that carry information.
For example, if digital data is represented in the computer 5B signal signals for code 1 and 0.2B for code 0, then when transmitting this data to the communication line, the levels of signals are converted accordingly in + 12V and -12V. Such coding is carried out, in particular, using asynchronous RS-232-C successive adapters when transferring digital data from one computer to another to small (dozens and hundreds of meters) distances.
Synchronization of elements TKS. Synchronization is part of the communication protocol. In the communication synchronization process, a synchronous operation of the receiver hardware and the transmitter is ensured, in which the receiver selects the incoming information bits (i.e., the level of signal level in line) is strictly at the moments of arrival. Synchterignals set up the receiver on the transmitted message before it arrives support the receiver synchronization with the receiving data bits.
Depending on how to solve the synchronization problem, the synchronous transmission is distinguished by asynchronous transmission and transmission with auto-adjustment.
Synchronous transmission It is distinguished by the presence of an additional communication line (except for the main one for which data is transmitted) to transmit synchronizing pulses (C) stable frequency. Each SI adjusts the receiver. The issuance of data bits in the communication line with the transmitter and the selection of information signals receiver are made at the moments of the appearance of C. In synchronous transmission, synchronization is carried out very reliably, but this is achieved by an expensive price - the need for an additional communication line.
Asynchronous transmission Does not require an additional link. Data transmission is carried out by small fixed-length blocks (usually bypass). The receiver synchronization is achieved by the fact that an additional bit is sent before each transmitted byte - startbits, and after the transmitted byte, another additional bit is a stock. Startbit is used for synchronization. This synchronization method can only be used in low-speed data rates.
Transmission with automatic configuration, Also, not requiring an additional communication line, is used in modern high-speed data transmission systems. Synchronization is achieved by using self-synchronizing codes (SC). Encoding the transmitted data using the SC is to provide regular and frequent changes (transitions) of the signal levels in the channel. Each signal level transition from high to low or vice versa is used to adjust the receiver. The best is considered to be such an IC, which provide a signal level transition of at least once over the time interval required to receive one information bit. The more often the signal level transitions, the more reliably the receiver synchronization is carried out and the identification of received data bits is identified more confident.
The most common are the following self-synchronizing codes:
Nrz code (code without return to zero);
RZ code (code with a return to zero);
Manchester code;
Bipolar code with alternate level inversion (for example, AMI code).
Fig.Message coding schemes using self-crying codes
In fig. The coding schemes of the message 0101100 are presented using these SC.
For the characteristics and comparative assessment of the UK used the following indicators:
level (quality) synchronization;
Reliability (confidence) of recognition and allocating received information bits;
The required speed change rate in the communication line when using the SC, if the bandwidth of the line is specified;
The complexity (and, consequently, the cost) of the equipment implementing the SC.
Digital communication networks (TSSs). In recent years, digital communications networks are increasingly distributed in TVS, which use digital technology.
Causes of digital technology distribution in networks:
Digital devices used in TSSs are produced on the basis of high integration integrated circuits; Compared to analog devices, they differ in great reliability and resistance to work and, moreover, in production and operation, as a rule, cheaper;
Digital technology can be used to transmit any information on one channel (acoustic signals, television video data, fax data);
Digital methods overcome many of the limitations of transmission and storage, which are inherent in analog technologies.
In the CSS, when transferring information, an analog signal is transformed into a sequence of digital values, and when receiving the reverse transformation.
Analog signal is manifested as a constant change in the amplitude in time. For example, when talking on a telephone, which acts as a converter of acoustic signals into electrical, mechanical air fluctuations (alternation of high and low pressure) is converted to an electrical signal with the same characteristic of the envelope of amplitude. However, the direct transmission of an analog electrical signal on the telephone communication link is associated with a number of shortcomings: the signal distortion due to its nonlinearity, which increases the amplifiers, attenuation of the signal when transmitted through the medium, exposure to the effects of noise in the channel, etc.
In the TSSs these shortcomings are overcome. Here the form of an analog signal is represented as digital (binary) images, digital values \u200b\u200brepresenting the appropriate values \u200b\u200bof the envelope of the amplitude of sinusoidal oscillations at points at discrete levels. Digital signals are also affected by weakening and noise when they are passing through the channel, but only the presence or absence of a binary digital pulse should be noted at the receiving point, and not its absolute value, which is important in the case of an analog signal. Therefore, digital signals are increasingly taken, they can be fully restored before they become lower than the threshold value due to attenuation.
Converting analog signals to digital is carried out by various methods. One of them - impulse-code modulation (ICM) proposed in 1938 A.H. Rivis (USA). When using IRM, the conversion process includes three stages: mapping, quantization and coding (Fig. 12.2).
Fig. 12.2. Convert analog signal to 8-element digital code
First stage (display) Based on the theory of mapping Nyquist. The main position of this theories is: "If an analog signal is displayed at a regular range with a frequency at least twice the maximum source signal frequency in the channel, the mapping will contain information sufficient to restore the source signal." When transmitting acoustic signals (speech), their electrical signals in the telephone canal occupy frequency band from 300 to 3,300 Hz. Therefore, the TSSS received the frequency of mappings, equal to 8000 times per second. Display, each of which is called a pulse-amplitude modulation signal (EAM), is remembered, and then transformed into binary images.
At the quantization stage Each signal is given a quantized value corresponding to the nearest level of quantization. And TSSs The entire range of changes in the amplitude of the signals of the EAM is divided into 128 or 256 quantization levels. The more quantization levels, the more precisely the amplitude of the EAM signal seems to be a quantized level.
At the encoding stage Each quantized mapping is put in accordance with 7-bit (if the number of quantization levels is 128) or 8-bit (with 256-step quantization) binary code. In fig. 12.2 shows 8-element signals binary code 00101011, corresponding to a quantum signal with a level 43. When encoding 7-element codes, the data transfer rate via the channel should be 56 kbps (this is the product of the display frequency to the bit rate of the binary code), and when encoding 8-element codes - 64 kbps.
In modern CSS, another concept of converting analog signals into digital, at which they are quantized and then not the signals themselves are encoded, but only their changes, and the number of quantization levels is accepted as the same. Obviously, such a concept allows you to transform signals with greater accuracy.
Satellite communications networks. The appearance of satellite communications networks caused the same revolution in the transmission of information as the invention of the phone.
The first satellite of communication was launched in 1958, and in 1965 the first commercial communication satellite was launched (both in the USA). These satellites were passive, later the satellites began to install amplifiers and transceivers.
To manage data transfer between satellite and ground RTS, the following methods are used:
1. Normal multiplexing - With frequency separation and temporary separation. In the first case, the entire frequency spectrum of the radio channel is divided into subchannels that are distributed between users to transmit any graph.
Costs of this method: with irregular gear, subchannels are used irrational; A significant part of the initial bandwidth of the channel is used as a separation strip to prevent the undesirable influence of subchannels to each other. In the second case, the entire time spectrum is divided between users, which are managed by temporary quanta (slots) at their discretion (slots). It is also possible to idle the channel due to the irregular use.
2. Normal discipline "Primary / secondary" with using methods and interview / selection. As a primary body that sells such a discipline of satellite communications, one of the ground RTS is more often, and less often - satellite. The survey cycle and choice takes considerable time, especially if there is a large number of speakers. Therefore, the reaction time to the user request may be unacceptable for it.
3. Discipline of control type "Primary / Secondary" without survey, with the implementation of the multiple access quantization method (TDMA). Here the slots are prescribed primary RTS, called reference. Taking requests from other RTS, the reference station, depending on the character of the schedule and the busy to the channel, satisfies these requests by appointing the stations of specific slots to transfer frames. This method is widely used in commercial satellite networks.
4. Equifing disciplines of management. It is characteristic that all users have an equal right to access the channel and rivalry occurs between them. In the early 1970s, N. Abramson from the University of Hawaii proposed a method of effective rivalry for the channel between non-coordinated users called the Aloha system. There are several variants of this system: a system that implements the random access method (random ALOHA); Equiform priority solid system (Slota Aloha), etc.
TO the main advantages Communication satellite networks include the following:
Big bandwidth due to the work of satellites in a wide range of gigahertz frequencies. Satellite can support several thousand speech communication channels. For example, one of the currently used commercial satellites has 10 transponders, each of which can transmit 48 Mbps;
Ensuring communication between stations located at very long distances, and the possibility of servicing subscribers in the most hard-to-reach points;
The independence of the cost of transmitting information from the distance between the interacting subscribers (the cost depends on the duration of the transfer or the volume of the transmitted schedule);
The ability to build a network without physically implemented switching devices due to broadcasting of satellite communications. This feature is associated with a significant economic effect that can be obtained compared to the use of a conventional non-subsidized network based on numerous physical communication lines and communication devices.
disadvantages Communication satellite networks:
The need for funds and time to ensure the confidentiality of data transfer, to prevent the possibility of intercepting data by "other people's" stations;
The presence of a delay of radio signal reception by the ground station due to long distances between the satellite and the RTS. This can cause problems associated with the implementation of channel protocols, as well as a response time;
The possibility of mutual distortion of radio signals from ground stations operating in neighboring frequencies;
Signal exposure to land - satellite and satellite-overall influence of various atmospheric phenomena.
To solve problems with frequency distribution in the ranges of 6/4 and 14/12 GHz and the placement of satellites in orbit, there is an active collaboration of many countries using satellite communications techniques.
Telecommunications and network technologies are currently the driving force that ensures the development of world civilization. There is practically no area of \u200b\u200bproduction and public relations, which would not use the possibilities of modern information technologies On the basis of telecommunications.
Telecommunication - data transmission over long distances.
Telecommunications Tools are a set of technical, software and organizational tools for transmitting data over long distances.
Telecommunication networks are:
1 telephone networks for the transfer of telephone data (voice);
2 radio networks to transmit audio data;
3 television networks for video data transmission;
4 digital (computer) networks or data networks (SPD) for transmission of digital (computer) data.
Data in digital telecommunication networks are formed as messages having a certain structure and considered as a whole.
Data (messages) can be:
1 continuous;
2 discrete.
Continuous data can be represented as a continuous time function, such as speech, sound, video. Discrete data consists of signs (characters).
Transmission of data in the telecommunications network is carried out using their physical representation - signals.
The following types of signals are used in computer networks for data transmission:
1 electric (electric current);
2 optical (light);
3 electromagnetic (electromagnetic radiation field - radio wave.
Cable lines of communication are used to transmit electrical and optical signals:
1 Electrical (ELS)
2 Fiber Optic (Vols)
The transmission of electromagnetic signals is carried out through radiolines (radar) and satellite communication lines (SLS).
Signals, as well as data, can be:
1 continuous;
2 discrete.
At the same time, continuous and discrete data can be transmitted in the telecommunications network or in the form of continuous, or in the form of discrete signals.
The conversion process (method of representation) of the data in the view required for transmission over the communication line and allowing, in some cases, to detect and correct errors that occur due to interference when they are transmitted is called coding. An example of coding is the presentation of data in the form of binary characters. Depending on the parameters of the transmission environment and requirements, various coding methods can be used.
The communication line is a physical environment for which information signals are transmitted formed by special technical means relating to linear equipment (transmitters, receivers, amplifiers, and the like). Communication line is often considered as a set of physical chains and technical means that have common linear structures, their maintenance devices and the same distribution environment. The signal transmitted in the communication line is called linear (from the word word).
Communication lines can be divided into 2 classes:
1. Cable (electrical and fiber optic communication lines):
2. Wireless (radar).
Based on communication lines are built by channel channels.
The communication channel is a combination of one or more communication lines and channel-forming equipment that ensures data transmission between interacting subscribers in the form of physical signalscorresponding to the type of communication line.
The communication channel may consist of several consecutive communication lines, forming a composite channel. At the same time, several communication channels can be formed in one link, providing simultaneous data transmission between several couples of subscribers.
Telecommunication network (TVS) is a network of sharing and distributed processing of information, formed by many interrelated subscriber systems and communications.
Means of transfer and processing information are focused on the collective use of public resources of hardware, information, software.
Telecommunication is a remote data transfer based on computer networks and modern technical communications.
Subscriber system (AC) is a set of computers, software, peripheral equipment, communication tools with a switching subnet of the computing network that perform application processes.
Communication subnet, or telecommunications system (TKS), represents a set of physical information transmission, hardware and software tools that ensure the interaction of the AC.
With the advent of TVS managed to solve two very important problems:
provision in the principle of unlimited access to computer computer, regardless of their territorial movement of large arrays of information over long distances. In TVS, all compounds of different subscriber systems are associated with each other automatically.
Each computer network is adapted as to work in offline mode Under the control of its operating system (OS) and as an integral network.
Twex allows you to solve such qualitatively new tasks, such as:
* ensuring distributed data processing and parallel processing by many computers;
* The ability to create a distributed database (RBD) placed in the memory of various computers;
* The ability to exchange large arrays of information between computers remote from each other for considerable distances;
* Collective use of expensive resources: application software products (PPP), databases (database), knowledge bases (BZ), storage devices (memory) printing devices (PU), network operating systems (OS);
* providing a large list of services, including such as email (EP), teleconference, electronic ads (EDO), distance learning, organization of paperless document management, electronic signature, making management decisions;
* Improving the efficiency of the use of computing equipment and computer science (SVTU) due to more intensive and uniform loads, as well as the reliability of user requests;
* The possibility of operational redistribution of computing power between network users depending on the change of their needs, as well as the redundancy of these capacities and data means in case of failure of individual network elements;
* reduction of costs for the acquisition and operation of the SVTU (due to collective use);
* Ensuring work on improving technical, software and information funds.
Telecommunication computing networks are the highest form of multi-milk associations. The main differences between computer networks from the multi-milk computing complex are as follows:
* dimension, that is, a large number of computers (from a dozen to several hundred), located at a distance from each other from tens of meters to several hundred and even thousand kilometers; EU function separation, i.e., data processing and system management, analysis and storage of information are distributed among various network computer;
* The need to solve the message routing task in the network, that is, a message from one computer to another on the network can be transmitted via various routes depending on the priority and state of communication channels connecting computers with each other.
On a functional basis, all multiple computer network systems can be divided into subscriber, switching and main (Host) systems.
The subscriber system is a computer focused on a computer network and providing users with access to its computing resources.
Switching systems are nodes of switching data network and provide the organization of compound data channels between system subscribers. The control elements of switching nodes are used by teleworking processors or special switching (network) processors.
The main (Host) system or network servers differ in a large variety.
The server is called a special computer that performs the main service functions: network management, collection, processing, storage and provision of information to computer network subscribers.
Depending on the territorial dispersal of subscriber systems, computer (computing) networks are divided into three main classes:
* Global networks (WAN - WIDE AREA NETWORK);
* Regional networks (MAN - Metropolitan Area Network);
* Local networks (LAN - Local Area Network).
The main function of telecommunication systems (TKS), or territorial communication networks (TSS), in the functioning of telecommunication networks (TVS) is to organize the operational and reliable exchange of information between subscribers, as well as in reducing data transfer costs.
The main indicator of the efficiency of TKS is the delivery time of information. It depends on a number of factors: communication network structures, communication lines bandwidth, communication channels connecting between interacting subscribers, information exchange protocols, subscriber access methods to the transmitting medium, package routing methods, etc.
The most common telecommunications systems, or territorial communication networks it is: X.25, Frame Relay (FR), IP, ISDN, SDN, ATM. Especially important advantage of one or another network technology It is its ability to most fully use the connection channel bandwidth and adapt to the quality of the channel. The technology of global Internet networks includes X.25, Frame Relay, SMDS, ATM networks. All these networks other than IP use packet routing based on virtual channels between the end nodes of the network.
In modern telecommunication systems, information is transmitted using electrical signals (current or voltage), radio signals or light signals - all these physical processes are oscillations of electromagnetic field of different frequencies and nature
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Branch of the Federal State Budgetary Educational Institution of Higher Professional Education
Tyumen State University
In Tobolsk
Tobolsky Pedagogical Institute. DI. Mendeleev
Department of Physics, Mathematics, Informatics and Teaching Methods
Course work
Telecommunication systems
student 5 courses for training
natural science faculty
directions "Vocational training
(Electronics, Radio Engineering and Communication) »
Sorochchenko Alexandra Nikolayevich
Lecturer: Candidate of Pedagogical Sciences,
associate Professor Kutumova A. A.
Tobolsk 2016.
Introduction
1. Characteristics and classification of information networks
2. Multi-level information network architecture
3. Varieties of communication channels
4. Organization of access to information networks
4.1 Structure of territorial networks
4.2 Main types of access
4.2.1 Telecommunication Technology Service
4.2.2 Email
4.2.3 File exchange
4.2.4 Teleconference and "Classified Boards"
4.2.5 Access to distributed databases
4.2.6 WWW Information System
Conclusion
Bibliography
Introduction
XXI century without exaggeration can be called an age of information technology. The concept of information technology includes many aspects. One of the most important parts of this area is directly transmitting information through information networks.
Telecommunications technologies are the principles of organizing modern analog and digital communication systems and communication networks, including computer and Internet networks.
Tools of telecommunications are a set of technical devices, algorithms and software, allowing to transmit and take on, information data, multimedia information With the help of electrical and electromagnetic oscillations through cable, fiber-optic and radiotechnical channels in various wave ranges. These are devices for converting information, its coding and decoding, modulation and demodulation, these are modern computer techologies Processing.
1. Characteristics and classification of information networks
Modern telecommunication technologies are based on the use of information networks.
Communication network is a system consisting of objects that perform the functions, transformation, storage and consumption of the product, called items (nodes) of the network and transmission lines (links, communications, compounds), transmitting the product between items.
A distinctive feature of the communication network is long distances between items compared with the geometric dimensions of the spaces occupied by paragraphs.
Information network - a communication network in which the product of generation, processing, storage and use is information.
Computing network - information network, which includes computing equipment. Computing network components can be computer and peripheral devices that are sources and data receivers transmitted over the network. These components make up the terminal data equipment (ADD or DTE - Data Terminal Equipment). As an OOD, computer, printers, plotters and other computing, measuring and executive equipment automatic and automated systems. Actually, data transfer occurs with the help of media and means that are combined under the name of the data transfer environment.
Preparation of data transmitted or obtained by the ODA on the data environment is carried out by a functional block called the data channel ending equipment (ACD or DCE - DATA Circuit-Terminating Equipment). ACD can be structurally separate or built into the ODO block. The OOD and ACD together are a data station, which is often called the network node. An example of AKD can serve as a modem.
Computing networks are classified for a number of signs.
Depending on the distances between the connected nodes, the computing networks distinguish:
Territorial, encompassing significant geographical space; Among the territorial networks, networks are regional and global, which have, respectively, regional or global scale; Regional networks are sometimes called MAN networks (Metropolitan Area Network), and a general English-language name for territorial networks - WAN (Wide Area Network);
Local (LAN)? covering limited territory (usually within the remoteness of stations by no more than several dozen or hundreds of meters from each other, less often by 1 ... 2 km); Local networks denote LAN (Local Area Network);
Corporate (enterprise scale)? The set of interconnected LANs covering the territory on which one enterprise or institution in one or several closely located buildings is placed. Local and corporate computing networks are the main type of computing networks used in automated design systems (CAD).
Especially allocate a single global Internet network (WORD WIDE WIDE WIDE (WWW) information service in it is translated into Russian as a worldwide web); This is a network of networks with its technology. In the Internet, there is a concept of intranet (Intranet) - corporate networks within the Internet.
There are integrated networks, unintegrated networks and subnets. The integrated computing network (INTERSET) is an interconnected set of many computing networks that are called subnets in the interset.
In automated systems of large subnet enterprises include computing means of individual design units. Interseti is needed to combine such subnets, as well as to combine the technical means of automated design and production systems into a single integrated automation system (CIM - Computer Integrated Manufacturing).
Typically, the interset is adapted for various types of communication: telephony, email, video transmission, digital data, etc., and in this case they are called integral service networks. The development of internets is to develop means of interfacing of heterogeneous subnets and standards for building subnets initially adapted to pairing. Subnets in internets are combined in accordance with the selected topology using the interaction blocks.
2. Multi-level information network architecture
In general, two problems need to be solved for computer networks:
Convey the data on the purpose in the correct form and timely;
Entering data to the user must be recognizable and have a proper form for their proper use.
The first problem is related to routing tasks and is provided by network protocols (low-level protocols).
The second problem is caused by using different types of computers, with different codes and language syntax. This part of the problem is solved by introducing high-level protocols.
Thus, the complete architecture focused on the terminal user includes both protocols.
The developed reference model of interaction of open systems (BB) supports the concept in which each level provides services to a higher level and based on the underlying level and uses its services. Each level performs a specific data transfer function. Although they should work in a strict sequence, but each of the levels allow several options. Consider the reference model. It consists of 7 levels and is a multi-level architecture, which is described by standard protocols and procedures.
Three lower levels provide network services. Protocols implementing these levels should be provided in each network node.
Four top levels provide services to the terminal users themselves and thus associated with them, and not with the network.
Physical level. In this part of the model, the physical, mechanical and electrical characteristics of the lines of communication constituting the LAN (cables, connectors, fiber optic lines, etc.) are determined.
We can assume that this level is responsible for hardware. Although the functions of other levels can be implemented in the respective chips, but they still relate to software. The functions of the physical layer are to ensure that the symbols entering the physical transmission medium at one end of the channel have achieved another end. When using this subordinate symbol transportation service, the channel Protocol task is to ensure reliable (error-free) transmission of data blocks. Such blocks are often called cycles, or frames. The procedure usually requires: synchronization on the first character in the frame, recognition of the end of the frame, the detection of erroneous characters, if any, and correcting such characters in any way (is usually done by requesting a frame for re-transmitting a frame in which one or more erroneous characters are detected ).
Level channel. The level of data transmission channel and the physical layer under it provide an error-free transmission channel between two nodes on the network. At this level, the rules for using the physical level of network nodes are determined. Electrical presentation of data in the LAN (data bits, data coding methods and markers) are recognized on this and only at this level. Here are detected (recognized) and errors are corrected by repeated data requirements.
Network level. Function network level It is to establish a route for transmitting data over the network or if necessary through several networks from the transfer node to the destination node. This level also provides for the flow or overload control to prevent overflow of network resources (drives in nodes and transmission channels), which can lead to termination of work. When performing these functions, the network level is used on the network level - the data transmission channel that provides an error-free receipt by the network data block entered into the channel at the opposite end.
The main task of the lower levels is sent along the route data blocks from the source to the recipient by delivering them in a timely manner in the desired end.
Then the task of the upper levels is the actual data delivery in the correct form and recognizable. These upper levels do not know about the existence of the network. They provide only the service requested from them.
Transport level. Provides reliable, consistent data exchange between two terminal users. For this purpose, a network level service is used at the transport level. It also controls the stream to ensure the correct reception of data blocks. Due to the difference in terminal devices, data in the system can be transmitted with different speeds, therefore, if flow control does not act, slower systems can be filled with high-speed. When in the processing process is more than one package, the transport level controls the priority of the message component. If a duplicate of the previously received message arrives, then this level recognizes this and ignores the message.
Level session. The functions of this level consist in coordinating the relationship between two applications operating at different workstations. It also provides services to a higher level view. This happens in the form of a well-structured dialogue. These functions include the creation of a session, managing the transfer and reception of message packets during the session and the termination of the session. This level, if necessary, also manages negotiations to ensure proper data exchange. The dialogue between the user of the session service (i.e., the parties to the presentation level and the higher level) may consist of a normal or accelerated data exchange. It can be duplex, i.e. simultaneous bilateral transmission, when each party has the ability to independently transfer, or half duplex, i.e. With simultaneous transmission only one way. In the latter case, special labels are used to transmit control on one side to another. The session level provides synchronization service to overcome any errors detected. With this service, the synchronization label must be inserted into the data flow by users of the session service. If an error is detected, then the session connection must be returned to a specific state, users must return to the set point of the dialog stream, reset part of the transmitted data and then restore the transmission starting from this point. Computer Teleconference Communication Network
Level representation. Manages and converts the syntax of data blocks that ended end users. Such a situation may occur in non-uniform PC (IBM PC, Macintosh, Dec, Next, Burrogh), which must be exchanged data. Assignment - Converting data syntactic blocks.
Applied level. Applied level protocols give the appropriate semantics or meaning of exchange information. This level is border between PP and the processes of the OSI model. A message intended for transmission through a computer network falls into the OSI model at this point, passes through the level 1 (physical), forwarded to another PC, and passes from level 1 in reverse order until the PC is on the other PC through its application level. Thus, the application level ensures mutual understanding of two application programs on different computers.
3. Varieties of communication channels
Data transfer medium is a set of data transmission lines and interaction units (i.e. network equipment that is not included in the data station) intended for data transfer between data stations. Data transfer media can be public or dedicated to a specific user.
Data transfer line - means used in information networks to propagate signals in the desired direction.
Channel (communication channel) - means of one-sided data transfer. An example of a channel may be a frequency band allocated to one transmitter during radio communications.
Data Transmission Channel - Data Bilateral Means, including Data Channel End and Data Data Line. By nature, the physical data transmission medium (PD) distinguish data transmission channels on optical communication lines, wired (copper) communication lines and wireless.
Wired lines: Wired telecommunication lines are divided into cable, air and fiber optic.
Fax communications: Fax (or photothelevphny) Communication is an electrical way to transfer graphic information - still image of text or tables, drawings, schemes, graphs, photos, etc. It is carried out using facsimile apparatuses: telefax and telecommunication channels (mainly telephone).
Fiber optic communication lines: Mostly telephone lines and television cables are used as wired communication lines. The most developed is telephone wired communication. But it has serious disadvantages: susceptibility to interference, attenuation of signals when transmitting them to considerable distances and low bandwidth. All these flaws are deprived of fiber-optic lines - a type of communication in which the information is transmitted according to optical dielectric waveguides ("optical fiber").
Optical fiber is considered the most advanced medium for transmitting large information flows over long distances. It is made of quartz, the basis of which is a silicon dioxide - widespread and inexpensive material, unlike copper. Optical fiber is very compact and easy, it has a diameter of only about 100 microns.
Fiber optic lines are distinguished from traditional wired lines:
Very high speed transfer rate (for a distance of more than 100 km without repeaters);
The security of the transmitted information from unauthorized access;
High resistance to electromagnetic interference;
Resistance to aggressive media;
The ability to transmit one fiber at the same time up to 10 million telephone conversations and one million video signals;
Flexibility fibers;
Small sizes and weight;
Spark, explosion and fire safety;
Easy installation and styling;
Low cost;
High durability of optical fibers - up to 25 years.
Currently, the exchange of information between continents is carried out mainly through the underwater fiber cables, and not through satellite communications. At the same time, the main driving force of the development of underwater fiber optic communication lines is the Internet.
Wireless communication systems: Wireless communication systems are carried out by radio channels.
In the 1930s. The meter was mastered, and in the 40s - decimeter and centimeter waves propagating straightforwardly, non-ribous of the earth's surface (i.e., within the limits of direct visibility), which limits the direct link on these waves to 40-50 km in flat locality, And in mountainous areas - a few hundred kilometers. Since the width of the frequency ranges corresponding to these wavelengths is from 30 MHz to 30 GHz - 1000 times higher than the width of all frequency ranges below 30 MHz (waves longer than 10 m), they can transmit huge information flows and multichannel communications. At the same time, the limited range of propagation and the possibility of obtaining an acute orientation with an antenna simple design can use the same wavelengths in a variety of points without mutual interference. The transmission to significant distances is achieved by using multiple relay in the lines of the radio relay communication or with the help of communication satellites located at high height (about 40 thousand km) above the ground (see "Space Communication"). Allowing tens of thousands of telephone conversations at large distances at the same time and transmit tens of television programs, radio relay and satellite communications in their capabilities are much more efficient than the usual long-distance radio communication on meter waves.
Radio relay communication lines: Radio relay communication was originally used to organize multichannel telephone lines in which messages were transmitted using an analog electrical signal. The first such line 200 km with 5 telephone channels appeared in the United States in 1935. She joined New York and Philadelphia.
Over the past decades, the need to transmit data - the information presented in digital video- led to the creation of digital transmission systems. Digital radio relay data transmission systems appeared, capable of communicating digital information.
Satellite communications and navigation: Space or satellite bond is essentially a type of radio relay communication and is characterized by the fact that its repeaters are not on the surface of the earth, but on satellites in outer space.
In the 1980s, the development of personal satellite communications began. At the beginning of the XXI century, the number of its subscribers is several million people, and after another 10 years - much more. There will be a combination of satellite and ground communication systems into a single global personal communication system. Any subscriber will be achieved by setting its phone number, regardless of its location. This is the advantage of satellite communications compared to cellular (it is discussed below in this chapter), since it has no binding to concrete terrain. Indeed, at the beginning of the XXI century, the coverage area of \u200b\u200bthe cellular connection is only 15% of the earth's surface. Therefore, the demand for personal mobile communications in many regions of the world can only be provided with satellite communication systems. In addition to speech (radiotelephone) communications, they allow you to determine the location (coordinates) of consumers.
The satellite phone is directly connected to the satellite located in an near-earth orbit. From the satellite, the signal goes to the ground station, from where is transmitted to the normal telephone network. The number of satellites needed for a stable connection at any point of the planet depends on the radius of the orbit of a particular satellite system.
Currently there is the first global communication system "Iridium". It allows the client to stay in touch, wherever he would have, and use the same phone number with the same phone number.
The system consists of 66 low-bit satellites located at a distance of 780 km from the surface of the Earth. It provides a reception and transmission of a signal from a mobile phone located at any point of the globe. The signal received on the satellite is transmitted over the chain to the next satellite until it reaches the ground station to the called subscriber. This ensures high quality signal.
The main lack of personal satellite communications is its relative high cost compared to cellular. In addition, high power transmitters are embedded in satellite phones. Therefore, they are considered unsafe for the health of users.
The most reliable satellite phones operate in the network of Inmarsat, created more than 20 years ago. Inmarsat Satellite Phones are a suitcase with a folding lid size with the first portable computers. The satellite telephone cap is also an antenna that needs to be rotated towards the satellite (the signal level is displayed on the phone display). Basically, such phones are used on ships, trains or heavy vehicles. Each time you need to call or answer someone's call, you will need to install a satellite phone on some flat surface, open the lid and twist it, defining the direction of the maximum signal. There are such satellite phones over $ 2,500 and weigh from 2.2 kg. A minute of conversation on such a satellite telephone costs 2.5 US dollars and above.
Padzhing communication: A paging communications is a radio telephone connection, sending messages dictated by the subscriber-sender and receiving them on the radio channel by the recipient's subscriber using a radio lager with a radio device with a liquid crystal display, on which the adopted alphanumeric texts are displayed. A pager is a one-sided connection tool: you can only receive messages on it, but you cannot send messages from it.
The history of pajing as a personal radio program began since the mid-1950s in England. The first such device was developed in 1956. The number of subscribers could be no more than 57. When the subscriber received a tone, it had to bring the device to the ear and listen to the message that the dispatcher passed. The users of the first network in England are doctors. Networks that existed at the time were local and served as specific services. The largest of them were airport services. Some similar networks exist today. Wide distribution of pajing began in the late 1970s in the United States.
Since then, pajing systems have received a fairly widespread in the cities of Europe and the United States. At the same time, Pejing came to Russia.
The first pagers were simple frequency-modulated signal receivers. They contained several configured contours that track the characteristic sequence of low-frequency signals (tones). Upon receipt of these tones, the device served sound signals. Therefore, such pagers are called tonal.
The transition to digital systems was inevitable. Tonal coding was not suitable for transferring alphanumeric messages.
Mobile cellular communication: Communication is called mobile if the source of information or its recipient (or both) is moved in space. Radio communication from the moment of occurrence was mobile. The first radio stations were intended for communication with mobile objects - ships. After all, one of the first devices of radio communications A.S. Popova was installed on the battleship "Admiral Apraksin". And precisely thanks to the radio communications with him, it was possible in the winter of 1899/1900 to save this ship, lured in the ice in the Baltic Sea.
For many years, for the implementation of individual radio communications between two subscribers, a separate radio channel operating at one frequency was required. Simultaneous radio communication on many channels could be provided by highlighting each channel a certain frequency strip. But frequencies are needed for broadcasting, television, radar, radio navigation, military needs. Therefore, the number of radio channels was very limited. It was used for military purposes, government communications. So, in cars used by members of the Politburo of the CPSU Central Committee, mobile phones were installed. They installed in police cars and radiotaxi. In order for the mobile communication to become a mass, it took a new idea of \u200b\u200bits organization. This idea in 1947 expressed D. Ring, an employee of the American company Bell Laboratories. It consisted in separation of space into small sections - cells (or cells) with a radius of 1-5 kilometers and in the radio compartment within the same cell on the connection between the cells. This made it possible to use in different hundreds of the same frequencies. In the center of each cell was proposed to locate the Basic - receiving-transmitter - radio station to provide radio communication within the cell with all subscribers. Each subscriber has its own micro-stations - "Mobile Phone" - a combination of a telephone, transceiver and mini-computer. Subscribers bind to each other through base stations connected to each other and with the city telephone network.
Each cell must be serviced by a basic radio transmitter with a limited range and fixed frequency. This makes it possible to reuse the same frequency in other cells. During the conversation, the cellular radiotelephone is connected to the base station with a radio channel, which is transmitted by a telephone conversation. The sizes of the cells are determined by the maximum range of the radio telephone apparatus with the base station. This maximum range is a cell radius.
The idea of \u200b\u200ba mobile cellular connection is that, without having come out of the zone of a single base station, the mobile phone falls into the zone of action any neighboring right up to the outer border of the entire network zone.
For this, an antennas-repeater systems are created, overlapping their "honeycomb" - region of the surface of the Earth. In order for the connection to be reliable, the distance between two adjacent antennas should be less than the radius of their action. In cities it is about 500 meters, and in the countryside - 2-3 km. Mobile phone can receive signals immediately from several repeater antennas, but it is always configured to the most powerful signal.
The idea of \u200b\u200bmobile cellular connection was also to apply computer control over the telephone signal from the subscriber when it moves from one cellular cell to another. It is computer control that has allowed the mobile phone to switch the mobile phone from one intermediate transmitter to another for a thousandth. Everything happens so quickly that the subscriber simply does not notice it.
The central part of the mobile system is computers. They find a subscriber who is in any of the cells and connect it to the telephone network. When the Subscriber moves from one cell to another, they transmit subscriber from one base station to another, and also connect the subscriber from the "foreign" cellular network to "its" when it turns out to be roaming (which is carried out in English means "travel" or "vagrancy").
The principles of modern mobile communications were the achievement of the late 40s. However, in those days, the computer technique was still at such a level that its commercial use in telephone systems was difficult. Therefore, the practical application of cellular communications has become possible only after the invention of microprocessors and integral semiconductor chips.
An important advantage of mobile cellular communication is the ability to use it outside the general zone of its operator - roaming. For this, various operators agree on the mutual opportunity to use their zones for users. The subscriber, leaving the overall zone of his operator, automatically switches to the zones of other operators, even when moving from one country to another, for example, from Russia to Germany or France. Either, being in Russia, the user can call on cellular communications to any country. Thus, cellular communication provides the user with the opportunity to contact the phone with any country where it is not.
Leading manufacturers of cell phones are focused on a single European standard - GSM. That is why their equipment is technically perfect, but relatively inexpensive. After all, they can afford to produce huge parties of phones that are selling.
A convenient addition to the cell phone has become the SMS short message system (Short Message Service). It is used to transfer short messages directly to the modern digital phone. gSM systems Without use of additional equipment, only with a numeric keypad and a cell phone screen display. Acceptance of SMS messages is also made on a digital display, which is equipped with any cell phone. SMS can be used in cases where the usual telephone conversation is not the most convenient type of communication (for example, in a noisy crowded train). You can send your phone number to an SMS. Due to the low cost SMS is an alternative to telephone conversation. The maximum value of the SMS message is 160 characters. You can send it in several ways: a call to a special service, as well as using your GSM phone with the send function, using the Internet. SMS system can provide additional services: send a currency exchange rate to your GSM phone, weather forecast, etc. Essentially, the GSM phone with the SMS system is an alternative to the pager.
But the SMS system is not the last word in cellular communication. In the most modern cell phones (for example, Nokia), the Chat function appeared (in the Russian version - "dialogue"). With it, you can communicate in real time with other owners of cell phones, as is done on the Internet. Essentially, this is a new type of exchange of SMS messages. To do this, you make a message to your interlocutor and send it. The text of your message appears on the displays of both cell phones - your and your interlocutor. Then he answers you and his message is displayed on displays. So you lead the electronic dialogue. But if your interlocutor's cell phone does not support this feature, it will receive ordinary SMS messages.
There are also cell phones with support for high-speed Internet access via GPRS (General Packet Radio Service) - a packet data standard for radio channels, in which the phone does not need to be "dial": the device constantly supports the connection, sends and receives data packets. Cell phone devices with a built-in digital camera are available.
According to the research company Informal Telecoms & Media (ITM), the number of mobile users in the world in 2007 is 3.3 billion people.
Finally, the most complex and expensive devices are smartphones and communicators combining cell phone and pocket computer.
Internet telephony: One of the most modern and cost-effective links has become Internet telephony. Its birthday can be considered on February 15, 1995, when Vocaltec released its first Soft-Phone - a program that serves to exchange voice over the IP network. Then Microsoft released the first version of NetMeeting in October 1996. And already in 1997, they became quite ordinary connections through the Internet of two ordinary telephone subscribers located in completely different places of the planet.
Why is the usual long-distance and international telephone right? This is explained by the fact that during the conversation you take a whole channel of communication, and not only when you say or listen to the interlocutor, but when you are silent or distracted from the conversation. This happens when the voice is transmitted by a conventional analog way.
With the digital method, information cannot be transmitted continuously, but separate "packages". Then one channel of communication can be sent simultaneously from many subscribers. This principle of batching information is similar to the transportation of multiple letters with different addresses in one postcard. After all, do not "chase" the same postal car for the transport of each letter separately! Such a temporary "packet seal" allows much more efficient to use existing communication channels, "compress" them. At one end of the communication channel, the information is divided into packages, each of which, like a letter, is supplied with its individual address. On the communication channel, the packets of many subscribers are transmitted to "intelligence". At the other end of the communication channel, packages with one address are again combined and sent to their addressee. Such a batch principle is widely used on the Internet.
Through a personal computer, you can internet Send and receive letters, texts, documents, drawings, photos. But Internet Telephony (IP Telephony) is also working - a telephone conversation of two users of personal computers.
To do this, both users must have microphones connected to a computer, and headphones or sound columns, and their computers are sound cards (preferably for bilateral communication). In this case, the computer converts an analog "voice" signal (electrical sound analog) in a digital (pulse combination and pauses), which is then transmitted by Internet networks.
At the other end of the line, the computer of your interlocutor produces an inverse conversion (digital signal to analog), and the voice is played as in the usual phone. Internet telephony is much cheaper than long-distance and international conversations on the usual telephone. After all, when IP-telephony needs to pay only for the use of the Internet.
Having a personal computer, sound cardIt is compatible with her microphone and headphones (or sound speakers), you can call any subscriber with the help of Internet telephony with the usual city telephone. In this conversation, you will also pay only for the use of the Internet.
Before using the Internet telephony subscriber, the owner of a personal computer needs to establish a special program on it.
To use the services of Internet telephony, it is not necessary to have a personal computer. To do this, it is enough to have a regular phone with a tonal set. In this case, each dialed digit goes into line not in the form of a different amount of electrical pulses, as when the disk is rotated, and in the form of variable currents of different frequency. Such a tone mode is in most modern telephones.
To use Internet telephony using a telephone, you need to buy a credit card, and call a powerful central computer server to the number indicated on the card. Then the server of the server by voice (on the choice in Russian or English) reports commands: to type the serial number and key card using the country code, dial the country code and the number of your future interlocutor.
Next, the server turns an analog signal into digital, sends it to another city, a country or another continent in the server that is located there, which again converts the digital signal into analog and sends it to the desired subscriber. The interlocutors talk both along the usual telephone, however, sometimes a small (for a split second) is a response delay. Recall once again that, to save communication channels, voice information is transmitted by "packages" of digital data: your voice information is dismembered by segments, packets, called Internet protocols (IP).
TCP / IP (Transmission Control Protocol / Internet Protocol) is the main Internet protocol, or data transfer format on the Internet. At the same time, the IP provides the promotion of a packet over the network, and TCR guarantees the reliability of its delivery. They provide a breakdown of transmitted data to packages, transmitting each of them to the recipient along an arbitrary route, and then - the assembly is correct and without loss.
Not only your packages are sequentially transmitted via the communication channel, but also packages of several other subscribers. At the other end of the communication line, all your packages are united again, and your interlocutor hears all your speech. In order not to feel the delay in the conversation, this process should not exceed 0.3 seconds. This is how compression of information is made, thanks to which Internet telephony is several times cheaper than conventional long-distance and even more international negotiations.
In 2003, the Skype program was created (www.skype.com), completely free and not requiring practically no knowledge for its installation or for use. It allows you to talk with the video to the interlocutors sitting at their computers at different ends of the world. In order for the interlocutors to see each other, each of them must be equipped with a webcam.
Here is a long way in the development of communication facilities, humanity has done: from signal bones and drums to a cellular mobile phone, which allows you to almost instantly to contact two people at any points of our planet.
4. Organization of access to information networks
4.1 Structureterritorialnetworks
The global Internet network is the largest and only one of its kind network in the world. Among global networks, it occupies a unique position. It is more correct to consider it as a combination of many networks that retain an independent value.
Indeed, the Internet has neither a clearly pronounced owner or a national affiliation. Any network may have a connection with the Internet and, therefore, to be considered as part of it if the TCP / IP received for Internet protocols are used in it or there are converters in TCP / IP protocols. Almost all National and Regional Networks have access to the Internet.
A typical territorial (national) network has a hierarchical structure.
Upper level - federal nodes related to the trunk communication channels. The main channels are physically organized on the Volt or on satellite communication channels.
Middle level - regional nodes forming regional networks. They are associated with federal nodes and, possibly, among themselves allocated highly or medium-speed channels, such as channels T1, E1, B-ISDN or radio relay lines.
Low level - local nodes (access servers) associated with regional nodes, mainly switching or dedicated telephone communication channels, although the trend towards the transition to high and medium-speed channels is noticeable.
Local networks of small and medium enterprises are connected to local nodes, as well as computers of individual users. Corporate networks Large enterprises are connected to regional nodes dedicated highly or medium-speed channels.
4.2 Maintenanceviewsaccess
4.2. 1 Telecommunication technology service
The main services provided by telecommunication technologies are:
Email;
File transfer;
Teleconference;
Reference services (bulletin boards);
Video conferencing;
Access to information resources (information bases) network servers;
Mobile cellular communication;
Computer telephony.
The specifics of telecommunications are manifested primarily in application protocols. Among them are the most famous protocols associated with the Internet, and ISO-IP protocols (ISO 8473) relating to the seven-level model of open systems. The Internet application protocols include the following:
Telnet - Terminal emulation protocol, or, in other words, the remote control protocol is used to connect the client to the server when they are placed on different computers, the user through its terminal has access to a server computer;
FTP is a file sharing protocol (a remote node mode is implemented), the client may request and receive files from the server whose address is specified in the request;
HTTP (Hypertext Transmission Protocol) - a protocol for communication of WWW servers and WWW clients;
NFS is a network file system that provides access to the files of all unix-machines of the local network, i.e. File systems nodes look like a single file system;
SMTP, IMAP, POP3 - Email Protocols.
These protocols are implemented using appropriate software. For Telnet, FTP, SMTP on the server side highlighted fixed numbers of protocol ports.
4.2. 2 Email
Email (e-mail) - messaging tools for electronic communications (in OFF-LINE mode). You can send text messages and archived files. The latter may contain data (for example, texts of programs, graphic data) in various formats.
4.2. 3 File exchange
File exchange - access to files distributed across different computers. On the Internet network at the application level uses the FTP protocol. Access is possible in OFF-LINE and ON-LINE modes.
In Off-Line mode, a request to the FTP server is sent, the server generates and sends an answer to the request. In ON-LINE mode, an interactive view of the FTP server directories, selection and transfer the necessary files. An FTP client is needed on the user's computer.
4.2. 4 Teleconference and "Bulletin Boards"
Teleconference - access to information allocated for group use in separate conferences (Newsgroups). Global and local teleconferences are possible. Enable materials in Newsgroups, mailing notifications about new materials received, orders are fulfilled - the main functions of teleconferencing software. E-mail and on-line modes are possible.
SAMI large system Teleconferences - Usenet. In usenet information is organized hierarchically. Messages are sent or avalanche, or through mailing lists.
Teleconference can be with a moderator or without it. Example: the work of the team of authors over the book on the mailing lists.
There are also means of audio conferencing (voice teleconferences). Call, connection, conversation occur for the user as in the usual phone, but the connection goes through the Internet.
The electronic "BBS Bulletin Board" board is a technology that is close to the teleconference to the teleconference allows centrally and promptly send messages for many users.
BBS software combines email, teleconferencing and file sharing. Examples of programs in which there are BBS, - Lotus Notes, World-Group.
4.2. 5 Access to distributed databases
In the "Client / Server" systems, the request must be formed in the user's computer, and the data search organization, their processing and the formation of an answer to the request belongs to the EUM server.
In this case, the desired information can be distributed across different servers. The Internet has special database servers called WAIS (WIDE AREA INFORMATION SERVER), which may contain a set of databases running various DBMSs.
Typical work scenario with WAIS server:
Selection of the desired database;
Forming a query consisting of keywords;
Sending a query to a WAIS server;
Getting from the server headers appropriate keywords;
Select the desired title and its parcel to the server;
Getting text document.
Unfortunately, WAIS is currently not developing, therefore it uses little, although indexing and searching for indexes in large arrays of unstructured information, which was one of the main functions of WAIS, is the task is relevant.
4.2. 6 WWW Information System
WWW (World Wide Web - World Wide Web) - An Hypertext Information System of the Internet. Other her brief name - Web. This more modern system provides users with great opportunities.
First, it is a hypertext - structured text with cross-references in it reflecting the semantic links of text parts. Links are highlighted by color and / or underline. The link selection calls on the screen associated with the word-link text or drawing. You can search for the desired material by keywords.
Secondly, facilitated performance and receipt graphic images. Information available on Web technology is stored in Web servers.
The server has a program that constantly tracking the arrival to a specific port (usually this is port 80) requests from customers. The server satisfies requests by sending the client the contents of the requested Web pages or the results of the execution of the requested procedures. WWW client programs are called browsers.
There are text and graphic browsers. In browsers there are leaf commands, transition to the previous or subsequent document, printing, transition to hypertext link, etc.
To prepare the materials and their inclusion in the WWW base, a special HTML language has been developed and its software editors implementing its software editors, such as Internet Assistant, as part of the Word or Site Edit editor, preparation of documents is also provided as part of most browsers.
To communicate Web servers and customers, an HTTP protocol operating on TCP / IP is developed. The Web server receives a request from the browser, finds the file that corresponds to the request and transmits it to browser.
Conclusion
Intranet and the Internet technology continue to develop. New protocols are being developed; Older are revised. NSF significantly complicated the system by entering its main network, several regional networks and hundreds of university networks.
Other groups also continue to join the Internet. The most significant change occurred not because of the attachment of additional networks, but due to additional traffic.
Physicists, chemists, and astronomers work and exchange data volumes large than researchers in computer sciences that make up most of the Early Internet Traffic users.
These new scientists led to a significant increase in the loading of the Internet, when they began to use it, and the loading was constantly increased as they were increasingly used it.
To adapt to the growth of traffic, the bandwidth of the NSFNet main network was doubled by having leaving that the current bandwidth is approximately 28 times greater than the initial; Another increase is planned to bring this coefficient to 30.
At the moment it is difficult to predict when the need to further increase bandwidth will disappear. The growth of the needs for network exchange was not unexpected. The computer industry has gained great pleasure from the permanent requirements for increasing computing power and more memory for data for long years.
Users just started to understand how to use networks. In the future, we can expect a constant increase in interaction needs.
Therefore, technologies of interaction with greater bandwidth will be required to adapt to this growth.
The expansion of the Internet lies in difficulties arising from the fact that several autonomous groups are parts of the combined Internet. Source projects for many subsystems assumed centralized management. It took a lot of effort to finalize these projects to work with decentralized management.
So for further development Information networks will require higher-speed communication technologies.
Bibliography
1. Lazarev V.G. Intelligent digital networks: Reference. / Ed. Academician N.A. Kuznetsova. - M.: Finance and Statistics, 1996.
2. New information transfer technologies. - URL: http://kiberfix.ucoz.ru. - (date of handling: 12/18/2015).
3. Pushlin A.V., Yanushko V.V. Information networks and telecommunications. - Taganrog: Publishing TRTRU, 2005. 128 p.
4. Semenov Yu.A. Internet protocols and resources. - M.: Radio and Communication, 1996.
5. Telecommunication systems. - URL: http://otherreferats.allbest.ru/radio. - (date of handling: 12/18/2015).
6. Finain V.I. Information exchanges in complex systems: Tutorial. - Taganrog: Publishing House PRTR, 2001.
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Tire, tree, ring topology of telecommunication networks. Custom, Transport and Delivery Agents; Firewall and transport protocols. Synchronous and asynchronous data transmission. Application of the hub, switch, router.
test, added 11/10/2012
Purpose of the switch, its tasks, functions, specifications. Advantages and disadvantages in comparison with the router. Basics of the technology of the organization of cable systems of the network and the architecture of local compute networks. The reference model OSI.
practice Report, added 06/14/2010
Overview of data transfer networks. Means and methods used to design networks. Development of a draft network of high-speed subscriber access based on fiber-optic communication technologies using automated design tools.
thesis, added 04/06/2015
Modern telecommunications systems; Main standards of mobile GSM, CDMA 200, UMTS. The use of cellular network operators of new services and 3rd generation technologies. Characteristics the newest standards Wireless Access: Wi-Fi, Bluetooth.
tutorial, added 08.11.2011
Study of trends in the development of telecommunication and network information technologies. Distributed networks on fiber. Interactive commercial information services. Internet, email, electronic bulletin boards, video conferencing.
abstract, added 11/28/2010
Classification of telecommunication networks. Channel diagrams based on the telephone network. Varieties of noncommuted networks. The appearance of global networks. Problems of a distributed enterprise. The role and types of global networks. Variant of combining local networks.
presentation, added 10/20/2014
The concept of data networks, their types and classification. Optical fiber and fiber-coaxial networks. Using a twisted pair and subscriber telephone wires for data transmission. Satellite access systems. Personal cellular networks.
2 Two Root Computer Networks Computational and Telecommunication Technologies Evolution of Telecommunications Evolution of Computer Engineering Evolution of Computer Networks Evolution of Computer Networks at the junction of computing equipment and telecommunication technologies
3 Telecommunication systems 1. Basic information about telecommunication systems The main function of telecommunication systems (TKS), or territorial communication networks (TSS), is to organize the operational and reliable exchange of information between subscribers, as well as in reducing data transmission costs. The concept of "territorial" means that the communication network is distributed in a significant area. It is created in the interests of the whole state, institutions, enterprises or firms that have branches in the area, region or throughout the country. The main indicator of the effectiveness of the functioning of telecommunication systems the delivery time of information. It depends on a number of factors: communication network structures, communication lines bandwidth, communication channels connecting between interacting subscribers, information exchange protocols, subscriber access methods to the transmitting medium, package routing methods, etc.
4 Telecommunication systems 1. Basic information about telecommunication systems The characteristic features of territorial communication networks: the diality of communication channels from the wire channels of the tone frequency (telephone) to fiber optic and satellite; The limitations of the number of communication channels between remote subscribers, for which it is necessary to ensure the exchange of data, telephone communication, video communication, the exchange of facsimile messages; The presence of such a critical resource as the bandwidth of communication channels. Consequently, the territorial communication network (TCC) is a geographically distributed network that combines the functions of traditional data transmission networks (SPD), telephone networks and intended for transmitting traffic of various nature, with different probabilistic-time characteristics.
5 Telecommunication systems 1. Basic information about telecommunication systems Types of networks, lines and communication channels. Communication networks are used in TVS telephone, telegraph, television, satellite. As communication lines, it is used: cable (telephone lines, twisted steam, coaxial cable, fiber optic lines), radio relay and radio. Among cable lines of communication, the best indicators have fiber optic (i.e. fiber optic lines). Their main advantages: high bandwidth (hundreds of megabits per second); insensitivity to external fields and the absence of their own emissions; Low laboriousness of optical cable laying; Spark, explosion and fire safety; increased resistance to aggressive media; small specific mass; Different applications. Disadvantages: signal transmission is carried out only in one direction; The connection of additional computers significantly loosens the signal; high-speed road modems required for light guides; Filters connecting computers must be supplied with electrical signal transducers in light and back.
6 Telecommunication systems 1. Basic information about telecommunication systems In telecommunication systems, the following types of communication channels are found: Simplex, when the transmitter and receiver are associated with one communication channel, according to which the information is transmitted only in one direction (this is characteristic of TV networks); half-duplex when two nodes of communication are also connected by one channel by which the information is transmitted alternately in one direction, then in the opposite (this is characteristic of information and reference, request-response systems); Duplex, when two nodes are connected by two channels (direct and reverse), for which the information is simultaneously transmitted in opposite directions. Duplex channels are used in systems with decisive and informational feedback.
7 Telecommunication systems 1. Basic information about telecommunication systems Switable and dedicated communication channels. In networks (TKS, TCC) distinguish between the selected (non-commutable) communication channels and switched channels for the time of transmission on them. When using selected communication channels, the transceiver equipment of the communication nodes is constantly connected to each other. This ensures a high degree of system readiness to transmit information, higher quality communication, support for large traffic. Due to relatively large spending on the operation of networks with dedicated communication channels, their profitability is achieved only if there is enough to fully load the channels. For switched communication channels created only at the time of transfer of fixed information, high flexibility and relatively small cost are characterized. Disadvantages of these channels: loss of switching time (establishing a connection between subscribers), the ability to block due to the employment of individual links of the communication line, lower quality of communication, the big value with a significant amount of traffic.
8 Telecommunication systems 1. Basic information about telecommunication systems Analog and digital coding of digital data. Sending data from one network node to another is carried out by sequential transmission of all bits of the message from the source to the destination item. Physically information bits are transmitted as analog or digital electrical signals. Analog is called signals that can represent countless values \u200b\u200bof some values \u200b\u200bwithin a limited range. Digital (discrete) signals can have one value or a finite set of values. When working with analog signals, an analog-carrier signal of the sinusoidal form is used to transmit the encoded data, and when working with digital signals of a two and multi-level discrete signal. Analog signals are less sensitive to distortion due to attenuation in the transmitting medium, but the coding and decoding of data is simpler for digital signals.
10 Telecommunication systems 1. Basic information about telecommunication systems Synchronization of network elements This is part of the communication protocol. During the synchronization process, a synchronous operation of the receiver hardware and the transmitter is ensured, in which the receiver selects the incoming information bits strictly at the moments of their arrival. There are synchronous transmission, asynchronous transmission and transmission with auto-tuning. Synchronous transmission is distinguished by the presence of an additional communication line (except for the main) for transmitting synchronizing pulses (C) stable frequency. The issuance of the data bits by the transmitter and the signal sample receiver are made at the moments of the appearance of C. It is reliable, but an additional line is needed. Asynchronous transmission does not require an additional line. Transmission is carried out by small fixed blocks, and start-bit is used to synchronize. In the transmission with auto-adjustment, synchronization is achieved through the use of self-synchronizing codes (SC). Encoding the transmitted data using the SC is to provide regular and frequent changes in the signal levels in the channel. Each transition is used to adjust the receiver.
11 Satellite communications networks (CSS). Space devices (ka) of communication are launched to the height of the CM and are located on a geostationary orbit, the plane of which is parallel to the equator plane. Three such ka provide coverage of almost the entire surface of the Earth. The interaction between subscribers of the CSS is carried out by chain: AC-sender of the information\u003e Transferring ground station \u003e\u003e Satellite\u003e Reception ground station\u003e AS recipient. One ground station serves a group of nearby speakers. The following methods are used to manage data transfer between satellite and ground stations. 1. Normal multiplexing with frequency and temporary separation. 2. Normal discipline "Primary / secondary" using or without using methods and polling tools. 3. Equal-standing control disciplines with equal access to the channel in conjunction for the channel. Telecommunication systems 1. Basic information about telecommunication systems Transferring Ground Station \u003e\u003e Satellite\u003e Reception Ground Station\u003e As-Recipient. One ground station serves a group of nearby speakers. The following methods are used to manage data transfer between satellite and ground stations. 1. Normal multiplexing with frequency and temporary separation. 2. Normal discipline "Primary / secondary" using or without using methods and polling tools. 3. Equal-standing control disciplines with equal access to the channel in conjunction for the channel. Telecommunication systems 1. Basic information about telecommunication systems "\u003e 
12 Telecommunication Systems 1. Basic information about telecommunication systems The main advantages of communication satellite networks: a large bandwidth due to the work of satellites in a wide range of Gigahertz new frequencies. Satellite can support several thousand speech communication channels; Ensuring communication between stations located at very long distances, and the possibility of servicing subscribers in the most hard-to-reach points; independence of the cost of transferring information from distance between subscribers; The ability to build a network without physically implemented switching devices. Disadvantages of communication satellite networks: the need for funds and time to ensure the confidentiality of data transfer; the presence of a delay of radio signal reception by the ground station due to long distances between the satellite and the communication station; the possibility of mutual distortion of radio signals from ground stations operating in neighboring frequencies; Signal exposure to various atmospheric phenomena.
13 Telecommunication systems 2. Commuting in networks Switching is a vital element of communication of subscriber systems (AC) with each other and with control centers, processing and storing information in networks. Networks network are connected to some switching equipment, thus avoiding the need to create special communication lines. A commutable transport network is a network in which the end items are established between two (or more) end items on request. An example of such a network is a switched telephone network. There are the following switching methods: circuit switching (channels); Commuting with intermediate storage, sharing messages and switching packets.
15 Telecommunication systems 2. Communication in networks Switching channels (chains). When switching channels (circuits) between binding end items throughout the time interval, the connection is made in real time, and the bits are transmitted with constant speed over the channel with a constant bandwidth. The advantages of the circuit switching method: chain switching technology; work in dialogue and real time; ensuring transparency regardless of the number of compounds between the AU; Wide scope. Disadvantages of the chain switching method: for a long time to establish a through channel of communication due to the possible expectation of the release of individual sections; The need to re-transmit a call signal due to the employment of the switching device in the signal chain; the absence of the possibility of selecting information transfer rates; the possibility of channel monopolization by one source of information; the increase in the functions and capabilities of the network is limited; Uniformity of communication channels is not ensured.
17 Telecommunication systems 2. Communication in networks Switching messages - Early data transfer method (applied in email, news). Technology - "Remember and Send." The message entirely retains its integrity in the process of passing from one node to another until the destination, and the transit node cannot begin the further transmission of the message part if it is still accepted. The advantages of the method: no need to establish a channel; Formation of a route from sections with different bandwidth; implementation of query service systems taking into account their priorities; the possibility of smoothing peak loads by memorizing streams; Lack of service requests. Disadvantages: the need to implement serious memory capacity requirements in communication nodes for receiving large messages; insufficient possibilities for implementing the dialogue and real-time operation during data transfer; Channels are less efficient compared to other methods.
18 Telecommunication systems 2. Communication in networks Switching packets combines the benefits of switching channels and switching messages. Its main objectives: ensuring the full availability of the network and acceptable reaction time to the request for all users, smoothing the asymmetric flows between users, ensuring the multiplexing of the capabilities of the communication channels and the ports of the network computers, the dispersal of the critical network components. Data is divided into short fixed length packets. Each package is supplied with protocol information: the start and end of the package, the sender and recipient addresses, the packet number in the message, information to monitor the accuracy of the transmitted data. Independent packages of one message can be transmitted simultaneously on various routes as part of the datagram. Packages are delivered to the destination, where the initial message is formed from them. In contrast to switching messages, packet switch allows: to increase the number of connected stations; it is easier to overcome difficulties with connecting additional communication lines; carry out alternative routing, which creates elevated user amenities; Significantly reduce the time to transfer data, improve the bandwidth and efficiency of networking resources. Now batch switch is basic to transfer data.
20 Telecommunication Systems 2. Communication in Networks Conclusion Section The analysis of the considered switching technologies allows us to conclude the possibility of developing a combined switching method based on the use of messages, packages and providing more efficient management of heterogeneous traffic.
21 Telecommunication systems 3. Routing packages in networks. Essence, goals and routing methods. The routing task is to choose a route to transmit from the sender to the recipient. This is, first of all, on networks with arbitrary (cellular) topology, in which the packet switching is implemented. However, in modern networks with mixed topology (star-ring, star-tire, multi-transparent), the task of selecting a route for transmitting frames is actually solved, which uses appropriate means, such as routers. In virtual networks, the routing task when sending a message dissected on packages is solved by a single time when a virtual connection is established between the sender and the recipient. In datagram networks, where data is transmitted in the form of datagram, routing is performed for each individual package. The choice of routes in the communication nodes of telecommunication networks is made in accordance with the implemented algorithm (method) of routing.
24 Telecommunication Systems 3. Package Routing In Networks Routing Algorithm This is a rule of assignment of the output link for transmitting a packet based on the information contained in the packet header (sender and recipient address), information about the loading of this node (package queues) and networks in general . The main routing objectives are to provide: the minimum delay in the package when it is transferred from the sender to the recipient; maximum network bandwidth; maximum protection of the package from threats for the information contained in it; reliability package delivery addressee; The minimum cost of transferring a package address. The following routing methods distinguish: - centralized routing; - distributed (decentralized) routing; - Mixed routing
25 Telecommunication systems 3. Package routing in networks 1. Central routing is implemented in centralized control networks. The selection of the route for each package is carried out in the network management center, and communication network nodes only perceive and implement the results of solving the routing task. Such routing management is vulnerable to the denounces of the central node and does not differ in high flexibility. 2. Distributed (decentralized) routing is performed in networks with decentralized control. Routing control functions are distributed between network nodes, which have appropriate means for this. Distributed routing is more complicated by centralized, but differs in greater flexibility. 3. Mixed routing is characterized by the fact that it is implemented in a certain ratio of the principles of centralized and distributed routing. The routing task in networks is solved provided that the shortest route providing the packet transmission in the minimum time depends on the topology of the network, bandwidth and load on the communication line.
26 Telecommunication systems 3. Routing packets in networks Routing methods - simple, fixed and adaptive. The difference between them to the degree of accounting of changes in the topology and load of the network when the route is selected. 1. Simple routing is characterized by the fact that when choosing a route, neither the network topology change is not taken into account nor the change in its load. It does not provide directional packet transfer and has low efficiency. Its advantages are simplicity of implementation and ensuring the sustainable network operation when it fails to separate its elements. Practical use Received: Random Routing - One Random Free Direction is selected for transferring the package. The package "wanders" over the network and with the ultimate probability reaches the addressee. Avalanche routing provides for the transfer of a package from a node over all free output lines. There is a phenomenon of "reproduction" of the package. The main advantage of this method is guaranteed to ensure the optimal delivery time of the package address. The method can be used in unloaded networks when the requirements for minimizing the time and reliability of package delivery are quite high.
27 Telecommunication systems 3. Routing packets in networks 2. Fixed routing - when choosing a route, it takes into account the change in the network topology and the change in its load is not taken into account. For each destination node, the transfer direction is selected by the table of the shortest routes. The lack of adaptation to the load change leads to network packet delays. There are unintended and multiple fixed routing. The first is based on the only way to transfer packets between the two subscribers, which is associated with instability to failures and overloads, and the second based on several possible paths between the two subscribers from which the most preferred path is selected. Fixed routing is applied in networks with little changing topology and established packet streams. 3. Adaptive routing is characterized by the fact that the decision on the direction of transmission of packets is carried out taking into account the changes both topology and the network load. There are several adaptive routing modifications that differ in which information is used when choosing a route. Local, distributed, centralized and hybrid adaptive routing (is clear from the title) disappeared.
28 Telecommunication systems 4. Protection against errors in networks When transmitting data, one error per thousand transmitted signals can be seriously reflected in the quality of information. There are many methods for ensuring the reliability of information transfer (protection against errors), characterized: according to the funds used, on time spent on their use, to the degree of ensuring the reliability of information transfer. The practical embodiment of methods consists of two parts of the program and hardware. The ratio between them may be the most different, up to almost the absence of one of the parts. The main causes of errors when transferring in networks: Failures to some part of the network equipment or the occurrence of unfavorable events on the network. The data transfer system is ready for this and eliminates them using the plan provided by the plan; Interference caused by external sources and atmospheric phenomena.
29 Telecommunication systems 4. Protection against errors in networks among numerous methods Sewing from errors There are three groups of methods: group methods, noise-resistant coding and error protection methods in feedback transmission systems. From group methods, a large application of a majority method and the method of transmitting information blocks with a quantitative characteristic of the block were obtained. The essence of the majority method is that each message is transmitted several times (more often three times). Messages are remembered and compared, the correct chosen coincidence "2 out of 3". Another group method, which also does not require the transcoding of information, implies data transmission by blocks with a quantitative characteristic of the block (the number of units or zeros, the checksum of characters, etc.) at the receiving point, this characteristic is re-calculated and compared with the communication channel transmitted via the communication channel. If the characteristics coincide, it is believed that the block does not contain errors. Otherwise, a signal comes to the transmitting side with the requirement of re-transmission of the unit. In modern TVS, this method was widely distributed.
30 Telecommunication systems 4. Protection against errors in networks noise-resistant (excessive) encoding involves the development and use of corrective (noise-resistant) codes. Feedback transmission systems are divided: on systems with crucial feedback and information feedback system. A feature of systems with crucial feedback is that the decision on the need to re-transmit information receives the receiver. A noise-resistant encoding is applied by which the received information is checked at the receiving station. When an error is detected on the transmitting side over the feedback channel, the rewriting signal is sent to which the information is transmitted again. In information feedback systems, information transmission is carried out without interference coding. Receiver, accepting information on the direct channel and remembering, transfers it back, where it is compared. While matching the transmitter sends a confirmation signal, otherwise repeatedly transmitted all information, i.e. Transmission decision takes a transmitter.
Telecommunication -communication at a distance (lat.)
Communication(the process of information is a necessary condition for the existence of living organisms, environmental communities and human society. Public development is accompanied by the development of telecommunication technologies. Especially intensively telecommunication technologies are developing for several recent decades.
TelecommunicationMaguts can be defined as communication issues at a distance and can be explained in various ways. Figure 8.2 shows one of the possible representations of various sections of telecommunications.
Figure 8.2. Telecommunications: Forms and types
Telecommunications are divided into two types: unidirectional and bidirectional. Unidirectional, such as massive broadcasting and television, suggest the transfer of information in one direction - from the center to subscribers. Bidirectional support dialogue between two subscribers.
Telecommunications use mechanical electrical resources, because historically telecommunications developed from mechanical to electrical form, using more and more complex electrical systems. This is the reason why many traditional operators in telecommunications type of national mail, telegraph and telephone companies use both forms. The share of mechanical telecommunications such as ordinary mail and press (newspapers distribution) is expected to decrease, while the proportion of electrical, especially bidirectional, will increase and will become the main in the future. Already in our time, the corporation and press are interested, first of all, electrical telecommunications (telecommunication) as an opportunity for profitable business.
At the edges of Figure 8.2. Telecommunication services are shown, first mechanical: press (newspaper shipment), mail; Then electrical: Telegraph, Telex (Subscriber Telegraph), Telephone, Radio, Television, Computer Networks, Dedicated Networks, Cable TV and Mobile Phone.
In approximately such a manner, historically telecommunications developed.
Telecommunication system - A combination of technical objects, organizational measures and subjects that implement the processes consisting of: processes of connection, transmission processes and access processes.
To exchange information, telecommunication systems use a natural or artificial environment. Telecommunication systems together with the medium that is used for transmission form telecommunication networks. The most important telecommunications networks are (Fig. 8.2.): Postal Communications; public telephone network (TFOP); Mobile telephone networks; telegraph network; Internet is a global network of computer network interaction; Wired broadcasting network; Network cable television; network television and radio broadcasts; departmental communications networks that provide communication services by public service authorities, air and sea movement management systems, large manufacturing complexes; Global networks of salvation and security.
The telecommunications systems listed above are usually closely interacting with each other and use common resources to implement communication. To organize such cooperation in each state and globally, there are special bodies that regulate the procedure for using shared resources; define general rules of interaction (protocols) of telecommunication systems; Develop promising telecommunication technologies.
To implement communication at a distance, telecommunication systems are used: switching systems; transmission systems; Access systems and transmission channels.