Communication lines and data transmission channels. Communication channels Ways of transmitting information to communication channels

On fig. 1 adopted the same designation: X, Y, Z, W- signals, alerts ; f- Pereshkoda; LZ- tie line; ІІ, ПІ- Dzherelo that receiver of information; P- Conversion (coding, modulation, decoding, demodulation).

Identify different types of channels, which can be classified according to different signs:

1.For the type of line connection: conduct; cable; fiber optics;

power lines; too few radio channels.

2. For the nature of the signals: uninterrupted; discrete; discrete-uninterrupted (signals at the input of the system are discrete, and at the outputs without interruption, and in the same way).

3. For transitions: channels without pereshkod; with transitions.

Link channels are characterized by:

1. Capacity for the channel vynachaetsya as a dobutok to the hour of vikoristannya channel T to, frequency spectrum widths that are transmitted by the channel F to and dynamic range D to. , which characterizes the capacity of the channel to transmit different equal signals

V to = T to F to D to.(1)

Umova uzgodzhennya signal z channel:

Vc£ Vk ; Tc£ T k ; Fc£ F k ; Vc£ Vk ; Dc£ D k .

2.Transmission speed - The average amount of information that is transmitted in one hour.

3.

4. Overworld - ensure the reliability of information ( R= 0¸1).

One of the tasks of the theory of information is the designation of the reliability of the transfer rate of information and the capacity of the communication channel, the parameters of the channel, the characteristics of the signals and the transition.

Channel zv'yazku figuratively por_vnyuvati z roads. Vuzki roads - low throughput, but cheap. Wide roads - good throughput, but expensive. The building permit is determined by the largest city.

The speed of transmission of data to a significant world lies in the transmission medium in the channels of the link, like different types of line links.

Conducted:

1. Conducting- a couple is twisted (which is often used electromagnetic viprominuvannya other gerels). Transmission speed up to 1 Mb/s. Vikoristovuetsya in telephone networks and data transfers.

2. Coaxial cable. Transmission speed 10-100 Mb/s - vicorous at local lines, cable TV tower only.

3. Optical fiber. Transmission speed 1 Gb/s.

In the middle of 1–3 phases in dB, it is linear to lie in the middle, tobto. tension falls after the exhibitor. That is why it is necessary to put regenerators (pіdsilyuvachi) through the song.

Radiolines:

1.Radio channel. Transmission speed 100-400 Kb/s. Vikoristovuyu radio frequency up to 1000 MHz. Up to 30 MHz with the help of the ionosphere, it is possible to expand the electromagnetic waves between the line of sight. Ale cey range is more noisy (for example, amateur radio communication). Vіd 30 to 1000 MHz - the ionosphere of the gap and the line of sight is required. Antennas are installed on the heights (regenerators are installed on both sides). Vikoristovuyutsya in the radio and television.

2.Microwave lines. Transmission speed up to 1 Gb/s. Vykoristovuyut radio frequencies over 1000 MHz. For this reason, direct visibility of the parabolic antennas is necessary. Between regenerators 10-200 km. Vykorivuyutsya for phone call, TV broadcasts and data transmissions.

3. satellite call. Microwave frequencies are vibrated, and the satellite serves as a regenerator (moreover, with a lot of stations). Characteristics of your own, scho in micro-fluted lines.

2. Bandwidth for a discrete channel

Discrete Channel discrete signals.

Throughput of the building for the communication channel - the maximum theoretically available speed of transmission for the mind, that the cost is selected from a given value. Transmission speed - The average amount of information that is transmitted in one hour. Significantly, it is important to change the speed of transmission of information and the bandwidth of a discrete communication channel.

When transmitting a skin symbol to the middle channel, the link will pass a lot of information that is assigned to the formula

I (Y, X) = I (X, Y) = H (X) - H (X / Y) = H (Y) - H (Y / X), (2)

de: I (Y, X) - mutual information, so the amount of information that should be Y shodo X;H(X)- Entropy dzherela povіdomlen; H (X/Y)- Intelligent entropy, which signifies the loss of information per character, due to the obviousness of the shift and creation.

With overstretched support X T trivality T, what is shaping up n elementary symbols, the average amount of information with improved symmetry of the mutual amount of information is good:

I(Y T, X T) = H (X T) - H (X T / Y T) = H (Y T) - H (Y T / X T) = n. (4)

The speed of transmission to lie in the statistical powers of the dzherel, the method of coding and the power of the channel.

Bandwidth of a discrete channel

The maximum possible value, tobto. maximum functionality joking on all impersonal functions rozpodіlu imovіrnosti p (x).

The capacity of the building is to be deposited according to the technical characteristics of the channel (the speed of the equipment, the type of modulation, the level of the transition and the creation of the thin). Units for the bandwidth of the channel є: , , , .

2.1 Discrete link channel without hopping

If you switch to the channel during the day, then the input and output signals to the channel are unambiguous, functional fallow.

Whose mental entropy is equal to zero, and insane entropy is equal to that. the average amount of information in the received symbol and the value of the transmitted signal

I(X, Y) = H(X) = H(Y); H(X/Y) = 0.

Yakscho X T– number of characters per hour T, then the speed of transmission for a discrete channel is a call without a transfer code

de V = 1/ - Average speed of transmission of one character.

Bandwidth for discrete communication without reshuffle

Because If the maximum entropy is valid for equal moving symbols, then the bandwidth for equal distribution of subdivision and statistical independence of symbols that are transmitted is:

Shannon's first theorem for a channel: Yakshcho potik іnformatsії, viroblyuvany dzherelom, dosit close to the throughput building channel zv'yazku, tobto.

then you can always know such a coding method, which will ensure the transmission of all the alarms of the dzherel, moreover, the speed of the transmission will be even closer to the throughput of the channel.

The theorem does not support food, which is the order of coding.

example 1. Dzherelo viroblyaє 3 reminders with emotions:

p 1 = 0,1; p 2 = 0.2 tap 3 = 0,7.

Notifications of the independents are passed on to equals double code (m = 2 ) with character trivality, which is 1 ms long. Designate the speed of transmission of information by the channel zv'yazyka without reshkod.

Solution: Entropy dzherela dorіvnyuє

[bit/s].

For transmission 3, two ranks are required to be confirmed by an equal code, moreover, the trivality of the code combination is more expensive 2t.

Medium swedishness signal transmission

V =1/2 t = 500 .

Transmission speed

C = vH = 500 × 1.16 = 580 [bit/s].

2.2 Discrete link-to-passcode channel

We can look at discrete channels of communication without memory.

Channel without memory the channel is called, for which the skin of the transmission has a symbol for the signal, the crossovers are injected, independently of the way, as the signals were transmitted earlier. Therefore, crossovers do not create additional correlative links between symbols. The name "without memory" means that during the last transmission the channel somehow remembers the results of forward transmissions.

Computer telecommunication systems call the exchange of information between computers.

Computer channels can be classified according to the following signs:

• according to the method of coding information can be subdivided into digital and analog;
• according to the method of communication, it can be divided into views and commutations;
• according to the method of transmission of information, they are subdivided into wires and wireless, optical.

Analogue- for analog channels, the information that is transmitted is given in a non-permanent form, so that the value of a physical quantity looks like a non-permanent series.

digital- all channels, by which the information is transmitted as digital (discrete, pulsed) signals to those of other physical nature.

Switching- all channels, created from the same number of dealers, are less than timely transmission of information from them, after the end of the call session, such a channel is opened.

Viewed channels- all channels, which are organized for three hours and may have constant characteristics for a long time and throughput capacity.

Prior to the main characteristics of the channels, the link is given by the speed of the transmission, the superiority, the versatility, the reservation of the development.

Transmission speed is set to bit/s and baud. The number of changes in the informational parameter of a signal per second is measured in bauds.

Baud- this is so quick, if one signal (for example, an impulse) is transmitted per second regardless of the magnitude of the change. The unit of bit/s muting indicates a single change in the signal in the channel, the call is simple methods signal encoding; if the change is more than single, you can accept that: 1 baud = 1 bit / s; 1 kbaud = 103 b/s; 1 Mbaud = 106 b/s just.

As an element of data, there may be not two representations, but great kіlkistyu the value of any parameter to the signal, the value of 1 baud will be greater than 1 bit per second.

arrogance- transfer of information without її costs and changes. Transmitter and receiver - the same equipment for transmitting data, connecting the receiver and receiving information with the communication channel. Transmission equipment butts can be modems, terminal adapters, mesh cards and etc.

To improve the quality of the signal, which is transmitted by large stations, additional equipment is used: repeaters, switches, concentrators, routers, multiplexers.

Based on these principles, the classification is based, like a vrakhovu I will pass the building call channel:

• low-width communication channels, the speed of transmission in them should be set from 50 to 200 bit/s;
• medium-speed communication channels, transmission speed for some types of 300 to 9600 bit/s, and new standards up to 56,000 bit/s;
• high-speed (broadband) communication channels, which provide high-speed transmission more than 56,000 bit/s.

Shvidkіsnі characteristics of the channel are rich in why lie in the type of cables that vikoristovuyutsya.

Twisted couple- all insulated honey darts, with a maximum diameter of 1 mm, are wound in pairs, one on top of one near the looking spiral. Tse allows you to change the electromagnetic interplay of the number of hand-stitched hands of twisted pairs.

The most wide-spread stakes of twisted betting is a telephone line. You bet that you can compete on the great winds, you will unite in a cable, on which you are dressed up with a coat of arms. Yakby pair of wires, which are located in the middle of such cables, were not connected, the signals that pass through them would overlap one on one. Telephone cables with a diameter of a few centimeters can be stretched on the stovpah.

All pairs are victorious for the transmission of analog and digital signals. Smuha passing through the deposit of the diameter and the length of the dart, but on the great roads you can reach a few megabits for a second.

There are two types of betting twists:

• Unscreened twisted bet can achieve a high throughput building, efficient in robotics, do not require grounding, and the air is not high in price and is widely wide. Unscreened twisted pair does not stop in the local area, in which information is processed share access to what the field strength can do.
• Screened bets be good technical characteristics ale may be high versatility, zhorstki and handless in robots and sway grounding. Tsey view cable zastosovuєtsya more importantly at the borders with obmezhenim access to information.

coaxial cable- Zasіb data transmission. Win is shorter than screening, the pair is twisted lower, so you can ensure the transfer of data more far away with greater speed. Two types of cables are widely tapped. One type of cable is used to transmit only a digital signal, and the other type of cable - an analog signal.

The coaxial cable is stacked with a solid copper core covered with insulation, rolled out at the center of the cable. On top of the insulation there is a stretched cylindrical conductor, which sounds like a chiming sound at the sight of a fine mesh. Vіn pokritiy zovnіshnіshnіm zahіsnymi ball іzolyatsії (plastic shell). Design and special type of screening coaxial cable ensure high throughput and security clearance.

Coaxial cables for telecommunications are divided into two groups:

• "tovstі" coaxial;
• "thin" coax.

A thin coaxial cable with a diameter of 12.5 mm and a thin conductor (2.17 mm) ensures good electrical and mechanical characteristics.

The speed of data transmission over a thick coaxial cable up to 50 Mbit / s, but, protecting the same ineptitude of work with it, this value is significant, it is possible not to break it in data transmission networks.

A thin coaxial cable with a maximum diameter of 5-6 mm, is cheaper and more efficient for robots, and a thin conductor for a new one (0.9 mm) provides the best electrical and mechanical characteristics. The speed of data transfer to the “thin” coax does not exceed 10 Mb/s.

Coaxial cables have been widely used in telephone systems, long distance lines are being replaced by fiber optic cables. However, coaxial cables are widely used for cable television.

Fiber optic cables guess for its structure twisted couple. The core of the fiber-optic cable is made of a glass core, which expands lightly, sharpened with a hard backing and placed in a sheath with a diameter of 125 microns.

In one cable, there can be one to dekilkoh hundreds of such cores. The core was covered with a ball with a lower one, lower at the core, with a broken coefficient. Vіn appointments for more nadіynogo zabіgannya vykhod svіtla for mezhі core.

Zovnishniy ball is a plastic shell that protects the slope. Dzherelom widened over a fiber-optic cable of a light exchange, converting electrical signals into optical ones, for example, a light-emitting diode or a conductive laser.

The coding of information is determined by the changing intensity of the light exchange. The physical basis for the transmission of light exchange over the fiber is the principle of complete internal ventilation of the exchange through the fiber walls, which ensures the minimum signal loss, the greatest protection from outside electromagnetic fields. high speed transmission. On a fiber optic cable, which has a large number of fibers, it is possible to transmit a large number of messages. On the other end of the cable, the receiving attachment converts light signals to the electric.

The speed of transmission over a fiber-optic cable is 1000 Mb/s, but it is also expensive and there are no more laying of main channels for communication. Such a cable covers the capitals and great places of the country, as well as the continents.

AT counting measures and in the Internet, the fiber optic cable is victorious at the largest remote locations. The feasibility of fiber optic channels is truly boundless: over one long-distance fiber optic cable, it is possible to organize hundreds of thousands of telephone channels, a few thousand videotelephone channels and nearly a thousand television channels at once.

At this hour of wide breadth, there is a soundless communication: radio channels, infra-red and millimeter vipprominuvannya.

radio channel- tse drotovy channel zv'azku, scho is laid through the ether. The system for transmitting data over a radio channel includes a radio transmitter and a radio receiver, tuned to the same radio frequency range, which is determined by the frequency range of the electromagnetic spectrum, which is used for transmitting data.

Such a transmission system is simply called a radio channel. The speed of data transmission over the radio channel is practically not separated (stinks are separated by a lot of transmission of receiving equipment). High-speed radio access is given to short-range channels for free transmission of 2 Mb/s and even more. The next hour, radio channels with speeds of 20-50 Mbit/s will be checked.

Іnfrachervone that millimeter vipromіvannya without vikoristannya cable is widely used for communication on small distances. Remote controls management for televisions and video-tape recorders vikoristovuyut іnfrachervone vipromіvannya. The stench is well-directed, cheap and easy to install, but there is one important shortcoming: infrachervone viprominyuvannya do not go through the crisis of hard objects. On the other hand, the fact that infrachervone whil does not go through the wall is also positive. Adje tse suggesting protection infrared system eavesdropping at the port of the radio system.

Therefore, for vikoristannya іnfrachervonoї system zv'yazku do not need a sovereign license for the government in the form of radio communication (Crimean ISM bands). Communication in the infrared range zastosovuєtsya in the floor counting systems (for example, for connecting laptops with printers), but still does not play a significant role in telecommunications.

Voiceless channels Volodiyut filthy pereskodom, but ensure the highest possible mobility and efficiency of the call. In countless networks without wires, communication channels for transmitting data are most often found there, where traditional cable technologies are crowded, it is difficult to install them.

But in the nearest future situation may change - the development is actively carried out new technologies dartless sting bluetooth. Bluetooth is a technology for transmitting data over short-range radio channels that allows you to make calls wireless phones, computers and various peripherals should be installed in the fall, if the line of sight is broken.

On the back of Bluetooth, it was seen as an alternative to infrared devices between various portable devices. But at the same time fahіvtsі prophesy already two straight wide Bluetooth vikoristannya.

First - tse housewares, which include a variety of electronic equipment, computer hardware, televisions, etc. Another, more important directly - local offices of small firms, where the Bluetooth standard is positioned as a replacement for traditional wireless technologies. Insufficient Bluetooth and low speed of transmission - won't exceed 720 Kb/s, that's why the technology is not capable of ensuring the transmission of a video signal.

Topic 1.4: Fundamentals of local merging

Topic 1.5: Basic technologies of local merging

Topic 1.6: Main software and hardware components of LOM

Local networks

1.2. The middle and methods of transferring data from counting merezhs

1.2.2. Communication lines and data transmission channels

For pobudovi computer merezh zastosovuyutsya lines zvyazku, scho vikoristovuyut different physical medium. As a physical medium in communications, there are vicorist: metal (mainly copper), oversight glass (quartz) or plastic and ether. The physical medium of data transmission can be a twisted pair cable, a coaxial cable, a fiber optic cable and a wide area.

Lines of communication or lines of transmission of data - all intermediate equipment and physical medium, by which information signals (data) are transmitted.

In one line of communication, it is possible to establish a link of channels (virtual digital channels), for example, with a path of a frequency or hour sub-channel of channels. Communication channel - for one-way transmission of data. If the link line is monopolistically victorious as the link channel, then this link line is called the link channel.

Data transmission channel - to enable two-way data exchange, to enable communication lines and equipment for data transmission (receiver). Channels of transmission of data are related to each other between the source of information and the reception of information.

Fallen from the physical medium of transmission of data lines, the call can be added to:

• wire lines zv'yazku without insulating and screen braiding;
• cable, de transmission of signals, such lines are connected as "vita pair" cables, coaxial cables or fiber optic cables;
• bezdrotov (radio channels of terrestrial and satellite communications), which vikoristovuyut for the transmission of signals in electromagnetic waves, as if they are expanding on the air.

Carrying out lines of communication

Carrying out (repeat) lines of communication is carried out by telephone and telegraph signal transmissions, and navigating computer data transmissions. Tsі linії zv'yazku zastosovuyutsya like the main lines zv'yazku.

On the wired lines, the connection can be organized analogs and digital channels data transmission. The speed of transmission over the dart lines of the "simple old telephone line" (POST - Primitive Old Telephone System) is already low. In addition, to the shortcomings of these lines one can see the possibility of a simple unauthorized connection to the border.

Cable lines

Cable lines can be completed with a foldable structure. The cable is made up of conductors connected to the balls of insulation. AT computer networks three types of cables are twisted.

Twisted couple(twisted pair) - a tie-in cable, which is a twisted pair of medium wires (or a pair of wires), placed in a screened shell. Pairs of darts are twisted among themselves with a method of change. Vita pair є dosit stіykoy to pereshkod. Use two typical cables: unshielded UTP twisted pair and shielded STP twisted pair.

Characteristic for this cable is ease of installation. Danish cable is the found and widest type of connection, which is the most widely used in the widest local networks with the Ethernet architecture, prompting the topology of the "zirka" type. The cable is connected to the framing outbuildings for an additional RJ45 connection.

The cable is vikoristovuetsya for data transmission on the speed of 10 Mb/s and 100 Mb/s. Vita couple sing vicorist for a call on the vіdstan no more than a few hundred meters. Up to a small amount of "twisted pair" cable, you can see the possibility of a simple unauthorized connection to the wire.

coaxial cable(coaxial cable) - the same cable with a central mid-wire, which has a ball of insulating material in order to waterproof the central conductor in front of the outer wire screen (medium braid or aluminum foil ball). The outer wire screen of the cable is covered with insulation.

There are two types of coaxial cable: a thin coaxial cable with a diameter of 5 mm and a thin coaxial cable with a diameter of 10 mm. A thin coaxial cable has less noise, a thin one has a lower one. The variability of the coaxial cable is higher than the variability of the twisted pair and the installation of the folded wire, lower twisted pair.

The coaxial cable is installed, for example, in local networks with the Ethernet architecture, prompted by the topology of the "half bus" type.

The coaxial cable is more deflected, the pair is twisted at the bottom and the dampness is reduced. Throughput capacity - 50-100 Mbit / s. A long line of connection is acceptable - a sprat of kilometers. Unauthorized connection to coaxial cable folding, lower twisted bet.

Cable fiber optic channels. Fiber optic cable (fiber optic) - optical fiber on a silicon or plastic base, laid in a material with a low coefficient of light breaking, covered with a slick shell.

An optical fiber transmits signals and only one straight, that cable and two fibers. On the transmission end of the fiber optic cable, it is necessary to convert electrical signal at svіtlovy, ale in priymalny kіntsі zvorotne transformation.

The main advantage of this type of cable is the supra-high rіven of transmissibility and the daily vibrancy. Unauthorized connections are even more complicated. Transfer rate 3Gb/s. The main disadvantages of a fiber optic cable are the complexity of its installation, the mechanical strength and sensitivity to ionizing vibrations are small.

Bezdrotovі (radio channels of terrestrial and satellite communications) data transmission channels

The radio channels of the terrestrial (radio relay and satellite) and satellite links are established for additional transmission and reception of the radio signal and are considered for technology jetless transmission danich.

Radio relay data transmission channels

Radio relay channels are formed from a sequence of stations, which are repeaters. The call is made in the range of line of sight, the range between the land stations is up to 50 km. Digital radio relay lines (TsRRS) are installed as regional and local systems for communication and data transmission, as well as for communication between base stations of the telephone call.

Satellite data transmission channels

In satellite systems, antennas are installed in the low-frequency band for receiving radio signals from ground stations and relaying these signals back to ground stations. There are three main types of satellites that are located in geostationary orbits, medium or low orbits. Satellites start ringing in groups. Raznesenі one type of one can secure the hoarseness of all the surface of the Earth. The robot of the satellite transmission channel is represented by a little

Rice. one.

Dotsilnishe vikoristovuvat sputnikovuvat sv'yazok for organizatsii channel zv'yazku between stations, roztashovanie on the arch of great vіdstanyah, the possibility of servicing subscribers at important access points. The throughput of the building of the temple is a tens of Mbit / s.

Stilnikov data transmission channels

The radio channels of the telephone connection will follow the same principles as the telephone lines of the telephone system. style call- ce wireless telecommunication system, which is formed from a network of ground-based base receiving and transmitting stations and a telephone switch (or a mobile communication center).

The base stations are connected to the switching center, which secures the connection between both base stations and others telephone lines and the global network of the Internet. Behind the functions that are being used, the switching center is similar to the main PBX of a wired connection.

LMDS (Local Multipoint Distribution System) is a style standard for wireless transmission of information for fixed subscribers. The system will follow the style principle, one base station allows you to cover the area with a radius of a kilometer (up to 10 km) and connect a thousand subscribers. The BSs themselves are united with one high-speed terrestrial channels and radio channels. Transmission speed up to 45 Mb/s.

WiMAX data radio channels(Worldwide Interoperability for Microwave Access) similar to Wi-Fi. WiMAX traditional technologies radio access, working on the received signal, in direct line of sight of the base station. Experts care what mobile facilities WiMAX reveals rich prospects for corporate clients, low fixings of WiMAX, appointments for corporate clients. Information can be transmitted on a distance up to 50 km. with speed up to 70 Mb/s.

Data transmission radio channels MMDS(Multichannel Multipoint Distribution System). Qi systems of the building serve the territory within a radius of 50-60 km, and the transmission of the operator is directly visible and not obov'yazkovoy. The average speed of transmission is guaranteed to be 500 Kb/s - 1 Mb/s, but it is possible to secure up to 56 Mb/s on one channel.

Data radio channels local mesh . The standard for wireless communication for local networks is Wi-Fi technology. Wi-Fi secures connection in two modes: point-to-point (for connecting two PCs) and infrastructure connection (for connecting a PC to one access point). Data exchange rate up to 11 Mb/s with point-to-point connection and up to 54 Mb/s with infrastructure connection.

Data radio channels Bluetooht- the same technology of transmission on short distances (no more than 10 m) and can also be vikoristan for the construction of home meshes. Transmission speed does not exceed 1 Mb/s.

1. Vіdminnіst TKS vіd kom'yuternyh merezh.

Sliding apart computers and terminals. Computers are connected to computers, the skins of which can be processed autonomously. Terminal barriers ring out turn on the computer(mainframes) with terminals (add-ons for input - display of information). The butt of the terminal annexes and the chain can be the chain of ATMs or the sale of tickets.
The main feature of LAN and WAN is in the quality of the variant line communication and in the fact that in LOM there is only one way to transfer data between computers, and in WAN it is impersonal (there is an overhead channel connection). Since the line of communication in the LOM is larger than the one, then the speed of the transmission of information in the LAN is richer, lower in the WAN.

In addition, there is a gradual penetration of WAN LAN technologies and, at the same time, which significantly increases the quality of the network and expands the range of services. In such a manner, the differences between LAN and WAN are step by step smoothed out.

The trend of convergence (convergence) is typical not only for LAN and WAN, but also for telecommunication networks of other types, to which radio, telephone and television networks lie. Telecommunication barriers are made up of the following components: access barriers, backbones, information centers.

The computer mesh can be shown with a bagato-ball model, which is made up of balls:

• computers;
• communication possession;
• Operating systems;
• mezhezhі programs.

  At the computer chains there are different types of computers. Computers and these characteristics determine the ability of computer systems.

  Before the communication possession lie: modems, mesh cards, mesh cables and industrial equipment mesh. The following equipment can be seen: receivers or transivers (traceivers), repeaters or repeaters (repeaters), concentrators (hubs), bridges (bridges), switches, routers (routers), gateways (gateways).

2. SYNCHRONOUS AND ASYNCHRONOUS DATA TRANSFER

When exchanging these channels, the connection is made three methods data transmission:

1) Simplex (single-directed) - TV, radio;

2) Full duplex transmission - (acceptance and transmission of data are charged in advance);

3) Duplex (bidirectional) - the skin station simultaneously transmits and receives data.

For data transfer information systems most often, the last (short-duplex) transmission is delayed. It is subdivided into two methods:

a) asynchronous transmission;

b) synchronous transmission.

a) When transmitting asynchronously, a skin character is transmitted with a green hand. The starting beats are ahead of the start of the transfer. Then the symbol is transmitted. To ensure the reliability of the transmission, the parity bit is victorious (the parity bit is equal to 1, as the number of singles in the symbol is unpaired, and the parity bit is equal to 0, otherwise). The remaining bit signals the end of the transfer.

Advantages:

1) The system is clumsy;

2) Inexpensive interface setup.

Noodles:

1) One third of the bandwidth is spent on the transmission of service battles;

2) Low speed of transmission of data from the pair with synchronous;

3) With multiple pardons for an additional bit of pairing, it is impossible to determine the accuracy of the taken information.

Asynchronous transfer vikoristovuєtsya in systems, de exchange data vіdbuvaєєє іnоdі, і іn't nоbіbnа vіsoka svydkієєєєєєєєєєє і data transfer.

b) When vikoristanni synchronous method data is transmitted in blocks. For synchronization of the robot and the transmission, the bits of synchronization are transmitted to the block on the cob. Then the data is transmitted, the code of the pardon is shown and the symbol of the end of the transfer. The pardon display code is calculated after the data field and allows you to unambiguously determine the accuracy of the received information.

Advantages:

1) High transmission efficiency;

2) High speed of transmission;

3) Nadіyny vbudovaniya mekhanіzm vyyavlennya pardons.

Noodles:

3. Methods of transmission of digital information

Digital data on the conductor are transmitted by way of changing the flow voltage: no voltage - "0", no voltage - "1". There are two ways of transmitting information over the physical medium: digital and analog.

Notes: 1. If all subscribers of a computer network transmit data by a channel on the same frequency, such a channel is called vuzkosmugovim(Skip one frequency).

2. If a subscriber works on the same frequency on one channel, such a channel is called wide-ranging(Skip a lot of frequencies). The choice of wide-range channels allows you to save money, but also simplifies the process of managing the exchange of money.

At digital or Vuzkosmomumu transmission method(Fig. 6.10) data is transmitted from that natural eye on a single frequency. Vuzkosmugovyy sposіb allows you to transmit only digital information, secures at the moment of the skin the possibility of using the transmission medium only two koristuvachami and allow normal work only in the suburban area (the length of the line is more than 1000 m). At the same time, the high-speed mode of transmission ensures high security of data exchange - up to 10 Mbit / s and allows you to create counting volumes that are easy to configure. The number of local counts of vicorists is important for the Vuzkosmugovu transmission.

6.10. Digital transmission mode analog way transmission of digital data (Fig. 6.11) ensures wide-range transmission with the help of a single channel of signals in different carrier frequencies. With the analog transmission method, it is necessary to change the parameters to the signal of the carrier frequency of the transmission over the digital data communication channel. Carrier frequency signal to harmonic oscillations, which are described by equals: X = X max sin ( w t+j 0) de X max - the amplitude of coliving; w-Frequency of calls; t - Hour; j 0 is the cob phase of the colivan. It is possible to transmit digital data by an analog channel, depending on one of the parameters of the carrier frequency signal: amplitude, frequency or phase. It is necessary to transfer data to the two-eye view (sequence of ones and zeros), you can request such methods of control (modulation): amplitude, frequency, phase. Easier to understand the principle amplitude Rice. 6.11.a). Frequency Rice. 6.11.b). The most folding for rozumіnnya є phase fig 6.11.c). At the borders of the high level of the ієrarchії - global and regional vicorists are also wide range transmission which transmits to the robot for the skin subscriber at its own frequency within the same channel. Tse secure the cooperation of a large number of subscribers for the high speed of data transmission. Broadband transmission allows the transmission of digital data in one channel, image and sound, which necessary help modern multimedia systems.

Vuzkosmugov and wide range signal transmission

The most folding for rozumіnnya є phase modulation. The essence of її at tsomu, scho z transitions from 0 to 1і from 1 to 0, the phase of colivan changes, so. їх straight ahead (Fig. 6.11.c).

4. Warehouse and see the line link.

The fallow, in the middle of the transmission of data lines, the connection is divided into the following (Fig. 2.2):

Conducted (replaced) lines zv'azkuє darts without any insulating or screening braids, laid between stovpami and hanging from the window. Behind such lines, telephone or telegraph signals are traditionally transmitted, and for the availability of other possibilities, lines victorious and transmission of computer data. Shvidkіsnі yakosti and pereskodozakhischenіst tsikh linіy deprive bagat richly beautiful. Today, wired lines are connected by cable.

Cable lines є finish with a folding design. The cable is made up of conductors, laid at the ball joint of insulation: electrical, electromagnetic, mechanical, and also climatic. In addition, the cable can be equipped with roses, which allow you to quickly win the access to different possessions. There are three main types of cables installed in computer sheds: cables based on twisted pairs of copper wires, coaxial cables with a copper core, and also fiber-optic cables.

A twisted pair of wires is called torsion in pairs (twisted pair). Vita pair is available in a screened version (Shielded Twistedpair, STP), if a pair of copper wires is wrapped in an insulating screen, and not screened (Unshielded Twistedpair, UTP) if the insulation collar is daily. The twisting of the darts is lowered by injecting the ovnishnіkh transitions on the right signals, which are transmitted by cable. Coaxial cable (coaxial) maє asymmetrical design and folded from the inner midline lived that braided, vіdokremlenoї vіd lived as a ball of insulation. Use a few types of coaxial cable, which are modified by the characteristics and areas of congestion - for local ties, for global ties, for cable TV installations, too. Fiber optic cable (optical fiber) It is made up of thin (5-60 microns) fibers, which expand light signals. The most expensive type of cable - vіn secures data transmission with a high speed (up to 10 Gbit / s and more) and even more quickly for other types of transmission medium, it secures data transmission with zvnіshnіh transfers.

Terrestrial and satellite radio channels utvoryuyuyutsya for help transmitting that priymacha radiohvil. Isnuє great kіlkіst different types radio channels frequency range, and distance channel. Ranges of short, medium and long winds (KB, SV and DV), ranks and ranges of amplitude modulation (Amplitude Modulation, AM) according to the type of signal modulation method that is victorious in them, ensure a distant connection, even with a low speed of data transmission. Larger shifts are channels that operate on the ultrashort wave bands (VHF), which are characterized by frequency modulation (Frequency Modulation, FM), as well as the range of supratemporal frequencies (VHF or microwaves). In the low-frequency range (over 4 GHz), signals are no longer picked up by the Earth's ionosphere, and for steel communication, line-of-sight between the transmitter and receiver is required. Therefore, the frequencies of the vicorist are either satellite channels, or radio relay channels, where the mind is victorious.

Reliability of data transmission characterizes the ability to create for the skin bit of data that is transmitted. One-of-a-kind showcase is called intensity of pardons (Bit Error Rate, BER). BER value for communication channels without additional bones pardons (for example, codes that are self-correcting, or protocols with retransmission of instant frames) should, as a rule, be 10 -4 - 10 -6 , in fiber optic lines the connection - 10 -9 . The value of the reliability of the transmission, for example, in 10 -4 is to confirm that the value of one bit is maintained in the average of 10,000 bits.

The occasional bits are heard both because of the obviousness of the transition to the line, and through the creation of a signal, the transmission of the line is surrounded by a smog. Therefore, in order to improve the reliability of the data that are transmitted, it is necessary to increase the level of noise immunity of the line, to reduce the level of cross-pointing in the cable, and also to use a larger wide-range link.

5. Protocol. protocol stack. interface

Protocol - Tse set of rules to ensure the transfer of data from the borders.

The protocols are characterized:

1 . The protocols work on different levels of OSI models.

2 . The functions of the protocol are equal, de vin pracyuє.

3 . A dekilka of protocols can be taken in full. Whomever stink stinks up the stack .

protocol stack - A set of protocols for summaries of OSI models.

OSI model and equal protocols (functions):

7.Applied-Initsiatsija chi priyom zaputu.

6. Representative- Adding to the package the form and encryption information.

5.Session- additional information about traffic (from the appointed hour of the packet dispatch).

4. Transport- Adding information for processing pardons.

3. Merezhevy- adding address information and information about the place of the package in the sequence of packages that are being transmitted.

2.Duct- Addition of information for re-verification of pardons and preparation of data for transmission by physical order.

1. Physical- Transferring the package as a stream of battles.

Standard protocol stacks of different companies:

1. Set of ISO protocols - ISO/OSI

2. Set of protocols IBM - SNA

3. Set of protocols Digital - DEC Net

4. Novell Protocol Set – IPX/SPX

5. Apple Protocol Dial – Apple Talk

6. A set of Microsoft protocols - TCP/IP

By a private type of decomposition of the order of the day, when all the impersonal modules that violate the order are divided into hierarchically ordered groups - equal. For the skin level, a set of function-supplements is selected, from which to the modules this equal You can use modules higher than equal to complete your tasks. Such a formal appointment of a set of functions, which is given by a given equal for a more recumbent equal, as well as the format of improvement, by which two judicial equals are exchanged for an hour of their mutual modality, are called interface.

The interface designates a successful service, which hopes to be equal to a recumbent equal.

Transmission codes Special codes are used to transmit information over the communication channels. This code is standardized and approved by ISO (International Organization for Standardization) recommendations. - The International Organization for Standardization (ISO) or the International Consultative Committee for Telephony and Telegraphy (CCITT). The most widely used transmission code by communication channels is the ASCII code, which makes it possible to exchange information practically with the whole world (the equivalent of KOI-7). Krіm radio and satellite link, LOM vikoristovuyut і zv'yazok for auxiliary data cable. Information cable - the price of a set of wires, with which signals are transmitted from one computer to the next. To ensure the security of the code, the skin signal was seen to be of the same amount. Signals are transmitted in song sequences and in song combinations one by one.

For the transmission of the code combination, the lines of the lines are victorious, the battle lines of the combination are to be avenged. The leather bit is transmitted by a wire. Tse parallel transmission or transmission by parallel code. The success of such a transfer is expected during the organization of local IACs, for internal EOMs and for small vistas between subscribers of a measure Transmission by a parallel code secures a high security code, but it also allows for the movement of the wires to the creation of a physical transmission medium and may be a mess. For the transmission of a code combination of a two-wire line, a group of battles is transmitted over one wire bit by bit. Tse transmission of information by the last code. There is more, shards of data have been transformed into a parallel code of further processing in the EOM, but it is also economically viable for the transfer of information to the great authorities.

Types of synchronization of data Transmission processes of chi receivers in counting lines can be tied to the first time symbol, tobto. one of the processes can start more than once, as we take more data from another process. Such processes are called synchronous. At that very hour, there are processes, for which there are no such ties, and they can be vikonuvatysya independently from the equal number of all transferred data. Such processes are called asynchronous. Synchronization of data - the use of various processes at the hour. Data transmission systems have two methods of data transmission: synchronous and asynchronous. With synchronous transmission, information is transmitted in blocks, which are framed by special characters. Before the storage block, there are also special synchro-symbols, which ensure the control of the physical medium, and symbols, which allow to show pardons during the exchange.

For example, a data block in case of synchronous transmission to the channel, the connection is seen as a control sequence, formed by a special algorithm. According to this algorithm, a control sequence is formed for receiving information from the communication channel. If the offenses of the consequences are escaping - there are no pardons. Data block accepted. If the sequence does not match - a pardon. The transfer is repeated until the result of the recheck. If repeated transmission operations give a positive result, then an accident becomes fixed. Synchronous transmission - visokoshvidkіsna and mayzhe bezpomilkova. She will victoriously exchange notes between the EOM. Synchronous transmission requires expensive synchronization Bits of synchronization Symbol for the end of transmission field of tribute

When transmitting data asynchronously, the communication channel is transmitted as a sequence of bits, including when receiving it is necessary to see bytes for further processing. A part of this leather byte is interspersed with start and stop bits, which allow them to be seen from the transmission stream. Somewhere in the lines there is a connection with a low supremacy of vicarious kilka of such battles. Added start and stop bits will reduce the efficiency of data transmission and the bandwidth of the communication channel. At that very hour, the asynchronous transmission of the expensive setup and the help of the organization of the dialogue with the interaction of the EOM. Start bits Stop bits Transmitted characters Parity bits Data field

Hardware implementation of data transmission Digital data about the conductor are transmitted by way of changing the flow voltage: no voltage "0", є voltage "1". There are two ways of transmitting information over the physical medium: digital and analog. In the case of digital or airborne transmission, data is transmitted in the same natural way at a single frequency. The Danish method allows to transmit only digital information, ensuring at the skin moment the possibility of a transmission medium with only two short-haired speakers, and it allows a normal robot to work only at an intermediary distance (no more than 1000 m). At that very hour, such a way to ensure high security of the exchange of danim. To this, the number of scrap vicorists is more important.

The analog method of transmitting digital data ensures wide-range transmission with the help of a single channel of signals of different carrier frequencies. With the analog transmission method, it is necessary to change the parameters to the signal of the carrier frequency of the transmission over the digital data communication channel. Carrier frequency signal to harmonic vibrations, which are described by equals X=Xm sin(wt+f0) de Xm – amplitude of vibration; w is the frequency of colivans; t - hour; f0 - Pochatkov phase. It is possible to transmit digital data by an analog channel, depending on one of the parameters of the carrier frequency signal: amplitude, frequency or phase. Amplitude modulation - "0" daytime signal. Frequency modulation transmits the transmission of signals "0" and "1" at different frequencies. When changing from 0 to 1 or from 1 to 0, the frequency changes. Phase modulation - under the hour of the transition from one station to the next, the colivane changes directly.

Hardware facilities In order to ensure the transfer of information from the EOM to the communication medium, it is necessary to provide signals to the internal interface of the EOM with the parameters of the signals that are transmitted by the communication channels. For whom can be vikonano as a physical convenience (shape, amplitude and signal trivality), and code. Technical attachments that enable the functions of obtaining EOM with communication channels are called adapters or tie adapters. One adapter provides a link to the EOM for one channel. A wide range of single-channel adapters are available and rich-channel attachments - transmission multiplexers or simply multiplexers.

Transmission multiplexer - an attachment for obtaining EOM from a small number of communication channels. As it was said earlier, the transmission of digital information from the communication channel needs to be converted to analog signals, and for receiving information from the communication channel in the EOM, the turnaround is to convert the analog signals to the communication flow, so you can convert the EOM. Such a transformation vikonu special attachment- modem. The modem is attached, vikonu modulation and demodulation of information signals in the hour of transmission from the EOM to the communication channel to the reception in the EOM from the communication channel. A hub (HUB, Switch) is an extension, which switches a small number of channels to a link on one path of a private subdivision. The repeater is an extension, which ensures the safety of the formation of the amplitude of the signal when transmitting yoga to a larger lower transmission by the physical medium of the camp.