Pulse communication channel Definition. Communication channels: species, characteristics. Cell channel data channels

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Communication, Communication, Radioelectronics and Digital Devices

Communication channel is a system of technical means and signal distribution environment for messaging (not only data) from the source to the recipient (and vice versa). The communication channel, understood in a narrow sense (communication path), represents only the physical environmental distribution medium, for example, a physical communication line.

Question number 3 "Communication channels. Classification of communication channels. Communication channel parameters. The signal transmission condition over communication channel.

Link

Link - System of technical means and signal distribution environment for messaging (not only data) from the source to the recipient (and vice versa). Communication channel, understood in a narrow sense (communication path ) Represents only a physical signal distribution environment, for example, a physical communication line.

The communication channel is designed to transmit signals between remote devices. Signals carry information intended for the user's presentation (person) or for use of computer applications.

Communication channel includes the following components:

transmitting device;
receiving device;
medium of the transfer of various physical nature (Fig. 1).

The signal that is generated by the transmitter, which brings information, after passing through the transmission medium enters the receiving device input. The information is released from the signal and is transmitted to the consumer. The physical nature of the signal is chosen in such a way that it can spread through the transmission medium with minimal weakening and distortion. The signal is necessary as a carrier of information, it does not carry information.

Fig.1. Communication channel (option number 1)

Fig.2 Communication channel (option number 2)

Those. This is (channel) - technical device (technique + medium).

Classification

Classifications will be given exactly three types. Choose taste and color:

Classification number 1:

There are many types of communication channels, among which most often allocatechannels wired communication ( air, Cable, Lightwaterand others) and radiocommunication Channels (tropospheric, satellite and etc.). Such channels in turn are customary to qualify based on the characteristics of the input and output signals, as well as by changing the characteristics of the signals, depending on such phenomena occurring in the channel, like fading and attenuation of signals.

By type of distribution medium, communication channels are divided into:

wired;
acoustic;
optical;
infrared;
radio channels.

Communication channels are also classified on:

continuous (input and channel output - continuous signals),
discrete or digital (input and channel output - discrete signals),
continuously discrete (at the input channel-continuous signals, and at the output-discrete signals),
discrete-continuous (input channel-discrete signals, and at the output-continuous signals).

Channels can be likelinear and nonlinear, temporary and spatio-temporal.

Possible classification of communication channels valid frequency range.

Information transfer systems aresingle-channel and multichannels . The type of system is determined by the communication channel. If the communication system is built on the communication channels of the same type, then its name is determined by the type name of the channels. Otherwise, the detailing of classification features is used.

Classification number 2 (more detailed):

Classification of the range of used frequencies

Kilometer (DV) 1-10 km, 30-300 kHz;
Hectometer (SV) 100-1000 m, 300-3000 kHz;
Decamer (kV) 10-100 m, 3-30 MHz;
Meter (MV) 1-10 m, 30-300 MHz;
Decimeter (DMV) 10-100 cm, 300-3000 MHz;
Santimeter (SMV) 1-10 cm, 3-30 GHz;
Millimeter (MMB) 1-10 mm, 30-300 GHz;
Decimilimitone (DMMV) 0.1-1 mm, 300-3000 GHz.
1. In the direction of communication lines
  - directed ( various conductors are used):
coaxial
twisted pairs based on copper conductors,
fiber optic.
- non-directional (radar);
direct visibility;
tropospheric;
ionospheric
cosmic;
radiolese (relaying on decimeter and shorter radio waves).
1. By type of messages transmitted:
telegraph;
telephone;
data transmission;
facsimile.
1. By type of signals:
analog;
digital;
pulse.
1. According to the type of modulation (manipulation)
  - In analog communication systems:
with amplitude modulation;
with single-band modulation;
with frequency modulation.
In digital communication systems:
with amplitude manipulation;
with frequency manipulation;
with phase manipulation;
with relative phase manipulation;
with tonal manipulation (single elements manipulate the subcarring oscillation (tone), after which the manipulation at a higher frequency is carried out).
1. By the value of the radio signal base
broadband (b \u003e\u003e 1);
narrowband (B "1).

7. By the number of simultaneously transmitted messages

single-channel;
multi-channel (frequency, temporary, code separation of channels);

8. In the direction of messaging

one-sided;
bilateral.
9. In order to exchange
simplex communication- Bilateral radio communication at which the transfer and reception of each radio station is carried out alternately;
duplex communication- Transmission and reception is carried out simultaneously (the most operational);
half duplex communication- refers to the simplex, which provides for an automatic transition from the transmission to the reception and the ability to write a correspondent.

10. According to the protection methods of the transmitted information

open connection;
closed connection (classified).

11. According to the degree of automation of information

non-automated - radio control and messaging is performed by the operator;
automated - manually carried out only information input;
automatic - the messaging process is performed between the automatic device and the computer without the participation of the operator.

Classification number 3 (something can repeat):

1. By appointment

Telephone

Telegraph

Television

- broadcasts

2. In the direction of transmission

- simplex (transmission only in one direction)

- half duplex (transmission alternately in both directions)

- duplex (transmission at the same time in both directions)

3. By the nature of the communication line

Mechanical

Hydraulic

Acoustic

- electric (wired)

- radio (wireless)

Optical

4. By the nature of the signals at the input and output of the communication channel

- analog (continuous)

- discrete in time

- signal level discrete

- digital (discrete and time and level)

5. By the number of channels per line of communication

Single-channel

Multichannel

And more drawing here:

Fig.3. Classification of communication lines.

Characteristics (parameters) of communication channels

Channel gear ratio: it appears in the formamplitude-frequency characteristics (ACH)and shows how the amplitude of the sinusoids at the output of the communication channel falls compared to the amplitude at its input for all possible frequencies of the transmitted signal. The normalized amplitude-frequency response of the channel is shown in Fig.4. Knowledge of the amplitude-frequency characteristics of the real channel allows you to determine the form of the output signal for almost any input signal. To do this, you need to find the spectrum of the input signal, convert the amplitude of the components of its harmonics in accordance with the amplitude-frequency response, and then find the form of the output signal by resulted in converted harmonics. For experimental verification of the amplitude-frequency response, it is necessary to test the channel with references (equal to amplitude) sinusoids over the entire frequency range from zero to a certain maximum value that can occur in the input signals. Moreover, it is necessary to change the frequency of the input sinusoid with a slight step, which means the number of experiments should be large.

- the ratio of the spectrum of the output signal to the input
- bandwidth

Fig.4 The normalized amplitude-frequency response of the channel

Bandwidth: it is a derivative characteristic of response. It is a continuous frequency range for which the ratio of the amplitude of the output signal to the input exceeds some predetermined limit, that is, the bandwidth determines the signal frequency range in which this signal is transmitted over the communication channel without significant distortion. Usually the bandwidth is counted at 0.7 from the maximum response. The bandwidth is best affected by the maximum possible information transfer rate over the communication channel.
Attenuation: it is defined as a relative decrease in the amplitude or signal power when transmitting a certain frequency signal over the signal channel. Often, when operating the channel, the main frequency of the transmitted signal is known in advance, that is, the frequency, the harmonic of which has the greatest amplitude and power. Therefore, it is enough to know the attenuation at this frequency to approximately estimate the distortion of the signals transmitted over the channel. More accurate estimates are possible with the knowledge of attenuation at several frequencies corresponding to several main harmonics of the transmitted signal.

The attenuation is usually measured in decibels (DB) and is calculated according to the following formula: where

- signal power at the channel output,

- Signal power at the input channel.

The attenuation is always calculated for a certain frequency and is correlated from the channel length. In practice, they always use the concept of "robust attenuation", i.e. Atoquence of the signal per unit of channel length, for example, attenuation 0.1 dB / meter.

Transmission speed: it characterizes the number of bits transmitted via the channel per unit of time. It is measured in bits per second -bIT / S. as well as derived units:Kbps, Mbit / C, Gb / s. The transmission rate depends on the width of the channel bandwidth, noise level, type of coding and modulation.
Canal noise immunity: it characterizes its ability to transmit signals under interference conditions. Interference is made to divide oninternal (representsthermal noises of the equipment) and external (they are diverse anddepend on the transfer medium). The noise resistance of the channel depends on the hardware and algorithmic solutions for the processing of the received signal, which are laid in the receiving-transmitting device.Noise immunity Signal transmission through channelmay be elevated Due to coding and special processing Signal.
Dynamic range: logarithm The ratio of the maximum power of signals transmitted by the channel to the minimum.
Noise immunity: This is noise immunity, t.e. noise immunity.

Signal transfer condition over communication channels.

Channel, in fact, is a filter. To the signal passes through it without distortion, the volume of this channel must be larger than the signal or equal to it (see fig).

Mathematically, the condition can be written like this: where

; (1)

In the above formulas

- channel bandwidth, or frequency band, which canal can skip with a normalized signal attenuation;

- dynamic range equal to the ratio of the maximum permissible signal level in the channel to the level of interference normalized for this channel types;

- the time during which the channel is used to transmit data;

- the width of the signal frequency spectrum, i.e. the interval on the frequency spectrum scale occupied by the signal;

- dynamic range equal to the ratio of the average signal power to the medium interference power in the channel;

- Signal duration, or its existence.

Another form of recording condition (deployed):

P. S. .: The "Channel" parameter in some sources is also indicated as one of the parameters of the communication channel, but not everywhere. The mathematical formula is given above in (1).

Literature

1. http://edu.dvgups.ru/metdoc/enf/bgd/bgd_chs/metod/andreev/webumk/frame/1.htm.;

2. http://supervideoman.narod.ru/index.htm..

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To organize data transfer, it is necessary to use lines and communication channelswhich communicate between computers, telephones, telegraphs and other means of communication.

Transmitted information is in a physical environment that can consist of various types of cables and wires, as well as the surrounding space.

What is the difference between communication channels from communication lines

Despite the fact that both concepts are often identified, they have some differences that you need to know to build correct information communication.

On the channels, the connection is transmitted to one side or in two if the exchange occurs between the receiver and the transmitter.

The communication lines, in turn, are formed from connecting multiple channels, there can also be only one channel in them.

There are links such:

Wired;

Cable;

Wireless.

Consider more detailed every type of lines and learn about their possibilities, advantages and disadvantages.

Wired (air) lines

These lines can be used to transmit a telegraph, telephone or computer signal. They consist of wires through which data is exchanged. This type of communication is suitable for transmitting digital and analog signals, because its popularity is high enough.

The disadvantages of such a connection include a relatively low signal transmission rate and a low degree of interference protection.

It is also possible a banal unauthorized connection of unscrupulous subscribers, which leads to a decrease in the quality of data transfer and financial losses of broadcasters.

Cable lines

The structure of the cable can be different, but mostly all of them consist of groups of conductors, which are treated with reliable insulation.

Types of cables are used to exchange data in computer networks:

Twisted para - Consists of two wires made of copper, which are suitable with each other and are covered with an unshielded or shielded shell. This method of connection of conductors helps to increase noise immunity, it is possible that several twisted pairs of wires are in one cable. Such a connection is the cheapest and affordable, the installation of cables is quite simple, which leads to unauthorized connection to networks all the same unscrupulous subscribers.

Coaxial cable - It consists of a central conductor, the role of which performs the copper wire, and the conductive screen, most often in its capacity is the aluminum foil or copper braid. There is an insulating material between the main conductor and the screen, the outer part of the screen is also covered with isolation. This connection method is more costly and time-consuming, therefore unauthorized connections are less. For such lines is characterized by good protection against interference and high information transfer rate.

Fiber optic cable - Looks like its structure with coaxial, but instead of a copper conductor in this cable uses thin fiberglass, the role of internal insulation is performed by plastic or glass shell, which does not allow the light to exit, it forms complete internal reflection. It is noteworthy that through fiber signals can be held solely in one direction, it is for this reason that they are located pairwise in cables. The installation of such lines of communication is very laborious, the cable itself is quite sensitive to damage, but it provides the highest signal transmission rate of up to 3 Gb / s. Subject to the use of the fiber optic cable on the transmission side, an electrical signal converter should be used in the light, and on the reception side - the transducer of the light signal to the electric.

Wireless communication channels

Lines and communication channels Can be built on the work of wireless ground or satellite radio channels.

Radio relay channels are a group of repeater stations that are located in a certain order on a certain distance from each other.

Stations and repeaters are used in the field of cellular communications and to transfer other types of signals within one city or region.

Satellite communications is provided by satellites, which are located on earth orbit and are repeaters. The signal from the ground transmitting station goes to the satellite, and from the satellite it is transmitted to the ground receiving station.

This method of communication allows you to communicate the inhabitants of the most remote parts of the planet, since the satellites are most often launched by one, but by groups.

All repeaters are located in orbit in some distance from each other, because together they can embrace almost the entire globe.

Examples of lines and communication channels at the exhibition

Find out which lines and communication channels are used modern companies, you can at the specialized exhibition "Communication"to be held in the Expocentre Fairground.

The exhibition will be devoted to new items in the field of IT. The event will present the latest technical solutions to provide communication.

Read the other our articles:

State exam

STATE EXAMINATION)

Question number 3 "Communication channels. Classification of communication channels. Communication channel parameters. The signal transmission condition over communication channel.

(Plyaskin)

Link. 3.

Classification. five

Characteristics (parameters) of communication channels. 10

Signal transfer condition over communication channels. 13

Literature. fourteen

Link

Link - System of technical means and signal distribution environment for messaging (not only data) from the source to the recipient (and vice versa). Communication channel, understood in a narrow sense ( communication path) Represents only a physical signal distribution environment, for example, a physical communication line.

The communication channel is designed to transmit signals between remote devices. Signals carry information intended for the user's presentation (person) or for use of computer applications.

Communication channel includes the following components:

1) transmitting device;

2) receiving device;

3) medium of transmission of various physical nature (Fig. 1).

Fig.1. Communication channel (option number 1)

Fig.2 Communication channel (option number 2)

Those. This is (channel) - technical device (technique + medium).

Classification

Classifications will be given exactly three types. Choose taste and color:

Classification number 1:

There are many types of communication channels, among which most often allocate channels wired communication ( air, Cable, Lightwaterand others) and radiocommunication Channels (tropospheric, satellite and etc.). Such channels in turn are customary to qualify based on the characteristics of the input and output signals, as well as by changing the characteristics of the signals, depending on such phenomena occurring in the channel, like fading and attenuation of signals.

By type of distribution medium, communication channels are divided into:

Wired;

Acoustic;

Optical;

Infrared;

Radio channels.

Communication channels are also classified on:

· Continuous (input and channel output - continuous signals),

· Discrete or digital (input and channel output - discrete signals),

· Continuous-discrete (at the input channel-continuous signals, and at the output-discrete signals),

· Discrete-continuous (at the input channel-discrete signals, and at the output-continuous signals).

Channels can be like linear and nonlinear, teemless and spatio-temporal.

Possible classification Communication channels valid frequency range .

Information transfer systems are single-channel and multichannel. The type of system is determined by the communication channel. If the communication system is built on the communication channels of the same type, then its name is determined by the type name of the channels. Otherwise, the detailing of classification features is used.

Classification number 2 (more detailed):

1. Classification of the range of used frequencies

Ø Milometer (DV) 1-10 km, 30-300 kHz;

Ø hectometer (SV) 100-1000 m, 300-3000 kHz;

Ø Decadener (kV) 10-100 m, 3-30 MHz;

Ø meter (MV) 1-10 m, 30-300 MHz;

Ø decimeter (DMV) 10-100 cm, 300-3000 MHz;

Ø Santimeter (SMV) 1-10 cm, 3-30 GHz;

Ø millimeter (MMB) 1-10 mm, 30-300 GHz;

Ø Devimilimitre (DMMV) 0.1-1 mm, 300-3000 GHz.

2. In the direction of communication lines

- directed (various conductors are used):

Ø coaxial,

Ø Twisted pairs based on copper conductors,

Ø fiber optic.

- non-directional (radar);

Ø direct visibility;

Ø tropospheric;

Ø ionospheric

Ø cosmic;

Ø Radio relay (relaying on decimeter and shorter radio waves).

3. By type of messages transmitted:

Ø Telegraph;

Ø telephone;

Data Ø;

Ø facsimile.

4. By type of signals:

Ø analog;

Ø digital;

Ø pulse.

5. According to the type of modulation (manipulation)

- In analog communication systems:

Ø with amplitude modulation;

Ø with single-band modulation;

Ø with frequency modulation.

- In digital communication systems:

Ø with amplitude manipulation;

Ø with frequency manipulation;

Ø with phase manipulation;

Ø with relative phase manipulation;

Ø with tonal manipulation (single elements are manipulated by subcarrive oscillation (tone), after which the manipulation at a higher frequency is carried out).

6. By the value of the radio signal base

Ø Broadband (B \u003e\u003e 1);

Ø Narrowband (B "1).

7. By the number of simultaneously transmitted messages

Ø single-channel;

Ø multichannel (frequency, temporary, code separation of channels);

8. In the direction of messaging

Ø one-sided;

Ø bilateral.
9. In order to exchange

Ø simplex communication - Bilateral radio communication at which the transfer and reception of each radio station is carried out alternately;

Ø duplex communication - Transmission and reception is carried out simultaneously (the most operational);

Ø half duplex communication - refers to the simplex, which provides for an automatic transition from the transmission to the reception and the ability to write a correspondent.

10. According to the protection methods of the transmitted information

Ø Open communication;

Ø Closed communication (Classified).

11. According to the degree of automation of information

Ø non-automated - radio control and messaging is performed by the operator;

Ø automated - manually only input information is carried out;

Ø Automatic - the messaging process is performed between the automatic device and the computer without the participation of the operator.

Classification number 3 (something can repeat):

1. By destination

Telephone

Telegraph

Television

Broadcasts

2. In the direction of transmission

Simplex (transmission only in one direction)

Half duplex (transmission alternately in both directions)

Duplex (transmission at the same time in both directions)

3. By the nature of the communication line

Mechanical

Hydraulic

Acoustic

Electric (wired)

Radio (wireless)

Optical

4. By the nature of the signals at the input and output of the communication channel

Analog (continuous)

Discrete in time

Signal level discrete

Digital (discrete and time and level)

5. By the number of channels per line of communication

Single-channel

Multichannel

And more drawing here:

Fig.3. Classification of communication lines.

Characteristics (parameters) of communication channels

1. Channel gear ratio: it appears in the form amplitude-frequency characteristics (ACH)animals how the amplitude of the sinusoids at the output of the communication channel falls compared to the amplitude at its input for all possible frequencies of the transmitted signal. The normalized amplitude-frequency response of the channel is shown in Fig.4. Knowledge of the amplitude-frequency characteristics of the real channel allows you to determine the form of the output signal for almost any input signal. To do this, you need to find the spectrum of the input signal, convert the amplitude of the components of its harmonics in accordance with the amplitude-frequency response, and then find the form of the output signal by resulted in converted harmonics. For experimental verification of the amplitude-frequency response, it is necessary to test the channel with references (equal to amplitude) sinusoids over the entire frequency range from zero to a certain maximum value that can occur in the input signals. Moreover, it is necessary to change the frequency of the input sinusoid with a slight step, which means the number of experiments should be large.

- the ratio of the spectrum of the output signal to the input
- bandwidth

Fig.4 The normalized amplitude-frequency response of the channel

2. Bandwidth: It is a derivative characteristic of response. It is a continuous frequency range for which the ratio of the amplitude of the output signal to the input exceeds some predetermined limit, that is, the bandwidth determines the signal frequency range in which this signal is transmitted over the communication channel without significant distortion. Usually the bandwidth is counted at 0.7 from the maximum response. The bandwidth is best affected by the maximum possible information transfer rate over the communication channel.

3. Attense: It is defined as a relative decrease in the amplitude or signal power when transmitting a certain frequency signal over the signal channel. Often, when operating the channel, the main frequency of the transmitted signal is known in advance, that is, the frequency, the harmonic of which has the greatest amplitude and power. Therefore, it is enough to know the attenuation at this frequency to approximately estimate the distortion of the signals transmitted over the channel. More accurate estimates are possible with the knowledge of attenuation at several frequencies corresponding to several main harmonics of the transmitted signal.

The attenuation is usually measured in decibels (DB) and is calculated according to the following formula: where

Signal power at the channel output,

Signal power at the input of the channel.

4. Transmission speed: It characterizes the number of bits transmitted via the channel per unit of time. It is measured in bits per second - bIT / S.as well as derived units: Kbps, Mbit / C, Gb / s. The transmission rate depends on the width of the channel bandwidth, noise level, type of coding and modulation.

5. Canal noise immunity: It characterizes its ability to transmit signals under interference conditions. Interference is made to divide on internal (represents thermal noises of the equipment) I. external (they are diverse and depend on the transfer medium). The noise resistance of the channel depends on the hardware and algorithmic solutions for the processing of the received signal, which are laid in the receiving-transmitting device. Noise immunity Signal transmission through channel may be elevated Due to coding and special processing Signal.

6. Dynamic range : logarithm of the ratio of the maximum power of signals transmitted by the channel, to the minimum.

7. Noise immunity: This is noise immunity, i.e. Noise immunity.

The communication line and communication channel is not the same.

Communication line(LS) is physical environmentBy which information signals are transmitted. In one line of communication, several communication channels can be organized by temporary, frequency code and other sections - then they speak of logical (virtual) channels. If the channel is completely monopolized, it can be called a physical channel and in this case coincides with the line of communication. Although it is possible, for example, talking about analog clamp of a digital communication channel, but absurd about the analog or digital communication line, for the line is only a physical environment in which channel communication channels of different types can be formed. However, even speaking of a physical multichannel line, it is often referred to as a communication channel. L C is a mandatory link of any information transfer system.

Fig. 15. 2. Classification of communication channels

The classification of communication channels (COP) is shown in Fig. 15. 2. In the physical nature of the drugs and the COP on them are divided into:

mechanical - used to transfer material media

acoustic - transmit a beep;

optical - transmit a light signal;

electric - transmit an electrical signal.

Electrical and opticalCOP can be:

wired using conductive communication lines (electrical wires, cables, fiber, etc.);

wireless (radio channels, infrared channels, etc.), using electromagnetic waves extending to the ether.

In the form of the submission of the transmitted information, the COP is divided into:

analog- according to the analog channels, the information presented in continuous form is transmitted, that is, in the form of a continuous range of any physical values;

digital- According to digital channels, information presented in the form of digital (discrete, impulse) signals of one or another physical nature is transmitted.

Depending on the possible information transfer directions, distinguishes:

simplexCOP, allowing to transmit information only in one direction;

half duplexCOP, providing alternate transmission of information in direct and reverse directions;

duplexCOP, allowing to transfer information simultaneously in direct, and in reverse directions.

Communication channels can be finally:

switched;

uncommunicable.

Switchedchannels are created from individual segments (segments) only for the time of transmission on them; At the end of the transfer, such a channel is eliminated (separated).

Uncommunicable(Selected) Channels are created for a long time and have permanent characteristics in length, bandwidth, noise immunity.

By bandwidth can be divided into:

low-speedCOP, information transfer rate in which from 50 to 200 bt / s; These are telegraph COP, both switched (subscriber telegraph) and non-commutable;

medium-speedCOP, such as analog (telephone) CS; The transfer rate in them from 300 to 9600 bps, and in the new standards V 90-V. 92 of the International Advisory Committee on Telegraph and Telephony (ICTT) and up to 56,000 bits / s

high Speed(Broadband) COP, providing information transfer rate above 56,000 bps.

It should be especially noted that the telephone COP is more narrowly band, rather than telegraph, but the data transfer rate is higher thanks to the mandatory presence of a modem that significantly reduces F from the transmitted signal. With simple coding, the maximum achievable data transfer rate over the analog channels does not exceed 9600 baud \u003d 9600 bps. Currently, the complex data coding protocols of the transmitted data are used not two, but several values \u200b\u200bof the signal parameter to display the data item and allow you to reach the data rate by analog telephone lines of 56 kbps \u003d 9600 baud.

According to digital COP, organized on the basis of telephone lines, the data transmission rate due to a decrease in F C and an increase in the digitized signal also: may be higher (up to 64 kbps), and when multiplexing multiple digital channels in one in such a compound COP transmission speed can double, triple, etc.; There are similar channels with tens and hundreds of megabits per second.

Physical environmentinformation transmission in low-speed and medium-speed CS is usually wired communication lines: groups or parallel or twisted ("twisted pair") wires.

For the organization of broadband CS, various cables are used, in particular:

unshielded with twisted pairs of copper wires (UTP unshielded twisted pair);

shielded with twisted pairs of copper wires (SHIELDED TWISTED PAIR - STP);

fiber Optic Cable - FOC);

coaxial (COXIAL CABLE - CC);

wireless radio channels.

Twisted para- These are isolated conductors, pairwiseinets with each other to reduce crosspads between conductors. Such a cable consisting of usually from a small amount of twisted pairs (sometimes even two) is characterized by a smaller signal attenuation when transmitted at high frequencies and less sensitivity to electromagnetic tips than a parallel pair of wires.

UTP cablesmore often than others are used in data transmission systems, in particular in computing networks. Severe five categories of twisted pairs UTP: The first and second categories are used at low-speed data transmission; The third, fourth and fifth - when transmission rates, respectively, up to 16, 25 and 155 Mbit / s (and using the Gigabit Ethernet technology standard, introduced in 1999, and up to 1000 Mbps). With good technical characteristics, these cables are relatively inexpensive, they are comfortable in operation, do not require grounding.

STP cablesthey have good technical characteristics, but have a high cost, tough and inconvenient in operation, require a screenshot. They are divided into types: round 1, tour 2, round 3, round 5, round 9. Of these, round 3 defines the characteristics of the unshielded telephone cable, and the round 5 - fiber optic cable. The most popular IBM standards cable 1, consisting of two pairs of twisted wires shielded by conductive braid, which is grounded. Its characteristics approximately correspond to the characteristics of the UTP cable category 5.

Coaxial cableit is a copper conductor coated with a dielectric and surrounded by a retinue from thin copper conductors by shielding protective sheath. Coaxial cables for telecommunications are divided into two groups:

thick coaxials;

thin coaxials.

Fatthe coaxial cable has an outer diameter of 12, 5 mm and a sufficiently thick conductor (2, 17 mm), providing good electrical and mechanical characteristics. The speed of data transmission over a thick coaxial cable is quite high (up to 50 Mbps), but, given the certain inconvenience of working with it and its significant cost, to recommend it for use in data transmission networks, it is not always possible. Thincoaxial cable has an outer diameter of 5-6 mm, it is cheaper and more convenient in operation, but the thin conductor in it (0, 9 mm) determines the worst electrical (transmits a signal with permissible attenuation to a smaller distance) and mechanical characteristics. The recommended data transfer rates on the "fine" coaxial will not exceed 10 Mbps.

Foundation fiber-optic cablemake up "internal podcabels" - glass or plastic fibers with a diameter of 5 (single mode) to 100 (multimode) microns surrounded by solid aggregate and placed in a protective shell with a diameter of 125-250 μm. In one cable may be contained from one to several hundred such "internal subcabs". The cable, in turn, is surrounded by the aggregate and is covered with a thicker protective sheath, inside which one or more power elements are laid that make up the mechanical strength of the cable.

According to a single-mode fiber (diameter of their 5-15 μm), the optical signal spreads, almost without reflecting the walls of the fiber (enters into the fiber parallel to its walls), which provides a very wide bandwidth (up to hundreds of gigahertz per kilometer). Multimode fiber (the diameter of its 40-100 μm) is distributed immediately many signals, each of which is included in the fiber at its own angle (its fashion) and, accordingly, it is reflected from the walls of the fiber in different places (the bandwidth of the multimode fiber 500-800 MHz / km).

The source of the light beam distributed over the fiber optic cable is the transducer of electrical signals to optical, such as a LED or semiconductor laser. Information encoding is carried out by changing the intensity of the light beam. The physical basis of the transmission of the light beam on the fiber is the principle of complete internal reflection of the beam from the walls of the fiber, providing minimal attenuation of the signal, the highest protection against external electromagnetic fields and high transmission rate. By fiber optic cable having a large number of fibers, you can transmit a huge number of messages. At the other end of the cable, the receiving device converts light signals into electrical. The data transfer rate on the fiber optic cable is very high and reaches 1000 Mbps, but it is very expensive and is usually used only for laying responsible main communication channels. Such a cable connects the capital and large cities of most countries of the world, and the Cable laid along the bottom of the Atlantic Ocean binds Europe with America. The fiber optic cable connects St. Petersburg with Moscow, the Baltic and Scandinavian countries, in addition, it is laid in the subway tunnels and binds all areas of the city. In computing networks, the fiber optic cable is used on their most responsible areas, in particular on the Internet. Opportunities of fiber optic channels are truly limitless: one to one thick main fiber optic cable can simultaneously organize several hundred thousand telephone channels, several thousand video telephone channels and about a thousand television channels.

Radio channel- This is a wireless communication channel deployed through the ether. The data transmission system (SPD) on the radio channel includes a radio transmitter and a radio receiver configured to the same radio wave range, which is determined by the frequency band of the electromagnetic spectrum used for data transmission. Often, such a SPD is called simply radio channel. Data transfer rates on the radio channel are practically not limited (they are limited to the transmission-transmitting equipment bandwidth). High-speed radio access provides users with channels with a transmission rate of 2 Mbit / "C and higher. In the near future, radio channels are expected with rates of 20-50 Mbps. In Table 15. 1 shows the names of radio waves and the corresponding frequency bands.

Table 15. 1.. Radio ranges

For commercial telecommunication systems, frequency ranges of 902-928 MHz and 2, 4-2, 48 GHz are most often used (in some countries, for example, the United States, with small radiation power levels - up to 1 W - allowed to use these ranges without state licensing).

Wireless communication channels have a bad noise immunity, but provide the user with maximum mobility and efficiency. In computing networks, wireless communication channels for data transmission are most often used where the use of traditional cable technologies is difficult or simply impossible. But in the near future, the situation may change - the development of new Bluetooth wireless technology is actively underway.

Bluetooth- This is the technology of data transfer by radio channels for short distances, allowing you to communicate with wireless phones, computers and different peripherals even in cases where the requirement of direct visibility is violated.

Completely well-known are the compounds of electronic equipment among themselves with the help of an infrared communication channel. But these compounds require direct visibility. For example, the TV remote control cannot be used if there is at least a sheet of newspaper paper between you and the TV.

Initially Bluetoothconsidered exclusively as an alternative to the use of infrared compounds between various portable devices. But now experts are predicted by two directions of wide use of Bluetooth. The first direction is home networks that include various electronic equipment, in particular computers, televisions, etc. The second, a much more important direction is local networks of small firms, where the Bluetooth standard can change the traditional wired technologies.

The disadvantage of Bluetooth is a relatively low data transfer rate - it does not exceed 720 kbps, so this technology is not able to ensure the transmission of the video signal.

Telephone linesare the most branched and widely used. On telephone lines of communication, sound (tonal) and facsimile messages are transmitted, they are the basis for building information and reference systems, email systems and computing networks.

On telephone lines, both analog, and digital information transmission channels can be organized. Consider this question, due to its high relevance, several more.

"Simple Old Telephone System", in the English-speaking abbreviation of Pots, consists of two parts: a main communication system and subscriber access networks to it. The simplest version of subscribers to the main system is the use of a subscriber analogue communication channel. Most telephone sets are connected to the automatic telephone exchange (PBX), which is an already element of the main system, just like this.

The telephone microphone converts sound oscillations into an analog electrical signal, which is transmitted via the subscriber line in the PBX. The frequency band required to transmit the human voice is approximately 3 kHz, in the range of 300 Hz to 3, 3 kHz. When removing the handset, a "OFF-HOOK" signal is generated by calling the call, and if the telephone station is not busy, the desired phone number is recruited, which is transmitted to the PBX as a sequence of pulses (with a pulsed set) or as a combination of sound frequency signals (with a tonal set). The conversation is completed by the "on-hook" signal, formed when lowering the tube. This type of call procedure is called "in Band", since the transmission of call signals is made on the same channel as the transmission of speech.

Topic 1.4: Basics of local networks

Topic 1.5: Basic Local Network Technologies

Topic 1.6: Basic software and hardware components LAN

Local networks

1.2. Wednesday and data transfer methods in computing networks

1.2.2. Communication lines and data channels

To build computer networks, communication lines using various physical environments are applied. As a physical environment in communications, it is used: metals (mainly copper), supercast glass (quartz) or plastic and ether. The physical data transmission medium may be a cable "twisted pair", coaxial cable, fiber optic cable and surrounding space.

The communication lines or data line is an intermediate hardware and a physical environment for which information signals are transmitted (data).

In one link, you can form multiple communication channels (virtual or logical channels), for example by frequency or temporary separation of channels. Communication channel is a means of one-sided data transfer. If the communication line is monopolized by the communication channel, then in this case the communication line is called communication channel.

Data Transmission Channel is a bilateral data exchange tools that include communication lines and data transmission equipment. Data transmission channels associate information sources and information receivers.

Depending on the physical transmission medium, the communication line data can be divided into:

wired communication lines without insulating and shielding braids;
cable, where bonds are used to transmit such links as cables "twisted pair", coaxial cables or fiber optic cables;
wireless (ground and satellite communications radio channels) that use electromagnetic waves to transmit signals that apply to ether.

Wired lines

Wired (air) communication lines are used to transmit telephone and telegraph signals, as well as for transmitting computer data. These lines are used as trunk communication lines.

Over wired communication lines, analog and digital data transmission channels can be organized. The transfer rate over the wired lines of the "simple old telephone line" (PRIMITIVE OLD TELEPHONE SYSTEM) is very low. In addition, the disadvantages of these lines include noise immunity and the possibility of simple unauthorized connection to the network.

Cable lines

Cable lines have a rather complicated structure. The cable consists of conductors concluded in several layers of isolation. Computer networks use three types of cables.

Twisted para (Twisted pair) - a communication cable that is a twisted pair of copper wires (or several pairs of wires) enclosed in the shielded shell. Wiring pairs are twisted with each other in order to reduce the tip. Twisted steam is quite noiseful. There are two types of this cable: unshielded twisted pair UTP and shielded twisted pair of STP.

Characteristic for this cable is the simplicity of installation. This cable is the cheapest and most common type of communication, which has been widely used in the most common local networks with Ethernet architecture built by the topology type "Star". The cable connects to the network devices using the RJ45 connector.

The cable is used to transmit data at a speed of 10 Mbps and 100 Mbps. Twisted steam is usually used to communicate at a distance of no more than a few hundred meters. The disadvantages of the "Twisted Pair" cable can be attributed to a simple unauthorized connection to the network.

Coaxial cable (Coaxial Cable) is a cable with a central copper wire that is surrounded by a layer of insulating material in order to separate the central conductor from an external conductive screen (copper braid or aluminum foil layer). The external cable screen is insulated.

There are two types of coaxial cable: thin coaxial cable with a diameter of 5 mm and a thick coaxial cable with a diameter of 10 mm. At the thick coaxial cable, the attenuation is less than that of thin. The cost of the coaxial cable is higher than the value of the twisted pair and the installation of the network is more complicated than the twisted pair.

The coaxial cable is applied, for example, in local networks with the Ethernet architecture built on the topology of the type "total tire".

Coaxial cable is more observed than twisted steam and reduces its own radiation. Blowing capacity - 50-100 Mbps. The permissible length of the communication line is somewhat kilometers. Unauthorized connection to a coaxial cable is more complicated than to twisted pair.

Cable fiber optic communication channels. The fiber optic cable (Fiber Optic) is an optical fiber on a silica or plastic basis, concluded in the material with a low refractive index of light, which is closed by an outer shell.

Optical fiber transmits signals in only one direction, so the cable consists of two fibers. The transmitting end of the fiber optic cable requires the transformation of an electrical signal in the light, and at the receiving end the reverse transformation.

The main advantage of this type of cable is an extremely high level of noise immunity and lack of radiation. Unauthorized connection is very difficult. Data transfer rate 3gbit / c. The main disadvantages of the fiber optic cable are the complexity of its installation, small mechanical strength and sensitivity to ionizing radiation.

Wireless (terrestrial and satellite communications radio channels) data transmission channels

Radio channels of ground (radio relay and cellular) and satellite communications are formed using a transmitter and radio receiver and refer to wireless data transmission technology.

Radio Radio Data Transfer Channels

Radio relay communication channels consist of a sequence of stations that are repeaters. Communication is carried out within the limits of direct visibility, the range between adjacent stations is up to 50 km. Digital radio relay communication lines (CRS) are used as regional and local communication and data communication systems, as well as for communication between cellular base stations.

Satellite data channels

In satellite systems, the antennas of the microwave frequency range are used for receiving radio signals from ground stations and relaying these signals back to ground stations. In satellite networks, three main types of satellites are used, which are located on geostationary orbits, medium or low orbits. Satellites are launched, as a rule, groups. They can provide coverage of almost the entire surface of the earth. The operation of the data satellite channel is presented in the picture

Fig. one.

It is more expedient to use satellite communications to organize a communication channel between stations located at very long distances, and the availability of subscribers in the most hard-to-reach points. High bandwidth is a few dozen Mbps.

Cell channel data channels

Cellular radio channels are built according to the same principles as cellular telephone networks. Cellular communication is a wireless telecommunications system, consisting of a network of ground basic receiving and transmitting stations and a cellular switch (or mobile switching center).

Basic stations are connected to the switching center, which provides communication, both between base stations and with other telephone networks and with a global Internet network. According to the functions executable, the switching center is similar to the usual wired communication PBX.

LMDS (Local Multipoint Distribution System) is a standard of cellular network networks for fixed subscribers. The system is built on a cellular principle, one base station allows the area to reach a radius of several kilometers (up to 10 km) and connect several thousand subscribers. The BS themselves unite with each other high-speed ground-based communication channels or radio channels. Data transfer rate up to 45 Mbps.

WiMAX data transmission radio channels WORLDWIDE INTERPERABILITY FOR MICROWAVE ACCESS) are similar to Wi-Fi. WiMAX, unlike traditional radio access technologies, works on a reflected signal, out of the direct visibility of the base station. Experts believe that WiMAX mobile networks open up much more interesting prospects for users than a fixed WiMAX intended for corporate customers. Information can be transmitted at a distance of up to 50 km at a speed of up to 70 Mbps.

MMDS data transmission radio channels Multichannel MultiPoint Distribution System). These systems are able to serve the territory within a radius of 50-60 km, while the direct visibility of the operator's transmitter is not mandatory. The average guaranteed data transfer rate is 500 kbps - 1 Mbps, but can be provided up to 56 Mbps per channel.

Data radio channels for local networks. The standard of wireless communication for local networks is Wi-Fi technology. Wi-Fi provides a connection in two modes: point-point (for connecting two PCs) and an infrastructure connection (for connecting several PC to one access point). Data exchange rate up to 11 Mbps when connecting point-point and up to 54 Mbps with infrastructure compound.

Bluetooht data transmission radio channels - This is the data transfer technology for short distances (no more than 10 m) and can be used to create home networks. The data transfer rate does not exceed 1 Mbps.