Smudge of frequencies in traditional telephony. Technical channels are the flow of information that is transmitted through communication channels. Modems for analog telephone lines

2.1.1. Analogue telephone connections

Analog telephone networks are connected to global networks with circuit switching, which were created to provide secretly accessible telephone services to the population. Analog telephone connections are oriented towards connection, which is installed before the start of communication (voice transmission) between subscribers. The telephone network is established (connected) behind additional switchboards of automatic telephone exchanges.

Telephone barriers are formed by:

automatic telephone exchanges (ATS);
telephone devices;
trunk line connection (line connection between automatic telephone exchanges);
subscriber lines (lines that connect telephone devices to the PBX).

The subscriber sees the line that connects his telephone set to the PBX. Trunk lines are connected via vikorist by subscribers via.

Analog telephone networks are also used for transmitting data in the network:

to the extent of access through packet switching, for example, connecting to the Internet (stating both switched and visible telephone lines);
highways and packet networks (mainly stagnation of visible telephone lines).

Analog telephone circuitry with circuit switching provides packet circuitry with physical level services, after switching with a physical point-to-point channel.

Zvichaina telephone number or POTS(Plain Old Telephone Service - an old “flat” telephone service) will ensure the transmission of voice signals between subscribers with a frequency range of up to 3.1 kHz, which is completely sufficient for normal communication. To communicate with subscribers, a two-wire line is used, so that the signals from both subscribers travel at the same time in interconnected directions.

The telephone line consists of an impersonal station, where hierarchical connections exist among themselves. The switches of these stations lay routes between the PBX calls and subscriber calls under the control of information provided by the alarm system. Trunk lines between telephone exchanges are responsible for ensuring the possibility of one-hour transmission of a large amount of information (supporting a high volume of connections).

It is insufficient to see for the skin connection around the main line, and for a more effective vicinity of the physical lines to stool:

method of frequency amplification of channels;
digital channels and multiplexing of digital streams without the presence of subscribers.

Method of frequency amplification of channels (FDM - Frequency Division Multiplexing)

In this case, a single cable transmits multiple channels, in which a low-frequency voice signal is modulated by a high-frequency generator signal. The skin channel is powered by a moisture generator, and the frequencies of these generators are separated from each other in order to transmit signals at a frequency of up to 3.1 kHz from the normal level.

Installation of digital channels for long-distance broadcasts

For this purpose, the analog signal from the subscriber line at the telephone exchange is digitized and then delivered in digital form to the recipient's telephone exchange. There it is reverse converted and transmitted to an analog subscriber line.

To ensure two-way communication at the telephone exchange, the end of the subscriber line contains a pair of converters - ADC (analog-to-digital) and DAC (digital-to-analog). For voice communication with standard dark bandwidth (3.1 kHz), a quantization frequency of 8 kHz is adopted. A pleasant dynamic range (the ratio of the maximum signal to the minimum) is ensured with 8-bit reversal.

It turns out that the telephone channel has a data transmission speed of 64 kbit/s (8 bit x 8 kHz).

Often, 7-bit samples are interleaved to transmit a signal, and the eighth (least significant) bit is sampled for signaling purposes. In this situation, the pure voice stream drops to 56 kbit/s.

For efficient transmission of highway lines, digital streams from unattended subscribers at telephone exchanges are multiplexed into channels of different capacities to connect telephone exchanges with each other. At the other end of the channel, demultiplexing is carried out - seeing the necessary flow from the channel.

Multiplexing and demultiplexing, of course, is carried out at both ends simultaneously, since telephone calls are two-way. Multiplexing operates at the same time per hour (TDM - Time Division Multiplexing).

On the main channel, information is organized in a seemingly uninterrupted sequence of frames. The cutaneous subscriber channel in the skin frame is introduced The hour interval during which data is transmitted to this channel.

Thus, in current analog telephone lines, analog signals are transmitted over the subscriber line, and digital signals are transmitted in trunk lines.

Modems for analog telephone lines

Telephone networks of the Internet, in addition to voice transmission, allow the transmission of digital data using additional modems.

A modem (modulator-demodulator) is used to transmit data to large distances from cable networks and switched telephone lines.

The modulator converts dual information from the computer into analog signals with frequency or phase modulation, the spectrum of which is consistent with the transmission of voice telephone lines. The demodulator from this signal extracts encoded double information and transmits it to the receiving computer.

Fax modem (fax-modem) allows you to send and receive fax images, including those of other fax machines.

Modems for viewing telephone lines

The visible physical lines have a wide range of bandwidth, but are not connected. For them, special modems are produced to ensure data transmission at speeds up to 2048 kbit/s on the data station.

xDSL technologies

xDSL technologies are based on converting a telephone subscriber line from analogue to digital xDSL (Digital Subscriber Line). The essence of this technology lies in the fact that at both ends of the subscriber line - on the PBX and at the subscriber - splitter filters are installed.

The low-frequency (up to 3.5 kHz) signal is transmitted to the primary telephone equipment (PBX port and the subscriber’s telephone set), and the high-frequency (more than 4 kHz) signal is used to transmit data via additional xDSL modems.

xDSL technologies allow one and the same telephone line to be used simultaneously for both data transmission and voice transmission (telephone conversations), which is not allowed by primary modems for switched lines.

Please tell us that we don’t care how the telephone line works (unless we have to shout into the telephone receiver: “Repeat, please, don’t hear anything!”).

Telephone companies provide their customers with a number of unsolicited services. It’s not so easy to find out about the price lists for these services - it’s better to pay for each service, and how much to pay for each service. This article does not say a word about prices, but we will try to understand the difference between the most frequently sold products and services in the field of telephone calling.

ANALOGUE LINES, DIGITAL LINES

First of all, the lines are analog and digital. The analog signal changes continuously; The song always has meaning, which represents, for example, the depth and height of the voice conveyed or the color and brightness of the song's image. Digital signals contain only discrete values. As a rule, the signal is either on or off, either on or off. In other words, its value is either 1 or 0.

Analog telephone lines have been used in telephones since time immemorial. Most telephones from fifty years ago can be connected to a subscriber loop - the line between the home telephone socket and the central telephone exchange. (The central telephone exchange is not a blazing light in the center of the city; the subscriber line on average does not travel 2.5 miles (several kilometers), so the "central telephone exchange" is usually located in some unostentatious booth ik.)

During the telephone call, the microphone converts the signal into an analog signal, which is transmitted to the central telephone exchange, and is sent either to another subscriber loop or to other switching devices, such as a call There is a number that is located in the zone of the given station. When dialing a number, the telephone machine generates signals transmitted over the same main channel (in-band signals), which indicate who is receiving the call.

Within an hour of their existence, telephone companies have accumulated great expertise in transmitting language. It has been established that the generally sufficient frequency range for this kingdom is 300 to 3100 Hz. It is clear that hi-fi class audio systems produce sound without interference in the frequency range of 20-20000 Hz, which means that the telephone range increases in order for the subscriber to recognize who to call by voice (for Others stock this range with great compatibility It must be narrow - for transmitting music, for example, telephone calls are not suitable at all). The telephone company will ensure a smooth decline in the amplitude-frequency characteristics at high and low frequencies for an additional analog telephone channel of 4000 Hz.

The central telephone exchange typically digitizes the signal for further transmission over the telephone network. Between Gilbeth County (Arkansas) and Ret Fork (Wyoming), all American telephone networks transmit signals between central stations in digital form. Although many companies rely on digital PBX installations and data transmission methods, and all ISDN methods are based on digital coding, subscriber loops, as previously, are deprived of the “remaining stronghold” of analog communication. It is explained that most phones in private booths do not bear the cost of digitizing the signal and cannot work with lines with a bandwidth of over 4000 Hz.

WHAT IS 4000 Hz FOR?

A modem is a device that converts digital signals from a computer into analog signals with frequencies between the telephone line. The maximum capacity of the channel is directly related to the capacity of the channel. More precisely, the amount of data throughput (in bits/sec) is determined by the data throughput and the signal/noise tolerance. At this time, the maximum throughput of modems - 33.6 Kbit / s - is already close to this limit. Some modems with a throughput capacity of 28.8 kbit/s know that a noisy analog line rarely ensures their full throughput, which often turns out to be much lower. Compression, caching and other changes will help to correct the situation, and we will at least survive until the output of the eternal engine, even before the appearance of modems with a capacity of 50 or even 40 Kbps per primary analog lines.

Telephone companies do their best job of digitizing the analog signal. To transmit digital signals, channels with a capacity of 64 Kbit/s are used (light standard). This channel, called DS0 (digital signal, zero level), is the basic link from which all other telephone lines will be. For example, you can combine (the correct term is to amplify) 24 DS0 channels into DS1 channels. By renting the T-1 line, the customer actually takes away the DS1 channel. Due to the total throughput of DS1, the memory required is that after each 192 information bits (that is, 8000 times per second), one synchronization bit is transmitted: a total of 1.544 Mbit / s (64000 times go to 24 plus 8000).

SEEN LINES, connected lines

In addition to the T-1 line, the client can rent a line view or have access to local commutating lines. By renting a T-1 line or a low-speed data line from a telephone company, such as a dataphone digital service (DDS), the subscriber is actually renting a direct connection and, as a result, ends up with a single channel with a bandwidth of 1, 544 Mbit/s (T -1) or 56 Kbit/s (low-speed line).

Although frame relay technology transmits the switching of individual frames, related services are provided in the form of virtual channels connecting between fixed end points. From the point of view of the architecture of the network, frame relay can be seen rather than as seen, rather than as a switched line; The important fact is that the price of such a service with the same throughput is significantly lower.

Switching services (an example of these can be servicing a regular apartment telephone) - these are services attached to a telephone company. The subscriber may be required to establish an additional network of switchboards to connect with any telephone network node. In addition to the situation with visible lines, the fee in this case is charged per hour of connection or the actual traffic flow and to be based on the greater frequency and the duty of monitoring the network. Digital communications switching services can be provided based on X.25, Switched 56, ISDN Basic Rate Interface (BRI), ISDN Primary Rate Interface (PRI), Switched Multimegabit Data Service (SMDS) and ATM protocols. Some organizations, such as universities, highways or municipal organizations, create private networks with local power switches and leased ones, and sometimes run their own power lines.

Since the line assigned to the telephone company is digital, then for the exchange of data between the telephone network and end devices (this term telephone companies mean equipment such as computers, fax machines, and digital telephones) there is no need to convert digital signals into analog, and therefore the need for a modem disappears. In this case, the use of a telephone network imposes disadvantages on the subscriber. Zokrem, to ensure the correct termination of the subscriber loop, the correct transmission of traffic and support for diagnostics, installed by the telephone company.

The line that supports the ISDN BRI protocol is connected to a device called NT1 (network termination 1). In addition to the termination of the line and supporting the diagnostic procedures of the NT1 devices, it is possible to use a two-wire subscriber loop with several digital termination systems. When renting T-1 or DDS digital lines, as well as digital communications services, the connection to the line is limited to a channel service unit (CSU). The CSU acts as a terminator, ensuring correct line activation and operational diagnostic commands. The final equipment, available to the client, interacts with the data service unit (DSU), which converts digital signals to a standard form and transmits them to the CSU. Structurally, CSU and DSU are often combined into one module called CSU / DSU. DSU can be built into a router or multiplexer. In this case, and in this case (although modems are not needed here), it will be necessary to install new interface devices.

WEARING FOR TELEPHONE CALL

Most analog subscriber loops can only provide a throughput of 33.6 Kbit/s even with the most willing minds. On the other hand, the same twisted pair that connects the office to the central telephone exchange can be used to work with ISDN BRI, which gives data throughput of 128 Kbit/s and another 16 Kbit/s for Corrections and settings. What's on the right? The signal transmitted over analog telephone lines is subject to filtering to suppress all frequencies above 4 kHz. When there are multiple digital lines, such filtering is not required, so the throughput of the pair’s spins is much wider, and hence the throughput increases.

Leased lines with a capacity of 56 and 64 Kbps are two-wire or multi-wire digital lines (in the remaining case, one pair is used for transmission, and the other for reception). These lines are attached to the carrier for providing digital communication services, for example, frame relay or Switched 56. In the carrier for T-1, as well as ISDN PRI and frame relay, there are often several lines or optical lines cables Lines T-3 inodes are a coaxial cable, but more often than not they are still connected to an optical cable.

Although ISDN has always received the greatest respect for its high-bandwidth signal transmission over large distances, more new connections have appeared for the “remain mile” (or local loop). PairGain and AT&T Paradyne offer products based on Bellcore's proprietary high bit-rate digital subscriber loop (HDSL) technology. These products allow for the equalization of all active subscriber loops; By installing HDSL devices at both ends of the line, you can reduce the throughput of DS1 (1.544 Mbps) on almost all other subscriber loops. (HDSL up to 3.7 km can be installed on subscriber loops without repeating in different standard 24-gauge wires. For the operation of T-1 calling lines, it is necessary to install repeaters through every kilometer-repeat). An alternative to HDSL with the available bandwidth of DS1 on the “remaining mile” is either the replacement of fiber optic cable (which is very expensive), or the installation of several repeaters on the skin line (which is not as expensive as fiber optic technology, but still not cheap o). In addition, in this period, the telephone company's, and therefore the customer's, costs for maintaining the line in the work place are increasing.

And HDSL is the word of technology in the field of increasing capacity on the “remaining mile”. It turns out that HDSL, asymmetrical digital subscriber line (ASDL) technology, can provide a throughput of 6 Mbit/s in one direction; The bandwidth of the other source is quite lower - almost 64 Kbit/s. Ideally, or at a minimum, if there is a monopoly, it is important to ensure that the value of the service for the customer is approximately equivalent to the value for the telephone company - a great deal The entities could be purchased with ISDN PRI (or other T-1 based services) at a cost , which can be compared to the current ISDN BRI price.

However, today's ISDN adopters, who have paid for everything, don't have to worry about anything; In most cases, telephone companies can increase the capacity of the line and put all profits into the mix without reducing the quality of service for the client. It is not at all obvious that tariffs for guilty services are based on sound principles.

Table 1. Types of telephone services

Line type	servant	type of commutation	Nose of the subscriber loop
analog line		line commutation	Two-wire twisted pair
DS0(64 Kbit/s)	DDS (rented line)	Line visible
		PVC with switching	Double or multi-conductive twisted pair
		commutation	Double or multi-conductive twisted pair
		line commutation	Double or multi-conductive twisted pair
		line commutation	Double or multi-conductive twisted pair
		line commutation	Two-wire twisted pair
sprat DS0 (Video 64 Kbit/s to Thousand five hundred thirty six Mbit/s Krokom 64 Kbit/s)		Line visible	Double or multi-conductive twisted pair
		PVC with switching	Double or multi-conductive twisted pair
(One thousand five hundred and forty four Mbit/s) (24 lines DS0)	Line T-1 leased	Line visible
		PVC with switching	Highly conductive twisted pair or optical fiber
		packet switching	Highly conductive twisted pair or optical fiber
		line commutation	Highly conductive twisted pair or optical fiber
(44736 Mbit/s) (28 DS1 lines, 672 lines DS0)		Stilnikovy commutation
(44736 Mbit/s) (28 DS1 lines, 672 lines DS0)		packet switching	Coaxial cable or optical fiber

You can contact Steve Steinke via the Internet at:

Smuga transparency (prosorosti)- the frequency range within which the amplitude-frequency response (AFC) of an acoustic, radio engineering, optical or mechanical device must be maintained equally in order to ensure signal transmission without any distortion of its shape. Alternatively, instead of the term “bandwidth”, the term “effectively transmitted frequencies (ECHR)” is used. The ECHR focuses on the main energy of the signal (not less than 90%). This frequency range is established for the skin signal experimentally as accurately as possible.

Main parameters of smudge throughput

The main parameters that characterize the range of frequency transmission are the width of the range of transmission and the unevenness of the frequency response between the ranges.

Width of smudge throughput

The bandwidth is a range of frequencies, within which the unevenness of the frequency response does not exceed the specified one.

The width of the smudge is determined as the difference between the upper and lower limiting frequencies of the frequency response section f 2 - f 1 (\displaystyle f_(2)-f_(1)), To what extent is the amplitude of Kolivan older? 1 2 (\displaystyle (\frac (1) (\sqrt (2))))(Or, which is equivalent 1 2 (\displaystyle (\frac (1)(2))) for tension) to the maximum. This level approximately corresponds to -3 dB.

The transmission width is expressed in frequency units (for example, in hertz).

In radio communications and information transmission devices, increased bandwidth allows for the transmission of more information.

frequency response unevenness

The unevenness of the frequency response characterizes the stage of its evolution from the direct, parallel frequency axis.

Reducing the frequency response unevenness in a smoothie improves the shape of the signal that is transmitted.

separate:

Absolute transmission: 2Δω = Sa
Vidnosna smuga transmission: 2Δω / ωo = So

specific butts

In the antenna theory, transmission is the range of frequencies at which the antenna operates effectively, depending on the region of the central (resonant) frequency. Depend on the antenna type and geometry. In practice, the amount of throughput is determined by a given SWR level (standing power ratio), for example, equal to 2.

The high transmittance shows that the dispersion imposes limitations on the transmission range and on the upper frequency of signal transmission.

It is possible to pass through various devices according to their purposes. For example, for telephone communication a range of approximately 3 kHz (300-3400 Hz) is sufficient, for high-quality musical production - no less than 30-16000 Hz, and for television communication - up to 8 MHz wide)

Types: 9

Feeding for the knowledgeable: Kokova Smuha transmission of sound frequencies to telephone calls

With respect, Nurslan

Beautiful species

Mikola Ivanov:

300 Hz - 3400 Hz. or 0.3 - 2.7 kHz

What do you mean by sound frequencies, the frequency in the transmission channel - either a drone or a drone - is the frequency of the electromagnetic field, and the frequency of the sound does not lie under the speaker in the telephone handset. The sound is not transmitted in the communication channels))

battalion commander:

The range of frequencies of telephone channels 0.3-3.4 kHz (standard telephone channel) is effectively transmitted, for the possibility of strengthening the channel, i.e., transmitting to a channel that, in addition to sound, vicorizes established channels 0.3-2.7 kHz

Video clip

This video will help you get started

Types of scientists

Volodymyr Nikolaev:

If the signal has a sinusoidal appearance, then there is one frequency of this sinusoid, if the signal is pulsed, then it can be divided into a series.

An Drew:

Ruslan Mamishev:

If you don’t know your words, figure it out, and when you understand, set your nutrition accordingly...

Great wind:

Well, the food itself and the answer is a range of frequencies, in short from what to this.... It’s already scary to go to Wikipedia, felting and there, ultrasound was raised from 20 kHz to 1 GHz, I didn’t fall much, and still hypersound is over 1 GHz. ...))))))))))) What kind of felting did they hit him with? Why write something like that in Wiki...

Everything is fine:

Whether the signal ends at the end of the hour, it has an IMMENSELY large spectrum width.
Slide talk about
the effect of a new spectrum width, in which 90% of the energy is concentrated (over the year)
signal.
osnovy-elektrotekhniki. ru / energeticheskie-xarakteristiki /

Voice frequency circuit is a combination of technical features and a widened midrange that ensures the transmission of electrical signals in an effectively transmitted mix of frequencies (EPF) 0.3 - 3.4 kHz. Telephony communications are often abbreviated with the abbreviation KCH. The voice frequency channel is a unit of capacity dimming (amplification) of analogue transmission systems (for example, K-24, K-60, K-120). At the same time, for digital transmission systems (for example, IKM-30, IKM-480, IKM-1920), the unit of variable capacity is the main digital channel.
The range of frequencies is effectively transmitted - the range of frequencies, excessive attenuation at extreme frequencies, which increases from excessive attenuation at a frequency of 800 Hz by no more than 1 Np at the maximum communication range, according to the system.
The width of the ECHR indicates the capacity of telephone transmission, and the ability to use a telephone channel to transmit other types of communications. In accordance with the international standard for telephone channels of multi-channel equipment, an ECHR of 300 to 3400 Hz has been installed. With such a smoothie, a high level of speech intelligibility is ensured, the sound is well natural and there is great potential for re-strengthening telephone channels.

Almost all electrical signals that display real information span an endless spectrum of frequencies. For the unrestricted transmission of such signals, a bi-channel with uninterrupted capacity is required. On the other hand, you want to spend at the reception one of the warehouse spectrum until it matches the time-clock form of the signal. Therefore, the task is to transmit the signal in the interconnected channel in such a way that the signal is supported by the capabilities and capacity of information transfer. Thus, the range of frequencies does not limit the spectrum of the signal (due to technical and economic reduction and the transmission speed).

The width of the range of frequencies ΔF is determined by the difference between the upper FB and lower fn frequencies in the spectrum of the signal, with the arrangement of its boundary. Thus, for a periodic sequence of forward pulses, the orientation of the signal can be determined from the virus:

where tn is the severity of the impulse.

The first telephone signal (messenger notification), also known as subscriber signal, is a non-stationary phased process with a range of frequencies from 80 to 12,000 Hz. The clarity of the voice is indicated by formants (stronger areas of the frequency spectrum), most of which are distributed in the smoothie 300 ... 3400 Hz. Therefore, based on the recommendation of the International Advisory Committee on Telephony and Telegraphy (ICITT), a range of frequencies 300 ... 3400 Hz was effectively transferred for telephone transmission. This signal is called a tone frequency (TV) signal. When the intensity of transmitted signals remains high, the warehouse diversity becomes close to 90%, and the diversity of phrases becomes 99%.

Sound communication signals. In terms of sound when transmitting programs, musical instruments or a person’s voice. The spectrum of the sound signal occupies a range of frequencies from 20 to 20,000 Hz.

For high power (first class channels) the range of ΔFC frequencies must be 50 ... 10000 Hz, for uncontrolled programming (high class channels) - 30 ... 15000 Hz, for other classes - 100 ... 6800 Hz .

In general, television has adopted a method of step-by-step conversion of a skin element of an image into an electrical signal with further transmission of this signal through one communication channel. To implement this principle, special electron-exchange tubes are installed on the transmitting side, which transform the optical image of the object, which is transmitted into the electrical video signal activated at the hour.

Malyunok 2.2.1 - Design of the transfer tube

Like a butt for a baby 2.2.1 representations in a simplified form is one of the options for the transmission tube. In the middle of the glass flask, which is under high vacuum, there is a removable high-visibility photocathode (target) and an electronic spotlight (EP). The call is placed on the neck of the tube (OS). The searchlight forms a thin electronic membrane, which, when injected, accelerates the fields towards the target. Behind the help of the system that animates the target, it moves to the right (along the rows) and down (along the frame), going around the entire surface of the target. The totality of all (N) rows is called a raster. An image is projected onto a tube target coated with a light-sensitive ball. As a result, the skin of the target area acquires an electrical charge. This creates a potential relief. The electronic circuit interacts with the skin area (point) of the potential relief, as if erasing (neutralizing) its potential. The flow that flows through the vanation support Rн will lie under the illumination of the target area, which consumes the electronic circuit, and the video signal Uc is visible on the vanator (Figure 2.2.2). The voltage of the video signal will vary from a “black” level, which corresponds to the darkest parts of the transmitted image, to a “white” level, which corresponds to the most light parts of the image.