What in digital communications is called Ivan. Analog and digital communication lines

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Features of digital PBXs

The advantages of digital PBXs include high reliability, the possibility of flexible programming (for example, LCR), and the availability of microcellular communications. They provide excellent speech quality and have the ability to create a call center. Using a digital PBX allows you to connect system units (up to two devices), develop video telephony, and integrate with a computer network. With its help you can work with BRI and PRI digital lines, as well as Internet telephony.

The functions of digital PBXs are as follows:
- auto attendant - tone dialing of a subscriber, which helps connect the caller to an internal subscriber;
- voice - if the subscriber is busy, the caller can leave a voice message;
- DECT communication - allows employees to move around the office with a DECT handset;
- IP telephony - a communication system that transmits a voice signal over other IP networks or the Internet;
- CTI (computer telephone integration) - allows you to integrate a mini-PBX with software;
- conference calling - provides communication between several participants simultaneously;
- remote administration of digital mini-PBXs - allows you to configure and program the PBX at a distance;
- external loud notification (pedging), which allows you to find the right employee or notify all employees about an event.

Signals are information codes that people use to convey messages in an information system. The signal can be given, but it is not necessary to receive it. Whereas a message can only be considered a signal (or a set of signals) that was received and decoded by the recipient (analog and digital signal).

One of the first methods of transmitting information without the participation of people or other living beings were signal fires. When danger arose, fires were lit sequentially from one post to another. Next, we will consider the method of transmitting information using electromagnetic signals and will dwell in detail on the topic analog and digital signal.

Any signal can be represented as a function that describes changes in its characteristics. This representation is convenient for studying radio engineering devices and systems. In addition to the signal in radio engineering, there is also noise, which is its alternative. Noise does not carry useful information and distorts the signal by interacting with it.

The concept itself makes it possible to abstract from specific physical quantities when considering phenomena related to the encoding and decoding of information. The mathematical model of the signal in research allows one to rely on the parameters of the time function.

Signal types

Signals based on the physical environment of the information carrier are divided into electrical, optical, acoustic and electromagnetic.

According to the setting method, the signal can be regular or irregular. A regular signal is represented as a deterministic function of time. An irregular signal in radio engineering is represented by a chaotic function of time and is analyzed by a probabilistic approach.

Signals, depending on the function that describes their parameters, can be analog or discrete. A discrete signal that has been quantized is called a digital signal.

Signal Processing

Analog and digital signals are processed and directed to transmit and receive information encoded in the signal. Once information is extracted, it can be used for various purposes. In special cases, information is formatted.

Analog signals are amplified, filtered, modulated, and demodulated. Digital data can also be subject to compression, detection, etc.

Analog signal

Our senses perceive all information entering them in analog form. For example, if we see a car passing by, we see its movement continuously. If our brain could receive information about its position once every 10 seconds, people would constantly get run over. But we can estimate distance much faster and this distance is clearly defined at each moment of time.

Absolutely the same thing happens with other information, we can evaluate the volume at any moment, feel the pressure our fingers exert on objects, etc. In other words, almost all information that can arise in nature is analogue. The easiest way to transmit such information is through analog signals, which are continuous and defined at any time.

To understand what an analog electrical signal looks like, you can imagine a graph that shows amplitude on the vertical axis and time on the horizontal axis. If we, for example, measure the change in temperature, then a continuous line will appear on the graph, displaying its value at each moment in time. To transmit such a signal using electric current, we need to compare the temperature value with the voltage value. So, for example, 35.342 degrees Celsius can be encoded as a voltage of 3.5342 V.

Analog signals used to be used in all types of communications. To avoid interference, such a signal must be amplified. The higher the noise level, that is, interference, the more the signal must be amplified so that it can be received without distortion. This method of signal processing spends a lot of energy generating heat. In this case, the amplified signal may itself cause interference for other communication channels.

Nowadays, analog signals are still used in television and radio, to convert the input signal in microphones. But in general, this type of signal is being replaced or replaced by digital signals everywhere.

Digital signal

A digital signal is represented by a sequence of digital values. The most commonly used signals today are binary digital signals, as they are used in binary electronics and are easier to encode.

Unlike the previous signal type, a digital signal has two values “1” and “0”. If we remember our example with temperature measurement, then the signal will be generated differently. If the voltage supplied by the analog signal corresponds to the value of the measured temperature, then a certain number of voltage pulses will be supplied in the digital signal for each temperature value. The voltage pulse itself will be equal to “1”, and the absence of voltage will be “0”. The receiving equipment will decode the pulses and restore the original data.

Having imagined what a digital signal will look like on a graph, we will see that the transition from zero to maximum is abrupt. It is this feature that allows the receiving equipment to “see” the signal more clearly. If any interference occurs, it is easier for the receiver to decode the signal than with analog transmission.

However, it is impossible to restore a digital signal with a very high noise level, while it is still possible to “extract” information from an analog type with large distortion. This is due to the cliff effect. The essence of the effect is that digital signals can be transmitted over certain distances, and then simply stop. This effect occurs everywhere and is solved by simply regenerating the signal. Where the signal breaks, you need to insert a repeater or reduce the length of the communication line. The repeater does not amplify the signal, but recognizes its original form and produces an exact copy of it and can be used in any way in the circuit. Such signal repetition methods are actively used in network technologies.

Among other things, analog and digital signals also differ in the ability to encode and encrypt information. This is one of the reasons for the transition of mobile communications to digital.

Analog and digital signal and digital-to-analog conversion

We need to talk a little more about how analog information is transmitted over digital communication channels. Let's use examples again. As already mentioned, sound is an analog signal.

What happens in mobile phones that transmit information via digital channels

Sound entering the microphone undergoes analog-to-digital conversion (ADC). This process consists of 3 steps. Individual signal values are taken at equal intervals of time, a process called sampling. According to Kotelnikov’s theorem on channel capacity, the frequency of taking these values should be twice as high as the highest signal frequency. That is, if our channel has a frequency limit of 4 kHz, then the sampling frequency will be 8 kHz. Next, all selected signal values are rounded or, in other words, quantized. The more levels created, the higher the accuracy of the reconstructed signal at the receiver. All values are then converted into binary code, which is transmitted to the base station and then reaches the other party, which is the receiver. A digital-to-analog conversion (DAC) procedure takes place in the receiver's phone. This is a reverse procedure, the goal of which is to obtain a signal at the output that is as identical as possible to the original one. Next, the analog signal comes out in the form of sound from the phone speaker.

Stations are divided into analog and digital based on the type of switching. Telephone communication, which operates on the basis of converting speech (voice) into an analog electrical signal and transmitting it over a switched communication channel (analog telephony), has long been the only means of transmitting voice messages over a distance. The ability to sample (by time) and quantize (by level) the parameters of an analog electrical signal (amplitude, frequency or phase) made it possible to convert an analog signal into a digital (discrete) one, process it using software methods and transmit it over digital telecommunication networks.

To transmit an analog voice signal between two subscribers in the PSTN (public telephone network) network, a so-called standard voice frequency (VoF) channel is provided, the bandwidth of which is 3100 Hz. In a digital telephony system, the operations of sampling (in time), quantization (in level), encoding and eliminating redundancy (compression) are performed on an analog electrical signal, after which the data stream thus generated is sent to the receiving subscriber and upon “arrival” at the destination is subjected to reverse procedures.

The speech signal is converted using the appropriate protocol, depending on the network through which it is transmitted. Currently, the most efficient transmission of the flow of any discrete (digital) signals, including those carrying speech (voice), is provided by digital electrical networks that implement packet technologies: IP (Internet Protocol), ATM (Asynchronous Transfer Mode) or FR ( Frame Relay).

The concept of digital voice transmission is said to have originated in 1993 at the University of Illinois (USA). During the next flight of the Endeavor shuttle in April 1994, NASA transmitted its image and sound to Earth using a computer program. The received signal was sent to the Internet, and anyone could hear the voices of the astronauts. In February 1995, the Israeli company VocalTec offered the first version of the Internet Phone program, designed for owners of multimedia PCs running Windows. Then a private network of Internet Phone servers was created. And thousands of people have already downloaded the Internet Phone program from the VocalTec home page and started communicating.

Naturally, other companies very quickly appreciated the prospects offered by the ability to talk while in different hemispheres and without paying for international calls. Such prospects could not go unnoticed, and already in 1995, a flood of products designed for voice transmission over the Network hit the market.

Today, there are several standardized methods of transmitting information that are most widespread in the digital telephony services market: these are ISDN, VoIP, DECT, GSM and some others. Let's try to briefly talk about the features of each of them.

So what is ISDN?

The abbreviation ISDN stands for Integrated Services Digital Network - a digital network with integration of services. This is the modern generation of the worldwide telephone network, which has the ability to transfer any type of information, including fast and correct data transmission (including voice) of high quality from user to user.

The main advantage of the ISDN network is that you can connect several digital or analog devices (telephone, modem, fax, etc.) to one network end, and each can have its own landline number.

A regular telephone is connected to a telephone exchange using a pair of conductors. In this case, one pair can only have one telephone conversation. At the same time, noise, interference, radio, and extraneous voices can be heard in the handset - the disadvantages of analog telephone communication, which “collects” all the interference in its path. When using ISDN, a network termination is installed for the subscriber, and the sound, converted by a special decoder into a digital format, is transmitted through a specially designated (also completely digital) channel to the receiving subscriber, while ensuring maximum audibility without interference and distortion.

The basis of ISDN is a network built on the basis of digital telephone channels (also providing the possibility of packet-switched data transmission) with a data transfer rate of 64 kbit/s. ISDN services are based on two standards:

Basic access (Basic Rate Interface (BRI)) - two B-channels 64 kbit/s and one D-channel 16 kbit/s

Primary access (Primary Rate Interface (PRI)) - 30 B-channels 64 kbps and one D-channel 64 kbps

Typically, BRI bandwidth is 144 Kbps. When working with PRI, the entire digital communication backbone (DS1) is fully used, which gives a throughput of 2 Mbit/s. The high speeds offered by ISDN make it ideal for a wide range of modern communications services, including high-speed data transfer, screen sharing, video conferencing, large file transfer for multimedia, desktop video telephony and Internet access.

Strictly speaking, ISDN technology is nothing more than one of the varieties of “computer telephony”, or, as it is also called CTI telephony (Computer Telephony Integration).

One of the reasons for the emergence of CTI solutions was the emergence of requirements to provide company employees with additional telephone services that were either not supported by the existing corporate telephone exchange, or the cost of purchasing and implementing a solution from the manufacturer of this exchange was not comparable with the convenience achieved.

The first signs of CTI service applications were systems of electronic secretaries (autoattended) and automatic interactive voice greetings (menus), corporate voice mail, answering machines and conversation recording systems. To add the service of a particular CTI application, a computer was connected to the company’s existing telephone exchange. It contained a specialized board (first on the ISA bus, then on the PCI bus), which was connected to the telephone exchange via a standard telephone interface. Computer software running under a specific operating system (MS Windows, Linux or Unix) interacted with the telephone exchange through a program interface (API) of a specialized board and thereby provided the implementation of an additional corporate telephony service. Almost simultaneously with this, a software interface standard for computer-telephony integration was developed - TAPI (Telephony API)

For traditional telephone systems, CTI integration is carried out as follows: some specialized computer board is connected to the telephone exchange and transmits (translates) telephone signals, the state of the telephone line and its changes into a “software” form: messages, events, variables, constants. The telephone component is transmitted via the telephone network, and the software component is transmitted via a data network or IP network.

What does the integration process in IP telephony look like?

First of all, it should be noted that with the advent of IP telephony, the very perception of a telephone exchange (Private Branch eXchange - PBX) has changed. IP PBX is nothing more than another network service of the IP network, and, like most IP network services, it operates in accordance with the principles of client-server technology, i.e., it assumes the presence of service and client parts. So, for example, an email service on an IP network has a service part - a mail server and a client part - a user program (for example, Microsoft Outlook). The IP telephony service is structured similarly: the service part - the IP PBX server and the client part - the IP telephone (hardware or software) use a single communication medium - the IP network - to transmit voice.

What does this give the user?

The advantages of IP telephony are obvious. Among them are rich functionality, the ability to significantly improve employee interaction and at the same time simplify system maintenance.

In addition, IP communications are evolving in an open manner due to protocol standardization and global IP penetration. Thanks to the principle of openness in the IP telephony system, it is possible to expand the services provided and integrate with existing and planned services.

IP telephony allows you to build a single centralized management system for all subsystems with differentiated access rights and operate subsystems in regional divisions using local personnel.

The modularity of the IP communications system, its openness, integration and independence of components (unlike traditional telephony) provide additional opportunities for building truly fault-tolerant systems, as well as systems with a distributed territorial structure.

Wireless communication systems of the DECT standard:

The DECT (Digital Enhanced Cordless Telecommunications) wireless access standard is the most popular mobile communication system in a corporate network, the cheapest and easiest to install option. It allows you to organize wireless communication throughout the enterprise, which is so necessary for “mobile” users (for example, enterprise security or heads of workshops and departments).

The main advantage of DECT systems is that with the purchase of such a phone you get a mini-PBX for several internal numbers almost free of charge. The fact is that you can purchase additional handsets for the DECT base once purchased, each of which receives its own internal number. From any handset you can easily call other handsets connected to the same base, transfer incoming and internal calls, and even carry out a kind of “roaming” - register your handset on another base. The reception radius of this type of communication is 50 meters indoors and 300 meters outdoors.

To organize mobile communications in public networks, cellular networks of GSM and CDMA standards are used, the territorial efficiency of which is practically unlimited. These are the standards of the second and third generation of cellular communications, respectively. What are the differences?

Every minute, several phones located in its vicinity try to contact any base station of a cellular network. Therefore, stations must provide “multiple access”, that is, simultaneous operation of several telephones without mutual interference.

In first generation cellular systems (standards NMT, AMPS, N-AMPS, etc.), multiple access is implemented by the frequency method - FDMA (Frequency Division Multiple Access): the base station has several receivers and transmitters, each of which operates at its own frequency, and the radiotelephone tunes to any frequency used in the cellular system. Having contacted the base station on a special service channel, the phone receives an indication of which frequencies it can occupy and tunes to them. This is no different from the way a particular radio wave is tuned.

However, the number of channels that can be allocated at the base station is not very large, especially since neighboring cellular network stations must have different sets of frequencies so as not to create mutual interference. Most second-generation cellular networks began to use the time-frequency method of channel division - TDMA (Time Division Multiple Access). In such systems (and these are networks of GSM, D-AMPS, etc. standards) different frequencies are also used, but each such channel is allocated to the phone not for the entire communication time, but only for short periods of time. The remaining same intervals are alternately used by other phones. Useful information in such systems (including speech signals) is transmitted in “compressed” form and in digital form.

Sharing each frequency channel with several phones makes it possible to provide service to a larger number of subscribers, but there are still not enough frequencies. CDMA technology, built on the principle of code division of signals, was able to significantly improve this situation.

The essence of the code division method used in CDMA is that all phones and base stations simultaneously use the same (and at the same time the entire) frequency range allocated for the cellular network. In order for these broadband signals to be distinguished from each other, each of them has a specific code “coloring”, which ensures that it stands out from the others.

Over the past five years, CDMA technology has been tested, standardized, licensed and launched by most wireless equipment vendors and is already in use around the world. Unlike other methods of subscriber access to the network, where signal energy is concentrated on selected frequencies or time intervals, CDMA signals are distributed in a continuous time-frequency space. In fact, this method manipulates frequency, time, and energy.

The question arises: can CDMA systems, with such capabilities, “peacefully” coexist with AMPS/D-AMPS and GSM networks?

It turns out they can. Russian regulatory authorities have allowed the operation of CDMA networks in the radio frequency band 828 - 831 MHz (signal reception) and 873-876 MHz (signal transmission), where two CDMA radio channels with a width of 1.23 MHz are located. In turn, the GSM standard in Russia is allocated frequencies above 900 MHz, so the operating ranges of CDMA and GSM networks do not overlap in any way.

What I want to say in conclusion:

As practice shows, modern users are increasingly gravitating towards broadband services (video conferencing, high-speed data transfer) and increasingly prefer a mobile terminal to a regular wired one. If we also take into account the fact that the number of such applicants in large companies can easily exceed a thousand, we get a set of requirements that only a powerful modern digital exchange (PBX) can satisfy.

Today, the market offers many solutions from various manufacturers that have the capabilities of both traditional PBXs, switches or routers for data networks (including ISDN and VoIP technologies), and the properties of wireless base stations.

Digital PBXs today, to a greater extent than other systems, meet these criteria: they have broadband channel switching, packet switching capabilities, are easily integrated with computer systems (CTI) and allow the organization of wireless microcells within corporations (DECT).

Which of the following types of communication is better? Decide for yourself.

Every day people are faced with the use of electronic devices. Modern life is impossible without them. After all, we are talking about TV, radio, computer, telephone, multicooker and so on. Previously, just a few years ago, no one thought about what signal was used in each working device. Now the words “analog”, “digital”, “discrete” have been around for a long time. Some types of signals listed are of high quality and reliable.

Digital transmission came into use much later than analogue. This is due to the fact that such a signal is much easier to maintain, and the technology at that time was not so improved.

Every person encounters the concept of “discreteness” all the time. If you translate this word from Latin, it will mean “discontinuity.” Delving far into science, we can say that a discrete signal is a method of transmitting information, which implies a change in time of the carrier medium. The latter takes any value from all possible. Now discreteness is fading into the background, after the decision was made to produce systems on a chip. They are holistic, and all components closely interact with each other. In discreteness, everything is exactly the opposite - each detail is completed and connected to others through special communication lines.

Signal

A signal is a special code that is transmitted into space by one or more systems. This formulation is general.

In the field of information and communications, a signal is a special data carrier that is used to transmit messages. It can be created, but not accepted; the latter condition is not necessary. If the signal is a message, then “catching” it is considered necessary.

The described code is specified by a mathematical function. It characterizes all possible changes in parameters. In radio engineering theory, this model is considered basic. In it, noise was called an analogue of the signal. It represents a function of time that freely interacts with the transmitted code and distorts it.

The article describes the types of signals: discrete, analog and digital. The basic theory on the topic described is also briefly given.

Types of signals

There are several signals available. Let's look at what types there are.

Based on the physical medium of the data carrier, they are divided into electrical, optical, acoustic and electromagnetic signals. There are several other species, but they are little known.
According to the method of setting, signals are divided into regular and irregular. The first are deterministic methods of data transmission, which are specified by an analytical function. Random ones are formulated using the theory of probability, and they also take on any values at different periods of time.
Depending on the functions that describe all signal parameters, data transmission methods can be analog, discrete, digital (a method that is quantized in level). They are used to power many electrical appliances.

Now the reader knows all types of signal transmission. It won’t be difficult for anyone to understand them; the main thing is to think a little and remember the school physics course.

Why is the signal processed?

The signal is processed in order to transmit and receive information that is encrypted in it. Once it is extracted, it can be used in a variety of ways. In some situations it will be reformatted.

There is another reason for processing all the signals. It consists of a slight compression of frequencies (so as not to damage the information). After this, it is formatted and transmitted at slow speeds.

Analog and digital signals use special techniques. In particular, filtering, convolution, correlation. They are necessary to restore the signal if it is damaged or has noise.

Creation and formation

Often, an analog-to-digital converter (ADC) is needed to generate signals. Most often, both of them are used only in situations where DSP technologies are used. In other cases, only using a DAC will do.

When creating physical analog codes with the further use of digital methods, they rely on the information received, which is transmitted from special devices.

Dynamic range

It is calculated by the difference between the higher and lower volume levels, which are expressed in decibels. It completely depends on the work and the characteristics of the performance. We are talking about both music tracks and ordinary dialogues between people. If we take, for example, an announcer who reads the news, then his dynamic range fluctuates around 25-30 dB. And while reading any work, it can rise to 50 dB.

Analog signal

An analog signal is a time-continuous method of data transmission. Its disadvantage is the presence of noise, which sometimes leads to a complete loss of information. Very often situations arise that it is impossible to determine where the important data is in the code and where there are ordinary distortions.

It is because of this that digital signal processing has gained great popularity and is gradually replacing analog.

Digital signal

A digital signal is special; it is described by discrete functions. Its amplitude can take on a certain value from those already specified. If an analog signal is capable of arriving with a huge amount of noise, then a digital signal filters out most of the received noise.

In addition, this type of data transmission transfers information without unnecessary semantic load. Several codes can be sent at once through one physical channel.

There are no types of digital signal, since it stands out as a separate and independent method of data transmission. It represents a binary stream. Nowadays, this signal is considered the most popular. This is due to ease of use.

Application of digital signal

How does a digital electrical signal differ from others? The fact that he is capable of performing complete regeneration in the repeater. When a signal with the slightest interference arrives at communication equipment, it immediately changes its form to digital. This allows, for example, a TV tower to generate a signal again, but without the noise effect.

If the code arrives with large distortions, then, unfortunately, it cannot be restored. If we take analog communications in comparison, then in a similar situation a repeater can extract part of the data, spending a lot of energy.

When discussing cellular communications of different formats, if there is strong distortion on a digital line, it is almost impossible to talk, since words or entire phrases cannot be heard. In this case, analog communication is more effective, because you can continue to conduct a dialogue.

It is precisely because of such problems that repeaters form a digital signal very often in order to reduce the gap in the communication line.

Discrete signal

Nowadays, every person uses a mobile phone or some kind of “dialer” on their computer. One of the tasks of devices or software is to transmit a signal, in this case a voice stream. To carry a continuous wave, a channel is required that has the highest level of throughput. That is why the decision was made to use a discrete signal. It does not create the wave itself, but its digital appearance. Why? Because the transmission comes from technology (for example, a telephone or computer). What are the advantages of this type of information transfer? With its help, the total amount of transmitted data is reduced, and batch sending is also easier to organize.

The concept of “sampling” has long been steadily used in the work of computer technology. Thanks to this signal, not continuous information is transmitted, which is completely encoded with special symbols and letters, but data collected in special blocks. They are separate and complete particles. This encoding method has long been relegated to the background, but has not disappeared completely. It can be used to easily transmit small pieces of information.

Comparison of digital and analog signals

When buying equipment, hardly anyone thinks about what types of signals are used in this or that device, and even more so about their environment and nature. But sometimes you still have to understand the concepts.

It has long been clear that analog technologies are losing demand, because their use is irrational. In return comes digital communication. We need to understand what we are talking about and what humanity is refusing.

In short, an analog signal is a method of transmitting information that involves describing data in continuous functions of time. In fact, speaking specifically, the amplitude of oscillations can be equal to any value within certain limits.

Digital signal processing is described by discrete time functions. In other words, the amplitude of oscillations of this method is equal to strictly specified values.

Moving from theory to practice, it must be said that the analog signal is characterized by interference. There are no such problems with digital, because it successfully “smoothes” them out. Thanks to new technologies, this method of data transfer is capable of restoring all the original information on its own without the intervention of a scientist.

Speaking about television, we can already say with confidence: analogue transmission has long outlived its usefulness. Most consumers are switching to a digital signal. The disadvantage of the latter is that while any device can receive analog transmission, a more modern method requires only special equipment. Although the demand for the outdated method has long fallen, these types of signals are still not able to completely disappear from everyday life.

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What in digital communications is called Ivan. Analog and digital communication lines

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