We all use mobile phones, but rarely who thinks - how do they work? In this article we will try to figure out how, in fact, communication is being implemented regarding your mobile operator.
When you call your interlocutor, or someone calls you, your phone is connected by a radio channel with one of the antennas of the neighboring base Station (BS, BS, Base Station). How the base station of cellular communication (in common - cellular tower) includes from one to twelve receiving and transmitting antennhaving directions in different directions in order to provide quality subscribers in the radius of their action. Such antennas experts on their jargon are called "Sectors"Representing gray rectangular designs that you can almost every day to see on the roofs of buildings or special masts.
The signal from such an antenna enters the cable directly to the control unit of the base station. The base station is a combination of sectors and control block. At the same time, a certain part of the settlement or territory serves several basic stations connected to a special block - local zone controller (Abbreviated LAC, Local Area Controller or just "controller"). As a rule, one controller unites up to 15 base stations of a certain area.
For its part, controllers (they can also be several) are connected to the most important unit - Mobile Services Management Center (MSC, Mobile Services Switching Center)which to simplify perception is called simply "Switch". The switch, in turn, exercises input and output to any lines of communication - both cellular and wired.
If you display written in the form of a schema, then the following will be obtained: 
GSM networks of a small scale (as a rule, regional) can use only one switch. The largest, such as our "Large Troika" operators MTS, Beeline or Megaphone served at the same time millions of subscribers use several merged MSC devices at once.
Let's figure it out why you need such a complex system and why can not be connected by the basic stations antennas to the switch directly? To do this, you need to tell about another term, called technical language. handover (Handover). It characterizes the transfer of service in mobile networks on the relay principle. In other words, when you move along the street on foot or in a vehicle and talk at the same time, then that your conversation is not interrupted, you should switch your device in a timely manner from one BS sector to another, from the zone of a single base station or controller local zone to another, etc. Consequently, if the base stations sector were connected to the switch directly, he would have to carry out this handder procedure for all its subscribers, and the switch had enough tasks from the switch. Therefore, to reduce the likelihood of equipment failures associated with its overloads, the GSM cellular network construction scheme is implemented by multi-level principle.
As a result, if you move with your phone from the service zone of one BS sector to the other area of \u200b\u200bthe other, then this movement performs a block of controlling this base station, without touching with it more "highly" devices - LAC and MSC. If Handover takes place between different BS, then the LAC is already taken for it, etc.
The switch is nothing more than the main "brain" of GSM networks, so its work should be considered in more detail. A cellular network switch assumes about the same tasks as the PBX in the networks of wired operators. It is he who understands where you call a call or who calls you, regulates the work of additional services and, in fact, decides whether you are currently your call or not.
Now let's figure it out what happens when you turn on your phone or smartphone?
So you pressed the "magic button" and your phone turned on. On the SIM card of your cellular operator is a special number that is called IMSI - International Subscriber Identification Number (international subscriber identification number). It is a unique number for each SIM card not only from your MTS operator, Beeline, MegaFon, etc., and a unique number for all mobile networks in the world! It is on it that operators are distinguished by subscribers each other.
At the moment of turning on the phone, your device sends this IMSI code to the base station, which transmits it further on the LAC, it, in turn, sends it to the switch. At the same time, two additional devices shown directly with the switch are entering our game. HLR (Home location register) and VLR (VISITOR LOCATION REGISTER). Translated into Russian, accordingly, Register of home subscribers and Register of guest subscribers. HLR keeps the IMSI of all subscribers of their network. VLR also contains information about those subscribers who use the network of this operator at present.
The IMSI number is transmitted to the HLR using the encryption system (another device is responsible for this process. AUC - Authentication Center). HLR checks if there is a subscriber with this number in its database, and if its fact is confirmed, the system looks whether it can currently use communication services or, let's say, has a financial blocking. If everything is fine, this subscriber is sent to the VLR and then gets the ability to call and use other communication services.
For clarity, you will display this procedure using the scheme:
Thus, we briefly described the principle of operation of GSM cellular networks. In fact, this description is sufficiently superficially, because If you go deep into technical details, then the material would have turned out many times the volume and much less understandable for most readers.
In the second part, we will continue to get acquainted with the operation of GSM networks and consider how and for that the operator writes off funds from our account with you.
Mobile phone is an integral part of a modern, technologically developed society. Despite the events and external simplicity of this device, very not many know how the mobile phone works.
Mobile phone device
Modern technologies and constantly moving forward progress allow you to create phones with a huge number of functions and opportunities. With each new model, the phones are becoming thinner, more beautiful and more affordable in finance. Despite the tremendous variety of models and manufacturers, all these devices are arranged according to one principle.
In fact, the mobile phone is a receiving-transmission device, which in its package has a receiver, transmitter and radio antenna. The receiver provides the reception of the radio signal, converts it to electrical pulses and sends to the speaker of your phone in the form of electrical waves. The speaker converts these electrical impulses into the sound that we hear when talking with the interlocutor.
The microphone perceives your speech, converts it to electrical signals and sends to the built-in transmitter. The transmitter problem to convert electrical pulses to radio waves and transfer to the nearest station by an antenna. The antenna is used to enhance the reception and transfer of radio waves from the phone to the nearest cellular station.
How the telephone is working stationary
The device of a stationary phone is not very different from the mobile. In the stationary phone there is no need to convert electrical pulses to radio waves, because the contact with the subscriber occurs on the telephone cable through the automatic telephone station (PBX). The station does not need to find a device in the zone of its action and when the number is set, it automatically connects you to the telephone set to which this number is registered.
How does mobile communication work?
Each of us has the ability to visually observe a large number of radio communications located in different parts of the city. These tows are usually installed on the maximum elevated places, on the roofs of high-rise buildings, on the structures of other communications or on their own stationary gearboxes. These radio communications are called base stations (BS). You may notice that in cities such stations are set much more often than under the intercity space. This is due to the fact that in urban conditions there are many natural interference in the form of concrete buildings and various metal structures that significantly worsen the signal quality. At the same time, a larger number of subscribers are concentrated in cities that create a strong load on the cellular network and to maintain a good quality of communication requires an increase in the coating zone.
Your phone has its own identification in the form of your SIM card mobile number. In the on state, the mobile phone constantly scans the space in search of the network and automatically selects the base station that provides better signal quality. At the same time, he informs the station about its location and state, so the central computer of the cellular operator always knows, in the area of \u200b\u200bthe base station there is a telephone and is it ready to take a call signal. Once another subscriber makes calling your number, the computer determines your location and sends a call signal to your phone. If the phone is turned off or is not in the zone of the nearest base station, the computer tells you that the subscriber is out of the coverage area and cannot accept the call.
To do this, we suggest you go to Beeline.
In Russia, a huge number of BS - base stations has been established. Probably, many of you seen the red-white designs towering in the fields or installed on the roofs of non-residential buildings of the structure. Each such basic station is capable of catching a signal from a cell phone at a distance of up to 35 km by contacting him by service or voice channels.
After you scored the number of the desired subscriber on your phone, the following happens: the mobile phone comes with the nearest BS, contacts it on the service channel and requests the voice channel. After that, the BS sends a request to the controller (BSC), which then goes to the communicator. If the called subscriber is serviced at the same operator as you, the communicator will reconcile with the home location register database (HLR) to find out where the one who is calling, and redirect the call to the desired switch, which will then translate the call on the controller and then on the base station. Well, finally, the base station will contact the mobile phone of the right person and connect you with it. And if the one with whom you want to talk is a subscriber of another cellular operator, or you call the city number, then the switch "will find" the corresponding switch of another network and turn to it. Sounds quite confusing, right? Let's try to disassemble this question in more detail.
But back to the equipment. As we have said, the call is translated from the BS to the controller (BSC). Externally, it differs little from the base station:
The number of BS, which is able to serve the controller, can reach six dozen. The controller and BS bind to optical or radio relay channels. The controller manages the operation of the radio channels.
Below you can see what the switch represents:
The number of controllers served by the switch varies from two to thirty. Switches are placed in large rooms filled with metal cabinets with equipment.
The switch task is to manage traffic. If earlier to talk to each other, the subscribers needed to first bind to the telephonist, which then manually rearranged the necessary wires, now the switch copes with its role.
Inside cars are located devices designed for removal and data processing:
Controllers and switches are under watch control 24 hours a day. Tracking is conducted in the so-called CCS (center control center of the CEFTRA CEAT).
Cellular communication is considered one of the most useful inventions of humanity - along with wheel, electricity, internet and computer. And only in a few decades this technology experienced a number of revolutions. Where did the wireless communication begun, how the cells work and what opportunities will open a new mobile standard 5G?
The first use of mobile telephone radio comes to 1921 - then in the US, Detroit police used a one-way dispatch connection in the 2 MHz band for transmitting information from the central transmitter to receiver in police cars.
How to appear cellular communication
For the first time, the idea of \u200b\u200bcellular communications was nominated in 1947 - engineers from Bell Labs Douglas Ring and Ray Yang worked on it. However, the real prospects of its incarnation began to be charged only by the beginning of the 1970s, when the company's employees developed a working architecture of a cellular hardware platform.
Thus, American engineers offered to place the transmission stations not in the center, but in the corners of the "cells", but a little later, a technology was invented, allowing subscribers to move between these cells, without interrupting communications. After that, there remained to develop existing equipment for such technology.
The task was successfully solved by Motorola - its engineer Martin Cooper on April 3, 1973 demonstrated the first working prototype of a mobile phone. He called the head of the research department of a competitor directly from the street and told him about his own successes.
Motorola's leadership has immediately invested in a promising project of $ 100 million, but technology has been released on the commercial market only in ten years. Such a delay is related to the fact that it was first required to create a global infrastructure of cellular base stations.
In the USA, this work was engaged in this work, the company AT & T - the telecommunications giant has achieved from the federal government licensing the necessary frequencies and built the first cellular network that covered the largest American cities. As the first mobile phone made the famous model Motorola Dynatac 8000.
For sale, the first cell phone entered on March 6, 1983. He weighed almost 800 grams, could work on a single charge of 30 minutes in the conversation mode and charged about 10 hours. At the same time, the device cost 3995 dollars - a fabulous amount for those times. Despite this, the mobile phone instantly became popular.
Why is the connection called cell
The principle of mobile communication is simple - the territory on which the connection of subscribers is ensured is divided into separate cells or "honeycombs", each of which serves the base station. At the same time, in each "honey", the subscriber receives identical services, so he does not feel the intersection of these virtual borders.
Typically, the base station in the form of a pair of iron cabinets with equipment and antennas is located on a specially built tower, however, in the city they are often placed on the roofs of high-rise buildings. On average, each station catches a signal from mobile phones at a distance of up to 35 kilometers.
To improve service quality, operators also establish femtosotes - low-power and miniature cellular stations intended for servicing a small area. They allow you to drastically improve the coating in those places where it is necessary. Considation in Russia will be united with space
A mobile phone listens to the ether and finds a base station signal. In a modern SIM card, except for the processor and RAM, sews a unique key that allows you to log in in a cellular network. The phone connection with the station can be carried out by different protocols - for example, digital DAMPS, CDMA, GSM, UMTS.
Cellular networks of different operators are connected to each other, as well as with a stationary telephone network. If the phone comes out of the base station's action field, the device sets up with the other - the compound established by the subscriber is unnoticed by other "cells", which ensures continuous connection when moving.
In Russia, three bands are certified for broadcasting - 800 MHz, 1800 MHz and 2600 MHz. The range of 1800 MHz is considered the most popular in the world, as it combines high capacity, a large radius of action and a high penetrating ability. It is in it that most mobile networks work now.
What mobile standards are
The first mobile phones worked with 1G technologies - this is the most first generation of cellular communication, which relied on the analog telecommunications standards, the main of which was NMT - Nordic Mobile Telephone. It was intended exclusively for voice traffic.
By 1991, the birth of 2G is the main standard of the new generation of GSM (Global System for Mobile Communications). This standard is still supported. Communication in this standard has become digital, the possibility of encrypting voice traffic and send SMS has appeared.
Data transfer rate inside GSM did not exceed 9.6 kbps, which made it impossible to transmit video or high-quality sound. The problem was designed to solve the GPRS standard, known as 2.5G. He for the first time allowed us to use the network of online mobile phone owners.
Such a standard has already provided the data transfer rate to 114 kbps. However, soon he also stopped satisfying the constantly growing requests of users. To solve this problem in 2000, 3G standard was developed, which provided access to network services at 2 Mbps data transfer rates.
Another difference of 3G was assigned to each subscriber an IP address, which made it possible to turn mobile phones into small computers connected to the Internet. The first 3G commercial network was launched on October 1, 2001 in Japan. In the future, the bandwidth of the standard has repeatedly increased.
The most modern standard is the fourth-generation 4G connection, which is intended only for high-speed data services. 4G network bandwidth is capable of reaching 300 Mbps, which gives the user almost unlimited work opportunities on the Internet.
Cellular communication of the future
4G Standard is sharpened to the continuous transfer of information gigabytes, it even does not even have a channel for voice transmission. Due to the extremely effective multiplexing schemes, the high-resolution film loading in such a network will take the user for 10-15 minutes. However, even its capabilities are already considered limited.
In 2020, the official launch of a new summary of the communication of the 5G standard is expected, which will allow the transfer of large amounts of data on ultra-high speeds up to 10 Gb / s. In addition, the standard will allow you to connect to a high-speed Internet to 100 billion devices.
It is 5G that the present Internet of things will appear - billions of devices will exchange real-time information. According to experts, network traffic will soon increase by 400%. For example, cars will start constantly being in the global network and receive data on the road atmosphere.
Low delay will provide a link between vehicles and real-time infrastructure. It is expected that a reliable and permanent connection will first open the opportunity to launch completely autonomous vehicles on the roads.
Russian operators are already experimenting with new specifications - for example, work in this direction leads Rostelecom. The company signed an agreement on the construction of 5G networks in the Skolkovo Innovation Center. The project implementation is included in the State Program "Digital Economics", recently approved by the government.
Do you know what happens after you scored a friend's number on your mobile phone? How does the cellular network find it in the mountains of Andalusia or on the coast of the distant Island of Easter? Why sometimes an unexpected conversation is interrupted? Last week I visited Beeline and tried to figure out how a cellular connection was arranged ...
The large area of \u200b\u200bthe inhabited part of our country is covered with base stations (BS). In the field, they look like red and white towers, and in the city are hidden on the roofs of non-residential homes. Each station catches a signal from mobile phones at a distance of up to 35 kilometers and communicates with a mobile phone on service or voice channels.
After you scored a friend's number, your phone is associated with the base station nearest to you (BS) on the service channel and asks to allocate voice channel. The base station sends a request to the controller (BSC), and it will redirect it to the switch (MSC). If your friend is a subscriber of the same cellular network, the switch will be queried with Home Location Register (HLR), will find out where the called subscriber is currently located (at home, in Turkey or in Alaska), and will translate the call to the corresponding switch, where does it come from Critter to the controller and then on the base station. The base station will contact the mobile phone and connect you with the other. If your friend is another network subscriber or you call the city phone, then your switch will contact the corresponding switch to another network. Complicated? Let's deal with more details. The base station is a pair of iron cabinets, locked in a well-conditioned room. Given that in Moscow it was on the street +40, I wanted to live a little in this room. Usually, the base station is either in the attic of the building, or in a roof container:
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The base station antenna is divided into several sectors, each of which "shines" to its side. The vertical antenna communicates with telephones, the round connects the base station with the controller:
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Each sector can serve up to 72 calls at the same time, depending on the configuration and configuration. The base station may consist of 6 sectors, so one base station can serve up to 432 calls, however, usually at the station there is a smaller number of transmitters and sectors. Cellular operators prefer to put more BS to improve the quality of communication. The base station can operate in three ranges: 900 MHz - the signal at this frequency applies further and better penetrates the 1800 MHz buildings - the signal extends to shorter distances, but allows you to install a larger number of transmitters on the 1st sector of 2100 MHz - 3G network like this wardrobe with 3G equipment:
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The base stations in the fields and villages are set to 900 MHz transmitters, and in the city where basic stations are naked as needles at the hedgehog, mainly communication is carried out at a frequency of 1800 MHz, although there may be transmitters of all three ranges at any base station at the same time.
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The 900 MHz signal signal can beat up to 35 kilometers, although the "range" of some base stations behind the tracks can reach up to 70 kilometers, by reducing the number of simultaneously serviced subscribers at the station twice. Accordingly, our phone with its small built-in antenna can also transmit a signal to a distance of up to 70 kilometers ... All base stations are designed in such a way as to ensure optimal coating with a radio signal at the ground level. Therefore, despite the range of 35 kilometers, the radio signal is simply not sent to the height of the flight aircraft. However, some airlines have already begun to install low-power base stations on their aircraft, which provide coating inside the aircraft. Such BS is connected to the ground cellular network using the satellite channel. The system is complemented by the control panel, which allows the crew to enable and disable the system, as well as individual types of services, for example, turn off voice over night flights. The phone can measure the signal level from 32 base stations at the same time. Information about 6 best (by signal level) It sends on the service channel, and already the controller (BSC) decides which BS to transfer the current call (handover) if you are in motion. Sometimes the phone may be mistaken and transfer you to the BS with the worse signal, in this case the conversation may interrupt. It may also be that on the base station, which your phone chose, all voice lines are busy. In this case, the conversation will also interrupt. I also talked about the so-called "problem of the upper floors." If you live in a penthouse, then sometimes, when moving from one room to another, the conversation can be interrupted. This is because in the same room the phone can "see" one BS, and in the second one - the other, if it goes on the other side of the house, and, with these 2 base stations are at a great distance from each other and are not spelled out as " Neighboring "at the cellular operator. In this case, the transfer of a call from one BS to another will not happen:
Communication in the metro is provided in the same way as on the street: the base station is the controller - the switch, with the only difference that small base stations are used, and in the tunnel, the coating is not provided with an ordinary antenna, but a special emitting cable. As I wrote above, one BS can produce up to 432 calls at the same time. Usually this power is enough for the eyes, but, for example, during some holidays, the BS may not cope with the number of those who want to call. This usually happens for the new year, when everyone starts to congratulate each other. SMS are transmitted by service channels. On March 8 and on February 23, people prefer to congratulate each other using SMS, moving funny poems, and phones often cannot agree with the BS on the allocation of the voice channel. I was told an interesting case. From one district of Moscow, complaints from subscribers were made that they could not reach anywhere. Technical specialists began to understand. Most voice channels were free, and all the official were busy. It turned out that next to this BS was the institute, in which exams came and students were continuously exchanged by Esemash. Long SMS phone divides some short and sends each separately. Technical service staff advise you to send such congratulations using MMS. It will be faster and cheaper. From the base station, the call hits the controller. It looks as boring as the BS itself is just a set of cabinets:
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Depending on the equipment, the controller can serve up to 60 base stations. The boss between the BS and the controller (BSC) can be carried out on the radio relay channel either by optics. The controller controls the operation of the radio channels, incl. Controls the movement of the subscriber, the transmission of the signal from one BS to another. The switch looks much more interesting:
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Each switch serves from 2 to 30 controllers. It occupies a large hall for various cabinets with equipment:
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The switch automatically controls traffic. Remember old movies, where people first dialed to the "Girls", and then she already joined them with another subscriber, pretty wiring? These are also engaged in modern switches:
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To control the network, Bilane has several cars that they are affectionately called "hedgehogs". They move around the city and measure the level of the signal of their own network, as well as the level of network of colleagues from the "big triple":
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The whole roof of such a car is cooked by antennas:
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Inside there is equipment that carries out hundreds of calls and relieving information:
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24-hour monitoring of switches and controllers is carried out from the Center for Flying Control Center Network (CCS):
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There are 3 main directions for cellular control: emergency, statistics and feedback from subscribers. Just as in airplanes, there are sensors that send a signal to the CCS and display information to computers of dispatchers. If any equipment has failed, then the monitor will begin to "flash the light bulb". The CCS also tracks statistics on all switches and controllers. He analyzes it, comparing with previous periods (hour, days, week, etc.). If the statistics of some kind of nodes have become sharply different from previous indicators, then on the monitor again will begin to flash the light bulb. Feedback accepts the subscriber service operators. If they cannot solve the problem, the call is translated into a technical specialist. If it turns out to be powerless, then the company creates an "incident", which solve engineers engaged in the operation of relevant equipment. The switches are watching 2 engineers around the clock:
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The graph shows the activity of Moscow switches. It is clearly seen that night almost no one calls:
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Controllers control (sorry for tautology) is carried out from the second floor of the network control center:
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