FAQ about the work of the cellular network for the smallest

- What is the difference between cellular communication and radio communication?
Communication is the so-called point-to-multipoint option, when information from one radio is transmitted on a selected frequency, and everyone who is tuned to the same frequency hears the call. So far you have 10 subscribers - everything is simple. When people become more, they begin to quickly sort out the frequencies, and very soon there is no place to create new conversations - there are no free frequencies. Cellular communication uses the same frequency channel, but does not give it the undivided property of one subscriber, but divides it between several, allocating to each only a short period of time for transmitting information. In this case, you can use frequencies more efficiently and be able to connect people with each other directly. However, in order to quickly process such a flow of information and separate information to one subscriber in the frequency channel from the information to another, a new node is needed that will perform the necessary calculations — a base station or repeater appears.

- Ok, for now, just. Let's skip a couple of steps in the evolution of infrastructure, what happens?
The phone communicates with the nearest repeater (base station), it delivers the data to the base station controller and then via the voice Core Network carries to another base station that the second subscriber uses. That, in turn, gives the data and voice to him. Thus, each subscriber has an entry point to a common network, and the network provides switching and delivery of information.
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- How is authorization done in such a network?
By a special key. In addition to the processor, RAM and I / O facilities , a key is sewn into your SIM card, allowing you to log in to the cellular network. The same key, using other algorithms, provides signal encryption: conversations in the cellular network are “closed”.

- How does the base station know that the called subscriber is in its coverage area?
When a subscriber calls another subscriber, a command comes to all base stations from the voice Core Network, with the requirement to check the presence of the called subscriber: something like “Vasya, are you here?”. This verification procedure is called Paging. In theory, the subscriber's phone answers one of them, that he is here. Next, the connection is established through the necessary nodes. But with the growing number of base stations they began to be combined into geographic groups - the Location Area, which are controlled from the voice switch node - MSC.

- OK, new node type, switch. What is he doing?
Moving to a new level of complexity. There are regions, each of them has its own group of base stations, coordinated by a common controller node. The controller provides connection to itself of all base stations, and the collection of their calls from subscribers. But what to do with these calls, he does not know and transmits all the information to that same Switch. The switch knows where and when the last time each subscriber was in his area of ​​coverage, and therefore, when you call Vasya:

1. First, your phone radio transmits a call to the BS.
2. BS retransmits data to controller
3. The controller sends the same data to the switch.
4. The switch checks the number you are calling - is there such a one in its service area?
5. If yes, the switch sends the call to the desired Location Area to receive a response from the base station, where Vasya was last logged
6. If such a number does not belong to our switch, he sends a call to another switch in accordance with the routing tables he has and searches for our Vasya in other networks
7. The switch of another network also sends a call to its base stations via the known Location Area, where Vasya was last registered
8. One of the base stations answers our call, and you can finally start a conversation.

- Ok, and how does the switch learn that Vasya is in his zone (LA)?
Base stations have an area code - LAC. When your phone switches to a base station, the LAC of which differs from the previous one used, a special package is sent with the location update - Location Area Update. This signaling packet is processed by the switch, it also stores information that your phone is registered at the base station with the new LAC. In the future, all calls to your number will be sent to base stations with this LAC until the switch receives a new Location Area Update package, where there will be information about the new geographic code. In addition, just in case such a package is sent every few hours, even if you do not budge.

- That is, when the phone is near the speakers, and they make strange sounds - aren't the aliens listening to me?
No, it’s just a Location Area Update or some other signal packet that the phone sends and receives regularly, even if you don’t do anything with it.

- Who builds base stations?
Cell phone operators. Or rather, their contractors who have the appropriate licenses for construction and experience. As a simple calculation shows, Russia needs from a few dozen to several hundred thousand base stations to cover 95% of the territory. Very approximately, one BS costs about 2 million - it costs as much as opening a small restaurant. This is even if you found a suitable suitable pillar. If there is no post, feel free to write up to 8 million, especially if the tower is somewhere in the steppe or on a mountain with difficult access.

- What does the operator’s infrastructure consist of and where does my money go?
In addition to base stations, controllers, switches, trunk transport lines and other network nodes (which only to list, you will need half a page), you need spare parts warehouses, engineering services, service, and so on. Base stations on houses require rent deductions for owners, people need salaries, equipment needs to be changed, maintenance is carried out, and electricity bills are paid. Plus, operators are constantly expanding - this is a new hardware, an update of old, new software. And then there are offices with those who write software, call centers, analytics, marketing, advertising, sales and connection shops - in general, a complete set.

- Wait a minute, forget the data center!
True, for the work of the cellular operator you need to process a huge amount of data. That is why cellular operators usually have not only a good backbone network, but also the most modern data centers. In data centers is everything. One of the most resource-intensive tasks is real-time balance calculation. By the way, cellular network operators have been working with data centers for so long and successfully that their experience and resources are used by many others - by renting the resources of data centers of cellular operators for their projects.

- OK, that's understandable. And how are the networks of different operators interconnected?
The principle is about the same as calling one switch of another. Simplifying, you communicate with the BS, it connects with the controller, it connects with the switch, and the switch searches for an entry node into another network by the called subscriber number. The switch of the home network finds the required number in its tables and determines which external switch it is necessary to send a call to, after which it creates a route to the required node.

- And roaming?
The phone usually tries to find a home network. If this fails, he begins to search for other networks and tries to register with them. The network switch where you are trying to register, checks if the operator has a roaming agreement with your home operator. If this permission is found, the switch knows for sure that subscribers like you can be serviced, and you get a connection. For example, when you come to a new country, you are almost immediately "picked up" by another network with which your operator has an agreement. These agreements are rarely updated in the majority, so traffic prices can be very high. Where you have unlimited roaming traffic, most likely the agreement has been updated relatively recently with the incredible blood of the legal departments of both operators.

- Is it possible to go to roaming in your region?
Technically, yes, another operator has the ability to “pick up” you. But to prevent this from happening, your SIM contains settings not to cling to foreign domestic networks, and switches from foreign networks do not allow your phone to register at base stations of a non-native operator. Otherwise you would be roaming in the elevator, on the border of the region, and so on. The exception is emergency inter-network roaming, when all networks work for all subscribers during an emergency. Well, you should always remember that you can always make calls to the rescue service, even through someone else's network! When “Emergency calls only” or “SOS” appears on your screen, this means that your operator in this place does not have its base stations, but through the network of another operator you can make a free call to the emergency number “112”.

- Why Verizon phones do not work in the Russian Federation?
The reasons may be mass. The most common is the “zalochka” of the phone for a specific network code of the operator. According to the cellular communication standard, each operator has a unique code that is not repeated anywhere in the world, and it is technically quite easy to ensure that when the phone is turned on, a SIM card is checked whether the network code is used on it. Another possible reason is that each country uses its own frequencies for organizing communications, and each operator has a license for certain ranges. Accordingly, if the device suddenly does not support the ranges used in the Russian Federation, it will not work in domestic networks.

- What you need to know about the transport to the BS?
A transport channel is required for each base station to transmit information from subscribers, which is collected through radio channels. Most often the transport to the base station today is either a radio relay channel (RRL) or cables: copper and optical. Optics are fast and cool, copper is cheaper and easier to use, and the radio allows you not to put the cable where it is difficult or expensive to do. Given that the channels are reserved by rings, the usual architecture is a pair of optical rings to the city and region, plus the branches of the base stations on the copper transport and carrying out for 1-2 hop on the RRL.


Cheboksary and Novocheboksarsk, the scheme of the end of 2012

- What about highways?
Only optics, and, today - with a spectral densification (DWDM). For reliability - also rings. The main enemy of the highway is an excavator, which decided to dig where the cable channel lies. And even a red ribbon with warnings half a meter before the cable does not save - it is usually removed from the bucket after the fact.

- What is the difference between 2G, 3G and 4G?
These are different generations of cellular network standards, which can be guessed by the letter G, which means Generation. 2G networks are mainly designed for voice transmission, the data transfer rates there are very low by modern standards. In 3G networks, you can transmit high-quality voice, and at the same time provide data transfer services at high speed. 4G networks are now the latest generation of networks and are intended only for high-speed data services, voice switching in this network is not provided by the standard, so it’s worth remembering that even if the operator provides voice services in 4G networks, this is some kind of voice transmission in IP networks. As a rule, several sets of equipment are installed on one site to create networks of different standards that provide subscribers with different services. In the near future - the replacement of many different types of base station blocks for common - multistandard. Standards of a cellular network differ in the mass of technical functionality, but you almost do not see it. The most significant differences for an ordinary subscriber are different Internet speeds, different coverage areas, different voice quality ( HD-Voice is very cool).