The past and the future of cellular communication in areas where there is no GSM
Despite the fact that telecom operators are constantly increasing the number of installed base stations, even in large cities there are still areas with unstable reception.
A subscriber who by chance finds himself in such a zone has to either accept and wait for the operator to think about the coverage, or correct the situation on his own. We will not consider ways to “bypass” our operator at the expense of third-party services, but let's talk about how services can be organized by the same provider in such “dead” zones.
It is clear that communication can not be organized from scratch. When there is no coverage of base stations, you have to use a different transmission medium. And today the most accessible is the Internet.
')
The idea of ​​making calls over the Internet without switching to another service provider has been in the industry for a long time. At first, it was implemented as an additional device - femtocell, which allows creating a kind of “bridge” between the user devices and the network of the cellular operator through the public Internet of any provider. Such a "bridge" helps to locally improve the quality of reception. The only limitation is that the user device must support the communication standard used by the femtocell (in general, it may not coincide with the standard used in the operator’s network).
Femtocells never reached the mainstream market when they were replaced by Wi-Fi calling — a technology that allows you to simply call via Wi-Fi using your smartphone, but not using additional intermediary devices. But let's talk about everything in order.
The femtocell concept has been developing since 2001 as part of the idea of ​​small cells. Among the "brothers" femtocells are distinguished by the fact that they are subscriber devices, not operator devices, and work through a channel that is not controlled by the operator - the usual Internet channel.
The idea of ​​creating a “miniature cell” appeared even earlier: along with the development of mobile communications, interesting solutions appeared, but in the 1990s they were far from modern femtocells. The first product, reminiscent of today's femtocell (self-configuring home GSM base station), was announced by Alcatel in 1999, but never entered the mainstream market, as it turned out quite bulky and expensive. It took five years to miniaturize the components and further technological growth, so that several companies, including picoChip and Ubiquisys, were busy at the same time, who are still arguing about who among them is the author of the term popular today.
Since 2007, the concept was developed by the international organization Femto Forum, which includes several equipment manufacturers (now it is the Small Sell Forum, whose responsibility covers all small cells, both user and operator). In 2008, the world saw several solutions that enabled the construction of femtocell-based commercial services. The cost and consumer characteristics of these devices no longer hindered the introduction of the concept to the masses. In the same 2008, with the direct participation of the Femto Forum, femtocells were standardized. The document became part of the 3GPP standard, and dozens of equipment manufacturers and operators around the world became interested in the topic itself.
The first carrier services, implying renting or selling femtocell, were launched in the USA and Japan in 2009. By 2011, the concept came to Russia, despite certain restrictions of the legislation, which is more detailed later.
Now femtocell is a device about the size of a familiar Wi-Fi router distributed by mobile operators. Femtocells may vary in performance - for home, office use or for outdoor use. They may include a set of functions of a router or other network devices. However, in contrast to the same routers, at the moment in Russia femto cells cannot be purchased from an independent supplier without being tied to an operator.
Femtocell power is no more than 100 mW. Thus, they are designed for servicing small premises - for example, an office or an apartment. The coverage area depends on the type of room (configuration and material of the walls), the electromagnetic environment, in particular, the presence of other signal sources operating in the same range. On average, it has a radius of 10 - 30 m.
The most common UMTS standard devices (Megafon and other Russian operators, for example, use the UMTS2100), however, there are femtocells that support other communication standards. But talk about the exotic goes beyond the scope of this article.
In Russia, the femtocell operates in the licensed frequency range, but to install it, the user does not need to obtain a permit (like radio amateurs, who used to carry radios operating at 27 MHz to the divisions of the Ministry of Communications). These issues are resolved by the operator, and the subscriber is only required not to change the device’s “address of registration”.
Device movements are tracked by the operator by IP address. Some manufacturers even embed GPS in femtocells (used or not - depends on the operator). But sometimes small movements are still possible - in particular, “Megaphone”, using a lock on the surrounding cells, allows femtocell movements within a radius of 250 meters. And with the notification of the service provider, you can transfer the femtocell within the licensed area of ​​the operator’s branch.
The described difficulties with moving are associated with the obligations of the operator in certain situations to provide information about calls to the Emergencies Ministry and the Ministry of Internal Affairs, as well as to serve emergency calls, which is required by law.
These same requirements previously restrained the development of femtocell in the direction of private users: legally “carrier” equipment could not be leased to home users, only to business. Since 2013, some femto cells have finally ceased to be considered as “carrier” equipment (Rules for the use of subscriber terminals of mobile radio telephone communication systems of the UMTS standard with duplex frequency and frequency-code division of radio channels operating in the 2000 MHz frequency band, approved by the Order of the Ministry of Information Technology and Communications of the Russian Of the Federation of August 27, 2007 No. 100 (Order of the Ministry of Information Technologies and Communications of the Russian Federation No. 147 of June 25, 2013). To do this, its capacity must be limited, and the manufacturer must go through the procedure of certifying the device as a home device. However, so far there is no mass demand for "home" cells, even in large cities. Attempts by some operators to introduce such a service have not yet been crowned with success. Licensable radio band also does not allow to create and sell femto independent operators, i.e. bring from abroad (order from China) more interesting or cheaper counterparts, as users are accustomed to do with other "network" electronics.
The femtocell requires an electrical connection and internet connection. The minimum Internet connection speed, providing technical information transfer and servicing of one client device to 3G, is at least 500 Kbps (preferably 2–5 Mbps), but as the number of connected users and services involved increases, naturally, growing proportionally.
High-quality voice transmission additionally requires connection stability
(without short-term interruptions, jitter fluctuations of more than 50 ms and loss of more than 1.5% of packets) and the absence of blocking of the ports and protocols used by the femtocell.
In contrast to the large-scale base station, the femtocell is installed and launched not by the operator, but by the final subscriber, respectively, here is a slightly different approach to tuning: everything works out of the box and is controlled by the operator. All that is needed from the user is to set the network parameters for connecting to the Internet and the list of "allowed" numbers for service (i.e., indicate the SIM cards that will be allowed to use the device). All this can be done through the web interface by analogy with the configuration of the same network router.
Authorization in the operator's network is performed using a technological SIM card. Connection to it is via the Security Gateway (SeGW) - the femtocell does not matter if it uses a static or dynamic IP address. To transfer packages of voice calls, a secure communication channel with the operator is organized using IPsec.
Although the network periodically appeared information about the detection of vulnerabilities of some femtocells, allowing attackers to make calls at the expense of subscribers serviced by the device, and even “clone” their phones, all these incidents related to specific firmware versions of specific devices (tied to certain operators) and allowed to cheat only in the range of the femto. By itself, the femtocell for vulnerability is comparable to a custom smartphone. Known problems with femto cells in most situations were solved by updating the firmware; Moreover, Russian operators are still not lit in such reports.
After installation and the simplest setting, the femtocell behaves almost like a “big” base station: when entering the reception area (when its signal is stronger than the base station signal), the user mobile device switches to it, regardless of the standby / talk mode. The network receives a notification about this event, which can be used to track visitors through third-party tools or SMS messages (the availability of this service depends on the policy of the operator).
The device can support 4 to 32 simultaneous voice calls and 4 to 16 channels of packet data (depending on the configuration and settings of the operator). In the case of UMTS femtocells, end devices must support 3G to connect to the network.
For the femtocell operator - a way to expand the network coverage without installing “full-fledged” base stations, as well as partially reduce the load from the existing segments by connecting some subscribers to femtocells. Well, you should not forget about the additional monetization of the services provided.
Yes, and from the point of view of users, femtocells can come up with quite a few applications.
First, it is the organization of mobile communication where there is none or the quality leaves much to be desired (but where there is a broadband channel). Actually, this is primarily for offices in industrial areas and in industrial premises, where enclosing structures shield the signal of “ordinary” base stations or cellular coverage is absent, as well as for those who expand their activities in the literal sense “in the field”.
Femtocell can also work via satellite Internet, which provides servicing of cell phones even in the dense forest. True, satellite Internet is characterized by long delays, respectively, delays / breaks in communication will be in conversation. Femtocell via satellite - rather exotic.
When using more stable wired internet, femto cells can not only improve the quality of voice services, but also reduce the overall electromagnetic background, since the phone, being in close proximity to the cell, automatically reduces the radiation power (setting it to a level sufficient for stable signal transmission).
Secondly, a femtocell can become a tracking tool, both in a good and in a bad way.
The simplest phone tracking tool is notification of a certain subscriber in the femtocell coverage area. With it, restless parents can set up a notification about registering their children's phones in the “home network” so that they know that they have returned home from school; bosses in the same way can control the time of arrival of employees. Automation can also monitor alerts by, for example, triggering data synchronization on a smartphone with an office server.
A different level of surveillance can be achieved through the use of "modified" femtocells, for example, the spyware equipment InfoWatch. The device announced by the company intercepts and records conversations of subscribers connected to the femtocell, protecting the interests of the state or an individual business. Technologies can come up with a lot of applications, both “honest” and not so, from the banal analysis of the effectiveness of a call center to total control over employees, even using personal smartphones.
In general, the functionality of femto cells depends on the tariff policy of the operator, the options it supports and the adopted principles of network expansion.
For example, femtocells can be used to combat network overload, namely, a relatively quick response to an increase in the number of connected devices. This is true, for example, for events held in non-standard places (outside exhibition complexes, sharpened by a large flow of visitors). It may be important for the organizers that the participants at any time can communicate with each other or with the outside world. It is possible to distribute the load both for all devices that are in the femtocell range, and only for “their” (SIM-cards from the “white list”). Although in “Megaphone” such decisions are not applied.
Femtocells did not have time to massively enter the Russian consumer market, and they have already been replaced by another way to organize communications in areas not covered by base stations - Wi-Fi calling. This is a service that allows you to make calls from smartphones via an available Wi-Fi network in the absence of a GSM connection.
Wi-Fi calling is also part of a broader concept - the so-called unlicensed mobile access (Unlicensed Mobile Access - UMA) - a way to connect external IP subscribers to the carrier's network. This access is provided by the Generic Access Network (GAN), and the transfer of IP packets from the unmanaged Internet to the operator's network is carried out by the corresponding controller - GAN Controller (in this sense, the femtocell is standard GAN equipment).
The methodology for providing such access was described in the 3GPP Release 6 document. And the first commercial implementations of UMA appeared back in 2005-2006.
On the subscriber’s side, the function must be implemented in the smartphone software (as a built-in or additionally installed program module). It is activated through the settings of the device and works if it is supported by the cellular operator.
Wi-Fi calling technology supports seamless call transfer from a cellular network to Wi-Fi and vice versa, so this is not similar to the usual Skype or Viber (though there may be communication breaks when moving from the service area of ​​one Wi-Fi router to another is determined by the Wi-Fi technology itself). When you turn on the smartphone software option, you can select the priority - where to send the call if both networks are available; then the device and the operator’s network will control how the call goes, independently.
From the point of view of any other subscriber, a Wi-Fi calling call looks like a normal call. You can call the numbers of any operators. When such a call is received, the caller’s number will appear on the screen of the interlocutor’s phone, and the call will be charged in accordance with the selected tariff.
It should be noted that Wi-Fi calling does not allow to bypass costly international roaming. Part of the standard is the search for existing GSM-towers of any operators when the device is turned on, which automatically gives information about the location of the subscriber. Thus, the possibility of saving on calls via Wi-Fi calling is completely determined by the policy of the operator.
Wi-Fi calling is already certified in Russia. Its introduction a couple of years ago was hampered by legislative conflict, which prohibits the provision of local telephony subscribers with access to a voice network in accordance with the license. But the issue was resolved last year.
Wi-Fi calling services are already available to subscribers of Russian operators (at least in some regions). Testing this opportunity and "Megaphone".
From a user point of view, technology has a number of advantages against the background of a femtocell. The main thing is the lack of additional equipment, i.e. additional costs and bureaucratic difficulties associated with licensing frequencies. Intermediate devices are not used at all, which means there is no talk about obtaining any permits, tying something to the “place of registration”, etc. (about what we spoke above with reference to femtocell).
The only "but" is that Wi-Fi calling calls are not available on all devices. To support Wi-Fi calling (and UMA in principle), it is necessary that the phone be equipped not only with GSM, but also with a Wi-Fi module, which is initially more expensive - i.e. The cheapest "dialers" will never get the support of this technology.
The absence of intermediate devices leads to the fact that Wi-Fi calling, unlike femto cells, does not allow any additional services to be deployed. Thus, for femtocells, there is still a place in the market. Therefore, these devices continue to actively develop. The need for them is primarily in the corporate sector, where it is important to provide communication to all visitors to a particular zone. This problem through Wi-Fi calling is not yet solved.
Thus, conditionally, the old and the new technologies complement each other, jointly solving the issue of providing voice services where GSM coverage leaves much to be desired.
A subscriber who by chance finds himself in such a zone has to either accept and wait for the operator to think about the coverage, or correct the situation on his own. We will not consider ways to “bypass” our operator at the expense of third-party services, but let's talk about how services can be organized by the same provider in such “dead” zones.
It is clear that communication can not be organized from scratch. When there is no coverage of base stations, you have to use a different transmission medium. And today the most accessible is the Internet.
')
The idea of ​​making calls over the Internet without switching to another service provider has been in the industry for a long time. At first, it was implemented as an additional device - femtocell, which allows creating a kind of “bridge” between the user devices and the network of the cellular operator through the public Internet of any provider. Such a "bridge" helps to locally improve the quality of reception. The only limitation is that the user device must support the communication standard used by the femtocell (in general, it may not coincide with the standard used in the operator’s network).
Femtocells never reached the mainstream market when they were replaced by Wi-Fi calling — a technology that allows you to simply call via Wi-Fi using your smartphone, but not using additional intermediary devices. But let's talk about everything in order.
Femtocells - the birth of ideas
The femtocell concept has been developing since 2001 as part of the idea of ​​small cells. Among the "brothers" femtocells are distinguished by the fact that they are subscriber devices, not operator devices, and work through a channel that is not controlled by the operator - the usual Internet channel.
The idea of ​​creating a “miniature cell” appeared even earlier: along with the development of mobile communications, interesting solutions appeared, but in the 1990s they were far from modern femtocells. The first product, reminiscent of today's femtocell (self-configuring home GSM base station), was announced by Alcatel in 1999, but never entered the mainstream market, as it turned out quite bulky and expensive. It took five years to miniaturize the components and further technological growth, so that several companies, including picoChip and Ubiquisys, were busy at the same time, who are still arguing about who among them is the author of the term popular today.
Since 2007, the concept was developed by the international organization Femto Forum, which includes several equipment manufacturers (now it is the Small Sell Forum, whose responsibility covers all small cells, both user and operator). In 2008, the world saw several solutions that enabled the construction of femtocell-based commercial services. The cost and consumer characteristics of these devices no longer hindered the introduction of the concept to the masses. In the same 2008, with the direct participation of the Femto Forum, femtocells were standardized. The document became part of the 3GPP standard, and dozens of equipment manufacturers and operators around the world became interested in the topic itself.
The first carrier services, implying renting or selling femtocell, were launched in the USA and Japan in 2009. By 2011, the concept came to Russia, despite certain restrictions of the legislation, which is more detailed later.
Modern femtocell
Now femtocell is a device about the size of a familiar Wi-Fi router distributed by mobile operators. Femtocells may vary in performance - for home, office use or for outdoor use. They may include a set of functions of a router or other network devices. However, in contrast to the same routers, at the moment in Russia femto cells cannot be purchased from an independent supplier without being tied to an operator.
Service zone
Femtocell power is no more than 100 mW. Thus, they are designed for servicing small premises - for example, an office or an apartment. The coverage area depends on the type of room (configuration and material of the walls), the electromagnetic environment, in particular, the presence of other signal sources operating in the same range. On average, it has a radius of 10 - 30 m.
frequency range
The most common UMTS standard devices (Megafon and other Russian operators, for example, use the UMTS2100), however, there are femtocells that support other communication standards. But talk about the exotic goes beyond the scope of this article.
In Russia, the femtocell operates in the licensed frequency range, but to install it, the user does not need to obtain a permit (like radio amateurs, who used to carry radios operating at 27 MHz to the divisions of the Ministry of Communications). These issues are resolved by the operator, and the subscriber is only required not to change the device’s “address of registration”.
Device movements are tracked by the operator by IP address. Some manufacturers even embed GPS in femtocells (used or not - depends on the operator). But sometimes small movements are still possible - in particular, “Megaphone”, using a lock on the surrounding cells, allows femtocell movements within a radius of 250 meters. And with the notification of the service provider, you can transfer the femtocell within the licensed area of ​​the operator’s branch.
The described difficulties with moving are associated with the obligations of the operator in certain situations to provide information about calls to the Emergencies Ministry and the Ministry of Internal Affairs, as well as to serve emergency calls, which is required by law.
These same requirements previously restrained the development of femtocell in the direction of private users: legally “carrier” equipment could not be leased to home users, only to business. Since 2013, some femto cells have finally ceased to be considered as “carrier” equipment (Rules for the use of subscriber terminals of mobile radio telephone communication systems of the UMTS standard with duplex frequency and frequency-code division of radio channels operating in the 2000 MHz frequency band, approved by the Order of the Ministry of Information Technology and Communications of the Russian Of the Federation of August 27, 2007 No. 100 (Order of the Ministry of Information Technologies and Communications of the Russian Federation No. 147 of June 25, 2013). To do this, its capacity must be limited, and the manufacturer must go through the procedure of certifying the device as a home device. However, so far there is no mass demand for "home" cells, even in large cities. Attempts by some operators to introduce such a service have not yet been crowned with success. Licensable radio band also does not allow to create and sell femto independent operators, i.e. bring from abroad (order from China) more interesting or cheaper counterparts, as users are accustomed to do with other "network" electronics.
Internet requirements
The femtocell requires an electrical connection and internet connection. The minimum Internet connection speed, providing technical information transfer and servicing of one client device to 3G, is at least 500 Kbps (preferably 2–5 Mbps), but as the number of connected users and services involved increases, naturally, growing proportionally.
High-quality voice transmission additionally requires connection stability
(without short-term interruptions, jitter fluctuations of more than 50 ms and loss of more than 1.5% of packets) and the absence of blocking of the ports and protocols used by the femtocell.
Customization
In contrast to the large-scale base station, the femtocell is installed and launched not by the operator, but by the final subscriber, respectively, here is a slightly different approach to tuning: everything works out of the box and is controlled by the operator. All that is needed from the user is to set the network parameters for connecting to the Internet and the list of "allowed" numbers for service (i.e., indicate the SIM cards that will be allowed to use the device). All this can be done through the web interface by analogy with the configuration of the same network router.
Security
Authorization in the operator's network is performed using a technological SIM card. Connection to it is via the Security Gateway (SeGW) - the femtocell does not matter if it uses a static or dynamic IP address. To transfer packages of voice calls, a secure communication channel with the operator is organized using IPsec.
Although the network periodically appeared information about the detection of vulnerabilities of some femtocells, allowing attackers to make calls at the expense of subscribers serviced by the device, and even “clone” their phones, all these incidents related to specific firmware versions of specific devices (tied to certain operators) and allowed to cheat only in the range of the femto. By itself, the femtocell for vulnerability is comparable to a custom smartphone. Known problems with femto cells in most situations were solved by updating the firmware; Moreover, Russian operators are still not lit in such reports.
Service continuity
After installation and the simplest setting, the femtocell behaves almost like a “big” base station: when entering the reception area (when its signal is stronger than the base station signal), the user mobile device switches to it, regardless of the standby / talk mode. The network receives a notification about this event, which can be used to track visitors through third-party tools or SMS messages (the availability of this service depends on the policy of the operator).
The device can support 4 to 32 simultaneous voice calls and 4 to 16 channels of packet data (depending on the configuration and settings of the operator). In the case of UMTS femtocells, end devices must support 3G to connect to the network.
Practice
For the femtocell operator - a way to expand the network coverage without installing “full-fledged” base stations, as well as partially reduce the load from the existing segments by connecting some subscribers to femtocells. Well, you should not forget about the additional monetization of the services provided.
Yes, and from the point of view of users, femtocells can come up with quite a few applications.
First, it is the organization of mobile communication where there is none or the quality leaves much to be desired (but where there is a broadband channel). Actually, this is primarily for offices in industrial areas and in industrial premises, where enclosing structures shield the signal of “ordinary” base stations or cellular coverage is absent, as well as for those who expand their activities in the literal sense “in the field”.
Femtocell can also work via satellite Internet, which provides servicing of cell phones even in the dense forest. True, satellite Internet is characterized by long delays, respectively, delays / breaks in communication will be in conversation. Femtocell via satellite - rather exotic.
When using more stable wired internet, femto cells can not only improve the quality of voice services, but also reduce the overall electromagnetic background, since the phone, being in close proximity to the cell, automatically reduces the radiation power (setting it to a level sufficient for stable signal transmission).
Secondly, a femtocell can become a tracking tool, both in a good and in a bad way.
The simplest phone tracking tool is notification of a certain subscriber in the femtocell coverage area. With it, restless parents can set up a notification about registering their children's phones in the “home network” so that they know that they have returned home from school; bosses in the same way can control the time of arrival of employees. Automation can also monitor alerts by, for example, triggering data synchronization on a smartphone with an office server.
A different level of surveillance can be achieved through the use of "modified" femtocells, for example, the spyware equipment InfoWatch. The device announced by the company intercepts and records conversations of subscribers connected to the femtocell, protecting the interests of the state or an individual business. Technologies can come up with a lot of applications, both “honest” and not so, from the banal analysis of the effectiveness of a call center to total control over employees, even using personal smartphones.
In general, the functionality of femto cells depends on the tariff policy of the operator, the options it supports and the adopted principles of network expansion.
For example, femtocells can be used to combat network overload, namely, a relatively quick response to an increase in the number of connected devices. This is true, for example, for events held in non-standard places (outside exhibition complexes, sharpened by a large flow of visitors). It may be important for the organizers that the participants at any time can communicate with each other or with the outside world. It is possible to distribute the load both for all devices that are in the femtocell range, and only for “their” (SIM-cards from the “white list”). Although in “Megaphone” such decisions are not applied.
Wi-Fi calling
Femtocells did not have time to massively enter the Russian consumer market, and they have already been replaced by another way to organize communications in areas not covered by base stations - Wi-Fi calling. This is a service that allows you to make calls from smartphones via an available Wi-Fi network in the absence of a GSM connection.
Technology
Wi-Fi calling is also part of a broader concept - the so-called unlicensed mobile access (Unlicensed Mobile Access - UMA) - a way to connect external IP subscribers to the carrier's network. This access is provided by the Generic Access Network (GAN), and the transfer of IP packets from the unmanaged Internet to the operator's network is carried out by the corresponding controller - GAN Controller (in this sense, the femtocell is standard GAN equipment).
The methodology for providing such access was described in the 3GPP Release 6 document. And the first commercial implementations of UMA appeared back in 2005-2006.
On the subscriber’s side, the function must be implemented in the smartphone software (as a built-in or additionally installed program module). It is activated through the settings of the device and works if it is supported by the cellular operator.
Wi-Fi calling technology supports seamless call transfer from a cellular network to Wi-Fi and vice versa, so this is not similar to the usual Skype or Viber (though there may be communication breaks when moving from the service area of ​​one Wi-Fi router to another is determined by the Wi-Fi technology itself). When you turn on the smartphone software option, you can select the priority - where to send the call if both networks are available; then the device and the operator’s network will control how the call goes, independently.
From the point of view of any other subscriber, a Wi-Fi calling call looks like a normal call. You can call the numbers of any operators. When such a call is received, the caller’s number will appear on the screen of the interlocutor’s phone, and the call will be charged in accordance with the selected tariff.
It should be noted that Wi-Fi calling does not allow to bypass costly international roaming. Part of the standard is the search for existing GSM-towers of any operators when the device is turned on, which automatically gives information about the location of the subscriber. Thus, the possibility of saving on calls via Wi-Fi calling is completely determined by the policy of the operator.
Russian reality
Wi-Fi calling is already certified in Russia. Its introduction a couple of years ago was hampered by legislative conflict, which prohibits the provision of local telephony subscribers with access to a voice network in accordance with the license. But the issue was resolved last year.
Wi-Fi calling services are already available to subscribers of Russian operators (at least in some regions). Testing this opportunity and "Megaphone".
Benefits versus femtocell
From a user point of view, technology has a number of advantages against the background of a femtocell. The main thing is the lack of additional equipment, i.e. additional costs and bureaucratic difficulties associated with licensing frequencies. Intermediate devices are not used at all, which means there is no talk about obtaining any permits, tying something to the “place of registration”, etc. (about what we spoke above with reference to femtocell).
The only "but" is that Wi-Fi calling calls are not available on all devices. To support Wi-Fi calling (and UMA in principle), it is necessary that the phone be equipped not only with GSM, but also with a Wi-Fi module, which is initially more expensive - i.e. The cheapest "dialers" will never get the support of this technology.
The absence of intermediate devices leads to the fact that Wi-Fi calling, unlike femto cells, does not allow any additional services to be deployed. Thus, for femtocells, there is still a place in the market. Therefore, these devices continue to actively develop. The need for them is primarily in the corporate sector, where it is important to provide communication to all visitors to a particular zone. This problem through Wi-Fi calling is not yet solved.
Thus, conditionally, the old and the new technologies complement each other, jointly solving the issue of providing voice services where GSM coverage leaves much to be desired.
Source: https://habr.com/ru/post/327820/
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