Wi-Fi Calling is a solution that allows you to make voice and video calls, as well as exchange text messages over the mobile operator's core network by connecting to any Wi-Fi network. In fact, it solves the problem of poor quality voice service or its complete absence in premises without the need to develop a mobile network in individual buildings. All that is needed is support for this technology by the mobile operator’s networks and a subscriber device that implements the corresponding function (“hardwired” into the smartphone at the system level).

Technologically, Wi-Fi Calling (or Voice-over-Wi-Fi) is a continuation of the Voice-over-LTE service (transmission of voice data over LTE networks), which is based on voice transmission over the IP protocol. The fundamental difference between WiFi Calling and existing IP telephony services (Skype or many applications such as WhatsApp, Viber, Facebook Messenger, etc.) is that the call is made over the core network of the mobile operator and is an ordinary telephone call from the subscriber’s mobile number.

“Currently, Wi-Fi Calling is used mainly to improve the quality of voice coverage inside buildings, where for some reason the quality of cellular communications is insufficient and the use of VoLTE is impossible. And “white spots” in the coverage can be present both in suburban houses, far from base stations, and in densely populated areas, for example, in buildings built using energy-saving materials, which significantly impede the penetration of a cellular signal. If there is not enough bandwidth, video calls can only be made over a Wi-Fi network (even if voice connections are made over LTE). In these cases, Wi-Fi Calling technology can complement VoLTE, giving operators the opportunity to launch IMS-based voice and video services even at an early stage of LTE network construction. This will provide a better user experience compared to CSFB,” explains Sergey Vorobiev, leading expert in the development of mobile broadband solutions at Ericsson in the Northern Europe and Central Asia region.

The Wi-Fi Calling solution, developed by Sweden's Ericsson, is based on an enhanced EPC packet core with support for mobile Wi-Fi (ePDG combined with TWAG), and an IMS core. This solution is fully supported by all smartphones with integrated Wi-Fi Calling functionality.

Convenience for the subscriber

The main advantage of Wi-Fi Calling for subscribers is, first of all, the ability to use voice communication services from their smartphone in case of poor mobile network coverage or its absence. Being in a cafe located in the basement, you will no longer need to go outside in order to catch a signal or download special applications - the connection can be established through a Wi-Fi router, which is found almost everywhere today. The same applies to both country houses with poor mobile coverage and densely populated urban areas, where the signal indoors often leaves much to be desired, and the number of Wi-Fi routers is off the charts.

A smartphone with Wi-Fi Calling functionality installed automatically connects to an available Wi-Fi network the moment the mobile signal becomes too weak to make a call or disappears completely.

Another advantage of Wi-Fi Calling for the subscriber is the ability to significantly reduce the cost of voice communications, including roaming costs when calling from abroad on the home operator’s network. Firstly, operators do not charge additional fees for voice communications over IP protocol. Secondly, since voice over Wi-Fi is transmitted over the Internet, the call is not tied to the geographic location of the caller. Calls to numbers on your home network from abroad will remain free. At the same time, calls to the networks of international operators are charged as usual. Thus, while on a business trip or on vacation abroad, in a hotel with Wi-Fi, you can make and receive calls as if you were in your home region.

“Because Wi-Fi calling connections are made over the public Internet, subscribers can access their carrier’s network from anywhere in the world. In addition, users are freed from the need to install additional applications when traveling outside the home network, and the process of using the subscriber device is no different from the usual,” notes Vorobiev.

Benefits for operators

Wi-Fi Calling helps reduce subscriber churn by improving the quality of voice and video coverage inside the building, where, as a rule, there are access points to the Wi-Fi network. The technology of voice transmission over Wi-Fi networks can become a decisive argument for a subscriber when choosing an operator in cases where there is no mobile coverage in an apartment or house, or the signal is weak, the network is overloaded, etc.

In addition to increasing the level of subscriber loyalty and attracting new customers, the economic component of the technology may also be significant for operators. According to Ericsson specialists, it is much more profitable for operators to reuse the huge number of existing Wi-Fi access networks in the world, including the home routers of their subscribers, rather than, for example, investing in stimulating the development of femtocells, which are not particularly popular among Russians . Considering that the functionality to support the Wi-Fi Calling service is initially integrated into smartphones by the manufacturer, operators will not need to spend additional funds on the support and development of individual voice applications (for example, roaming ones).

The introduction of Wi-Fi telephony also opens up new opportunities for operators in the field of mobile and fixed communications convergence (FMC). For example, this service gives mobile operators the opportunity to take the place of fixed-line operators in cases where we are talking about clients from the category of small companies that own fiber optics and their own access point in their office. Thanks to WiFi telephony, office employees will be able to keep their fixed numbers, replacing landline phones with smartphones that support Wi-Fi Calling, and continue to use them outside the office. In addition, possible integration between various subscriber devices (mobile and landline phones, tablets and STB-set-top boxes) of all members of the same family can also help reduce customer churn.

Difficulties

Along with the opportunities that WiFi Calling opens up for both subscribers and operators, the new technology poses a number of difficult challenges for communications companies and equipment manufacturers. The main one is the inability to switch between 2G/3G networks and Wi-Fi. The possibility of seamless transition is currently implemented only for the LTE network, because... At the heart of both technologies is the IMS core. Therefore, outside the coverage area of the Wi-Fi router, if there is LTE coverage, the conversation will not be interrupted. “Packet data transfer removes the question of which network is used - Wi-Fi or cellular, since, theoretically, packets are transmitted along the route and using the technology that is currently optimal for the user experience,” says Vorobiev.

Another challenge for operators tasked with providing quality voice services is the ability to predict and control the quality of Wi-Fi networks. The operator has no relation to the access point installed by the user, and the quality of the voice services it provides will depend on the operation of the Wi-Fi network. Difficulties may be caused by interference from a neighboring access point, high network congestion, or the long range of the router. In addition, modern Wi-Fi technologies provide the transmission of large volumes of data, but the quality of voice transmission depends not so much on the channel width as on the reliability and continuity of packet transmission from the subscriber device to the access point.

Another aspect that also requires a technological solution is calls to emergency services via Wi-Fi Calling, since voice transmission over the Internet does not allow obtaining subscriber location data. In the United States, the problem of calling emergency services is solved when the user activates the Wi-Fi Calling service - he can complete it only after he automatically tells the 911 service his home address. The situation is more complicated with international calls to emergency services, since they should not be made through the home networks of a subscriber located in another country. One of the solutions to this problem, Ericsson specialists see is the ability to configure the system so that the IMS network automatically recognizes such calls and transfers them to the home networks of the host country.

In addition to technological problems, the solution of which depends on equipment manufacturers and telecom operators, there is also a risk of legislative restrictions or simply insufficient elaboration of the legal aspect of voice transmission over a Wi-Fi network in various countries.

Wi-Fi Calling in the world

There are still few examples of the implementation of Wi-Fi Calling - this service is fully provided in the USA by the operators Sprint and T-Mobile, as well as by the British operator EE. On the way are the American AT&T and Verizon, the British Vodafone, the Singaporean Singtel and other companies that have already announced plans to introduce Wi-Fi Calling.

Different operators use the technology and provide the service in different ways. Subscribers of US operators can use Wi-Fi Calling from anywhere in the world, while EE allows its customers to make calls via Wi-Fi networks only while in the UK. Operators assess the prospects of the new technology differently. For example, Wi-Fi Calling has been available to EE subscribers since April of this year, while the launch of VoLTE on the operator’s networks will only be possible by the end of summer. The management of the American AT&T last fall, in turn, said that the company is in no hurry to introduce Wi-Fi Calling, considering this technology primarily to expand the capabilities of LTE networks in addition to VoLTE. Therefore, this technology will be introduced only after the full deployment of fourth generation networks and the introduction of VoLTE.

As for subscriber devices that support the Wi-Fi Calling function, their number is rapidly increasing. If quite recently they were limited to a few models of smartphones, today they are offered by most major manufacturers: Samsung, Apple, LG, Alcatel, Nokia, Sony, ZTE, Microsoft.

Russia

Russian operators have not yet announced launch dates or prospects for introducing Wi-Fi Calling on their networks, and are busy developing LTE and WCDMA technology in buildings. At the same time, however, major operators also consider this technology, primarily as an addition to the VoLTE service.

“We see promise in the development of Voice over Wi-Fi (or Wi-Fi Calling) technology, which allows voice calls to be transmitted over Wi-Fi, since when implementing the functionality of voice transmission in LTE (VoLTE) networks, it will give operators the opportunity to improve the quality of communication within premises with weak signal penetration, relieve the radio access network in places of intense traffic consumption, and also reduce subscribers’ roaming costs,” says Dmitry Solodovnikov, head of MTS media relations. – We are technologically ready to support Voice over Wi-Fi technology. For this purpose, we have created the IMS (IP Multimedia Subsystem) core, around which VoLTE technology will be built in the future. However, today in Russia there are regulatory and technological obstacles to the development of Voice over Wi-Fi.”

According to him, in Russia there is no regulatory framework that defines the principles of routing voice calls from data networks to the public telephone network, as well as providing SORM. In addition, there is not yet sufficient penetration of mobile terminals on the market that support Voice over Wi-Fi technology at the kernel and operating system level.

“We are introducing the Wi-Fi Calling service on the network, and we believe in its demand over time,” said Megafon spokeswoman Aliya Beketova, adding that the company is also looking into the issue of user devices that support this function.

WiFi Calling: calls over the operator’s Wi-Fi network – Ericsson – Kommersant