When the mobile network is unavailable: why start calls over the Internet

April 10, 2024
When the mobile network is unavailable: why start calls over the Internet
VoWiFi technology allows making calls by phone number outside the coverage area of the mobile network using Wi-Fi. Today, we decided to discuss the relevance of such service and key ways to set it up: from OTT and UMA to untrusted access to EPDG. We will also look at the prospects of the technology and the challenges faced by telecom operators offering the service of calls over the Internet.

Who uses the technology

First of all, VoWiFi technology attracts telecom operators. By offering the possibility to make calls over Wi-Fi, telecom companies expand the coverage area of their own network and attract customers who work in places with problematic access – for example, in reinforced concrete office buildings or basements. Wi-Fi calls are also convenient for residents of rural areas and country houses.

At the same time, VoWiFi allows operators to reduce infrastructure costs. They do not have to install new base stations and expand coverage to work in remote areas. In large cities, operators also have the opportunity to reduce the load on their networks. In megacities, users are close to access points not only at home. According to experts from consulting firm ACG Research, thanks to VoWiFi, U.S. telecoms save a cent on every minute of customer calls, and one major operator has saved $2.2 billion over five years.

VoWiFi technology is also becoming relevant in transportation, where it is difficult to ensure a high quality level of communication – for example, in trains. Special equipment receives a signal from the operator’s towers or satellite on an external antenna. Then Wi-Fi is distributed to the cars with the help of routers. This approach allows to manage Internet access in a centralized manner and monitor the connection status, switching between different signal sources if necessary. This makes Wi-Fi calls more stable than communication using a mobile network. Back in 2020, a group of Swedish engineers conducted a study and compared the quality of connectivity on a rail route between two major Swedish cities, Stockholm and Gothenburg. VoWiFi performed much better than GSM or UMTS.

Not only large operators, but also private businesses are showing interest in VoWiFi calling technology. VoWiFi allows them to set up communication between employees without being tied to the mobile network. Thus, it has been used in American medical institutions for communication between doctors since the early 2000s. Communication devices work within a virtual local network, where data exchange takes place. According to representatives of the University of California at Davis, VoWiFi technology reduces the number of communication tools, replacing voice mail, e-mail and faxes.

Today, the technology is also attracting ordinary enthusiasts who want to learn more about the nuances of communication networks. For example, one engineer launched a private mobile network and connected a smartphone to it. He also invited interested users to join the project to connect and communicate with friends directly.

How calls over the Internet work

In general, there are five ways to set up Wi-Fi calling.

UMA (Unlicensed Mobile Access). The switching between mobile networks and Wi-Fi is done by so-called GAN controllers. They receive packets from the Internet and transmit them to the phone network as if they came from an antenna on a cell tower. Today, the individual frequencies on which UMA operates are somewhat outdated, but some market players consider the technology to be extremely promising. UMA is offered as a commercial service in North America and a number of European countries.

Connection via the operator’s application. In this case, the user needs to download a special mobile application of the operator, enter login and password. A SIM card is not even required for connection, and this method of communication can be used on older devices that do not support VoWiFi by default.

Trusted EPC access. The setup takes place within a network built on the provider’s Wi-Fi hotspots, hence the name – trusted access. Such a trusted network provides QoS and secure user connection due to authentication mechanisms and traffic encryption. Client terminals interact with mobile networks using an s2b interface. But the price of subscriber equipment is quite high, so the implementation of trusted access to EPC and IMS may not be the most profitable approach for the operator.

Untrusted ePDG access. The device establishes a connection to the service provider core via EPDG and authenticates with the SIM card. Information from 3GPP servers responsible for authorization, authentication and user accounting allows to maintain call quality and monitor QoS. If desired, the operator can limit the choice of Wi-Fi points. The technology is launched on the basis of the existing infrastructure for VoLTE. There are vendors on the market ready to help with implementation.

For example, our solution provides for a secure connection from the subscriber’s device to the core. The phone raises an IPSec tunnel to the ePDG, which is then “bridged” to the GTP tunnel.

OTT (Over the Top). Essentially, this variant of VoWiFi implementation represents classic calls via messengers like Viber and Telegram. We can say that it is not used by telecom operators.

Prospects for the technology

Despite all the advantages of VoWiFi, the technology has a number of peculiarities. One of the significant limitations is related to “hardware”. Calls via Wi-Fi in most cases support the models of middle and high price range phones. At the same time, operators are not able to control the quality of Internet connection via third-party access points. Even a powerful Wi-Fi network can be overloaded with a large traffic flow, and if the operator is unable to determine this before switching the call, the quality of voice transmission can suffer. Operators pay special attention to the algorithms responsible for switching between networks, assessing access point congestion and compliance with acceptable delay levels. They try to allocate sufficient bandwidth on edge devices, and in case of poor Wi-Fi connection quality they implement handover to the mobile network.

Another issue is possible interference from radio devices when calling through public Wi-Fi networks. However, RRM algorithms are already being used to protect against interruptions in communication. They continuously analyze radio frequency data from access points to automatically optimize channel bandwidth, transmission power and more – including with the help of AI systems. Finally, they are developing technologies designed to increase coverage and signal quality. For example, a group of Spanish engineers has proposed using UAVs as repeaters to distribute Wi-Fi. This approach can be useful, for example, when dealing with the consequences of accidents or other emergencies far from the coverage area of operators.

At the same time, it should be noted that VoWiFi technology is potentially vulnerable to hacker attacks. Attackers can try to disrupt communication between users using DDoS attacks. In theory, they are also able to determine a person’s IP address and call statistics if they intercept Internet packets from a vulnerable access point. Although researchers are already developing special anti-virus solutions for operators providing VoWiFi services. It can be assumed that the proliferation of such systems will contribute to the further development of VoWiFi and expand the ecosystem of vendors’ offerings.

We use cookies to optimize site functionality and give you the best possible experience. To learn more about the cookies we use, please visit our Cookies Policy. By clicking ‘Okay’, you agree to our use of cookies. Learn more.