Voice Over Wi-Fi (VoWiFi): Technology Overview, Opportunities, and Challenges
Voice over Wi-Fi (VoWi-Fi), often known as Wi-Fi Calling, is a service that mobile operators increasingly provide to their clients. That's because it assists you in resolving coverage difficulties and reduces the load on your cellular network, customer service, and technical services. However, we must understand two things to provide a first-class VoWi-Fi service that will benefit businesses and satisfy consumers: how it operates and how to make it work efficiently.
People are so accustomed to using Wi-Fi many mobile operators see significant business potential in providing Voice over Wi-Fi (VoWiFi) in homes and businesses, thereby expanding the coverage provided by LTE and 2G/3G networks. Mobile users have had almost exclusive access to VoWiFi via over-the-top (OTT) smartphone and tablet clients from various vendors. As Voice over LTE (VoLTE) becomes more common, device manufacturers increasingly incorporate a complementary VoIP client for Wi-Fi into the terminal chipset. Because making a voice call is the same for both services, simply pressing the green button, this integrated client makes the introduction of VoLTE and VoWiFi transparent to users.
VoWiFi complements VoLTE because both are IMS-based services that can provide mobility and added-value services such as video and Rich Communication Services (RCS). A VoWiFi service can be introduced before, after, or in addition to VoLTE using the same IMS core infrastructure. A unified architecture and infrastructure ensure that VoWiFi call routing, service subscription, billing, and service execution are identical to VoLTE, providing each user with a unified and secure identification and significant cost savings for the operator.
Why is there a Need to Consider VoWiFi?
Always Use the Best Available Network
When a user is indoors in a home environment, VoWi-Fi handles their calling needs if their mobile reception is sufficiently poor to warrant it. But if they move outdoors into an area of better coverage, the cellular network kicks in again. The aim is always to select the best available network to connect the smartphone user, and that's the intelligent part of VoWi-Fi: always knowing which to use.
Voice over Wi-Fi (VoWi-Fi) is a relatively new technology that has received a good reception from mobile network operators. And that's because it fixes one of the customers’ top issues: poor indoor mobile reception.
Solving Problems at Home
Many consumers have been plagued by a bad radio signal when they want to use their mobile phones at home. VoWi-Fi solves this by allowing them to use a Wi-Fi connection instead of the cellular network for making calls. It reduces customer churn because the service users are less likely to jump ship in favor of another provider who might give them better coverage.
With the pervasiveness of Wi-Fi available everywhere, operator customers are now seeing an uptick in demand for VoWi-Fi. They are embracing the technology for many reasons because VoWi-Fi offers:
A cost-effective method to complement macro coverage: As many carriers continue to develop LTE/5G NR networks, there will be locations where coverage is insufficient. Those areas include indoor areas where Wi-Fi provides better coverage. Indoor coverage is a massive challenge for mobile operators, especially with the new energy-efficient building practices and 5G. People spend more time on Wi-Fi than on cellular with their mobile devices.
Utilizing cellular base stations for indoor coverage is like using streetlamps to provide reading light for your bed. Why not use the bedside lamp that is already there? And similarly, why not use Wi-Fi for indoor voice coverage?
Wi-Fi is everywhere. People are already running most of their data through Wi-Fi. According to different studies, almost 80% of all mobile data goes over Wi-Fi, and a significant portion is an indoor traffic.
Customer retention: Operators want to retain their customers to ensure they do not move to an OTT voice application.
Wi-Fi Calling is the perfect customer retention tool. This next-generation VoWiFi works transparently over any Wi-Fi connection. Voice calls, and texts will work from anywhere to anyone. Users will never have to consider whether they are connected to Cellular or Wi-Fi.
Deploying VoWiFi services is mainly a customer retention game. By providing coverage for your voice and text services via any Wi-Fi network, subscribers do not need to seek a service provider with better cellular coverage.
User experience: Enterprise employees want to be able to use a single number to be reached, regardless of the device or location.
A critical success factor is a simple, standard user interface for cellular and VoWiFi calls, with accessible user preferences to activate and deactivate. The voice service must also allow the same mobile number and phonebook for outgoing and incoming calls and messages, whether carried on the cellular network or as VoWiFi.
Although an operator has less control of VoWiFi speech quality and service availability when the service is accessed via a generic, third-party Internet hotspot, users can accept these variations if the service provides additional value, such as extended coverage or lower cost. Typically, a device using VoWiFi has a connection manager that measures the service experience received from the network and can decide which access is best.
How Do VoIP and Wi-Fi Calling Differ?
The "Wi-Fi calling" function on mobile devices has become more prominent recently. Although Wi-Fi calling appears to be a fancy new feature, the technology that powers it, known as Voice over Internet Protocol (VoIP), has been available for years.
VoIP may sound quite technical, but most of us have undoubtedly used it on several occasions, both as consumers and in the workplace. Skype, WhatsApp, Viber, Facebook Messenger, and Google Meet are popular VoIP platforms available as mobile applications. RingCentral, Vonage, Avaya, and Ooma are some of the most popular business VoIP solutions.
VoIP's accessibility, cost-effectiveness, and dependability prompted telecommunication operators to act. Carriers employed VoIP technology to create this new competitive feature known as "Wi-Fi calling," which would operate automatically on a user's smartphone while connected to a wireless network.
This distinction is critical because most people associate VoIP with a standalone application or platform that requires installation, such as the consumer and corporate applications listed above. When people talk about Wi-Fi calling, they're referring to the carrier-branded calling that comes with your phone. Wi-Fi calling does not require the installation of any software. Instead, you enable a phone setting that activates this capability.
Advantages and Disadvantages of Wi-Fi Calling
Here are the top advantages and disadvantages to consider.
The Advantages
Backup Plan for Limited Cellular Coverage
Wi-Fi calling does not require you to make all your phone calls via a Wi-Fi connection. Instead, it serves as a backup solution for your phone calls. It's usually a good idea to have a backup plan if your cellular service goes down.
You Don't Need to Download Any More Apps
Unlike VoIP applications, Wi-Fi calling does not require the installation of any apps or software. This feature is "built" into your phone so that you won't waste valuable phone storage and memory on another app.Can Provide a More Reliable Home Connection
Based on the typical home size of 2,400 square feet, you're within 50 feet of your Wi-Fi router if you call from home. That's much closer than the distance between your phone and the nearest cellular phone tower, which is probably kilometers away.
The Disadvantages
Signal Strength Variability in Public Places
While Wi-Fi calling can be a good option for calls from home, it could be more reliable in public places. If you're in a cafe or a hotel, think of all the bandwidth shared amongst numerous users actively using the same network. Your call quality may deteriorate when your phone competes for that bandwidth space.Wi-Fi Access is Not Always Available.
Although publicly available worldwide hotspots expanded by over 500% between 2016 and 2021, users are not assured of being close to one wherever they go.Carrier-Branded Wi-Fi Calling Is Still Fairly New
Although VoIP technology has existed for years, mobile carriers have only begun offering Wi-Fi calls to their users. While most major carriers offer this capability, some cellular operators and devices (particularly older models) will only enable Wi-Fi calling.
VoWiFi Architecture & Basics of Technology
Let's check which specification applies to the VoWifi Service. Technically speaking, VoWifi includes any Wi-Fi networks that connect to the IMS infrastructure, such as public Wi-Fi access points. It covers all unlicensed, untrusted, and trusted networks.
The GSMA produced the first document, covering the IMS Profile for Voice, Video, and SMS over Untrusted Wi-Fi access. The VoWifi Service is detailed in GSMA's Permanent Reference Documents IR.51 & IR.61.
The Second document, 3GPP's TS 23.402, deals with Architecture enhancements for non-3GPP [IP] accesses such as Wi-Fi.
Overview of VoWifi Solution
As we know, the UE is typically a smartphone that supports VoLTE & VoWifi. The UE is attached to a Wi-Fi access network. Here TWAG or ePDG gateway is used for integrating Wireless LAN access network into the Mobile Network Packet Core - EPC Network. The P-GW acts as the standard anchor to subscriber sessions irrespective of whether the UE is connected to Wi-Fi or LTE, which means both VoLTE & VoWifi streams terminate into PGW.
The PGW allows the IP Session to be preserved during the handover between VoLTE to VoWifi and vice versa. Ultimately these Sessions terminate in the IMS Network Node – SBC. Here IMS offers many functions related to SIP-based calling. On the control plane signaling, it handles SIP authentication, essential telephony services, and interoperability with other CS & IMS Ecosystems. Besides voice, multimedia functions such as video calling will be used and run on the same IMS infrastructure.
There are three types of access defined in the above VoWiFi Architecture.
Untrusted Wireless LAN
The first one is Untrusted Wireless LAN, where the operator needs to trust in Wi-Fi Network and Its - Access Path. The 3GPP Release 6 (2005) introduced the untrusted Wi-Fi concept. Untrusted access refers to any Wi-Fi communication the service provider has no control over, such as personal Wi-Fi, open Wi-Fi hotspots, and public hotspots. VoWifi Access from Home Broadband or DSL is a typical example of untrusted WLAN. Here, traffic flows from the user to the Internet and then to the Mobile Operator Network to which the SIM belongs. Here traffic comes on Operator ePDG from the Internet & further, it's terminated to Operator PGW. Since traffic is transiting via the Internet here, there is no trust in Access Path & hence it is called an Untrusted Wireless LAN. The network would require UE to undergo an additional authentication and security process in untrusted access. Since traffic is coming through the Internet using non-3GPP access, a unique IP tunneling mechanism, for example, IPsec, is used to make it secure. The service is offered to SIM-based phones and tablets, where complete authentication is done for users.
Trusted Wireless LAN
This was introduced in 3GPP Release 8 (2008) along with the LTE standard. Trusted Wireless LAN is directly connected to the Packet Gateway (PGW) via TWAG functionality. Here the Trusted Wireless LAN is managed by the operator, and from the security point of view, the Wi-Fi Networks and Access can be trusted. As we all know, 'Trust 'means something which can be relied upon. Here in VoWifi, Trusted Wireless LAN is a Wi-Fi Network and Access that can be managed somehow - like Corporate Wi-Fi Network. In the case of trusted Networks, UE would get authenticated differently, which is a bit relaxed compared to Untrusted Wireless LAN Access.
Below are mentioned some Security / Authentication methods that the operator may add in Trusted Wireless LAN;
802.1x-based authentication (Including RAN encryption)
3GPP-based network Access that uses the EAP authentication method
The UE is connected to trusted access through the Wi-Fi core's TWAG (Trusted Wireless Access Gateway). The TWAG is then connected to P-GW (Packet Gateway) in the Evolved Packet Core (EPC) over a secure tunnel (Ex, GTP, MIP, etc.). Here communication happens using the IMSI of the user. Therefore, this technique is typically offered only to SIM-based users.
IMS Direct Access
This approach directly connects the user to IMS Network using direct access. In this scenario, the app is installed on the handset responsible for authentication and access. Here software on the handset communicates with IMS Network to place voice-over IP Calls and assess the Wi-Fi Network. Here app provides various audio/video codecs and support for IMS adaptation.
Selection Criteria
All three models have advantages, disadvantages, benefits, and limitations. Let me take you through the factors affecting the Model; which should be chosen?
Who Owns Wi-Fi Access and Backhaul Network?
If a third-party broadband service provider provides Wi-Fi Access or Backhaul, there is no trust between the mobile operator & Wi-Fi Network. We must go for Untrusted WLAN in such situations. Wherever mobile operator has deployed their own Wi-Fi hotspots for distributing Voice and Data Traffic, Operator has their own Backhaul; we can always go for Trusted Wireless LAN as Operator has complete control.
Device Support
Older devices in the market don't support VoLTE and VoWifi. We can always use IMS Direct Access for app-based calling in such cases.
3GPP Vs Non-3GPP Access
3GPP supports multi-type of access. The idea was to offer a single core network that supports multiple access technologies and takes the benefits of numerous IP-based services.
3GPP Access supports existing 3GPP radio access networks specified in 3GPP specifications, such as:
· E-UTRAN (LTE and LTE-A)
· GERAN (GSM / GPRS radio access network)
· UTRAN (UMTS-based WCDMA and HSPA radio access network)
The EPC Network also enables non-3GPP technologies to connect the UE and the EPC Core. Many technologies and innovations are not specified under 3GPP; these include Fixed networks, WiMAX, CDMA, Wireless LAN, etc.
Non-3GPP Accesses can be Grouped into two Categories: Trusted accesses and Untrusted accesses, as discussed above.
Global VoWiFi Market Overview
From $2,035.3 million in 2019, the global VoWiFi market size is projected to reach $22,801.2 million by 2030, growing with a CAGR of 24.5% during the forecast period (2020–2030). The tremendous rise in the global Wi-Fi hotspot availability and significant improvement in the overall quality of service (QoS) for users are driving the growth of the worldwide voice-over Wi-Fi (VoWiFi) industry.
The VoWiFi market growth has shown a spike in revenue generation during the coronavirus disease (COVID-19) pandemic, owing to the increasing usage of Wi-Fi at home, for better call connectivity. Furthermore, the industry will experience rapid growth in the coming years due to the consistently rising need for organizations to establish efficient employee communication, smooth operations, and integrate advanced technologies, such as artificial intelligence (AI) and the Internet of Things (IoT).
However, maintenance is problematic, as carriers are not responsible for troubleshooting and repairing Wi-Fi networks. Instead, residential Wi-Fi users and enterprise IT departments are responsible.
Key Market Trends & Drivers
Offloading of Mobile Data Traffic to Wi-Fi Is Key Trend in the Industry
There is a continuous rise in mobile data usage worldwide, so the congestion on operators' networks is increasing. A highly congested network may offer a lower expected service quality to subscribers; thus, there is a trend of offloading mobile data traffic to the Wi-Fi network. As per research, by the year-end of 2022, mobile traffic offloaded to Wi-Fi networks will reach around 60% of the total mobile data traffic, or approximately 110 exabytes per month. The benefits of VoWi-Fi will fuel the use of Wi-Fi networks and, in turn, augment the VoWiFi market growth globally.
Tremendous Rise in Global Wi-Fi Hotspot Coverage Is Driving Market Growth
The rise in global Wi-Fi hotspot coverage is driving the growth of the VoWiFi market. Factors such as free access to Wi-Fi (promoting other services), community Wi-Fi hotspots, and higher capacity and speed of Wi-Fi support the market growth. In the past few years, governments have spent a sizeable amount on deploying Wi-Fi hotspots in public places. In 2017, there were 124 million public wireless local area networks (WLAN) and community hotspots worldwide, which is expected to reach 550 million by 2022.
Operators are likely to leverage the availability of Wi-Fi to use VoWiFi to extend coverage, particularly indoors and in areas of poor cellular coverage, to reduce churn, which may enhance the market growth in the future. The increase in the number of Wi-Fi hotspots may also help the operators free up their spectrums, as the users may use Wi-Fi hotspots to make a call instead of using the carrier network. Thus, operators can save their capital expenditure.
Significant Improvement in Overall QoS for Users Is Boosting Growth of Industry
A remarkable improvement has been witnessed in the QoS offered to subscribers since the launch of voice-over Wi-Fi services. This technology enables users to remain connected over the call, even without a mobile signal. VoWiFi allows users to make and receive calls reliably without installing additional apps or upgrading the smartphone. Further, voice-over Wi-Fi uses the existing subscriber identification module (SIM) security mechanisms to authenticate and protect communications. During the ongoing call, it also offers seamless network transfer from the Wi-Fi to the cellular network. Poor indoor coverage problems at homes, shops, and offices and low availability of voice-over Wi-Fi enable mobile operators to expand their services further.
Market Players Engaging in Partnerships and Agreements to Gain Competitive Edge
As the number of VoWi-Fi service launches in countries across the world is continuously increasing, the global VoWiFi market is moving toward a fragmented stage, with the presence of significant players such as Verizon Wireless, China Mobile Limited, AT&T Inc., T-Mobile USA Inc., and Vodafone Group Plc.
Industry players are forming partnerships and agreements to obtain a competitive advantage in the market. As an example:
In February 2020, Telefónica UK Limited signed a deal with Mavenir Systems Inc. to use Mavenir Systems Inc.'s virtualized IMS for VoLTE and VoWiFi, in its data center infrastructure. The solution will support mobile services for more than eight million customer connections.
In May 2019, Cellcom, a provider of nationwide communications services throughout Michigan and Wisconsin, selected Mavenir to deploy its virtualized IMS mobile core and voice-over Wi-Fi (VoWiFi) software solutions. This virtualized technology allows operators to create and manage Telco-grade services based on a wide range of commercially available off-the-shelf hardware quickly and easily.
In February 2018, Eastlink Inc., a Canadian telecom operator, selected Ericsson as the lead core network supplier for VoLTE and Wi-Fi calling. Eastlink's investment in VoLTE laid the foundation for future Wi-Fi calling and 5G services.
In March 2017, Convene Networks joined hands with Tech Mahindra Limited to support the deployment of VoLTE and VoWiFi as a managed service. This solution showcased the advantages of IP connectivity and element virtualization in mobile networks with the next generation of managed services.
Some of the Key Players in the VoWiFi Market Include:
Mitel Networks
Huawei Technologies Co. Ltd.
Ribbon Communications US LLC
T-Mobile USA Inc.
Orange SA
Verizon Wireless
AT&T Inc.
Telefonaktiebolaget LM Ericsson
Oracle Corporation
Cisco Systems Inc.
Nokia Corporation
KT Corporation
VoWi-Fi for Enterprise: Opportunities and Challenges
Opportunities
VoWi-Fi deployments increase, and their use rises in popularity. Therefore, mobile operators must provide consistent VoWiFi service in residential, business, and other platforms. More calls will likely be made over nonresidential systems, such as community Wi-Fi, hotspots, hot zones, big venues, business Wi-Fi networks, and city Wi-Fi networks.
Mobile operators have been focusing on enhancing indoor radio coverage for commercial areas for several years. Small cells and DAS are two of the most widely used options today. VoWiFi offers a cost-effective alternative to improving indoor coverage for businesses, particularly when they require support from multiple carriers. The Wi-Fi network, already a must-have in most companies, can support VoWi-Fi service with numerous mobile service providers. In contrast, a small cell solution typically supports only one mobile service provider. Furthermore, there is a considerable difference in CapEx/OpEx between Wi-Fi and small cell/DAS in business venues.
Mobile phones can be an extension of the workplace by integrating mobile operators' IMS and UCaaS/PABXaaS solutions. Businesses have the chance to use VoWi-Fi for fixed-mobile convergence use cases. Fixed-mobile convergence enhances business user experience and improves mobile operator/business stickiness. It adds differentiation to the mobile operator's service offerings.
Challenges
According to studies, mobile users use Wi-Fi 90% of the time at home, work, or school, where low-cost or free Wi-Fi is easily accessible. Mobility customers spend most of their time away from home in their workplaces. The key challenges for deploying VoWi-Fi in the business environment are:
Security: VoWi-Fi necessitates establishing an IPSec connection between the mobile phone and the ePDG over the network. Some companies choose to disable IPSec by default. IPSec tunnels pose some security issues because they are highly secure and do not allow monitoring. In comparison, with SSL connections, IT employees can preshared keys to owned devices and monitor them. This is particularly true with laptops and servers. The mobile UE already has access to the Internet using a 2G, 3G, or 4G mobile data network without monitoring.
The VoWi-Fi architecture also provides a safe connection to the ePDG of the mobile operator. Before being forwarded to the IMS system, which typically limits connections to audio or video, the UE must authenticate to the ePDG gateway for access. Fetching data from the IMS system to the Internet is often tricky. For example, hackers can use Denial of Service (DoS) attacks with hostile SIP clients via the Internet. Given these threats, implementing the proper security measures is vital for VoWiFi services. These measures include encryption for protecting device communications and user identity. When the VoWiFi architecture between the user device and the operator network is untrusted, the service access is based on EPC. The device and evolved Packet Data Gateway (ePDG) secure all communication using IPSec, offering the same data integrity and protection as LTE using SIM credentials.
With Trusted architecture and EPC-based access, WPA2-Enterprise authentication is mandatory. In the case of direct access to the operator's network, security should be provided using IMS border control for the device, typically with Transparent LAN Service (TLS) for signaling and Secure RTP (SRTP) for the user plane. Operators must also secure the transport link between the Wi-Fi access point (AP) and the Trusted Wireless Access Gateway (TWAG) for radio and authentication.
Network performance/QoS: Quality of Service becomes even more crucial in the office/business world. Factors that affect network performance for VoWi-Fi in the office environment are:
◦ Conventional Wi-Fi networks are designed to transport data. To support VoWi-Fi, Wi-Fi networks are required to deliver tiny voice packets and regular-sized data packets. In Wi-Fi, overhead and collisions of small periodic VoWi-Fi packets dramatically reduce the MAC efficiency, while cochannel interference (CCI) limits the bandwidth dedicated to voice packet transmission. This influences the VoWi-Fi call capacity in a Wi-Fi cell.
◦VoWi-Fi with a high Mean Opinion Score (MOS) requires a greater Packet Error Rate (PER) than pure data. This impacts the Wi-Fi cell size.
◦Complexity emerges when VoWi-Fi users with active voice call travel among multiple Wi-Fi cells. To maintain the voice call, a smartphone and Wi-Fi network are essential for inter-AP roaming more quickly and efficiently.
Generally, the network performance challenge for VoWi-Fi relates to delivering a consistent user experience irrespective of load, user location, and environment.
VoWi-Fi QoE: Organizations will naturally need good QoE for VoWi-Fi calls in conformity with their corporate policies. MOS values for VoWi-Fi calls and call success rates are the possible QoE parameters the business requires.
One of the significant challenges in enabling Wi-Fi calling on enterprise Wi-Fi networks is moving from MSP carrier-grade cellular networks to IT-managed enterprise Wi-Fi networks with different service level agreements (SLA). This means maintaining call quality and SLAs from SPs to IT network engineers. An Enterprise Wi-Fi infrastructure handles more than just carrier voice traffic; other applications and services like video streaming & web conferencing share this limited spectrum. The stringent requirement for voice in terms of latency and jitter warrants a network with good end-to-end quality of service design & Voice optimizations that would optimize the delivery of Wi-Fi calling packets in the presence of other applications.
Conclusion
With the industry's recent preference towards utilizing higher frequencies, such as mm-waves, to improve network capacity, indoor coverage has already become a concerning factor. This is because electromagnetic wave penetration depth is much lower at higher frequencies, making it difficult for the cellular signal to reach indoor users. Voice over Wi-Fi (VoWiFi) has recently emerged as a low-cost solution to this problem and an alternative to VoLTE, circuit-switched, and OTT voice services. Motivated by the fact that communication seamlessness and session continuity are the essential factors when offloading voice traffic through a Wi-Fi network.
Wi-Fi calling has been one of the most significant developments in smartphone communications in years. Finally, a single radio infrastructure, installed by a venue owner/manager, will offer carrier voice and text services in addition to the customary Wi-Fi data services. The operators are well-positioned to benefit from these expansions due to their relationships with consumer and business customers. And by combining the deployment of Wi-Fi for operators with the complete VoWi-Fi solution, operators can address VoWi-Fi demands on their network today and build deeper relationships with their customers.
References
[1]. https://blogs.cisco.com/sp/cisco-vowi-fi-solution-for-todays-voice-demands
[2]. https://www.forbes.com/advisor/business/software/what-is-wi-fi-calling/
[4]. https://www.enea.com/solutions/data-management-applications/wifi-calling/
[5]. https://www.psmarketresearch.com/market-analysis/voice-over-wifi-vowifi-market
[6]. https://www.telecomtutorial.info/post/02-vowifi-architecture
[7]. https://ieeexplore.ieee.org/abstract/document/7821871
[8]. https://kipdf.com/cisco-voice-over-wi-fi-solution_5ab206ab1723dd329c639858.html
[9]. https://www.arubanetworks.com/assets/wp/WP_WiFiCalling.pdf
Iman Ali
Associate Consultant & Member of Telecom & Wireless Technology Group at Lumenci
Iman is experienced in the IP domain with the expertise in Infringement Analysis, Patent Portfolio Mining, Prior Art Search, and (EoU)/Claim Chart creation services. He has patented innovative ideas recognized by Intellectual Property India in various technologies. He is interested in Wireless Cellular technologies, IoT, DIP & Network Traffic Analysis (NTA). He is an Electronics and Communication Engineer from Amity University, India.