Top 10 Questions About VoWiFi

  1. What is VoWiFi?
  2. Why should I deploy it?
  3. Which Wi-Fi networks matter?
  4. What is the expected voice quality; do I need QoS?
  5. Why should I bother, isn’t voice a dead service?
  6. Do I lose control of my subscribers when they’re on Wi-Fi?
  7. Can calls handover from Wi-Fi to cellular?
  8. Can I meet all my regulatory obligations?
  9. Do I need to deploy VoLTE first?
  10. How should I charge for a VoWiFi service?


1. What is VoWiFi?

What is VoWiFiThe most basic, but essential question of them all. While the answer is straight forward, the question is one that has become more frequent due the proliferation of so called Over-The-Top (OTT) voice and messaging services such as Skype, Viber and WhatsApp, which are all capable of working over any IP-based network, including Wi-Fi.

However, VoWiFi is actually very specific, it has been defined by mobile industry standards setting organizations (i.e. 3GPP and GSMA), is detailed in a set of industry specifications including the GSMA’s IR.51 and IR.92 documents, and is increasingly supported as a native feature in a number of smartphones, including Apple’s iPhone and Samsung’s Galaxy S6.

VoWiFi, as defined in those specification documents, is a solution whereby mobile service providers can deliver the same set of mobile voice and messaging services they currently offer over their macro cellular network, over any Wi-Fi network, globally. With VoWiFi, mobile operators can enable their subscribers to transparently transition between their cellular network and any home, office or public Wi-Fi network. Several key aspects of this specific VoWiFi solution include:

Same Mobile Number – As a subscriber moves between the macro cellular network and any Wi-Fi network, they continue to use their regular mobile telephone number. They do not have a separate identity when on Wi-Fi versus the macro network. When connected to Wi-Fi, the subscriber will receive all calls and messages to their regular mobile number over the Wi-Fi network. And all calls and messages they send will also be delivered over the Wi-Fi network using their regular mobile number.

Same Mobile Services – As a subscriber moves between the macro cellular network and any Wi-Fi network, they continue to receive the same set of mobile services. This not only includes standard mobile calling and SMS/MMS messaging, but also the myriad of supplementary services (e.g. call waiting, multi-party calling, CLID, etc…), IN-based services (e.g. prepaid, VPN, toll free,…) as well as emergency calling (more on full regulatory compliance later).

Same User Experience – Subscribers have the same user experience whether they are connected to the cellular network or Wi-Fi. Subscribers continue to make and receive calls using the regular native dialer on their phone. Subscribers send and receive messages using the same app whether they are connected to Wi-Fi or the cellular network. No change in end user behavior is required.

2. Why should I deploy VoWiFi?

Why should I deploy VoWiFiThe number one reason is indoor service coverage.

While the complete list of reasons to deploy a VoWiFi service will vary by region, country, and operator, the primary one is to address indoor service coverage challenges. Since the dawn of the mobile industry, providing subscribers with reliably, quality coverage for voice services while indoors has been a challenge. This is especially true in the locations subscribers spend most of their time and seek to use most of their mobile services, at home and in the office.

Whether you are a tier 1 mobile network operator (MNO) or a new mobile virtual network operator (MVNO), one of the top reasons for subscriber churn is poor indoor coverage, especially at home. Churn due to poor indoor coverage costs the mobile industry billions of dollars every month. In addition, poor indoor coverage is one of the top reasons for new subscriber 15/30 day returns (e.g. service cancellations), which are typically not reported in an operators monthly subscriber churn numbers.

Offering a VoWiFi service has been proven to provide a significant reduction in subscriber churn as well as returns, providing a very powerful business case.

The secondary reason for VoWiFi deployment will obviously vary based on region, country and operator type, but is typically either (i) macro network offload, (ii) subscriber acquisition, (iii) response to OTT services, or (iv) fixed-to-mobile substitution. For example, an MVNO will look at VoWiFi as a means to reduce the amount of voice traffic delivered over their macro partner’s cellular network, thereby lowering their operational costs. Or an MNO who is the first to deploy to a VoWiFi in a market will be able to provide a differentiated service offering that can increase overall subscriber acquisition.

3. Which Wi-Fi networks matter?

Which WiFi networks matterThe simple answer is private home Wi-Fi networks, followed by private office Wi-Fi networks, followed by public Wi-Fi networks.

One reason VoWiFi is such an elegant solution is that it is able to leverage the fact that the vast majority of existing Wi-Fi network deployments are in the exact same locations that operators have difficulty reaching with high quality service coverage using their macro network.

In addition, the vast majority of smartphone subscribers have already configured their smartphones to connect to Wi-Fi networks at their home and the office. Those operators who simply chose to begin making their voice and messaging services available over Wi-Fi can quickly make significant progress toward addressing their indoor service challenge.

The growing base of ‘carrier Wi-Fi’ somewhat overlays these 3 categories of networks and will make connectivity for users even easier.

4. What is the expected voice quality; do I need QOS?

VoWiFi quality will typically be as good as, if not better than, voice quality on macro cellular networks, without QoS, since connections are over the internet.

As discussed above in the answer to the question “Which Wi-Fi networks matter?”, the vast majority of VoWiFi usage is on private Wi-Fi networks at home and in the office. As Wi-Fi network performance (e.g. coverage, congestion, throughput,…) in these locations is usually very good, voice services operating over them experience a quality of service that is typically better than that received on the macro cellular network. However, some VoWiFi usage will be on public Wi-Fi networks, especially when subscribers travel internationally and seek to bypass international roaming fees. When using such public Wi-Fi networks, network performance will be more variable and can have an effect on VoWiFi quality. However, as VoWiFi usage on such networks is such a small percentage, overall VoWiFi quality will be better than that received on the cellular network.

5. Why should I bother, isn’t voice a dead service?

In many countries, while traditional mobile telephony minutes-of-use may be declining, overall voice usage on mobile phones is actually growing. This is being driven by the availability of many alternative mobile voice services (e.g. the so called OTT services).

However, even in those situations where mobile telephony minutes may be in decline, no one is predicting the service will disappear any time soon, for many reasons including its ubiquitous nature. While in certain use cases, a specific OTT voice service may be a better fit than mobile telephony for a specific real time voice requirement, the ability to “call” and speak to practically anyone in the world will continue to make mobile telephony an indispensable service for the foreseeable future.

In addition, in survey after survey, the coverage and performance of mobile telephony service, especially in the places subscribers spent most of their time (i.e. at home and the office) continues to be a key decision criteria for subscribers when they compare mobile service providers.

6. Do I lose control of my subscriber when they’re on Wi-Fi?

No, the operator retains complete control of subscribers and the voice and messaging services they deliver to them. When a VoWiFi-enabled subscriber connects to Wi-Fi, their handsets automatically attempt to connect to the operator’s core network over the Internet and register to receive voice and messaging services over that Wi-Fi connection.

Once authenticated and authorized, all the subscriber’s in-bound and out-bound voice and messaging traffic will be routed over the Wi-Fi/Internet connection rather than over the macro cellular network. The operator continues to handle all routing, billing, etc… for all mobile originated and terminated voice and messaging traffic over Wi-Fi. In effect, VoWiFi simply enables the Internet and existing Wi-Fi networks to function as an alternative radio access network.

7. Can calls handover from Wi-Fi to cellular?

Yes. VoWiFi standards and products allow for the handoff of active voice calls between Wi-Fi and cellular networks. In fact, standards support two different approaches for handover, one for handing over between Wi-Fi and VoLTE and another for handing over between Wi-Fi and 2G/3G voice services. However, not all vendor solutions support both methods.

8. Can I meet all my regulatory obligations?

Yes. VoWiFi standards and products were developed to ensure operators could meet all existing regulatory obligations, including emergency call handling. As discussed in the response to the question on whether or not operators lose control of subscribers when on Wi-Fi, as all in-bound and out-bound subscriber traffic is routed through the operator’s core network, the necessary systems are in place to ensure regulatory compliance.

9. Do I need to deploy VoLTE first?

No. While it is true that the same IMS core network supports delivery of both VoWiFi and VoLTE services, mobile operators are not required to offer VoLTE prior to, or in conjunction, with launching VoWiFi.

In fact, a growing number of operators are now viewing deployment of VoWiFi prior to VoLTE as the preferred industry approach. As delivering VoLTE service has a number of additional dependencies beyond deployment of the new IMS core, such as coverage and performance of the macro LTE network, starting with VoWiFi service gives the operator the opportunity to deploy and exercise the new IMS core prior to launching full VoLTE service.

10. How should I charge for a VoWiFi service?

The answer to this question is KISS, keep pricing very simple. While the technology enables operators, using their existing billing systems, to charge different rates for voice and messaging service usage by country, access point type, or even by specific access points, they must be careful not to confuse subscribers.

For mobile network operators whose primary objective with a VoWiFi service is to address indoor coverage challenges, then the simplest approach is to not charge any different for voice and messaging services consumed over Wi-Fi versus the macro network. In this situation, subscribers simply choose to use VoWiFi in certain locations to receive a better service experience.

However, for an MVNO whose secondary objective with VoWiFi is to offload the macro network, they may choose to charge a lower rate for calling over Wi-Fi in order to encourage subscribers to connect more frequently to Wi-Fi networks.