Since LTE is a data-only network, the networks realised that they can use WiFi for the access network in the same way. VoWiFi is using WiFi for access, and the PS network to guarantee the quality of service (QoS).
What is VoWifi?
VoWiFi stands for voice over (Evolved Packet Core-integrated) WiFi and is a complementary technology to VoLTE. It utilises IMS technology to provide a packet voice service that is delivered over IP via a WiFi network.
Benefits of VoWiFi for users?
No signal is needed for making calls
VoWiFi enables users to be connected even without a mobile signal. VoWiFi makes it possible for users to reliably make and receive calls, even when indoors, without having to install new equipment or upgrade their smartphone.
Leverage existing SIM-based security and authentication as for VoLTE
Instead of relying on user/password, or weak other cryptographic elements, VoWiFi uses existing SIM security mechanisms to authenticate and protect communications for subscribers. When using the SIM, the same security standards can be applied seamlessly across all technologies: CS, PS and WiFi.
Network of load
VoWiFi is an inexpensive way for mobile operators to augment services inside buildings. When macro network signals don’t penetrate well. VoWiFi is an easy way for mobile operators and enterprises wanting to deliver in-building wireless voice services. By relying on homeowners’ or enterprise-supplied WiFi hotspots, mobile operators can offload traffic from the macro network and likely provide superior service.
For enterprises, VoWiFi leverages an investment that, in most cases, has already been made by the enterprise - their WiFi network - so incremental expenditure may be minimal. As long as the user has a device that supports VoWiFi, the service is universal; it’s not specific to any operator, but can be used by anyone with a device that supports it and is granted access to the WiFi network.
How does VoWiFi work?
When using a VoWifi-enabled device, the mobile subscriber first needs to register to the network and establish the default data bearer to exchange data with the network or applications.
The UE will attach to WiFi and obtain IP connectivity, selecting the ePDG based on static IP configuration or DNS. The UE and ePDG will perform mutual authentication during IPsec tunnel establishment using public key certificates, while the UE sends encapsulated EAP-AKA messages over IKEv2 to ePDG including user identity (NAI) and potential APN (for IMS). The AAA fetch AKA authentication vectors generated by the HSS (if not available). AAA extract IMSI for the user. If successful, the AAA initiates the subscriber profile retrieval with the HSS to check if the user is authorized for the untrusted access and sends server registration. If successful, the AAA sends the final authentication answer including IMSI and Master Session Key.
Same as for VoLTE, once the bearer has been set, normal SIP/IMS procedures follow to enable making calls.
Voice over WiFi provides major cost savings and enables new IP services such as video calling, multi-device, single number, and multimedia sharing services across mobile broadband devices. Mobile operators are also increasingly relying on WiFi as a means to offload congested cellular networks. Deploying VoWiFi enables MNOs and MVNOs to quickly and easily extend their coverage or service range without costly radio access network (RAN) infrastructure build-outs, investing in new licensed spectrum or engaging in complex roaming agreements.
The same call features are delivered to the user, whether a subscriber is connected to the cellular network directly, or to WiFi.
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