VoWi-Fi stands for voice over (EPC-integrated) Wi-Fi. VoWi-Fi is a complementary technology to VoLTE and also utilises IMS technology to provide a packet voice service that is delivered over IP via a Wi-Fi access network. Where possible, VoLTE calls may be seamlessly handed over between LTE and Wi-Fi and vice versa. Conversational video is also possible via Wi-Fi (see ViLTE).

The first VoWi-Fi deployment occurred in the USA in 2014. VoWi-Fi enables an operator to leverage the existing SIM-based security and authentication as for VoLTE and to provide the same set of IMS-based services to the end user via a Wi-Fi access network as for LTE. Some operators are deploying VoWi-Fi prior to VoLTE as a means of proving their IMS-based solution.

The GSMA has published the VoWi-Fi Service Description, which describes VoWi-Fi for single network, interconnect and roaming scenarios. The document also describes seamless handover of voice calls between Wi-Fi and LTE and vice versa. See the GSMA PRD V2020.02, here.

Related documents

A number of the GSMA’s Permanent Reference Documents (PRDs) regarding VoWi-Fi, detailed below, are available for you to download here.

IR.51– IMS Profile for Voice, Video and SMS over Wi-Fi

This document defines a profile that identifies a minimum mandatory set of features which are defined in 3GPP specifications that a wireless device (the User Equipment [UE]) and network are required to implement in order to guarantee interoperable, high quality IMS-based telephony and conversational video services over Wi-Fi access.

IR.61 – Wi-Fi Roaming Guidelines

This document describes the Wi-Fi Access to the Evolved 3GPP Packet Switched domain also known as the Evolved Packet Core (EPC) as defined in the 3GPP specifications TS 23.402 and TS 24.302. The document is based on 3GPP Release 11 and later. The document also covers policy control and charging and authentication.

IR.34 – Guidelines for IPX Provider networks (Previously Inter-Service Provider IP Backbone Guidelines)

The Internet Protocol (IP) Packet eXchange (IPX) Network is an inter-service Provider IP backbone which comprises the interconnected networks of IPX Providers and General Packet Radio Service (GPRS) Roaming eXchange (GRX) Providers. The purpose of this document is to provide guidelines and technical information on how these networks are set up and interconnect and how service providers will connect to the IPX Provider networks.

IR.39 – IMS Profile for High Definition Video Conference (HDVC) Service

The IP Multimedia Subsystem (IMS) Profile for High Definition Video Conference (HDVC) service, documented in this Permanent Reference Document (PRD), defines a minimum mandatory set of features that a video communication client and the network are required to implement to guarantee an interoperable, high quality IMS-based video communication service over fixed and mobile access.

IR.95 – SIP/SDP Profile for inter-IMS NNI

This document describes a generic SIP/SDP profile for interconnection and roaming NNI between operators’ IMS networks for the purposes of exchanging traffic originating from and terminating to the respective operators’ customers. This document profiles SIP/SDP for the GSMA-defined, IMS-based services (i.e. VoLTE, ViLTE, VoWi-Fi, SMSoIP, and RCS services).

IR.64 – IMS Service Centralisation and Continuity Guidelines

The 3rd Generation Partnership Project (3GPP) has specified the solution for centralisation of services in the IP Multimedia Subsystem (IMS) and of IMS based service continuity in Release 8 onwards. The user shall receive services in a consistent manner when the user accesses IMS either via the Circuit Switched (CS) or the Packet Switched (PS) domain. Service continuity is supported between CS and PS domains.

IR.65 – IMS Roaming and Interworking Guidelines

The 3rd Generation Partnership Project (3GPP) architecture has introduced a subsystem known as the IP Multimedia Subsystem (IMS) as an addition to the Packet-Switched (PS) domain. IMS supports new, IP-based multimedia services as well as interoperability with traditional telephony services. IMS is not a service per se, but a framework for enabling advanced IP services and apps on top of a packet bearer.

IR.67 – DNS/ENUM Guidelines for Service Providers and GRX/IPX Providers

Inter Service Provider IP communications are starting to evolve to support services other than GPRS Roaming. Many, if not all, of these services rely upon DNS. Therefore, it is of utmost importance for the interworking and stability of such services that Service Providers have all the necessary information to hand to ease configuration of their DNS servers upon which such services rely.

NG.102 – IMS Profile for Converged IP Communications

This document defines a profile that identifies a minimum mandatory set of common IMS functionalities that are defined in 3GPP specifications and other GSMA PRDs that a wireless device (the User Equipment [UE]) and network are required to support in order to guarantee interoperable, high quality IMS-based and Mobile Operator provided Converged IP Communications Services (VoLTE, ViLTE, VoWi-Fi and RCS).


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