Wi-Fi calling, also called Voice over wireless LAN (VoWLAN) and VoWiFi, refers to mobile phone voice calls and data that are made over IP networks using Wi-Fi, instead of the cell towers provided by cellular networks. In essence, it is voice over IP (VoIP) over a Wi-Fi network. Using this feature, compatible handsets are able to route regular cellular calls through a wireless LAN (Wi-Fi) network with broadband Internet, while seamlessly changing connections between the two where necessary. This feature makes use of the Generic Access Network (GAN) protocol, also known as Unlicensed Mobile Access (UMA). Essentially, GAN/UMA allows cell phone packets to be forwarded to a network access point over the internet, rather than over-the-air using GSM/GPRS, UMTS or similar. A separate device known as a "GAN Controller" (GANC) receives this data from the Internet and feeds it into the phone network as if it were coming from an antenna on a tower. Calls can be placed from or received to the handset as if it were connected over-the-air directly to the GANC's point of presence, making the call invisible to the network as a whole. This can be useful in locations with poor cell coverage where some other form of internet access is available, especially at the home or office. The system offers seamless handoff, so the user can move from cell to Wi-Fi and back again with the same invisibility that the cell network offers when moving from tower to tower. Since the GAN system works over the internet, a UMA-capable handset can connect to its service provider from any location with internet access. This is particularly useful for travelers, who can connect to their provider's GANC and make calls into their home service area from anywhere in the world. This is subject to the quality of the internet connection, however, and may not work well over limited bandwidth or long-latency connection. To improve quality of service (QoS) in the home or office, some providers also supply a specially programmed wireless access point that prioritizes UMA packets. Another benefit of Wi-Fi calling is that mobile calls can be made through the internet using the same native calling client; it does not require third-party Voice over IP (VoIP) closed services like WhatsApp or Skype, relying instead on the mobile cellular operator.
Technology
The GAN protocol that extends mobile voice, data and multimedia (IP Multimedia Subsystem/Session Initiation Protocol (IMS/SIP)) applications over IP networks. The latest generation system is named VoWiFi by a number of handset manufacturers, including Apple and Samsung, a move that is being mirrored by carriers like T-Mobile US and Vodafone. The service is dependent on IMS, IPsec, IWLAN and ePDG.
Modes of operation The original Release 6 GAN specification supported a 2G (A/Gb) connection from the GANC into the mobile core network (MSC/GSN). Today all commercial GAN dual-mode handset deployments are based on a 2G connection and all GAN enabled devices are dual-mode 2G/Wi-Fi. The specification, though, defined support for multimode handset operation. Therefore, 3G/2G/Wi-Fi handsets are supported in the standard. The first 3G/UMA devices were announced in the second half of 2008. A typical UMA/GAN handset will have four modes of operation:
GERAN-only: uses only cellular networks GERAN-preferred: uses cellular networks if available, otherwise the 802.11 radio GAN-preferred: uses an 802.11 connection if an access point is in range, otherwise the cellular network GAN-only: uses only the 802.11 connection In all cases, the handset scans for GSM cells when it first turns on, to determine its location area. This allows the carrier to route the call to the nearest GANC, set the correct rate plan, and comply with existing roaming agreements. At the end of 2007, the GAN specification was enhanced to support 3G (Iu) interfaces from the GANC to the mobile core network (MSC/GSN). This native 3G interface can be used for dual-mode handset as well as 3G femtocell service delivery. The GAN release 8 documentation describes these new capabilities.
UMA/GAN beyond dual-mode While UMA is nearly always associated with dual-mode GSM/Wi-Fi services, it is actually a ‘generic’ access network technology that provides a generic method for extending the services and applications in an operator's mobile core (voice, data, IMS) over IP and the public Internet. GAN defines a secure, managed connection from the mobile core (GANC) to different devices/access points over IP.
Femtocells: The GAN standard is currently used to provide a secure, managed, standardized interface from a femtocell to the mobile core network. Recently Kineto, NEC and Motorola issued a joint proposal to the 3GPP work group studying femtocells (also known as ‘Home Node B's or HNB) to propose GAN as the basis for that standard. Analog terminal adaptors (ATAs): T-Mobile US once offered a fixed-line VoIP service called @Home. Similar to Vonage, consumers can port their fixed phone number to T-Mobile. Then T-Mobile associates that number with an analog telephone adapter. The consumer plugs the ATA into a home broadband network and begins receiving calls to the fixed number over the IP access network. The service was discontinued in 2010; however, earlier subscribers were "grandfathered" in. Mobile VoIP client: Consumers have started to use telephony interfaces on their PCs. Applications offer a low-cost, convenient way to access telephony services while traveling. Now mobile operators can offer a similar service with a UMA-enabled mobile VoIP client. The client provides a mirror interface to a subscriber's existing mobile service. For the mobile operator, services can now be extended to a computer, and they can give consumers another way to use their mobile service.
Design considerations A Wi-Fi network that supports voice telephony must be carefully designed in a way that maximizes performance and is able to support the applicable call density. A voice network includes call gateways in addition to the Wi-Fi access points. The gateways provide call handling among wireless IP phones and connections to traditional telephone systems. The Wi-Fi network supporting voice applications must provide much stronger signal coverage than what's needed for most data-only applications. In addition, the Wi-Fi network must provide seamless roaming between access points.
… excerpt ends here. Continue reading the full article.
