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Unlicensed mobile access (UMA) and generic access network (GAN) technologies hold out the promise of increased revenue growth with low risk for both wireless network operators and mobile device manufacturers. Simultaneously, they allow subscribers the convenience of using a single handset for their home, mobile, and office communications. The 3GPP standards are designed to enable this market to take off through the adoption of UMA/GAN. This article explains the background of UMA/GAN, how it works and introduces the test methods
that will enable manufacturers to deliver on the commercial promises that these fixed mobile convergence technology standards enable.
Mobile phone penetration has now reached well over 2 billion subscribers globally. Most
of these users want to use their mobile terminal as their one and only phone, saying
goodbye to the usual rack of numbers for the fixed line home phone and office phones.
This is often referred to as fixed-to-mobile substitution. However, the price premium to
use a mobile device and often-poor indoor reception has discouraged customers from using just the one device.
Early attempts at fixed-mobile convergence in the late 1990s looked at using
manufacturer-specific micro base stations in the house or office that could route a call made on a cellular handset through a locally installed fixed wire phone line. However,
the manufacturer-specific models were not economical for the mass market and still involved the need and costs associated with a fixed telephone line.
Over the last few years, the advance in digital subscriber line (DSL) and cable modems
have given domestic users a broadband experience for accessing the Internet at a very
reasonable price with most operators offering in excess of 2 Mbps of "all you can eat"
data plans. Voice over IP (VoIP) has also started to take off with services such as Skype
and Vonage, and an array of instant messaging programs incorporating free VoIP calls
such as MSN or Yahoo Messenger. Lastly, it has also become extremely affordable to
purchase a low-cost wireless access point, typically conforming to the IEEE 802.11b/g
standards.
This growth in broadband and VoIP, coupled with low-cost wireless access points located
everywhere from airports and cafs to homes and offices, has opened up a whole new
market for fixed/mobile convergence. And, it offers the possibility for wireless operators to further displace fixed line phone providers and increase revenues, with little financial risk from what is now considered by many to be a saturated market.
UMA and GAN
UMA/GAN, the 3GPP standard for cellular/Wi-Fi convergence, meets both
the desire of mobile phone users to completely remove the need for any other phones
in their lives, as well as the needs of wireless operators for low-risk growth.
UMA was founded by over a dozen leading operators and manufacturers under the
group name UMA Industry Forum. The work was introduced into 3GPP GSM EDGE
Radio Access (GERAN) group in June 2004 and was standardized and ratified by 3GPP
as GAN in 3GPP TS43.318 as a release 6 feature during April 2005. Although being the
newer of the two terms, GAN is usually marketed as UMA, despite there being some
further enhancements in how the lower layer headers are built up and differences in how
the authentication is implemented. Both, however, work in a similar manner, whereby the
user's device and the wireless operator's network are capable of supporting a cellular
service such as GSM/GPRS as well as a wireless LAN access technology, such as
802.11.
From a network operator's perspective UMA functionality is a low-cost introduction (Figure 1). It can be achieved simply by adding an UMA Network Controller (UNC), which acts much like a base station controller (BSC). The UNC is connected on one side to the Internet, thereby connecting to the WLAN access points. On the other side of the UNC is a standard A interface for the circuit-switched communications through to the mobile services switching center (MSC) and a Gb interface for the packet switched connectivity through to the serving GPRS support node (SGSN). GAN also uses the same principle, but calls the UNC the GAN controller (GANC). Therefore, when a device hands over from a GSM to a WLAN, it appears to the core network as just a different base station.
1. Typical components found in a UMA network.
Security
As the last mile to and from the access point is over the Internet, security is a key
requirement. Therefore, when the handset detects a WLAN access point, an IPSec
tunnel is started between the device and the security gateway (SEGW), which is located
in the UNC/GANC element. This is achieved by using the SIM or USIM credentials and
an encryption certificate embedded within the device detailing addresses of the fully
qualified domain name (FQDN) of the SEGW and the public DNS address of the SEGW. Internet Engineering Task Force (IETF) specifications define the protocols, IKEv2, EAP-SIM and EAP-AKA, for the authentication procedure to authenticate the user and establish a secure tunnel into the operator's network.
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