The Generic Access Network

Abstract
In telecommunication systems, a generic access network (GAN) is used by cellular device users to connect and interact with other types of communication devices. GAN protocols primarily evolved for wireless communication systems, allowing mobile phones to perform functions seamlessly between wireless local area networks (WLANs) and wide area networks (WANs) without interrupting the communication session. Modern GAN technology permits a subscriber to interact via voice, data, IP multimedia subsystem and Session Initiation Protocol (SIP) applications. Using GAN technology, a cell phone subscriber can communicate by voice, data and multimedia. As GAN technology is implemented, cellular telephone subscribers can expect improved coverage, the ability to use a single phone set for all their voice communications and perhaps cheaper rates with a single bill for Internet and voice communications.

Prior to 2005, a generic access network was commercially known as unlicensed mobile access (UMA)..

Introduction
The Generic Access Network (GAN) is an evolving wireless communications system in which mobile phone sets function seamlessly between local area networks (LANs) and wide-area networks (WANs). Using GAN technology, a cell phone subscriber can communicate by voice, data and multimedia. As GAN technology is implemented, cellular telephone subscribers can expect improved coverage, the ability to use a single phone set for all their voice communications and perhaps cheaper rates with a single bill for Internet and voice communications.
Main application of this GAN/UMA is the Dual-mode Handset service.
History of Generic Access Network
In September 2004, the participating companies published the initial UMA specifications and formally introduced them to the 3rd Generation Partnership Project (3GPP) standards body. In April 2005, an unprecedented eight months later, the UMA specifications were incorporated into the 3GPP release 6 specifications. While referred to as "Generic Access Network" or GAN, within the 3GPP specifications. In mid 2006, mobile operators around the world began announcing their intention to deploy dual-mode handset (DMH)-based UMA services. Throughout 2007, there were constant announcement of new UMA-enabled dual-mode phones to support the commercial service offers. In early 2008, the first commercial UMA-based fixed line VoIP service appeared as well as the first UMA-enabled softmobile client.
Problems of Generic Access Network
Subscribers must upgrade to Wi-Fi/UMA enabled handsets to take advantage of the service. Calls may be more prone to disconnect when the handset transitions from Wi-Fi to the standard wireless service and vice versa (because the handset moved out or within the Wi-Fi's range). How much this is a problem may vary based on which handset is used. The UMA may use different frequency that is more prone to some types of interference. Some setup may be required to provide connection settings (such as authentication details) before advantages may be experienced. This may take time for subscribes and require additional support to be provided. The costs of support may be for more than the wireless phone company: network administrators may be asked to help a user enter appropriate settings into a phone (that the network administrator may know little about).
The phones that support multiple signals (both the UMA/Wi-Fi and the type of signal used by the provider's towers) may be more expensive, particularly to manufacture, due to additional circuitry/components required. This uses the resources of the network providing the Wi-Fi signal (and any indirect network that is then utilized when that network is used). Bandwidth is used up. Some types of network traffic (like DNS and IPsec-encrypted) need to be permitted by the network, so a decision to support this may impose some requirement(s) regarding the network's security (firewall) rules.

Significance of Generic Access Network
Instead of erecting expensive base stations to cover dead zones, GAN allows carriers to add coverage using low cost 802.11 access points. Subscribers at home have very good coverage. In addition, GAN relieves congestion (meaning that networks can, through GAN, essentially piggyback on other infrastructure) on the GSM or UMTS spectrum by removing common types of calls and routing them to the operator via the relatively low cost Internet. GAN makes sense for network operators that also offer Internet services. Operators can leverage sales of one to promote the other, and can bill both to each customer.
Subscribers do not rely on their operator's ability to roll out towers and coverage, allowing them to fix some types of coverage dead zones (such as in the home or workplace) themselves. The cheaper rates for 802.11 use, coupled with better coverage at home, make more affordable and practical the use of cellphones instead of land lines. Using IP over 802.11 eliminates expensive charges when roaming outside of a carrier's network.
Definition of terms 1. Dual mode handset - is a telephone which uses more than one technique for sending and receiving voice and data. 2. Wireless Fidelity (wi-fi) - a local area network that uses high frequency radio signals to transmit and receive data over distances. 3. Local area networks (LANs) - a computer network that links devices within a building or group of adjacent buildings. 4. Wide area network (WANs) - computer network in which the computers connected may be far apart, generally having a radius of half a mile or more. 5. Femtocell - in telecommunications, a femtocell is a small cellular base station, typically designed for use in a home or small business.

Discussion
With dual-mode services(GSM and Wi-fi), subscribers make calls from outside the home as they would ordinarily, using the GSM radio network at the standard tariff rate. But inside the home, the call travels over the subscriber’s wireless broadband connection, so the operator can enjoy a similar economic structure as VoIP-over-broadband provider.
GAN Functional Structure
The GANC provides dual-mode handsets with alternative access to GSM voice and GPRS data services. For voice traffic, the GANC integrates directly into an operator Mobile Switching Center (MSC) through the A interface. For data traffic, the GANC integrates directly into an operator serving GPRS support node (SGSN) through the Gb interface. The introduction of a GAN solution into an operator network raises numerous security implications and vulnerabilities inherent in an IP-based architecture. The security gateway provides two important security roles in the GAN: Secure authentication (through Extensible Authentication Protocol–SIM [EAP-SIM] or EAP–Authentication and Key Agreement [EAP-AKA]) of mobile subscribers. Termination of secure tunnels (through IP Security [IPSec]) with InternetKey Exchange Version 2 [IKEv2]) from the handset.
GAN/UMA is not the first system to allow the use of unlicensed spectrum to connect handsets to a GSM network. The GIP/IWP standard for DECT provides similar functionality, but requires a more direct connection to the GSM network from the base station. While dual-mode DECT/GSM phones have appeared, these have generally been functionally cordless phones with a GSM handset built-in (or vice versa, depending on your point of view), rather than phones implementing DECT/GIP, due to the lack of suitable infrastructure to hook DECT base-stations supporting GIP to GSM networks on an ad-hoc basis. GAN/UMA's ability to use the Internet to provide the "last mile" connection to the GSM network solves the major issue that DECT/GIP has faced. Had GIP emerged as a practical standard, the low power usage of DECT technology when idle would have been an advantage compared to GAN. There is nothing preventing an operator from deploying micro- and pico-cells that use towers that connect with the home network over the Internet. Several companies have developed so-called Femtocell systems that do precisely that, broadcasting a "real" GSM or UMTS signal, bypassing the need for special handsets that require 802.11 technology. In theory, such systems are more universal, and again require lower power than 802.11, but their legality will vary depending on the jurisdiction, and will require the cooperation of the operator.
Service deployments
The first service launch was BT with BT Fusion in the autumn of 2005. The service is based on pre-3GPP GAN standard technology. Initially, BT Fusion used UMA over Bluetooth with phones from Motorola; since Jan 2007, it has used UMA over 802.11 with phones from Nokia, Motorola and Samsung and is branded as a "Wi-Fi mobile service". BT has since discontinued the service. On August 28, 2006, TeliaSonera was the first to launch a 802.11 based UMA service called "Home Free".The service started in Denmark and later expanded to Sweden and Norway. On September 25, 2006 Orange announced its "Unik service", also known as Signal Boost in the UK. The announcement, the largest to date, covers more than 60m of Orange's mobile subscribers in the UK, France, Poland, Spain and the Netherlands. Cincinnati Bell announced the first UMA deployment in the United States. The service, originally called CB Home Run, allows users to transfer seamlessly from the Cincinnati Bell cellular network to a home wireless network or to Cincinnati Bell's WiFi HotSpots. It has since been rebranded as Fusion WiFi. This was followed shortly by T-Mobile US on June 27, 2007. T-Mobile's service, originally named "Hotspot Calling", and rebranded to "Wi-Fi Calling" in 2009, initially allowed users to seamlessly transfer from the T-Mobile cellular network to an 802.11x wireless network or T-Mobile HotSpot in the United States. However, the current version of WiFi Calling no longer supports handoff. In Canada, both Fido and Rogers Wireless launched UMA plans under the names UNO and Rogers Home Calling Zone (later rebranded Talkspot, and subsequently rebranded again as Wi-Fi Calling), respectively, on May 6, 2008. Industry organization UMA Today tracks all operator activities and handset development. UMA is not implemented in Asia, Australia, Africa and some European countries.
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 Adaptor – 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 ATA (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. Developed by Vitendo, the client provides a mirror interface to a subscriber's existing mobile service. For the mobile operator, services can now be extended to a PC/laptop, and they can give consumers another way to use their mobile service.

Similar technologies
GAN/UMA is not the first system to allow the use of unlicensed spectrum to connect handsets to a GSM network. The GIP/IWPstandard for DECT provides similar functionality, but requires a more direct connection to the GSM network from the base station. While dual-mode DECT/GSM phones have appeared, these have generally been functionally cordless phones with a GSM handset built-in (or vice versa, depending on your point of view), rather than phones implementing DECT/GIP, due to the lack of suitable infrastructure to hook DECT base-stations supporting GIP to GSM networks on an ad-hoc basis. GAN/UMA's ability to use the Internet to provide the "last mile" connection to the GSM network solves the major issue that DECT/GIP has faced. Had GIP emerged as a practical standard, the low power usage of DECT technology when idle would have been an advantage compared to GAN.
There is nothing preventing an operator from deploying micro- and pico-cells that use towers that connect with the home network over the Internet. Several companies have developed so-called Femtocell systems that do precisely that, broadcasting a "real" GSM or UMTS signal, bypassing the need for special handsets that require 802.11 technology. In theory, such systems are more universal, and again require lower power than 802.11, but their legality will vary depending on the jurisdiction, and will require the cooperation of the operator.
Conclusion
GAN dual-mode services to the home give mobile operators the opportunity for a significant competitive advantage by accelerating fixed-mobile substitution, increasing penetration, and reducing turnover. The GAN architecture provides an essential prerequisite for dual-mode services—protecting the mobile operator’s voice network from threats originating from the Internet. Because the security infrastructure that is used to offer dual-mode services can be reused for other services, including IMS, the investment in the GAN solution provides a competitive advantage for tomorrow’s service as well as today’s.

References

1. GAN participating companies link http://www.umatechnology.org/participants/index.htm 2. UMA overview http://umatoday.com/umaOverview.php 3. A Brief History of UMA http://umatoday.com/briefHistory.php 4. 3GPP OVERVIEW http://www.3gpp.org/About/about.htm
5.Definitions
http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci1208707,00.htmL
6.All about protocols http://www.voxeo.com/products/voip-home.jsp 7. GSM, TDMA - CDMA, Wireless LAN http://whitepapers.techrepublic.com.com/abstract.aspx?docid=268373 8.http://whitepapers.techrepublic.com.com/thankyou.aspx?authId=ikq5icupT4KI8U8Gu92k KgRMRbkImtNEM82eO7wUxjdLDvUjT/ypXW8oj8PB4ZB4&&promo=100511&docid=268373&view=268373&load=1
9.GAN and its working http://en.wikipedia.org/wiki/Generic_Access_Network#Similar_technologies

Appendices
Figure 1. A note on the history of the GAN (also called as the UMA)
Figure 2. How does this dual-mode service work

Figure 3. GAN functional architecture