Network convergence ultimately aims a single access network to accommodate multiple services. Mobile operators target to seize the new opportunity arising due to abundance in dual-mode handsets that support GSM (Global System for Mobile Communications) and Wi-Fi as seen in the illustration below;
The 3GPP GAN standards evolved from an UMA (Unlicensed Mobile Access) specification specify the handling of secure connectivity, registration, and transmission in order to let subscribers make calls inside the home over subscriber’s unlicensed spectrum technologies (WLANs) to leverage VoIP over broadband service. A GAN-enabled handset after detecting the unlicensed wireless network contacts GAN Controller (GANC) over the broadband IP access network to be authenticated and authorized to access 3GPP voice and data services via the unlicensed wireless network. The GAN framework introduces Up interface between MS and GAN controller in order to create a tunnel to MS to build security and control over unsecure wireless access. GANC has interfaces to MSC, SGSN via A and Gb interfaces, respectively, in addition to Wm interface to AAA.
Lately, also GAN network introduces Iu interfaces in order to support femtocells as seen in the illustration below.
The femtocell proposals considered three options: Iu-b over IP, SIP/IMS, Iu over IP to RAN Gateway. Traditionally femtocell proposals considered lu-b interface to RNC, which exists between 3G RNCs and macro 3G Node Bs. But due to the basic design of RNCs that are optimized to support low number of very high capacity macro base stations and proprietary Iu-b interfaces, this method is fell out of favor. SIP/IMS method proposes to provide services from SIP core network when a handset is connected to a femtocell. SIP network may be favored less than RAN Gateway since operator needs to replicate the services in macronetwork as well as in SIP core. The RAN Gateway-based method proposes a Iu over IP interface from femtocell to a RAN gateway (GANC), which implements lu-CS and lu-PS interfaces to MSC and SGSN. The RAN Gateway lets mobile operators use the standard interfaces and brings low initial cost of deployment with flat-IP architecture in which RNC functions are moved to femtocell for scaling issues. The GAN specification intends to extend the services toward FMC and provides migration path toward an all-IP converged infrastructure.
