UMA/GAN Based Architecture
In early 2000, a few technology upstarts approached convergence between the fixed and mobile worlds by bridging two disparate wireless technologies " short-range, high-bandwidth, unlicensed 802.11 and long range, relatively lower-bandwidth, licensed 2G/3G wireless " using an underlying public IP network and dualmode- handsets.

This was marketed as Unlicensed Mobile Access (UMA) technology and later standardized within 3GPP as Generic Access Network (GAN) technology. UMA/GAN identifies a new device called GAN controller (GANC), or commonly known as UMA Network Controller (UNC), to integrate mobile traffic over the public IP network. As shown in Figure 4 below wireless interfaces are bridged using Dual-Mode Handsets (DMH). GAN defines a new Up interface between the GANC and mobile devices and a standard A/Gb and Iu interface toward the CN.

Figure 4: Protocol stacks for the UMA/GAN based architecture

In principle, UMA/GAN is similar to the femtocell approach except that femtocell attempts to extend the licensed 2G/3G wireless spectrum to the customer premises instead of bridging licensed and unlicensed wireless technologies.

So, the underlying UMA/GAN architecture can likewise be extended to support the femtocell approach by overloading the GANC with Iu FGW functionality. This architecture is best suited for those service providers who have an existing GAN infrastructure but want to offer innovative high-value, high bandwidth services using High Speed Packet Access (HSPA) capability requiring higher bandwidth than what current 802.11 deployments can offer.

The FAP presents the Up interface toward the FGW, which also acts as the GANC. The FGW communicates with the CN using the Iu interface. At startup, the FAP establishes a security association with the FGW to avoid compromising subscriber information over the public IP network; TR-069 or some other similar mechanism femtocell as an IP based device and these nodes communicate using IP address and port numbers.

The FAP converts voice packets to RTP packets and forwards these to the FGW, which may have to convert the RTP packets back to voice based on the CN transport network. Multiple transcoding due to different transport networks may lead to loss of voice quality, which needs to be overcome by implementing strict QoS at the Up interface.

Handovers in this approach are typically Intra-RNC/Inter-RNC in nature. If the FAP and macrocell are managed by the same RNC (GANC) it is of the Intra-RNC type, otherwise it becomes the Inter-RNC type. During hand-in, the CN together with the UE identifies the appropriate FAP (using an approved neighbor list, managed at the GANC) and sets up an Iu signaling and bearer transport tunnel toward the GANC.

The FAP sets up the Up signaling towards the GANC. The radio resource between the FAP and the UE is managed by interworking of the RRC, Generic Access " RRC (GA-RRC), and RANAP protocols. The interworking of RRC and GA-RRC protocols is managed by the FAP, whereas the interworking of GA-RRC and RANAP is managed by the GANC. RRC terminates at the UE, GA-RRC terminates at the FAP, and GANC and RANAP terminate at the MSC.

Once the Iu tunnel is set up, the CN transfers the call over to the femtocell environment using MM and CC protocols at the MSC and UE. During hand-out, the RANAP protocol at the MSC and RRC protocol at the new RNC set up the radio link in the macrocell environment before transferring the call over to the macrocell and terminating the Iu tunnel.

For femtocell-to-femtocell handover, the GANC mostly acts as an anchor to set up the Iu tunnel over the new FAP and set up the radio link at the new FAP using RRC/GA-RRC protocol interworking before transferring the call to the new FAP and terminating the radio link at the old FAP.