Generic Access Network Controller

Description

The Generic Access Network Controller (GANC) is a standardized network node defined by 3GPP for Generic Access Network (GAN) architecture, also known as Unlicensed Mobile Access (UMA). Its primary function is to serve as a convergence point, securely connecting mobile User Equipment (UE) over IP-based access networks (like broadband Wi-Fi) to the traditional 3GPP core network. The GANC appears to the core network as a standard Radio Network Controller (RNC) for circuit-switched services or a Serving GPRS Support Node (SGSN) for packet-switched services, abstracting the underlying unlicensed radio technology. It terminates the secure Up interface from the UE, which carries tunnelled GSM/GPRS signalling and user plane traffic over IPsec. The GANC performs critical functions including authentication, encryption, registration, and mobility management for UEs in GAN mode. It manages the handover of ongoing voice calls and data sessions between the licensed cellular network (e.g., GERAN/UTRAN) and the unlicensed Wi-Fi network, ensuring service continuity. Architecturally, the GANC consists of a Security Gateway (SEGW) for establishing secure tunnels and a GANC core that handles protocol conversion and session management. This allows operators to extend their cellular voice and data services into indoor and residential environments using cost-effective, widely available broadband connections, effectively treating Wi-Fi as another radio access technology under network control.

Purpose & Motivation

The GANC was created to address the challenge of providing seamless cellular service coverage indoors and in areas with poor macro network signal strength, leveraging the ubiquity of Wi-Fi and broadband internet. Prior to GAN, dual-mode Wi-Fi/cellular phones required separate, non-integrated clients for making calls over Wi-Fi (like VoIP applications), which did not offer seamless handoff, consistent user experience, or integration with core cellular services like SMS and voicemail. The technology was a key enabler for early Fixed-Mobile Convergence (FMC), allowing mobile network operators to compete with fixed-line voice services and reduce churn by improving in-home coverage. It solved the problem of 'coverage holes' without the high cost of deploying additional cellular macro sites or femtocells, by utilizing the customer's own broadband connection as a trusted access leg back to the operator's core. The standardization in 3GPP Rel-8 provided a vendor-interoperable framework for secure, carrier-grade Wi-Fi offload and calling, laying important groundwork for later evolved solutions like IP Multimedia Subsystem (IMS)-based Voice over Wi-Fi (VoWiFi) and Access Network Discovery and Selection Function (AND SF).

Key Features

• Secure IPsec tunnel termination for UE connectivity over untrusted access networks
• Protocol conversion between 3GPP radio signalling (e.g., RANAP, BSSAP) and IP-based transport
• Seamless handover (HO) of voice calls and data sessions between cellular and Wi-Fi networks
• Integration with core network elements (MSC, SGSN) as a standard RNC or SGSN proxy
• UE authentication, registration, and mobility management for GAN service area
• Support for circuit-switched voice (GSM), packet-switched data (GPRS), and SMS services over IP

Evolution Across Releases

Defining Specifications