Generic Access - Radio Resource Control

Description

GA-RRC (Generic Access - Radio Resource Control) is a protocol within the 3GPP Generic Access Network (GAN) architecture that functions as the adaptation layer for radio resource and mobility management over the unlicensed IP access network. It operates between the Generic Access - Mobile Station (GA-MS) and the Generic Access Network Controller (GANC). While the 'radio' in its name refers to the unlicensed wireless link (e.g., Wi-Fi, Bluetooth), GA-RRC's role is to emulate and interface with the cellular Radio Resource Control (RRC) procedures of the GERAN or UTRAN, allowing the core network to manage a device on IP access as if it were on a standard cellular radio access network.

Architecturally, GA-RRC is a peer-to-peer protocol that carries RRC-like messages over the secure IP connection established by the GA-RC protocol. Its key responsibility is to convey radio resource management information between the GA-MS and the GANC. This includes broadcasting system information (like a virtual cell identity and parameters) from the GANC to the GA-MS, and relaying measurement reports from the GA-MS (e.g., Wi-Fi signal strength, cellular pilot measurements) to the GANC. The GANC uses these reports, along with core network directives, to make handover decisions. For a handover from GAN to GERAN/UTRAN, the GA-RRC protocol is used to deliver the detailed handover command (including target cell parameters) from the core network, via the GANC, to the mobile station.

GA-RRC works by encapsulating standard GERAN RRC or UTRAN RRC messages within its protocol data units (PDUs) for transport over the IP-based Up interface. It does not manage the physical Wi-Fi link directly—that is handled by the underlying IEEE 802.11 protocols—but it provides the necessary abstraction and information flow for the mobile core's RRM algorithms. Key procedures facilitated by GA-RRC include GA-RRC SYSTEM INFORMATION broadcast, GA-RRC MEASUREMENT CONTROL and REPORTING, and GA-RRC HANDOVER preparation and execution. It is a crucial component for enabling seamless mobility, as it provides the control mechanism for the network to command the mobile station to leave the IP access point and tune to a specific cellular frequency and channel during a handover, ensuring active call or data session continuity.

Purpose & Motivation

The purpose of GA-RRC was to bridge the gap between the circuit-switched mindset of traditional cellular radio resource management and the packet-switched, best-effort nature of IP-based unlicensed access. In a pure cellular network, RRC is responsible for direct control of the radio link. GAN introduced an IP transport layer, so a new protocol was needed to carry the essential RRC information over this IP tunnel. GA-RRC solved the problem of how the core network's BSC or RNC functionality (now residing in or interfaced via the GANC) could still exert control over mobility and radio resource decisions for a device connected via Wi-Fi.

Without GA-RRC, the network would be blind to the radio conditions of the IP access leg and unable to coordinate controlled handovers. Previous convergence attempts often resulted in 'break-before-make' scenarios where a Wi-Fi call would drop before a cellular call could be established. GA-RRC enabled 'make-before-break' handovers by providing the signaling channel to prepare the cellular side while the call was still active on Wi-Fi. It was motivated by the requirement for carrier-grade service continuity, which demanded that handovers be network-controlled, fast, and reliable. GA-RRC translated the core network's radio commands into a form transmissible over IP, and reported device measurements back, thus extending the reach of cellular RRM into the unlicensed domain.

Key Features

• Transports cellular RRC messages (GERAN/UTRAN) over the GAN IP interface
• Broadcasts virtual system information from the GANC to GA-MSs on the IP network
• Relays measurement reports from the mobile station (for both IP and cellular radios) to the network
• Facilitates network-controlled handover preparation and command delivery between GAN and cellular access
• Provides an abstraction layer for radio resource management over unlicensed IP transport
• Works in conjunction with GA-RC for secure transport and GA-CSR/PSR for service continuity

Evolution Across Releases

Defining Specifications