WLAN 3GPP IP Access

Description

WLAN 3GPP IP Access is a core network feature that enables a User Equipment (UE) to access an IP network via a Public Land Mobile Network (PLMN) through a tunnel established over a WLAN radio connection. It is part of the broader effort to integrate non-3GPP access technologies, specifically WLAN, into the 3GPP service architecture. The term is defined in 3GPP specifications such as TS 23.234, TS 33.234, and TS 33.822, which cover the architecture, security, and interworking aspects of WLAN interworking with 3GPP systems.

Architecturally, WLAN 3GPP IP Access involves several key components. The UE connects to a WLAN access network, which may be operated by the mobile operator or a third party. Through this WLAN connection, the UE establishes a secure tunnel to a Packet Data Gateway (PDG) or a similar entity in the 3GPP core network. This tunnel, often based on IPsec, carries the user's IP traffic between the UE and the core network. The core network then provides connectivity to external IP networks, such as the Internet or operator services. Authentication and authorization are handled via the 3GPP AAA server, which interacts with the HSS/HLR to validate the subscriber and retrieve subscription data.

The feature supports two main modes: WLAN 3GPP IP Access and WLAN Direct IP Access. In WLAN 3GPP IP Access, the traffic is tunneled through the PLMN, allowing the operator to apply policies, charging, and security. In WLAN Direct IP Access, the UE accesses the IP network directly via the WLAN without traversing the PLMN, which is useful for local breakout scenarios. The term WLAN 3GPP IP Access specifically refers to the tunneled mode, where the PLMN is in the data path.

How it works: When a UE attaches via WLAN, it first performs access authentication with the 3GPP AAA server using EAP-AKA or similar methods. Once authenticated, the UE establishes a tunnel to the PDG. The PDG allocates an IP address to the UE and enforces policies such as QoS and charging. The tunnel ensures that the traffic is secure and that the operator can manage the connection. This architecture allows the operator to offer services like IMS-based voice and video over WLAN, while maintaining consistent security and policy control.

WLAN 3GPP IP Access was introduced in Rel-6 as part of the initial WLAN interworking effort. It evolved over subsequent releases, with changes in terminology and architecture. For example, in Rel-7, the related term was updated from "WLAN 3GPP Direct IP Access" to "WLAN Direct IP Access," reflecting a simplification in naming. The feature was later superseded by more advanced interworking solutions such as S2a/S2b interfaces in EPC and, eventually, access traffic steering, switching, and splitting (ATSSS) in 5G. Nevertheless, WLAN 3GPP IP Access laid the groundwork for integrating WLAN with cellular networks and for providing seamless mobility and service continuity across access technologies.

Purpose & Motivation

WLAN 3GPP IP Access was created to address the growing demand for mobile data services and the need to offload traffic from cellular networks to WLAN. In the early 2000s, WLAN technology was becoming ubiquitous, and users wanted to access operator services over WLAN hotspots. However, simply connecting to a WLAN did not provide the security, policy control, and service continuity that cellular networks offered. WLAN 3GPP IP Access solved this by defining a standardized way to tunnel traffic from the UE through the WLAN to the 3GPP core network, enabling the operator to authenticate users, apply policies, and charge for services.

The feature also addressed the limitation of earlier WLAN deployments, which were often isolated and lacked integration with cellular networks. By providing a PLMN-tunneled path, it allowed operators to extend their service footprint over WLAN and to offer a consistent user experience. It also enabled new business models, such as WLAN roaming and fixed-mobile convergence, where users could seamlessly move between cellular and WLAN access.

Historically, WLAN 3GPP IP Access was a precursor to more sophisticated interworking mechanisms. It introduced key concepts such as the PDG, AAA-based authentication, and IPsec tunneling, which were later refined in EPC and 5G. While the specific term is no longer used in the latest releases, its legacy lives on in the architecture of non-3GPP access in 5G, where similar principles are applied with greater flexibility and efficiency.