3GPP - Wireless Local Area Network Interworking

Description

3GPP - WLAN Interworking refers to the set of standards and mechanisms that enable interworking between 3GPP systems (e.g., UMTS, LTE) and Wireless Local Area Networks (WLANs). This interworking allows mobile devices to connect to WLANs for data services while maintaining connectivity to the 3GPP core network, providing benefits such as increased capacity, improved coverage, and seamless service continuity. The specifications covering this topic include 22.934, 23.234, 29.161, 33.234, and 33.822.

The interworking architecture defines several scenarios, from simple common billing to seamless service continuity. Key components include the WLAN Access Network (AN), which consists of WLAN access points and a WLAN Access Gateway (WAG), and the 3GPP core network elements such as the Packet Data Gateway (PDG) and the Authentication, Authorization, and Accounting (AAA) server. The terminal (UE) must support both 3GPP and WLAN access technologies and be capable of discovering and selecting WLANs based on operator policies.

Authentication and security are critical aspects. The 3GPP - WLAN interworking uses the Extensible Authentication Protocol (EAP) with SIM-based authentication (EAP-SIM, EAP-AKA) to leverage the existing 3GPP credentials. This allows a single subscription to be used across both access types. The security architecture also includes IPsec tunnels between the UE and the PDG to protect data traffic.

Mobility management is another key area. The interworking supports seamless handover between 3GPP and WLAN access, ensuring that ongoing sessions are not interrupted. This is achieved through mechanisms such as Mobile IP (MIP) or Proxy Mobile IP (PMIP), and more recently, through Access Network Discovery and Selection Function (ANDSF) policies that guide the UE in selecting the best access network.

Quality of Service (QoS) and policy control are also addressed. The 3GPP - WLAN interworking allows operators to apply consistent QoS policies across both access types, ensuring that real-time services like VoLTE maintain their quality when moving between networks. Charging and billing are unified, so users receive a single bill regardless of the access used.

The evolution of 3GPP - WLAN interworking has seen increasing integration, from early loose coupling to tight coupling in later releases, enabling seamless offloading and improved user experience. It is a fundamental enabler for heterogeneous networks (HetNets) and the concept of always-best-connected devices.

Purpose & Motivation

3GPP - WLAN Interworking was created to allow mobile operators to leverage WLAN (Wi-Fi) networks to complement their cellular networks. The primary motivation was to address capacity and coverage limitations of 3GPP systems, especially in indoor and hotspot environments where WLAN is abundant. By integrating WLAN, operators can offload data traffic, reduce congestion, and provide better user experience at lower cost.

Before this interworking, WLAN and cellular networks operated independently, requiring separate subscriptions and authentication. Users had to manually switch between networks, and there was no seamless service continuity. The 3GPP - WLAN interworking standards solve this by defining a common architecture that allows a single subscription, unified authentication, and seamless mobility between the two access types.

The interworking also enables operators to offer new services, such as Wi-Fi calling and seamless multimedia offload, and to manage networks more efficiently through policy control and charging integration. It has been a key enabler for the widespread adoption of Wi-Fi offloading, which is now a standard feature in smartphones and a critical component of mobile network capacity planning.