Visited Wireless Local Area Network

Description

A Visited WLAN is a Wireless Local Area Network (WLAN) that is used for interworking with a Visited Public Land Mobile Network (VPLMN). It is defined in 3GPP specifications such as TS 22.234, TS 22.934, TS 23.234, and TS 29.161. The concept is part of the 3GPP-WLAN interworking architecture, which allows mobile devices to connect to cellular services through WLAN access networks. A Visited WLAN specifically interworks only with a VPLMN, meaning that when a user is roaming and connects to a WLAN, that WLAN is associated with the visited network, not the home network. This is in contrast to a Home WLAN, which interworks with the HPLMN. The Visited WLAN enables roaming users to access their home services via WLAN in the visited country, leveraging the VPLMN's infrastructure and roaming agreements.

The 3GPP-WLAN interworking architecture defines several scenarios, from simple common billing to seamless service continuity. The Visited WLAN is relevant in scenarios where the WLAN is operated by the visited network operator or a partner. When a UE connects to a Visited WLAN, it may authenticate via the VPLMN's core network, which in turn communicates with the HPLMN for authentication and authorization. This allows the user to access services like IMS, internet, and operator-specific services. The Visited WLAN can be a trusted or untrusted WLAN, depending on the security and trust relationship with the VPLMN. For trusted WLANs, the UE can connect directly to the core network via the WLAN, while for untrusted WLANs, an IPsec tunnel to the evolved packet core (EPC) or 5G core is established.

The definition of Visited WLAN has remained essentially unchanged since its introduction in Release 2, with only minor capitalization differences. The core meaning is consistent: an interworking WLAN that interworks only with a visited PLMN. This stability reflects the maturity of the concept and its continued relevance in the era of Wi-Fi offloading and fixed-mobile convergence. In 5G, the concept extends to 5G-WLAN interworking, where the WLAN can connect to the 5G core via the N3IWF (Non-3GPP InterWorking Function) or TNGF (Trusted Non-3GPP Gateway Function). The Visited WLAN would interwork with the VPLMN's 5G core, allowing roaming users to access 5G services over WLAN.

The Visited WLAN is an important enabler for mobile data offloading and coverage extension. When cellular coverage is poor or congested, users can connect via WLAN, and if roaming, the Visited WLAN ensures that the traffic is routed through the visited network, which may have better connectivity to the home network. This also allows operators to offer competitive roaming data packages via WLAN. The Visited WLAN concept is thus a key part of the 3GPP strategy for heterogeneous networks and seamless connectivity.

Overall, the Visited WLAN is a well-established concept that continues to evolve with new releases, ensuring that users can enjoy seamless connectivity across cellular and WLAN technologies, even when roaming.

Purpose & Motivation

The Visited WLAN concept exists to support roaming users who connect to WLAN networks in visited countries. When a user travels abroad, they may encounter WLAN hotspots that are operated by the visited network operator or its partners. The Visited WLAN allows these hotspots to interwork with the VPLMN, so that the user can authenticate and access services without needing separate credentials. This solves the problem of fragmented WLAN access when roaming, where users would otherwise have to manually find and pay for WLAN access. By integrating WLAN with the VPLMN, 3GPP enables seamless and secure access to mobile services over WLAN, leveraging the existing roaming agreements.

Historically, before the standardization of WLAN interworking, WLAN access was separate from cellular networks. Users had to manage separate subscriptions and authentication for WLAN. The 3GPP-WLAN interworking work in Release 2 and later releases aimed to integrate WLAN as an access technology for cellular services. The Visited WLAN was defined to handle the roaming case, ensuring that the architecture supports both home and visited scenarios. This was particularly important for operators who wanted to offer dual-mode services (cellular + WLAN) with a single subscription. The Visited WLAN concept also facilitates offloading of cellular traffic onto WLAN, which can reduce congestion in the visited network.

In the 5G era, the Visited WLAN concept remains relevant as part of the non-3GPP access framework. The 5G core supports access via untrusted and trusted WLAN, and roaming scenarios are defined. The Visited WLAN ensures that when a user roams, their WLAN traffic is anchored in the VPLMN, which may have local breakout or home routing based on policy. This allows operators to maintain control and charging for WLAN access. The purpose of the Visited WLAN is thus to provide a standardized, scalable, and secure way for roaming users to use WLAN for mobile services.