Non-Seamless WLAN Offload Access Point Name

Description

The NSWO-APN (Non-Seamless WLAN Offload Access Point Name) is a configuration element within the 3GPP architecture that facilitates the offloading of user data traffic from the cellular network to a Wireless Local Area Network (WLAN), such as Wi-Fi, in a non-seamless manner. It functions as a logical identifier for a specific Packet Data Network (PDN) connection that is designated for offloaded traffic. When a User Equipment (UE) attaches to the network and requests a PDN connection using the NSWO-APN, the network's policy control functions, specifically the Policy and Charging Rules Function (PCRF) or Policy Control Function (PCF), recognize this APN and apply policies that divert the associated traffic flows. This diversion typically occurs at the Packet Gateway (PGW) in 4G or the User Plane Function (UPF) in 5G, where traffic matching the NSWO policy is routed directly to a local WLAN access network interface instead of being forwarded through the core network's SGi or N6 interface to the external data network.

Architecturally, the NSWO-APN is a key component in the ANDSF (Access Network Discovery and Selection Function) and later the ATSSS (Access Traffic Steering, Switching and Splitting) framework, though it specifically represents the simpler, non-integrated offload method. The process is governed by operator-defined policies provisioned in the PCRF/PCF, which are communicated to the gateway (PGW/UPF) via the Gx or N7 reference points. These policies specify the traffic filters (e.g., based on destination IP, port, or application) that should be offloaded when the UE is connected via a WLAN access point that is trusted by the operator. The UE itself must be configured with this APN, often via device management or an initial provisioning protocol.

The role of the NSWO-APN is purely for traffic routing and does not involve any mobility management between 3GPP and WLAN. This means that if the UE moves out of WLAN coverage, the offloaded IP sessions are dropped and must be re-established over the cellular interface. There is no IP address preservation or handover procedure. Its implementation is crucial for network operators seeking to leverage dense Wi-Fi deployments to alleviate congestion on licensed spectrum, especially in high-traffic areas like stadiums or urban centers, while offering a straightforward, policy-driven mechanism to manage which services (e.g., best-effort internet browsing, software updates) are suitable for offload.

Purpose & Motivation

NSWO-APN was introduced to address the growing demand for mobile data and the congestion on cellular radio access networks. Operators needed a standardized method to offload specific types of data traffic onto complementary WLAN networks, which often have greater available bandwidth and lower cost per bit. The primary motivation was network efficiency: by diverting traffic that does not require stringent mobility or quality-of-service guarantees (like background updates or general web browsing) to Wi-Fi, the licensed cellular spectrum could be preserved for real-time, delay-sensitive, or high-priority services.

Historically, before standardized non-seamless offload, operators relied on proprietary solutions or simple UE-based Wi-Fi selection, which lacked centralized policy control and often led to suboptimal user experiences (e.g., offloading critical traffic to poor-quality Wi-Fi). The introduction of NSWO-APN in 3GPP Release 11 provided a standardized, policy-controlled framework integrated into the core network. This allowed operators to define exactly which traffic flows could be offloaded based on deep packet inspection, user subscription, and network conditions, ensuring offload decisions aligned with business and technical objectives. It solved the problem of unmanaged offload by giving the network, not just the device, control over the routing decision.

Key Features

• Policy-controlled traffic diversion based on operator-defined rules
• Uses a dedicated APN to identify offload-specific PDN connections
• Offloads traffic at the PGW (4G) or UPF (5G) to a local WLAN interface
• No session continuity or mobility support during access change
• Integrates with PCRF/PCF for dynamic policy enforcement via Gx/N7 interface
• Typically used for best-effort traffic to relieve cellular congestion

Evolution Across Releases

Defining Specifications