WLAN Selection Policy

Description

WLAN Selection Policy (WLANSP) is a core component of the Access Network Discovery and Selection Function (ANDSF) management object. It is a structured XML-based policy that provides the User Equipment with deterministic criteria for when and how to connect to available WLAN networks. The policy is dynamically provisioned by the operator's ANDSF server to the UE over an S14 reference point. The UE's ANDSF client then interprets and enforces these rules, automating the network selection process which would otherwise be manual or based on simplistic signal strength.

The policy contains several key elements. It includes discovery information, which lists available WLAN access networks and their properties (SSIDs, roaming partners). More critically, it contains selection rules. These are prioritized "if-then" statements where the conditions (e.g., current cellular signal strength, WLAN signal quality, time of day, location, UE velocity) are evaluated against thresholds. If the conditions are met, the rule's action is executed, such as connecting to a specific WLAN, steering specific IP flows to WLAN, or forbidding a connection. The policies can be hierarchical, with global rules and more specific exceptions, and can be updated by the network based on changing conditions like congestion.

WLANSP works in conjunction with other ANDSF policies like Inter-System Routing Policies (ISRP) and Inter-System Mobility Policies (ISMP). While ISRP/ISMP govern traffic routing between 3GPP and WLAN for active connections, WLANSP specifically manages the initial selection and connection to the WLAN radio access point itself. Its enforcement is a continuous background process; the UE periodically re-evaluates the policy conditions to determine if a more preferred WLAN has become available or if the current connection should be released. This mechanism is crucial for implementing operator-controlled Wi-Fi offloading strategies and ensuring a high-quality, seamless user experience across heterogeneous networks.

Purpose & Motivation

WLANSP was created to solve the problem of inefficient and user-driven WLAN selection, which often led to poor network performance and underutilization of Wi-Fi resources. Before ANDSF and WLANSP, UEs typically connected to WLANs based solely on stored SSID preferences and received signal strength, with no awareness of the core network's load, the backhaul quality of the WLAN, or the user's service requirements. This resulted in users connecting to congested or poor-quality Wi-Fi networks even when a strong cellular signal was available, degrading the overall experience.

The motivation was to give mobile operators intelligent control over the UE's access selection behavior in a multi-access environment. By deploying WLANSP, operators could proactively manage traffic distribution between their cellular (3GPP) and Wi-Fi (non-3GPP) assets. For example, an operator could define a policy to offload delay-tolerant traffic to WLAN when the cellular cell is congested, or to connect to a carrier-grade Wi-Fi hotspot when the UE is stationary and indoors to provide higher throughput and conserve cellular spectrum.

WLANSP, introduced as part of the broader ANDSF framework in Release 8 and enhanced in later releases, represented a shift from network-centric to user-equipment-centric policy enforcement. It empowered the UE to make smart, real-time decisions based on a rich set of operator-provided parameters, moving beyond simple offload to enable truly optimized multi-access connectivity. This was a foundational concept for later traffic steering and network selection mechanisms in 4G and 5G.