WLAN Termination

Description

The WLAN Termination (WT) is a functional entity introduced in 3GPP Release 13 as part of the LTE-WLAN Radio Level Integration (LWIP) and LTE-WLAN Aggregation (LWA) features. It acts as a gateway or termination point for the WLAN side in these tight integration architectures. As defined in TS 36.300, the WT terminates the user plane and control plane protocols towards the WLAN Access Point (AP) and communicates with the LTE eNodeB (eNB) over a standardized interface (specifically, the Xw interface for control plane and user plane in LWA).

Architecturally, the WT sits between the eNB and one or more WLAN APs. In LWA, the WT terminates the PDCP protocol for the data radio bearers that are offloaded to WLAN. It receives PDCP Protocol Data Units (PDUs) from the eNB over the Xw user plane and forwards them to the WLAN AP for transmission to the UE, and vice versa. In LWIP, the WT acts more as an IPsec gateway, establishing secure tunnels with the UE for IP traffic offload. The WT is managed by the eNB, which makes centralized decisions on traffic steering, splitting, and switching between LTE and WLAN based on radio conditions.

Key components of the WT functionality include the termination of the Xw application protocol (Xw-AP) for control signaling with the eNB, management of data forwarding over the Xw user plane (using GTP-U or IPSec), and its interface with the WLAN AP (which is implementation-specific but logically controlled by the WT). Its role is critical for enabling the eNB to treat WLAN as a secondary cell group or a managed flow-offload path, allowing for true radio-level integration with coordinated scheduling, mobility, and QoS management across the two radio technologies. This provides a significantly better user experience compared to loose network-level interworking.

Purpose & Motivation

The WT was created to address the limitations of earlier 3GPP-WLAN interworking solutions (like I-WLAN and ANDSF-based steering), which operated at the core network or policy level and could not perform fast, radio-aware traffic management. These earlier approaches suffered from suboptimal user experience due to lack of coordination between LTE and WLAN radios, leading to issues like sticky clients and inefficient load balancing. The motivation for the WT arose from the need for tighter, radio-layer integration to fully exploit the combined capacity and coverage of LTE and Wi-Fi.

This technology solves the problem of uncoordinated dual connectivity. By introducing the WT as a subordinate node to the eNB, 3GPP enabled the LTE network to directly control and manage WLAN resources at the radio bearer level. This allows for seamless aggregation of data flows (LWA) or secure, network-controlled IP flow mobility (LWIP), improving throughput, reliability, and mobility performance. It represented a paradigm shift from network-level interworking to true access network convergence, driven by operator demands for more efficient use of all available radio assets.