Wireless Local Area Network Direct IP Access

Description

WLAN Direct IP Access is a 3GPP-defined capability that allows a user equipment (UE) connected via a WLAN Access Network (AN) to access an external IP network directly, without routing the data through the Public Land Mobile Network (PLMN) core via a tunnel. This is in contrast to WLAN 3GPP IP Access, where traffic is tunneled to the PLMN for operator-controlled services. The concept was introduced in Release 6 and is specified in 3GPP TS 23.234, 33.234, and 33.822. It is a key enabler for local breakout, allowing operators to offload internet-bound traffic at the WLAN edge, reducing core network load and improving latency.

Architecturally, WLAN Direct IP Access is realized through the WLAN Access Network, which includes WLAN access points and potentially a WLAN Access Gateway (WAG). When a UE attaches to the WLAN, it can request direct IP access. The WLAN AN then assigns an IP address to the UE, either from a local pool or via a DHCP server, and routes traffic directly to the internet or another external IP network. Authentication and authorization are still performed via the 3GPP AAA server, ensuring that only authorized users gain access. However, the user plane traffic does not traverse the 3GPP core network; it bypasses the PDG (Packet Data Gateway) and goes directly to the destination. This requires the WLAN AN to have its own IP routing and NAT capabilities.

The operation involves several steps. First, the UE discovers and associates with a WLAN AN that supports direct IP access. Second, the UE performs authentication using EAP-SIM/AKA or other methods, with the 3GPP AAA server validating credentials. Third, the WLAN AN allocates an IP address to the UE, often via DHCP. Fourth, the UE can then send IP packets directly to external networks. The WLAN AN may enforce policies, such as firewall rules or bandwidth limits, based on subscription data received from the AAA server. Charging for direct IP access may be based on volume or time, and can be reported to the 3GPP charging system.

WLAN Direct IP Access is particularly useful for offloading best-effort internet traffic, such as web browsing and video streaming, from the cellular core. It reduces capital and operational expenditure by leveraging the WLAN infrastructure and the public internet for transport. It also improves user experience by providing lower latency and higher throughput, as traffic does not need to traverse the mobile core. However, it may not be suitable for services requiring operator-controlled QoS or deep packet inspection. Therefore, it is often used in conjunction with WLAN 3GPP IP Access, where the UE can simultaneously have direct access for some traffic and tunneled access for operator services.

In summary, WLAN Direct IP Access provides a standardized mechanism for local breakout at WLAN access networks, enabling efficient traffic offloading and direct internet access. It is a fundamental component of 3GPP-WLAN interworking, offering flexibility and scalability for mobile operators.

Purpose & Motivation

WLAN Direct IP Access was created to allow mobile operators to offload internet-bound traffic from their cellular core networks to WLAN access networks, reducing congestion and cost. Before its introduction, all traffic from WLAN-connected users had to be tunneled back to the PLMN, which was inefficient for simple internet access. This approach solves the problem of core network bottlenecks and high transport costs by enabling local breakout at the WLAN edge. It also provides a better user experience for internet services by reducing latency and increasing throughput. The concept was motivated by the growing demand for mobile data and the need to leverage unlicensed spectrum and fixed broadband infrastructure. It complements WLAN 3GPP IP Access, giving operators a flexible tool to manage traffic based on service requirements.