Local IP Access PDN Connection

Description

Local IP Access (LIPA) is a feature introduced in 3GPP Release 10 that allows a User Equipment (UE) to access a local IP network, such as a home or corporate network, via a femtocell or small cell (HeNB/eNB). A LIPA PDN connection is a specific type of PDN connection where the default EPS bearer context (in LTE) or default PDP context (in GPRS/UMTS) is activated with an APN that is authorized for LIPA usage. The network authorizes an APN for LIPA based on the subscription profile stored in the Home Subscriber Server (HSS), as specified in 3GPP TS 29.272. Once authorized, the network treats this PDN connection as a LIPA PDN connection.

The architecture for LIPA involves the Local Gateway (L-GW) function, which is typically collocated with the HeNB. The L-GW provides a direct user plane path for local traffic, allowing data to be routed between the UE and the local network without traversing the mobile core network (i.e., the Serving Gateway and PDN Gateway). This reduces latency, offloads core network traffic, and enables access to local resources such as printers, file servers, or home media devices. The control plane for LIPA PDN connections still involves the Mobility Management Entity (MME) for session management, but the user plane is anchored at the L-GW.

When a UE requests a PDN connection with a LIPA-authorized APN, the MME checks the subscription profile and, if authorized, selects the L-GW for the connection. The MME then establishes the default bearer between the UE and the L-GW. The L-GW assigns an IP address to the UE from the local network's address space. Subsequent traffic on this PDN connection is routed directly between the UE and the local network via the HeNB/L-GW, without going through the core network. This is particularly useful for applications like media streaming within a home, where the content server is on the local network.

LIPA PDN connections are managed according to the procedures defined in 3GPP TS 23.060 (GPRS) and TS 23.401 (EPS), with additional details in TS 24.301 for NAS protocols. The UE indicates its desire for a LIPA PDN connection by including a specific APN in the PDN Connectivity Request. The network may also initiate LIPA PDN connections based on subscription. The LIPA PDN connection can be maintained even when the UE moves between cells served by the same HeNB, but it may be released if the UE moves to a cell without LIPA support.

In summary, a LIPA PDN connection is a PDN connection that provides local IP access through a femtocell, enabling efficient local traffic offload and access to local resources. It is a key enabler for residential and enterprise small cell deployments, offering benefits in terms of latency, backhaul savings, and new service opportunities.

Purpose & Motivation

The LIPA PDN connection concept was introduced in 3GPP Release 10 to address the growing demand for local IP access in home and enterprise environments. Traditional cellular networks route all user traffic through the mobile core network, which can be inefficient for local communication, such as accessing a home media server or a corporate file share. This approach consumes backhaul capacity, adds latency, and may incur unnecessary costs. LIPA was designed to allow UEs to access local IP networks directly via a femtocell, bypassing the core network for local traffic.

The motivation for LIPA stemmed from the proliferation of small cells and the need to offload traffic from the core network. By enabling local breakout, operators can reduce congestion in the core and backhaul, while users benefit from faster access to local resources. LIPA also enables new services, such as home automation and local content sharing, without requiring traffic to traverse the operator's network.

Prior to LIPA, there was no standardized way to access local networks through a cellular connection. While some proprietary solutions existed, they lacked interoperability and seamless integration with 3GPP networks. The standardization of LIPA in Release 10 provided a unified framework, ensuring that UEs and network equipment from different vendors could support local IP access. The LIPA PDN connection is a key element of this framework, defining how a PDN connection is authorized and established for local access. Since its introduction, LIPA has evolved with subsequent releases, but the core concept of a LIPA PDN connection has remained stable, as evidenced by its unchanged definition from Rel-10 through Rel-19.