Home Routed Access

Description

Home Routed Access is a roaming architecture defined in 3GPP specifications 29.215 and 29.217. In this model, the Packet Data Network Gateway (PGW) and the Policy and Charging Enforcement Function (PCEF) are located in the Home Public Land Mobile Network (HPLMN). When a subscriber roams into a Visited PLMN (VPLMN), the user plane traffic is routed back to the home network, where the PCEF enforces policy and charging rules received from the Policy and Charging Rules Function (PCRF) in the HPLMN. This is in contrast to Local Breakout (LBO), where the PCEF is in the VPLMN. The architecture ensures that the home operator retains full control over the subscriber's data session, including QoS, charging, and policy enforcement, regardless of the visited network.

The key components involved in Home Routed Access include the Serving Gateway (SGW) in the VPLMN, which acts as the mobility anchor for the user plane and forwards traffic to the PGW in the HPLMN. The PGW in the HPLMN allocates the IP address to the UE and connects to external packet data networks. The PCEF, integrated with the PGW, applies the policy and charging rules. The PCRF in the HPLMN makes policy decisions based on subscriber profiles, service data flows, and network conditions. The interface between the VPLMN and HPLMN is typically the S8 interface, which is an inter-PLMN variant of the S5/S8 interface. This interface carries both control plane (GTP-C) and user plane (GTP-U) traffic. The S9 interface between the VPLMN PCRF (if present) and HPLMN PCRF is used for roaming policy coordination, but in Home Routed Access, the VPLMN PCRF may not be involved for basic policy control.

How it works: When a UE attaches in a visited network, the MME in the VPLMN selects an SGW in the VPLMN and a PGW in the HPLMN based on the APN and subscription data. The SGW forwards user plane packets to the PGW over the S8 interface. The PGW enforces policies and charging as instructed by the HPLMN PCRF. The UE's IP address is allocated by the HPLMN PGW, making the session appear as if the UE is at home. This allows the home operator to offer consistent services and apply uniform charging. However, it introduces latency because traffic must traverse from the VPLMN to the HPLMN and back, which can be significant if the visited network is far from the home network. Also, it requires a roaming agreement that supports home routing and sufficient capacity on the inter-PLMN links.

Home Routed Access is essential for operators who want to maintain control over their subscribers' data sessions when roaming. It enables value-added services, differentiated QoS, and accurate charging. It is widely used in scenarios where the home operator has a strong business relationship with the visited operator or when regulatory requirements mandate home control. The architecture has evolved with releases, but the fundamental concept remains the same. In 5G, similar concepts exist with Home Routed roaming in Service-Based Architecture, where the SMF and UPF can be in the HPLMN. The term has been stable across releases, indicating its foundational role in roaming.

Purpose & Motivation

Home Routed Access exists to give the home network operator full control over a subscriber's data session while roaming. Before its introduction, roaming data services often used local breakout, where the visited network handled policy and charging, limiting the home operator's ability to enforce its own policies, offer differentiated services, or accurately charge for data usage. Home Routed Access solves this by anchoring the PGW and PCEF in the HPLMN, ensuring that all policy decisions and charging are performed by the home operator. This is crucial for maintaining service consistency, enabling home-based services, and complying with regulatory requirements. It also simplifies roaming agreements because the visited network only provides radio access and SGW functions, while the home network manages the IP session. The trade-off is increased latency and backhaul costs, but for many operators, the benefits of control outweigh these drawbacks.