Home-User Plane Function

Description

Home-User Plane Function (H-UPF) is a Rel-19 core network entity specified in 3GPP TS 33.513 and studied in TR 33.929. It represents a specialized deployment of the User Plane Function (UPF) that resides in the home network (HPLMN) and serves user plane traffic for roaming subscribers or for home network services. The H-UPF concept is closely related to the Home Routed (HR) roaming architecture, where the user plane is anchored in the home network to provide consistent policy and charging control, as well as to enable services that require home network presence.

In the 5G System architecture, the UPF is the core network function that handles packet routing and forwarding, QoS enforcement, and traffic measurement. The H-UPF is a UPF instance located in the HPLMN, as opposed to the Visited-UPF (V-UPF) in the VPLMN. In home-routed roaming, the H-UPF acts as the PDU Session Anchor (PSA) for the UE, while the V-UPF serves as the intermediate UPF in the visited network. This allows the home operator to apply home policies, charging, and lawful interception, and to provide services such as home network slicing.

The H-UPF is controlled by the SMF in the home network (H-SMF) via the N4 interface. It connects to the V-UPF via the N9 interface and to the Data Network (DN) via N6. The H-UPF may support multiple PDU sessions and can be deployed in a centralized or distributed manner. Security aspects, as covered in TS 33.513, include protection of the N4 interface, authentication of the H-UPF to the H-SMF, and secure communication with the V-UPF. TR 33.929 studies security threats and solutions for the H-UPF, such as unauthorized access and denial of service.

Key components of H-UPF include: (1) packet detection and forwarding rules; (2) QoS enforcement (e.g., 5QI, ARP); (3) usage reporting for charging; (4) support for lawful interception; and (5) integration with home network policy and charging functions (PCF, CHF). The H-UPF also plays a role in edge computing scenarios, where it can be deployed close to the home network edge to reduce latency.

H-UPF is important because it enables home operators to retain control over user plane traffic for roaming subscribers, which is essential for service differentiation, regulatory compliance, and revenue assurance. It also supports new business models such as home network slicing and private networks. As 5G roaming and home services evolve, the H-UPF will be a key enabler for seamless and secure user plane connectivity.

Purpose & Motivation

H-UPF was created to address the need for home network control over user plane traffic in roaming and residential scenarios. In earlier generations, home-routed roaming was limited, and visited networks often handled user plane traffic, which restricted the home operator's ability to apply policies, charging, and services. With 5G, the demand for home-routed roaming increased due to new use cases like network slicing, edge computing, and regulatory requirements for lawful interception.

The H-UPF solves this by providing a standardized UPF instance in the home network that anchors the user plane for roaming UEs. It allows the home operator to enforce home policies, perform charging, and offer value-added services regardless of where the UE is roaming. It also addresses security concerns by defining secure interfaces and procedures, as studied in TR 33.929. The H-UPF is a key component of the 5G roaming architecture, enabling operators to maintain control and deliver consistent services to their subscribers worldwide.