Visited Unified Data Repository

Description

The Visited Unified Data Repository (V-UDR) is a data storage function within the 5G core network's shared data layer architecture, specifically deployed in a Visited Public Land Mobile Network. It acts as a local cache or instance of the UDR for data pertaining to roaming subscribers. The primary role of the V-UDR is to store a subset of user data—such as policy data, subscription data, and application data—that is required for the VPLMN's network functions (NFs) to serve a roaming user efficiently. This data is typically provisioned or synchronized from the Home UDR (H-UDR) in the user's home network.

Architecturally, the V-UDR implements the same service-based interfaces as the standard UDR, namely Nudr (e.g., Nudr_DM, Nudr_DR). Network Functions in the VPLMN, such as the Visited Policy Control Function (V-PCF) or Visited Network Repository Function (V-NRF), can query the V-UDR directly via these interfaces to retrieve necessary data for policy decisions or service authorization. This local data access avoids the need for inter-PLMN signaling for every data request, which would introduce significant latency and load on the inter-operator interfaces. The data synchronization between H-UDR and V-UDR is a critical aspect, often governed by steering of roaming agreements and protocols to ensure data consistency and privacy.

In operation, when a UE roams into a VPLMN, relevant data is fetched from the H-UDR and stored in the V-UDR. Subsequent queries from VPLMN NFs are served locally. The V-UDR supports the 5G core's principle of data decoupling and independence. It enables advanced roaming features by allowing the visited network to apply policies based on the subscriber's profile without requiring real-time interaction with the home network for every transaction. This is particularly important for policy control, charging, and enabling network slicing for roaming users, where slice selection and policy enforcement may need to occur within the visited network.

Purpose & Motivation

The V-UDR was introduced to solve the performance and scalability challenges of centralized data storage in roaming scenarios. In earlier architectures, every policy or subscription data request from a visited network function required a query to the home network's UDR. This created significant signaling latency, increased dependency on the reliability of the inter-PLMN link (N32 interface), and limited the ability of the visited network to respond quickly to dynamic service requests.

Its creation was driven by the need for more autonomous operation in the visited network, which is essential for low-latency 5G services and efficient network resource utilization. By keeping a local copy of essential data, the V-UDR enables faster decision-making for session establishment, policy enforcement, and service authorization. This aligns with the 5G architectural goals of decentralization and network exposure, allowing the VPLMN to offer tailored services to roaming users while still adhering to the home operator's policies.

Key Features

• Stores local copies of roaming user subscription and policy data within the VPLMN
• Provides data access to Visited Network Functions (e.g., V-PCF, V-NRF) via Nudr service-based interfaces
• Reduces signaling latency and load on inter-PLMN links by serving data requests locally
• Supports data synchronization mechanisms with the Home UDR (H-UDR)
• Enables local policy enforcement and decision-making for roaming users
• Facilitates the implementation of network slicing and advanced services in roaming scenarios

Evolution Across Releases

Defining Specifications