Home Location Register Function Interface

Description

The Interface HlrFunction is a managed object class defined within the GenericNetworkResourcesNRMDefs::ManagedFunction hierarchy of the 3GPP Generic Network Resource Model (NRM). It represents the Home Location Register (HLR), a core network element that serves as the central database for subscriber information in GSM, UMTS, and LTE networks. The HLR stores subscription data such as the International Mobile Subscriber Identity (IMSI), authentication keys, subscribed services, and the current location of the mobile station. In the management plane, the HlrFunction object provides a standardized way to configure, monitor, and control HLR resources.

The managed function is specified in 3GPP TS 28.703, which defines the core network NRM, and referenced in TS 32.636, which covers the core network management IRP. In the NRM, the HlrFunction inherits from the ManagedFunction class and is typically contained within a ManagedElement that represents the physical HLR node or a logical partition of it. The object exposes attributes for the HLR's identity, operational state, administrative state, and configuration parameters. It also supports operations for querying and modifying subscriber data, although the actual subscriber data is often managed through separate provisioning systems rather than directly via the NRM.

Architecturally, the HLR is a key component of the circuit-switched (CS) and packet-switched (PS) domains. In the CS domain, it interacts with the Mobile Switching Center (MSC) and Visitor Location Register (VLR) to provide mobility management and call routing. In the PS domain, it interacts with the Serving GPRS Support Node (SGSN) and, in LTE, with the Home Subscriber Server (HSS), which is essentially an evolution of the HLR that includes additional functionality for IP-based services. The HlrFunction managed object models the HLR from a management perspective, allowing the OSS to manage the HLR's resources and to receive alarms and notifications about its status.

The HLR is a critical network element because it contains the authoritative subscriber data. If the HLR fails, subscribers cannot register, make calls, or use data services. Therefore, the management of the HLR is of utmost importance. The HlrFunction object supports fault management by allowing the OSS to monitor the HLR's health and to receive alarms when problems occur. It also supports configuration management, enabling operators to set parameters such as the HLR's capacity, redundancy configuration, and signalling point codes. Performance management is also supported, with the object providing counters and measurements for HLR transactions.

Since its introduction in Release 10, the HlrFunction has been a stable part of the 3GPP management specifications. Its definition has not changed in the quoted text across releases, reflecting the maturity of the HLR concept and its management. Although newer technologies like the HSS and the Unified Data Management (UDM) in 5G have largely superseded the HLR in terms of functionality, the HLR remains in use in many networks, and the HlrFunction managed object continues to be relevant for managing legacy and multi-generation networks.

Purpose & Motivation

The HlrFunction managed object exists to provide a standardized, interoperable way to manage Home Location Register resources in 3GPP networks. The HLR is one of the oldest and most critical elements in mobile networks, and its management has traditionally been vendor-specific. Before the introduction of standardized NRMs, operators had to use proprietary interfaces to configure and monitor HLRs from different vendors, which increased complexity and cost. The HlrFunction object solves this by defining a common set of attributes, operations, and notifications that all vendors must support, enabling multi-vendor management.

The HLR itself exists to solve the fundamental problem of subscriber mobility. When a subscriber moves between different areas of the network, the network needs to know where the subscriber is located in order to route incoming calls and data. The HLR stores this location information, along with the subscriber's service profile, and updates it as the subscriber moves. This allows the network to deliver services seamlessly, regardless of the subscriber's location. The HLR also plays a key role in authentication and security, storing the keys and algorithms used to verify the subscriber's identity.

As networks evolved from GSM to UMTS to LTE, the HLR evolved into the HSS, which combines the HLR and the Authentication Center (AuC) and adds support for IP-based services. However, the HLR remains in use in many networks, especially those that have not fully migrated to LTE or 5G. The HlrFunction managed object ensures that these legacy HLRs can still be managed in a standardized way, and it also provides a foundation for managing HSS and UDM resources in newer networks. The standardization of HLR management was motivated by the need to reduce operational costs, improve network reliability, and enable automated management processes.