Equivalent Home Public Land Mobile Network

Description

The Equivalent Home Public Land Mobile Network (EHPLMN) is a concept in 3GPP that defines a set of one or more Public Land Mobile Network Identifiers (PLMN IDs) that are considered equivalent to a subscriber's Home PLMN (HPLMN). The HPLMN is the network operated by the subscriber's service provider, identified by the Mobile Country Code (MCC) and Mobile Network Code (MNC) in their SIM/USIM. The EHPLMN list is stored on the SIM/USIM and is used by the User Equipment (UE) during the network selection and registration procedures. When the UE searches for available networks, it prioritizes networks whose PLMN ID matches either its HPLMN or any PLMN in the EHPLMN list. If such a network is found, the UE attempts to register with it as if it were the home network, often benefiting from home-like service treatment and potentially avoiding roaming charges depending on operator agreements.

Architecturally, the EHPLMN list is provisioned by the home network operator onto the SIM card. It is used by the UE's Mobility Management (MM) and Connection Management (CM) layers. During initial cell selection or after losing coverage, the UE scans radio frequencies and decodes the PLMN IDs broadcast by cells. The selection algorithm, defined in specifications like TS 23.122, mandates that the UE shall attempt to register on an EHPLMN with higher priority than a Visited PLMN (VPLMN). The core network, specifically the Home Subscriber Server (HSS) or Unified Data Management (UDM), may also use the concept to apply specific subscription policies when a user is on an EHPLMN.

EHPLMN works in conjunction with other PLMN lists like the Forbidden PLMN list (FPLMN) and the User Controlled PLMN Selector. Its role is critical for enabling national roaming, network sharing agreements, and multi-operator core networks (MOCN). For example, in a network sharing scenario where two operators share radio access infrastructure but have separate core networks, each operator can configure the other's PLMN as an EHPLMN for their subscribers. This allows subscribers to automatically connect to the shared network without manual selection and receive services as if they were on their home network, ensuring seamless mobility and service continuity.

Purpose & Motivation

EHPLMN was introduced to solve the problem of seamless network access in scenarios involving multiple cooperating operators, such as national roaming agreements, network sharing (e.g., MORAN, MOCN), and mergers/acquisitions. Prior to its definition, a UE would treat any PLMN different from its HPLMN as a visited network, leading to potential roaming indicators, different service treatment, and the need for manual network selection by the user. This degraded user experience and complicated operational models where operators wanted to present a unified network footprint.

The concept, introduced in 3GPP Release 7, was motivated by the growing complexity of operator partnerships and the need for more flexible subscriber management. It allows an operator to extend the 'home network' experience to partner networks transparently. This addresses limitations of the basic HPLMN/VPLMN dichotomy by providing a standardized way to define a set of 'equivalent home' networks. This enables operational efficiencies, improved customer experience by hiding network boundaries, and supports regulatory requirements for coverage obligations through partnerships.