Equivalent HPLMN list

Description

The Equivalent HPLMN (EHPLMN) list is a data structure stored on the USIM that contains a set of PLMN codes which the UE shall treat as equivalent to its Home PLMN (HPLMN) for the purpose of PLMN selection. The HPLMN is normally derived from the IMSI (the first 5 or 6 digits, i.e., MCC and MNC). However, an operator may own or operate multiple PLMN codes — for example, due to mergers, acquisitions, or the allocation of additional MNCs — and it is desirable that the UE considers all of these as home networks rather than as visited networks. The EHPLMN list provides this capability.

When the UE performs PLMN selection, it uses the EHPLMN list if present on the USIM. The PLMN codes in the EHPLMN list replace the HPLMN code derived from the IMSI. This means that any PLMN code in the list is treated as an HPLMN for the purposes of network selection priority. The EHPLMN list may also contain the HPLMN code derived from the IMSI; if it does, that code remains an HPLMN. If the HPLMN code derived from the IMSI is not present in the EHPLMN list, then it shall be treated as a Visited PLMN (VPLMN) for PLMN selection purposes. This is a crucial rule: it means that the EHPLMN list can effectively override the IMSI-derived HPLMN, and the UE will not give the IMSI-derived HPLMN any special preference unless it is explicitly included in the list.

The EHPLMN list is stored in the USIM file EF_EHPLMN (or EF_EHPLMNPI in later releases) and is managed by the operator. The list can contain up to 12 PLMN codes (in the original definition) and is used by the UE's NAS layer during PLMN selection procedures. The UE reads the EHPLMN list at power-on and whenever the USIM is inserted or refreshed. The list is used in both automatic and manual PLMN selection modes. In automatic mode, the UE will attempt to register on a PLMN that is either the HPLMN (as defined by the EHPLMN list) or an equivalent PLMN, according to the priority order. In manual mode, the UE presents the list of available PLMNs to the user, and the user can select any of them; however, the EHPLMN list still influences the presentation order and the indication of home/visited status.

The EHPLMN list is distinct from the Equivalent PLMN (EPLMN) list, which is provided by the network (via NAS signalling) and contains PLMNs that are considered equivalent for cell selection and reselection, but not necessarily for PLMN selection priority. The EHPLMN list is stored on the USIM and is under the control of the home operator, while the EPLMN list is dynamically provided by the serving network. Both lists can coexist and are used for different purposes: EHPLMN for PLMN selection (which network to register on), and EPLMN for cell selection/reselection (which cells are considered equivalent within a registered PLMN).

The EHPLMN list was introduced in 3GPP Release 7 and has been maintained in subsequent releases without changes to its core definition. It is specified in 3GPP TS 21.905 (Vocabulary) and the USIM file structure is defined in TS 31.102. The list is particularly important for operators that have multiple HPLMN codes, such as those resulting from mergers or those that use separate MNCs for different services (e.g., M2M). It ensures that the UE treats all these codes as home networks, providing a seamless user experience and avoiding unnecessary roaming charges or restrictions.

Purpose & Motivation

The EHPLMN list was created to address the limitations of deriving the HPLMN solely from the IMSI. In early 3GPP releases, the HPLMN was determined by the MCC and MNC in the IMSI, and any other PLMN was considered a visited network. This posed problems for operators that owned multiple PLMN codes, as UEs would treat those other codes as visited networks, potentially leading to different charging, service restrictions, or selection priorities. The EHPLMN list allows the operator to provision a list of PLMN codes on the USIM that are to be treated as equivalent to the HPLMN for PLMN selection. This solves the problem of multiple HPLMN codes and provides flexibility for operators to manage their network identities.

Another motivation was the need to support national roaming and shared networks. In some cases, an operator may have a PLMN code that is not derived from the IMSI but is still considered a home network for certain subscribers. The EHPLMN list enables this by allowing the operator to specify which PLMN codes are considered home. It also allows the operator to exclude the IMSI-derived HPLMN from the home list, treating it as a visited network if desired, which can be useful in scenarios where the IMSI-derived HPLMN is no longer used or has been re-farmed.

The EHPLMN list also enhances the user experience by ensuring that the UE automatically selects the correct home network without user intervention. It is a key enabler for seamless mobility and roaming, and it has been widely deployed in commercial networks. Its introduction in Release 7 was part of a broader effort to improve PLMN selection and network sharing capabilities in 3GPP systems.