Operator Controlled PLMN (Selector List)

Description

The Operator Controlled PLMN Selector List (OPLMN) is a crucial file (EF_OPLMNwACT) stored on a User Equipment's (UE) Universal Subscriber Identity Module (USIM) or SIM card. It contains a prioritized list of Public Land Mobile Network (PLMN) codes that the UE should use during the network selection and registration process, particularly when it is outside the coverage of its Home PLMN (HPLMN). The OPLMN is distinct from the user-controlled PLMN selector list; it is provisioned and updated by the mobile operator, not the end-user, giving the operator control over the roaming experience.

From a technical perspective, the OPLMN list is stored as a sequence of records, each containing a PLMN code (MCC+MNC) and an associated 'Access Technology' identifier. The access technology field (e.g., E-UTRAN, UTRAN, GERAN, NR) specifies the preferred radio access technology for that PLMN. When a UE is powered on or loses coverage, it executes the network selection procedure defined in TS 23.122. It first attempts to find and register on its HPLMN. If that fails (i.e., when roaming), the UE will consult the OPLMN list. It scans for available networks and attempts to register on the highest-priority PLMN from the OPLMN list that is found and allows access. The UE uses the associated access technology identifier to prioritize its search; for example, it will look for a 5G NR cell from a preferred partner before looking for a 4G LTE cell from the same partner.

The OPLMN works in conjunction with other lists on the USIM, namely the HPLMN, the User Controlled PLMN Selector List (UPLMN), and the Forbidden PLMN list (FPLMN). The standard selection priority is: HPLMN, then the OPLMN list (in priority order), then the UPLMN list, and then other available networks in order of signal strength. The FPLMN list contains networks the UE is temporarily forbidden to register on due to a previous rejection. Operators dynamically update the OPLMN list via Over-The-Air (OTA) provisioning, allowing them to change roaming partnerships, add new preferred networks in a visited country, or deprioritize networks with poor service quality or high costs, all without requiring user intervention.

Purpose & Motivation

The OPLMN was created to solve the fundamental problem of uncontrolled network selection during roaming, which existed in early cellular systems. Without an operator-provided list, a roaming UE would typically select a network based solely on radio signal strength from available networks in a visited country. This could lead to several issues: the UE might connect to a network with no roaming agreement, resulting in failed registration and service denial. Even if an agreement existed, connecting to the first available network might not be the optimal choice from the operator's perspective, as it could be a more expensive partner, offer poorer service quality, or lack support for certain services like data or IMS.

The primary purpose of the OPLMN is to give the home network operator commercial and technical control over the roaming experience of its subscribers. It ensures reliable and automatic service availability by steering subscribers to networks with validated roaming agreements. It allows operators to implement cost-control strategies by prioritizing partners with lower wholesale rates. Furthermore, it enables service quality management by directing subscribers to networks that support required technologies (e.g., 4G/5G for data services) or have proven service level agreements (SLAs). By pre-configuring this list, the operator guarantees a seamless 'home-like' experience for the user when traveling, as the device automatically connects to the best available partner network without requiring manual network selection by the user.

Key Features

• Operator-provisioned prioritized list of PLMN codes stored on USIM/SIM
• Includes associated preferred Access Technology (e.g., NR, E-UTRAN) for each PLMN
• Used by UE during automatic network selection, especially in roaming scenarios
• Takes precedence over user-controlled lists and signal-strength-based selection
• Can be updated dynamically by the operator via OTA SIM management
• Works alongside HPLMN, UPLMN, and FPLMN lists in a defined selection hierarchy

Evolution Across Releases

Defining Specifications