Group ID for Network Selection

Description

The Group ID for Network Selection (GIN) is a network identifier defined in 5G system specifications starting from 3GPP Release 17. It is structurally part of the Public Land Mobile Network (PLMN) ID or used in conjunction with it. A PLMN ID is typically composed of a Mobile Country Code (MCC) and a Mobile Network Code (MNC). The GIN provides an additional level of grouping, allowing multiple distinct PLMNs (each with their own MNC) to be logically associated under a single group identifier. This group could represent a consortium of operators, a corporate network spanning multiple countries, or a service provider with agreements with several access networks. The GIN is signaled in system information blocks (SIBs) over the radio interface and is used by the User Equipment (UE) during the cell selection and reselection procedures.

Architecturally, the GIN is broadcast by the Radio Access Network (RAN) in SIB1 and other relevant system information, as specified in TS 38.331 (Radio Resource Control protocol). The NG-RAN node (gNB) is configured with this parameter by the Operation and Maintenance (OAM) system or the Core Network. When a UE is searching for a suitable cell, it reads the PLMN ID and, if present, the GIN from the broadcast channels. The UE's policy, which may be pre-configured in the Universal Subscriber Identity Module (USIM) or provided by the network via ANDSP (Access Network Discovery and Selection Policy), can instruct it to prioritize cells broadcasting a specific GIN. For example, a UE belonging to a global enterprise may be configured to select any network broadcasting the enterprise's GIN, regardless of the specific MNC, ensuring connectivity on preferred partner networks while roaming.

How it works involves both the network and the UE. The network operator configures the gNBs belonging to a consortium to broadcast the agreed-upon GIN value. The UE, during its initial PLMN selection or higher-priority search, evaluates not just the PLMN ID but also the GIN. If the UE's policy contains a GIN entry with higher priority than the registered PLMN's HPLMN (Home PLMN) or other PLMNs, it may attempt to camp on a cell broadcasting that GIN. This mechanism is detailed in TS 23.501 (System Architecture) and TS 38.304 (User Equipment procedures in idle and inactive modes). The GIN thus adds a new dimension to network selection, moving beyond a strict one-to-one PLMN identity to a more flexible group-based model. This is particularly powerful for non-public networks (NPNs) and seamless roaming agreements, where service continuity and policy-driven access are paramount.

Purpose & Motivation

GIN was created to address the limitations of traditional PLMN-based network selection in increasingly complex 5G deployment scenarios. Prior to GIN, a UE selected a network based solely on its PLMN ID (MCC+MNC). This was insufficient for modern use cases like: 1) A global enterprise that has service agreements with multiple local operators in different countries – without GIN, each operator would be a separate PLMN, requiring complex policy lists in the UE. 2) Roaming consortia where members want to offer a unified "network brand" to users. 3) Network slicing scenarios where a slice provider might be a different entity than the infrastructure PLMN owner. The GIN provides a logical grouping mechanism to solve these problems.

Historically, network selection was driven by the Home PLMN and a list of Equivalent Home PLMNs (EHPLMN). This was a rigid, flat list. The introduction of GIN in Rel-17, part of the broader enhancements for 5G system efficiency and support for non-public networks, allows for a hierarchical or tag-based selection policy. It enables more dynamic and user-centric network attachment. For operators, it simplifies the management of roaming agreements and allows for new business models where service provision can be decoupled from a specific MNC. The motivation was to enhance mobility, especially for vertical and enterprise users, by providing a standardized way to identify a "group of networks" that should be treated with a common policy, thereby improving the user experience during automatic network selection.