Standalone Non-Public Network Identity

Description

SNPN Identity is a fundamental identifier in 5G networks for Standalone Non-Public Networks (SNPNs). An SNPN is a private network deployed by an organization (e.g., a factory, campus, or enterprise) that operates independently of a public land mobile network (PLMN). The SNPN Identity is defined as an identifier comprising a PLMN ID and a Network Identifier (NID) combination. This combination ensures global uniqueness and allows UEs to identify and select the correct SNPN. The PLMN ID part may be a dedicated PLMN ID assigned to the SNPN or a PLMN ID shared with a public network, while the NID is a unique identifier for the SNPN within that PLMN ID space. The SNPN Identity is broadcast by the SNPN's base stations (gNBs) in the System Information Block (SIB), specifically SIB1, and is used by UEs during cell selection and reselection.

The architecture for SNPNs is defined in 3GPP Release 16 and later, as part of the 5G System (5GS). An SNPN can be deployed in various configurations, including isolated operation, shared RAN, or shared core network. The SNPN Identity is crucial for the UE to determine whether it is allowed to access the SNPN. The UE may be configured with a list of SNPN Identities that it is authorized to access, either via the USIM or via other means. When the UE detects a cell broadcasting an SNPN Identity that matches its configured list, it can attempt to register with the SNPN. The SNPN Identity is also used in the registration and authentication procedures, where the UE provides the SNPN Identity to the network, and the network verifies the UE's subscription.

How it works: The SNPN Identity is composed of two parts: the PLMN ID and the NID. The PLMN ID is a 3-digit Mobile Country Code (MCC) and a 2- or 3-digit Mobile Network Code (MNC). The NID is a 10-digit hexadecimal number (44 bits) that uniquely identifies the SNPN within the PLMN ID. The combination of PLMN ID and NID forms a globally unique identifier. The SNPN Identity is broadcast in SIB1, which is transmitted periodically by the gNB. The UE reads SIB1 to discover available SNPNs. The UE may also use the SNPN Identity during handover to ensure that it remains connected to the correct SNPN. The SNPN Identity is used in the 5G-GUTI (Globally Unique Temporary Identifier) and other temporary identifiers to ensure proper routing and paging.

Key components include the SNPN Identity itself, the UE's configured SNPN list, and the network's SNPN configuration. The SNPN Identity is also used in the N2 and N3 interfaces for routing and policy enforcement. In the core network, the SNPN Identity is used by the Access and Mobility Management Function (AMF) to select the appropriate Session Management Function (SMF) and User Plane Function (UPF) for the SNPN. The SNPN Identity is also used in the Unified Data Management (UDM) to store subscription data. The SNPN Identity is a critical enabler for private 5G networks, allowing them to operate independently while still leveraging 3GPP technology.

In summary, the SNPN Identity is a unique identifier for an SNPN, comprising a PLMN ID and an NID. It is used for network selection, access control, and mobility management. Its definition has remained stable since Release 16, with only minor formatting changes in the specification text.

Purpose & Motivation

The SNPN Identity exists to provide a globally unique identifier for Standalone Non-Public Networks (SNPNs), which are private 5G networks deployed by enterprises, industries, and other organizations. Before the introduction of SNPNs in Release 16, private networks were often implemented using other technologies or by leveraging public network resources, which could be limiting in terms of customization, security, and control. The SNPN Identity solves the problem of identifying and selecting these private networks in a standardized way, ensuring that UEs can discover and connect to the correct SNPN. It also enables the network to enforce access control and apply specific policies for SNPN subscribers.

The motivation for defining SNPN Identity was to support the growing demand for private 5G networks in vertical industries such as manufacturing, logistics, and healthcare. These industries require dedicated networks with specific performance, security, and isolation requirements. The SNPN Identity allows such networks to be uniquely identified and accessed by authorized devices. It also facilitates roaming between SNPNs and public networks, as well as sharing of RAN and core network resources. The combination of PLMN ID and NID provides flexibility: the PLMN ID can be a dedicated one for the SNPN or a shared one, while the NID ensures uniqueness within that PLMN ID. This design allows for a large number of SNPNs to coexist.

Furthermore, the SNPN Identity is essential for the 5G system to manage SNPNs in a scalable manner. It is used in various procedures, including registration, handover, and session management. The term's definition has remained unchanged since Release 16, indicating its stability and the maturity of the SNPN concept. As 5G continues to evolve, the SNPN Identity will remain a key identifier for private network deployments.