non-removable Universal Subscriber Identity Module

Description

nrUSIM stands for non-removable Universal Subscriber Identity Module. It refers to a USIM application or equivalent functionality that is embedded or integrated into the Mobile Equipment (ME), rather than being contained in a removable SIM card. This concept is specified in 3GPP TS 31.117 and TS 31.127, which define the requirements for the non-removable USIM and its interface with the ME.

The USIM is a critical component in 3GPP networks, responsible for storing subscriber credentials, performing authentication and key agreement (AKA), and managing security contexts. Traditionally, the USIM resides on a removable Universal Integrated Circuit Card (UICC), which can be inserted into different devices. The nrUSIM changes this paradigm by integrating the USIM functionality directly into the device, either as a soldered chip or as a software module within a secure element.

Architecturally, the nrUSIM is part of the ME and communicates with the network through the same protocols as a traditional USIM. It supports all USIM functions, including authentication, ciphering, integrity protection, and storage of subscriber data. The interface between the nrUSIM and the ME is defined in 3GPP specifications, ensuring interoperability and security. The non-removable nature means that the USIM cannot be physically removed or transferred to another device, which has implications for device management, subscription provisioning, and security.

One of the key drivers for nrUSIM is the emergence of new device types, such as IoT devices, wearables, and automotive modules, where a removable SIM is impractical due to size, environmental, or reliability constraints. The nrUSIM enables these devices to have a permanent, secure identity that is provisioned during manufacturing or via remote SIM provisioning (RSP). It also enhances security by preventing physical theft or swapping of the SIM, which is a common attack vector.

The nrUSIM is specified in Release 19 and is expected to be used in conjunction with eSIM (embedded SIM) and iSIM (integrated SIM) technologies. It supports remote provisioning and management, allowing operators to update subscriptions over-the-air. The specifications TS 31.117 and TS 31.127 define the physical and logical characteristics, as well as the test specifications for the nrUSIM, ensuring compliance and interoperability across devices.

Purpose & Motivation

The nrUSIM was introduced to address the limitations of traditional removable SIM cards in emerging device categories. Removable SIMs are susceptible to physical damage, theft, and tampering, and they require physical access for insertion and removal, which is not feasible for many IoT and automotive applications. Additionally, the small form factor of removable SIMs (e.g., nano-SIM, MFF2) still imposes design constraints.

The nrUSIM solves these problems by embedding the USIM functionality directly into the device, eliminating the need for a physical card slot. This enables smaller, more rugged devices and improves security by making the SIM non-removable. It also simplifies manufacturing and logistics, as devices can be provisioned remotely without the need to insert a SIM.

Furthermore, the nrUSIM supports the growing trend towards eSIM and iSIM, where the subscriber identity is managed digitally. It provides a standardized approach for non-removable USIMs, ensuring interoperability and compliance with 3GPP security requirements. This is particularly important for 5G and beyond, where massive IoT deployments require scalable and secure identity management.