User:DontLickTheFrozenStone/USIM

USIM (acronym for Universal Subscriber Identity Module) is a module used in UMTS (3G) networks that allows a subscriber to be identified regardless of which terminal they are using (equivalent to the SIM card used in 2G networks).

Function
A USIM is an advanced version of the SIM card designed specifically for 3G and later 4G mobile networks. It functions as an application stored and executed on a Universal Integrated Circuit Card (UICC) platform. The technical specifications for USIM are primarily defined by:


 * European Telecommunications Standards Institute (ETSI) TS 102 221 (SIM application)


 * 3rd Generation Partnership Project (3GPP) TS 31.102 (USIM application)

The core function of a USIM is to authenticate subscribers (referred to as User Equipment in 3G and 4G standards) when connecting to Universal Mobile Telecommunications System (UMTS) or LTE networks. It achieves this by utilizing the International Mobile Subscriber Identity (IMSI) stored on the card. This unique identifier allows the network to recognize the subscriber and their mobile operator.
 * 3GPP TS 21.111 (USIM card)

It includes a set of enhancements to accommodate the advancements in 3G and 4G networks specified by the 3GPP. It also provides additional features for the user's benefit, such as an improved directory.

As this application is newer than the SIM (2G), it is often delivered on a newer UICC and is associated with the following benefits:


 * Larger memory capacity (able to store over 250 contacts, including mobile, landline, or email addresses).


 * Better customer identity management.


 * New authentication mechanism (EAP-SIM authentication algorithm).

Format
The USIM application itself is independent of the physical format of the UICC card. USIM functionality can be deployed on any SIM card with sufficient hardware resources (primarily memory size). Common SIM card formats compatible with USIM include:


 * Plug-in format card (officially ID-000)


 * Micro-SIM card (officially Mini-UICC)

For the emerging Machine-to-Machine (M2M) communication market, new UICC formats like MFF1 and MFF2 (M2M Form Factor 1 and 2) have been developed for integration into devices like telemetry equipment, vending machines, and industrial automation systems. These formats naturally support the USIM application, similar to how a computer's operating system can run on various case designs.
 * Nano-SIM card (introduced in 2012)