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31 series - USAT architecture and protocol stack

31.919 - 2G/3G Java Cardô Application Programming Interface (API) based applet interworking 31.213 - Test specification for subscriber (U)SIM; Application Programming Interface (API) for Java Cardô 34.131 - Test Specification for C-language binding to (Universal) Subscriber Interface Module ((U)SIM) Application Programming Interface (API) 31.120 - UICC-terminal interface; Physical, electrical and logical test specification 31.124 - Mobile Equipment (ME) conformance test specification; Universal Subscriber Interface Module Application Toolkit (USAT) conformance test specification 31.133 - Not available in this release 31.130 - (U)SIM Application Programming Interface (API); (U)SIM API for Java Card 31.131 - C-language binding for (Universal) Subscriber Identity Module ((U)SIM) API 31.101 - UICC-terminal interface; Physical and logical characteristics 31.111 - Universal Subscriber Identity Module (USIM) Application Toolkit (USAT) USAT security Up to the 31 series


The USAT is a set of commands and procedures, which allows the UICC to run applications that are specific to the card issuer (ie the network operator). Typical applications include information- and location-based services, and mobile banking.

As shown above, the UICC application typically uses the USAT to communicate with an external application system. To do this, it instructs the ME to send data to the application system, and wait for the response. The data can be sent by various mechanisms, such as SMS or GPRS, and are secured using the USAT security procedures.

The UICC application also uses the USAT to communicate with the ME's user interface. For example, it can instruct the ME to display a menu, and wait for the user's selection. In this situation, the protocols terminate in the ME.

A C API allows network operators not only to write C language applications, but also to download them after the card has been issued. There are also API's for Sun Java Cards, with separate specifications for cards running a USIM or an ISIM.

The ETSI specifications can be downloaded here.


APIApplication programming interface
CATCard application toolkit
ETSIEuropean telecommunications standards institute
GPRSGeneral packet radio service
GSMGlobal system for mobile communications
IPInternet protocol
ISIMIP multimedia services identity module
MEMobile equipment
SMSShort message service
UICCUniversal integrated circuit card
USATUSIM application toolkit
USIMUniversal subscriber identity module
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