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31 series - USIM architecture and protocol stack

31.900 - SIM/USIM internal and external interworking aspects 31.122 - Universal Subscriber Identity Module (USIM) conformance test specification 31.120 - UICC-terminal interface; Physical, electrical and logical test specification 31.121 - UICC-terminal interface; Universal Subscriber Identity Module (USIM) application test specification 31.103 - Characteristics of the IP Multimedia Services Identity Module (ISIM) application 31.102 - Characteristics of the Universal Subscriber Identity Module (USIM) application 31.101 - UICC-terminal interface; Physical and logical characteristics Up to the 31 series


The USIM is an application-layer protocol on the interface between the UICC and the ME. The ME uses the USIM to support its communications with the fixed network. For example:

  • The ME instructs the UICC to store and retrieve user-related information such as phone numbers and manually-selected network identities.
  • The ME instructs the UICC to run algorithms such as network authentication.

The specifications also define the ISIM application, which supports the ME's communications with the IP multimedia subsystem.

The ETSI specifications can be downloaded here.


ETSIEuropean telecommunications standards institute
GSMGlobal system for mobile communications
IPInternet protocol
ISIMIP multimedia services identity module
MEMobile equipment
UICCUniversal integrated circuit card
USIMUniversal subscriber identity module
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