An IP Multimedia Services Identity Module (ISIM) is an application running on a UICC

UICC

The UICC is the smart card used in mobile terminals in GSM and UMTS networks. The UICC ensures the integrity and security of all kinds of personal data, and it typically holds a few hundred kilobytes...

 smart card

Smart card

A smart card, chip card, or integrated circuit card , is any pocket-sized card with embedded integrated circuits. A smart card or microprocessor cards contain volatile memory and microprocessor components. The card is made of plastic, generally polyvinyl chloride, but sometimes acrylonitrile...

 in a 3G

3G

3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...

 mobile telephone in the IP Multimedia Subsystem

IP Multimedia Subsystem

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering Internet Protocol multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project , as a part of the vision for evolving mobile...

 (IMS). It contains parameters for identifying and authenticating the user to the IMS. The ISIM application can co-exist with SIM

Subscriber Identity Module

A subscriber identity module or subscriber identification module is an integrated circuit that securely stores the International Mobile Subscriber Identity and the related key used to identify and authenticate subscriber on mobile telephony devices .A SIM is held on a removable SIM card, which...

 and USIM on the same UICC making it possible to use the same smartcard in both GSM

Global System for Mobile Communications

GSM , is a standard set developed by the European Telecommunications Standards Institute to describe technologies for second generation digital cellular networks...

 networks and earlier releases of UMTS

Universal Mobile Telecommunications System

Universal Mobile Telecommunications System is a third generation mobile cellular technology for networks based on the GSM standard. Developed by the 3GPP , UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for...

.

Among the data present on ISIM are a IP Multimedia Private Identity (IMPI), the home operator domain name

Domain name

A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....

, one or more IP Multimedia Public Identity (IMPU) and a long-term secret used to authenticate and calculate cipher keys. The first IMPU stored in the ISIM is used in emergency registration requests.

External links

• 3GPP TS 31.103 - ISIM standard
• 3GPP TS 24.229