The IMS: IP Multimedia Concepts And Services, Second Edition

3.6. Identity modules

3.6.1. IP Multimedia Services Identity Module (ISIM)

An IP Multimedia Services Identity Module (ISIM) is an application residing on the Universal Integrated Circuit Card (UICC), which is a physically secure device that can be inserted and removed from UE. There may be one or more applications in the UICC. The ISIM itself stores IMS-specific subscriber data mainly provisioned by an IMS operator. The stored data can be divided into six groups as shown in Figure 3.5. Most of the data are needed when a user performs an IMS registration [3GPP TS 31.103]:

• Security keys consist of integrity keys, ciphering keys and key set identifiers. Integrity keys are used to prove integrity protection of SIP signalling. Ciphering keys are used to provide confidential protection of SIP signalling. Confidential protection is not used in Release 5; however, in Release 6 it should be possible to use confidential protection. At the time of writing there is a need for key set identifiers.

  Figure 3.5. IP Multimedia Services Identity Module.

  

• The private user identity simply contains the private user identity of the user. It is used in a registration request to identify the user's subscription (see Section 3.5.1.1 for further information).

• The public user identity contains one or more public user identities of the user. It is used in a registration request to identify an identity to be ...