This clause describes the UICC and USIM aspects for access to the IM CN subsystem. Additional requirements related to UICC usage for access to the IM CN subsystem are described in TS 33.203.

In case the UE is loaded with a UICC that contains a USIM but does not contain an ISIM, the UE shall:

• generate a private user identity;
• generate a temporary public user identity; and
• generate a home network domain name to address the SIP REGISTER request to.

All these three parameters are derived from the IMSI parameter in the USIM, according to the procedures described in TS 23.003. Also in this case, the UE shall derive new values every time the UICC is changed, and shall discard existing values if the UICC is removed.

For 3GPP systems, if ISIM is present, it is contained in UICC.

If the UE supports the UICC access to IMS USAT feature defined in TS 31.111 the following procedures in addition to the UE procedures in this specification apply. If the EF UICCIARI contains a list of IARIs associated with active applications installed on the UICC in either the USIM or the ISIM, then when performing the user-initiated registration procedure as described in subclause 5.1.1.2 the UE shall include in the REGISTER request the list of IARIs associated with active applications installed on the UICC in addition to any IARI values for active applications installed on the ME in g.3gpp.iari-ref media feature tag(s) in the Contact header field of the REGISTER request as defined in subclause 7.9.3 and RFC 3840. If the UE receives from the UICC an initial request for a dialog or a standalone transaction then after decapsulating the request as specified in TS 31.111 the UE shall send the request to the IM CN subsystem as specified in subclause 5.1.2A. When the UE receives from the UICC subsequent requests or responses related to dialogs or transactions already established for UICC applications then after decapsulating the request or response as specified in TS 31.111 the UE shall send the request or response to the IM CN subsystem as specified in subclause 5.1.2A. When sending requests or responses received from the UICC to the IM CN subsystem the UE shall modify or include any header fields necessary (such as Route, Via, Contact) in order to conform with the procedures in this specification.

3GPP TS 31.102 and TS 31.103 specify the file structure and contents for the preconfigured parameters stored on the USIM and ISIM, respectively, necessary to initiate the registration to the IM CN subsystem. Any of these parameters can be updated via Data Download or a USAT application, as described in TS 31.111. If one ore more EFs are changed and a REFRESH command is issued by the UICC, then the UE reads the updated parameters from the UICC as specified for the REFRESH command in TS 31.111. If the UE supports the UICC access to IMS USAT feature defined in TS 31.111 and the EF UICCIARI changes in either the USIM or the ISIM, the UE shall perform the user-initiated reregistration procedure as described in subclause 5.1.1.4 with the new values of the IARI parameter(s) residing on the UICC. In case of changes to EFs other than the EF UICCIARI, the UE is not required to perform deregistration but it shall wait for the network-initated deregistration procedures to occur as described in subclause 5.4.1.5 unless the user initiates deregistration procedures as described in subclause 5.1.1.6. From this point onwards the normal initial registration procedures can occur.