C.2 Derivation of IMS parameters from USIM

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

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 3GPP TS 23.003 [3]. 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.

NOTE: If there is an ISIM and a USIM on a UICC, the ISIM is used for authentication to the IM CN subsystem, as described in 3GPP TS 33.203 [19]. See also subclause 5.1.1.1A.