E.3 Address and identity management concepts
23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS
E.3.1 Deriving IMS identifiers from the USIM
If the UICC does not contain an ISIM application, then:
The Private User Identity shall be derived from the USIM’s IMSI, which allows for uniquely identifying the user within the 3GPP operator’s network. The format of the Private User Identity derived from the IMSI is specified in TS 23.003 [24].
– A Temporary Public User Identity shall be derived from the USIM’s IMSI, and shall be used in SIP registration procedures. The format of the Temporary Public User Identity is specified in TS 23.003 [24].
It is strongly recommended that the Temporary Public User Identity is set to barred for SIP non-registration procedures. The following applies if the Temporary Public User Identity is barred:
– A Temporary Public User Identity shall not be displayed to the user and shall not be used for public usage such as displaying on a business card.
– The Temporary Public User Identity shall only be used during the SIP initial registration, re-registration and mobile initiated de-registration procedures.
– The implicitly registered Public User Identities shall be used for session handling, in non-registration SIP messages and may be used at subsequent SIP registration procedures.
– A Temporary Public User Identity shall only be available to the CSCF and HSS nodes.
NOTE: If a Temporary Public User Identity is used, the user can not initiate any sessions until the implicitly registered public identities are available in the UE.
In order to support a pre-Rel‑5 UICC accessing IMS services, a Temporary Public User Identity is generated using an appropriate identity related to the subscriber’s subscription (e.g. in 3GPP it shall use the IMSI).
When a Temporary Public User Identity has been used to register an IMS user, the implicit registration will ensure that the UE, P‑CSCF & S‑CSCF have Public User Identity(s) for all IMS procedures after the initial registration has been completed.