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Base Specification : 24.229 4.2 URI and Address Assignment
Case 1 > When ISIM is available (24.229 188.8.131.52A Parameters contained in the ISIM)
: UE Extract User ID and Domain Name information from IMPI, IMPU,DOMAIN parameters (See TS 31.103 for ISIM Parameters)
Case 2 > When ISIM is NOT available and USIM is available (24.229 184.108.40.206A Parameters contained in the ISIM)
: UE has to provide all the information required for registration (private user identity, temporary public user identity, home network domain name).
Case 3 > When No ISIM, No USIM, ony IMC(IMS Credential) is available (24.229 220.127.116.11B.1 Parameters provisioned in the IMC)
: UE has to provide all the information required for registration(private user identity,a public user identity,a home network domain name) in the form of IMC.
Case 4 > When No ISIM, No USIM, No IMC(IMS Credential) is available (18.104.22.168B.2 Parameters when UE does not contain ISIM, USIM or IMC)
: UE shall generate a temporary public user identity, a private user identity and a home network domain name to address the SIP REGISTER request based on 3GPP TS 23.003: "Numbering, addressing and identification"
< Requirement from 3GPP 23.228 >
3GPP 23.228 describes about this topic in E.3 Address and identity management concepts
If the UICC does not contain an ISIM application, The Private User Identity shall be derived from the USIM's IMSI
Note : When there are multiple items stored in IMPU list, which one should be used for the steps shown above ? - It usually depends on the requirement from Service Provider.
For example : A service provider may set the requirement as follows.
i) If a provisioned SIM is used, use the first item in IMPU list
ii) If a non-provisioned SIM is used, use the second item in IMPU list
Note : This is only a general rule.. there may be variations of UE ID application for each steps depending on the requirement from each service provider. For example, Some service provider put MSISDN ID at higher priority and require UE to use this ID for registration.
< Requirement from IR 92 >
IR 92 2.2.1 SIP Registration Procedures specifies as follows.
All IMS public user identities provided in the implicit registration set used for VoLTE by the IMS core network must be alias user identities and must include a Tel URI. The following public user identity must be assigned to the implicit registration set used for VoLTE and it must be used by the UE when registering for VoLTE:
a) When ISIM is used, the public user identity in the first (or only) record in the Elementary File in the ISIM
b) The temporary public user identity derived from the IMSI.
No other implicit registration set must be used for VoLTE.