A.2 Originating call flows
24.1743GPPRelease 17Stage 3Support of multi-device and multi-identity in the IP Multimedia Subsystem (IMS)TS
A.2.1 UE-A indicates a non-native identity A1 registered by the UE
This call flow illustrates the handling of the identity A1 registered by the UE for originating call.
It applies to the cases when alternative identity registered by the UE or virtual identity registered by the UE is used.
In this case, only the AS of user A is involved on the originating side.
NOTE: A deployment option where the UE-A indicates an identity not registered by the UE and only the AS serving user A is involved is out of the scope of this specification.
Figure A.2.1-1: UE-A indicates a non-native identity A1 registered by the UE
1. UE-A sends an INVITE message to P/S-CSCF-A, for an example see table A.2.1-1
The UE-A includes in the initial INVITE request the From header field and the P-Preferred-Identity header field set to the identity A1 registered by the UE and sends the initial INVITE request to the P/S-CSCF-A according to TS 24.229 [3].
Table A.2.1-1: INVITE request (UE-A to P/S-CSCF-A)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Preferred-Identity: <tel:+11111111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
2. P/S-CSCF-A forwards the INVITE message to AS-A, for an example see table A.2.1-2
The P-CSCF-A populates the P-Asserted-Identity header field with the identity A1 registered by the UE following procedures defined in TS 24.229 [3].
The S-CSCF-A forwards the request to the AS-A using initial filter criteria.
Table A.2.1-2: INVITE request (P/S-CSCF-A to AS-A)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Asserted-Identity: <sip:+11111111@plmnA.net;user=phone>, <tel:+11111111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
3. AS-A forwards the INVITE message to the S-CSCF-A, for an example see table A.2.1-3
AS-A performs originating services as needed and forwards the request to the S-CSCF-A according to TS 24.229 [3].
Table A.2.1-3: INVITE request (AS-A to P/S-CSCF-A)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Asserted-Identity: <sip:+11111111@plmnA.net;user=phone>, <tel:+11111111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
4. S-CSCF-A forwards the INVITE message towards the PLMN-B
A.2.2 UE-A indicates an identity C
This alternative is applicable to the cases when the UE-A indicates an identity which has not been registered by UE-A (i.e., it applies to the cases when UE-A indicates an alternative identity not registered by the UE or a virtual identity not registered by the UE) or an external alternative identity.
Figure A.2.2-1: UE-A indicates an identity C
1. UE-A sends an INVITE message to P/S-CSCF-A, for an example see table A.2.2-1
User A at UE-A initiates a call on behalf of the identity C. The UE-A includes the Additional-Identity header field in the initial INVITE request to indicate that the user of UE-A wishes to use the identity C for this call, the From and the P-Preferred-Identity header fields set to the native identity and sends the initial INVITE request to the P/S-CSCF-A according to TS 24.229 [3].
NOTE 1: According to procedures defined in TS 24.229 [3] the P-Preferred-Identity header field can be omitted.
Table A.2.2-1: INVITE request (UE-A to P/S-CSCF-A)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
Additional-Identity: <tel:+22221111>
P-Preferred-Identity: <tel:+11111111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
2. S-CSCF-A forwards the INVITE message to AS-A, for an example see table A.2.2-2
The P-CSCF-A populates the P-Asserted-Identity header field with the native identity following procedures defined in TS 24.229 [3].
The S-CSCF-A forwards the request to the AS-A using initial filter criteria.
Table A.2.2-2: INVITE request (P/S-CSCF-A to AS-A)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Asserted-Identity: <sip:+11111111@plmnA.net;user=phone>, <tel:+11111111>
Additional-Identity: <tel:+22221111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
3. AS-A forwards the INVITE message to the S-CSCF-C, for an example see table A.2.2-3
AS-A verifies that the user is authorized to use the identity received in the Additional-Identity header field and if so, it does not modify the P-Asserted-Identity header field, it creates a P-Served-User header field with the identity copied from the received Additional-Identity header field and it insert a Route header field pointing to an I-CSCF or to the S-CSCF hosting the identity in the Additional-Identity header field and append the "orig" parameter to it. AS-A performs the originating services as needed and forwards the request to the S-CSCF-C.
Table A.2.2-3: INVITE request (AS-A to S-CSCF-C)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Asserted-Identity: <sip:+11111111@plmnA.net;user=phone>, <tel:+11111111>
Additional-Identity: <tel:+22221111>
P-Served-User: <tel:+22221111>
Route: <sip:server-C.plmnA.net; orig>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
4. S-CSCF-C forwards the INVITE message to AS-C, for an example see table A.2.2-4
The S-CSCF-C removes the Route header field pointing to it and forwards the request to the AS-C using initial filter criteria.
Table A.2.2-4: INVITE request (S-CSCF-C to AS-C)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+11111111>;tag=4fa3
P-Asserted-Identity: <sip:+11111111@plmnA.net;user=phone>, <tel:+11111111>
Additional-Identity: <tel:+22221111>
P-Served-User: <tel:+22221111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
5. AS-C forwards the INVITE message to the S-CSCF-C, for an example see table A.2.2-5
AS-C verifies that the identity C received in the Additional-Identity header field has been authorized to be used by user A. If it is the case, it creates the P-Asserted-Identity header field with the identity copied from the received Additional-Identity header field and performs originating services as needed. AS-C replaces the identity in the From header field with the identity copied from the received Additional-Identity header field, removes from the INVITE request the received P-Asserted-Identity, P-Served-User and Additional-Identity header fields and forwards the request to the S-CSCF-C according to TS 24.229 [3].
NOTE 2: Depending on local configuration, related to the operator policy and regulatory requirements, AS-C replaces the identity in the P-Asserted-Identity header field with the identity in the Additional-Identity header field, or if the P-Asserted-Identity header cannot be modified, AS-C sets the Privacy header field to value "id", as specified in clause 4.5.3.3.
Table A.2.2-5: INVITE request (AS-C to S-CSCF-C)
INVITE tel:+11112222 SIP/2.0
To: <tel:+11112222>
From: <tel:+22221111>;tag=4fa3
P-Asserted-Identity: <sip:+22221111@plmnA.net;user=phone>, <tel:+22221111>
Other SIP header fields and SDP according to 3GPP TS 24.229 [3]
6. S-CSCF-C forwards the INVITE message towards the PLMN-B