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Content for  TS 24.186  Word version:  19.4.0

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A.1.3 Explicit Communication Transfer  A.1.3.1 IMS serving the transferee provides data channel service  A.1.3.1.1 Blind Transfer  A.1.3.1.2 Consultation Transfer 
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A.1.3  Explicit Communication Transfer  p. 65

A.1.3.1  IMS serving the transferee provides data channel service  p. 65

A.1.3.1.1  Blind Transfer  p. 65
Copy of original 3GPP image for 3GPP TS 24.186, Fig. A.1.3.1.1-1: Blind Transfer when IMS serving the transferee provides data channel service
Figure A.1.3.1.1-1: Blind Transfer when IMS serving the transferee provides data channel service
(⇒ copy of original 3GPP image)
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Figure A.1.3.1.1-1 shows a call flow for blind transfer when IMS serving the transferee provides data channel service.
Step 1.
UE-A calls UE-B, UE-A sends an INVITE request towards the UE-B.
Step 2.
DC media resource is allocated by IMS-A for UE-A and UE-B.
Step 3-6.
UE-B answers the call, session connection is established between UE-A and UE-B. IMS-A establishes BDC connection for UE-A and UE-B. And then IMS-A establishes ADC connections between UE-A and UE-B.
Step 7.
UE-B starts transfer process.
Step 8.
UE-B sends a REFER message to transfer the call to UE-C.
Step 9-10.
IMS-B sends 202/NOTIFY to UE-B to accept the transfer request, and then sends BYE message to UE-B. UE-B releases reserved DC media resources of established BDC and ADC between UE-B and IMS-A/UE-A for A-B call.
Step 11-12.
IMS-B sends an initial INVITE message to UE-C without SDP, UE-C replies SDP offer with audio media in 18X/200 response.
Step 13.
IMS-B sends re-INVITE message to IMS-A and release the data channels between the IMS-B and UE-A.
Step 14-16.
IMS AS of IMS-A notifies session modify event to the DCSF and as per media instruction request from the DCSF, the IMS AS sends media resource management request to MF to update the data channel media resources for UE-B. IMS-A releases reserved DC media resources of established BDC and ADC between IMS-A and UE-B for A-B call.
Step 17-19.
IMS AS of IMS-A sends a re-INVITE message carrying SDP offer with data channel media towards UE-A. In SDP offer of re-INVITE message, the IMS AS of IMS-A adds previously established BDC and ADC between IMS-A and UE-A for A-B call with UDP ports set to zero. Earlier established BDC between UE-A and IMS-A (in step 4-1) can remain as it is or re-established as per operator policy. IMS-A releases the earlier established DC media resources between IMS-A and UE-A. UE-A releases the earlier established DC media resources between UE-A and IMS-A/UE-B and prepare SDP answer with earlier established DC media with UDP port zero. UE-A replies with the SDP answer with data channel media included in the 200 OK response.
Step 20-22.
IMS AS of IMS-A notifies session modify event to the DCSF and as per media instruction request from the DCSF, the IMS AS sends media resource management request to MF to update the data channel media resources for UE-A.
Step 23.
IMS AS of IMS-A sends a 200 OK message with updated data channel media to IMS-B.
Step 24.
IMS-B sends PRACK/ACK message towards UE-C with no DC media in SDP answer.
Step 25.
The session connection is established between UE-A and UE-C.
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A.1.3.1.2  Consultation Transfer  p. 67
Copy of original 3GPP image for 3GPP TS 24.186, Fig. A.1.3.1.2-1: Consultative Transfer when IMS serving the transferee provides data channel service
Figure A.1.3.1.2-1: Consultative Transfer when IMS serving the transferee provides data channel service
(⇒ copy of original 3GPP image)
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Figure A.1.3.1.2-1 shows a call flow for consultative transfer when IMS serving the transferee provides data channel service.
Step 1.
UE-A calls UE-B, UE-A sends an INVITE request towards the UE-B.
Step 2.
DC media resource is allocated by IMS-A for UE-A and UE-B.
Step 3-6.
UE-B answers the call, session connection is established between UE-A and UE-B. IMS-A establishes BDC connection for UE-A and UE-B. And then IMS-A establishes ADC connections between UE-A and UE-B.
Step 7-8.
UE-B holds UE-A, and then calls UE-C.
Step 9.
When UE-C sends 180 ringing or 200 response, UE-B starts transfer process.
Step 10.
UE-B sends a REFER message to transfer the call to UE-C.
Step 11-12.
IMS-B sends 202/NOTIFY to UE-B to accept the transfer request, and then sends BYE message to UE-B.
Step 13-15.
IMS-B sends a media re-negotiation request to UE-A, UE-A replies SDP offer with data channel media description.
Step 16-18.
IMS AS of IMS-A notifies session modify event to the DCSF and as per media instruction request from the DCSF, the IMS AS sends media resource management request to MF to update the data channel media resources for UE-A.
Step 19.
IMS AS sends a 200 OK response for re-INVITE to the IMS-B with updated data channel media.
Step 20-21.
IMS-B sends a re-INVITE message carrying SDP offer with data channel media towards UE-C, and receives 200 OK response for reINVITE carrying SDP answer with data channel media from UE-C.
Step 22.
IMS-B sends an ACK message carrying SDP answer with data channel media towards IMS-A.
Step 23-25.
IMS AS of IMS-A notifies session modify event to the DCSF and as per media instruction request from the DCSF, the IMS AS sends media resource management request to MF to update the data channel media resources for UE-C.
Step 26.
IMS AS of IMS-A sends an ACK message carrying SDP answer with data channel media towards UE-A.
Step 27.
The BDC media connection is established between IMS-A and UE-C.
Step 28.
The ADC media connections are established between UE-A and UE-C.
Step 29.
The session connection is established between UE-A and UE-C.
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