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Content for TR 23.872 Word version: 8.0.0

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4 Architecture p. 7

4.1 Architectural requirements p. 7

4.1.1 Multiple CAT Caused by Forking or Flexible Alerting (FA) p. 7

4.2 Reference architecture p. 8

4.2.1 Reference points p. 9

4.2.1.1 CAT Application Server - MRFC (Cr) Interface p. 9

4.2.2 Functional entities p. 9

5 Alternatives p. 9

5.1 Alternative 1 p. 9

5.1.1 Procedures p. 9

5.1.1.1 CAT provided by the terminating IMS domain based on the Early Session model (Flow 1) p. 9

5.1.1.2 CAT provided by the terminating IMS domain based on the Early Session model (Flow 2) p. 11

5.1.1.3 CAT provided by the terminating IMS domain based on the Early Session model (Flow 3) p. 14

5.1.1.4 CAT provided by the originating IMS domain based on the Early Session model p. 15

5.1.2 Interaction with supplementary services p. 15

5.1.3 Impact p. 15

5.2 Alternative 2 Forking model p. 16

5.2.1 Procedures p. 16

5.2.1.1 Procedures at the UE p. 16

5.2.1.2 Procedures at the CAT AS serving for the terminating UE p. 16

5.2.1.3 Forking-based CAT provided by the terminating IMS domain p. 16

5.2.2 Interaction with supplementary services p. 18

5.2.3 Impact p. 18

5.3 Alternative 3 (Content Indirection) p. 18

5.3.1 Architectural Details p. 18

5.3.1.1 Reference architecture p. 18

5.3.1.2 Reference points p. 18

5.3.1.3 Functional entities p. 18

5.3.1.3.1 Application Server supporting CAT p. 18

5.3.1.4 Information flows and Procedures p. 18

5.3.1.4.1 Procedures at the Originating UE p. 18

5.3.1.4.2 Procedures at the AS serving the Terminating UE p. 19

5.3.1.4.3 Information flow for CAT provided by the terminating IMS domain p. 19

5.3.1.4.4 Information flow for CAT provided by the Originating IMS domain p. 20

5.3.1.5 Interaction with supplementary services p. 20

5.3.2 Impact p. 20

5.4 CAT Control p. 20

5.4.1 CAT stop alternative 1: using out-band method p. 21

5.4.1.1 Early-Session Model p. 21

5.4.1.2 Non-Early-Session Model p. 22

5.4.2 CAT stop alternative 2: using in-band method p. 26

5.4.3 CAT priority and reject alternative 1: direct way p. 27

5.4.3.1 IMS CAT Priority p. 27

5.4.3.2 IMS CAT Reject p. 28

5.4.4 CAT priority and reject alternative 2: indirect way p. 28

5.4.4.1 Early-Session Model p. 28

5.4.4.2 Forking-Based Model p. 30

5.5 IMS CAT service notification p. 33

5.6 IMS CAT copy p. 33

5.6.1 Alternative 1: using in-band method p. 33

5.6.2 Alternative 2: using out-band method p. 34

5.6.2.1 SIP MESSAGE usage for copying CAT or changing CAT p. 34

5.6.2.2 Ut usage for copying CAT or changing CAT p. 34

5.7 CAT selection by the called party p. 35

6 Assessment p. 36

7 Interaction with other features p. 36

7.1 Interaction with other services and functions p. 36

7.2 Interaction with charging p. 36

8 Interworking with CS domain p. 37

8.1 Alternative 1 p. 37

8.1.1 Call flow for providing the IMS CAT to the originating UE in CS domain p. 37

8.2 Alternative 2 p. 38

8.2.1 Procedures p. 38

8.2.1.1 Session-based CAT provided by the terminating IMS domain p. 38

8.3 CAT provided by the terminating CS domain p. 40

9 Conclusion p. 40

$ Change history p. 42