Content for TR 23.756 Word version: 16.0.0
5 Key Issues p. 7
5.1 Key Issue #1: Enabling SRVCC from NG-RAN to UTRAN p. 7
5.2 Key Issue #2: SRVCC HO Procedure from NG-RAN to UTRAN p. 7
5.3 Key Issue #3: Return from UTRAN to E-UTRA or NR p. 7
5.4 Key Issue #4: Analysis of impacts for not supporting PS HO support in conjunction with SRVCC from NG-RAN to UTRAN p. 8
6 Solutions p. 8
6.1 Solution #1: Enable 5G SRVCC with existing mechanism p. 8
6.1.1 Description p. 8
6.1.1.1 General p. 8
6.1.1.2 5GS Registration for SRVCC p. 8
6.1.1.3 Service Request procedure for SRVCC p. 8
6.1.1.4 Intra-5GS PS Handover procedure for SRVCC p. 8
6.1.1.5 eSRVCC from 5G to 3G using ATCF enhancements p. 9
6.1.2 Procedures p. 9
6.1.3 Impacts on existing nodes and functionality p. 9
6.2 Solution #2: Indirect SRVCC procedure p. 9
6.2.1 Description p. 9
6.2.2 Architecture p. 9
6.2.3 Indirect SRVCC call flow p. 11
6.2.4 eSRVCC from 5G to 3G using ATCF enhancements p. 12
6.2.5 Impact on existing nodes and functionality p. 12
6.3 Solution #3: Returning UE from UTRAN to NR or E-UTRA using MME-lite p. 13
6.3.1 Description p. 13
6.3.1.1 Enhancement to SRVCC HO Procedure from NG-RAN to UTRAN CS p. 14
6.3.1.2 Returning UE to NR or E-UTRA p. 14
6.3.2 Impacts p. 14
6.3.3 Evaluation p. 15
6.4 Solution #4: Return to 5GS when the UE is switched into EPS after voice ends in 3G p. 15
6.4.1 Description p. 15
6.4.2 Procedures p. 16
6.4.3 Impact on existing nodes and functionality p. 17
6.5 Solution #5: PDU session release after 5G SRVCC procedure p. 17
6.5.1 Description p. 17
6.5.2 AMF requests SMF release the remained PDU session p. 17
6.5.3 Impacts on existing nodes and functionality p. 19
6.6 Solution #6: PDU session suspend after 5G SRVCC procedure p. 19
6.6.1 Description p. 19
6.6.2 AMF request SMF suspend the remained PDU session p. 19
6.6.3 Impacts on existing nodes and functionality p. 21
6.7 Solution #7: Returning UE from UTRAN to E-UTRA using MME-lite p. 21
6.7.1 Description p. 21
6.7.1.1 Enhancement to SRVCC HO Procedure from NG-RAN to UTRAN CS p. 22
6.7.1.2 Returning UE to E-UTRA p. 22
6.7.2 Additional Impacts p. 23
6.8 Solution #8: Solution for key issue 3# - 2 Step method Return 5GS After 5G SRVCC with existing mechanism p. 23
6.8.1 Description p. 23
6.8.2 Procedures p. 23
6.8.3 Impact on existing nodes and functionality p. 23
6.9 Solution #9: Solution for key issue 3# - Return 5GS After 5G SRVCC depend on UE implementation p. 23
7 Evaluation p. 24
7.1 Evaluation on solution for key issue #1 p. 24
7.2 Evaluation on solution for key issue #2 p. 24
7.3 Evaluation about solutions for Key Issue #4 p. 24
7.4 Evaluation on solutions for key issue #3 p. 25
8 Conclusions p. 26
$ Change History p. 27
