4.23.13 Non N26 based Interworking Procedures with I-SMF

23.5023GPPProcedures for the 5G System (5GS)Release 18TS

4.23.13.1 General

When UE moves a PDU Session from EPS to 5GS, the AMF determines whether I-SMF needs to be inserted based on the UE location and the service area of the SMF+PGW-C.

This clause describes the non N26 based Interworking Procedures with I-SMF insertion when UE move a PDU Session from EPS to 5GS and I-SMF removal when UE moves a PDU Session from 5GS to EPS.

This may happen e.g. when the UE moves a PDU Session between an ePDG (over EPC) and 3GPP access over 5GC;

4.23.13.2 Mobility procedure without N26 interface from EPS to 5GS

At Mobility procedure from EPS to 5GS without N26 interface the procedure described in Figure 4.11.2.3-1 takes place, with following difference:

– During step 9 of Figure 4.11.2.3-1 "UE requested PDU Session Establishment according to clause 4.3.2.2", the mechanisms described in clause 4.23.5.1 apply

4.23.13.3 Mobility procedure without N26 interface from EPC/ePDG to 5GS

At Handover from EPC/ePDG to 5GS, the procedure described in Figure 4.11.4.1-1 takes place, with following difference:

– During step 2 of Figure 4.11.4.1-1 "UE requested PDU Session Establishment according to clause 4.3.2.2", the mechanisms described in clause 4.23.5.1 apply

4.23.13.4 Mobility procedure without N26 interface from 5GS to EPS

At Mobility procedure from 5GS to EPS without N26 interface, the procedure described in Figure 4.11.2.2-1 takes place, with following difference:

– During step 14 of Figure 4.11.2.2-1 (SMF+PGW-C initiates release of the PDU Session(s) in 5GS transferred to EPS), if an I-SMF was involved in the PDU Session, the same mechanisms than in Home Routed roaming apply (release according to Figure 4.3.4.3-1) with the SMF playing the role of the H-SMF and the I-SMF playing the role of the V-SMF.

4.23.13.5 Mobility procedure without N26 interface from 5GS to EPC/ePDG

At Handover from 5GS to EPC/ePDG, the procedure described in Figure 4.11.4.2-1 takes place, with following difference:

– During step 3 of Figure 4.11.4.2-1 (5GC and NG-RAN resource release), if an I-SMF was involved in the PDU Session, the same mechanisms than in Home Routed roaming apply (Figure 4.3.4.3-1 steps 3a-16b) with the SMF playing the role of the H-SMF and the I-SMF playing the role of the V-SMF.