Section: 4.11.4.1 Handover from EPC/ePDG to 5GS
Content: Figure 4.11.4.1-1: Handover from EPC/ePDG to 5GS 0. Initial status: one or more PDN Connections have been established between the UE and the EPC/ePDG via untrusted non-3GPP access as specified in clauses 7.2.4 and 7.6.3 of TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26] with modification described in clauses 4.11.4.3.3 and 4.11.4.3.5. 1. For the UE to move its PDU session(s) from EPC/ePDG to 5GC/3GPP access, the UE's behaviour is as follows: - If the UE is operating in single-registration mode (as described in clause 5.17.2.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]) and the UE is attached to EPC/E-UTRAN: - the UE behaves as specified in clause 4.11.1 or clause 4.11.2 and gets registered to 5GC via 3GPP access. - otherwise i.e. either the UE is operating in single registration mode and is not attached to EPC/E-UTRAN, or the UE is operating in dual registration mode; and - if the UE is already registered in 5GS via 3GPP access, the UE skips to step 2. - otherwise (i.e UE is not registered in 5GS via 3GPP access), the UE performs Registration procedure of type initial registration in 5GS via 3GPP access as described in clause 4.2.2.2. 2. The UE initiates a UE requested PDU Session Establishment via 3GPP Access acording to clause 4.3.2.2 and includes the "Existing PDU Session" indication or "Existing Emergency PDU Session" and the PDU Session ID. For Request Type "Existing PDU Session", the UE provides a DNN, the PDU Session ID and S-NSSAI corresponding to the existing PDN connection it wants to transfer from EPC/ePDG to 5GS. The S-NSSAI and PLMN ID sent to the UE are set in the same way as for EPS to 5GS mobility as specified in clause 5.15.7.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the Request Type indicates "Existing Emergency PDU Session", the AMF shall use the Emergency Information containing SMF+PGW-C FQDN for the S2b interface it has received from the HSS+UDM. The SMF+PGW-C FQDN was sent by PGW-C when the Emergency PDN connection was established in EPC via ePDG and the AMF shall use the S-NSSAI locally configured in Emergency Configuration Data. 3. The combined PGW+SMF/UPF initiates a PDN GW initiated Resource Allocation Deactivation with GTP on S2b as described in clause 7.9.2 of TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26] to release the EPC and ePDG resources when S6b is used. When S6b is not used between SMF+PGW-C and AAA, impacts to step 5 of TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26] Figure 7.9.2-1 are captured in clause 4.11.4.3.6.