School of Specs 23.501v20.2.0

3GPP 23.501 v20.2.0 — the document's own text

5.17.3 Interworking with EPC in presence of Non-3GPP PDU Sessions

Taught in 19. Living next to 4G (The 5G system architecture, in depth), 7. Roaming, other accesses, the edge and the outside (The 5G system architecture, overview).

When a UE is simultaneously connected to the 5GC over a 3GPP access and a non-3GPP access, it may have PDU Sessions associated with 3GPP access and PDU Sessions associated with non-3GPP access. When inter-system handover from 5GS to EPS is performed for PDU Sessions associated with 3GPP access, the PDU Sessions associated with non-3GPP access are kept anchored by the network in 5GC and the UE may either:

  • keep PDU Sessions associated with non-3GPP access in 5GS (5GC+N3IWF or TNGF) (i.e. the UE is then registered both in EPS and, for non-3GPP access, in 5GS); or
  • locally or explicitly release PDU Sessions associated with non-3GPP access; or
  • once in EPS, transfer PDU Sessions associated with non-3GPP access to E-UTRAN by triggering PDN connection establishment with Request Type "Handover", as specified in TS 23.401 [26].