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

5.4.14.1 General

Taught in 9. Registration, reachability and paging (The 5G system architecture, in depth), 10. Radio, Wi-Fi, cable — every way in (The 5G system architecture, in depth).

To support UE-Satellite-UE communication for IMS services, network functions (e.g. UPF) transferring IMS user plane traffic in the 5G system shall be deployed onboard the satellites with regenerative payload that provide service link to the two UEs. The reference architecture for support of UE-Satellite-UE communication is described in TS 23.228 [15].

NOTE 1: In this Release, only IMS voice/video services between two UEs belonging to same PLMN and in non-roaming scenario are considered.

To keep the UE's IP address for IMS services unchanged, a UPF on the ground shall be selected during PDU Session establishment procedure as the PSA UPF for the duration of the IMS PDU session. The UPF on-board the satellite shall only be selected as an UL CL/BP and local PSA to route IMS user plane traffic.

NOTE 2: In this Release of the specification, the type of serving satellite can only be LEO or MEO.