3GPP 23.501 v20.2.0 — the document's own text
5.6.9.2.2 SSC Mode 2
Taught in 12. The connection to a data network (The 5G system architecture, in depth), 5. The connection, and what is promised on it (The 5G system architecture, overview).
If a PDU Session of SSC mode 2 has a single PDU Session Anchor, the network may trigger the release of the PDU Session and instruct the UE to establish a new PDU Session to the same data network immediately. The trigger condition depends on operator policy e.g. request from Application Function, based on load status, etc. At establishment of the new PDU Session, a new UPF acting as PDU Session Anchor can be selected.
Otherwise, if a PDU Session of SSC mode 2 has multiple PDU Session Anchors (i.e. in the case of multi-homed PDU Sessions or in the case that UL CL applies to a PDU Session of SSC mode 2), the additional PDU Session Anchors may be released or allocated.
SSC mode 2 may apply to any PDU Session type and to any access type.
SSC mode 2 is optional to be supported in the UE.
NOTE 1: Features depending on SSC mode 2 will not work with the lack of support for SSC mode 2 in the UE.
NOTE 2: In UL CL mode, the UE is not involved in PDU Session Anchor re-allocation, so that the existence of multiple PDU Session Anchors is not visible to the UE.