3GPP 24.501 v20.0.0 — the document's own text

6.4.1.1 General

Taught in 6. Getting on the network, and getting a connection through it (CT1 — the group that writes what your phone says, in depth), 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).

The purpose of the UE-requested PDU session establishment procedure is to establish a new PDU session with a DN, to perform handover of an existing PDU session between 3GPP access and non-3GPP access, to transfer an existing PDN connection in the EPS to the 5GS, to transfer an existing PDN connection in an untrusted non-3GPP access connected to the EPC to the 5GS, to establish an MA PDU session to support ATSSS (see 3GPP TS 24.193 [13B]), or to relay the service associated with the RSC for 5G ProSe layer-3 UE-to-network relay or for 5G ProSe multi-hop layer-3 UE-to-network relay (see 3GPP TS 24.554 [19E]). If accepted by the network, the PDU session enables exchange of PDUs between the UE and the DN.

The UE shall not request a PDU session establishment:

for an LADN, if the DNN used for that LADN is included in the LADN information IE and the UE is located outside the LADN service area indicated in the LADN information IE;

a1) for an LADN, if the DNN used for that LADN is included in the Extended LADN information IE and there is no S-NSSAI used for PDU session establishment;

a2) for an LADN, if the DNN used for that LADN is included in the Extended LADN information IE and the S-NSSAI used for PDU session establishment is not associated with that LADN;

a3) for an LADN, if the DNN and the S-NSSAI used for that LADN are included in the Extended LADN information IE and the UE is located outside the LADN service area indicated in the Extended LADN information IE;

to transfer a PDU session from non-3GPP access to 3GPP access when the 3GPP PS data off UE status is "activated" and the UE is not using the PDU session to send uplink IP packets for any of the 3GPP PS data off exempt services (see clause 6.2.10);
when the UE is in NB-N1 mode, the UE has indicated preference for user plane CIoT 5GS optimization, the network has accepted the use of user plane CIoT 5GS optimization for the UE, and the number of PDU sessions that currently has user-plane resources established equals to the UE's maximum number of supported user-plane resources;
to transfer a PDU session from 3GPP access to non-3GPP access when the UE has indicated preference for control plane CIoT 5GS optimization, the network has accepted the use of control plane CIoT 5GS optimization for the UE, and the Control plane only indication IE was received in the PDU SESSION ESTABLISHMENT ACCEPT message;
to transfer a PDU session from the non-3GPP access to the 3GPP access when the UE is in NB-N1 mode, the UE has indicated preference for user plane CIoT 5GS optimization, the network has accepted the use of user plane CIoT 5GS optimization for the UE, and the number of PDU sessions that currently has user-plane resources established equals to the UE's maximum number of supported user-plane resources;
associated to an S-NSSAI when the UE is not in the NS-AoS of the S-NSSAI; or
associated to an S-NSSAI included in the partially allowed NSSAI when the current TA is not in the list of TAs where the S-NSSAI is allowed.