5.15.9 Operator-controlled inclusion of NSSAI in Access Stratum Connection Establishment

The Serving PLMN can control per Access Type which (if any) NSSAI the UE includes in the Access Stratum when establishing a connection caused by Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities. In addition, the Home and Visited PLMNs can also instruct the UE to never include NSSAI in the Access Stratum, regardless of the procedure that causes a RRC Connection to be established, i.e. to always enable privacy for the NSSAI).

During the Registration procedure, the AMF may provide to the UE in the Registration Accept message, an Access Stratum Connection Establishment NSSAI Inclusion Mode parameter, indicating whether and when the UE shall include NSSAI information in the Access Stratum Connection Establishment (e.g. an RRC connection Establishment defined in TS 38.331 [28]) according to one of these modes:

• The UE shall include an NSSAI set to the Allowed NSSAI, if available, in the Access Stratum Connection Establishment caused by a Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities;
• The UE shall include a NSSAI with the following content:
• for the case of Access Stratum Connection Establishment caused by a Service Request: an NSSAI including the S-NSSAI(s) of the Network Slice(s) that trigger the Access Stratum Connection Establishment; i.e. all the S-NSSAIs of the PDU sessions that have the User Plane reactivated by the Service Request, or the S-NSSAIs of the Network Slices a Control Plane interaction triggering the Service Request is related to, e.g. for SM it would be the S-NSSAI of the PDU Session the SM message is about;
• for the case of Access Stratum Connection Establishment caused by a Periodic Registration Update or Registration procedure used to update the UE capabilities, an NSSAI set to the Allowed NSSAI;
• The UE shall not include any NSSAI in the Access Stratum Connection Establishment caused by Service Request, Periodic Registration Update or Registration procedure used to update the UE capabilities; or
• The UE shall not provide NSSAI in the Access stratum.

For the case of Access Stratum Connection Establishment caused by Mobility Registration Update or Initial Registration in modes a), b) or c) the UE shall include the Requested NSSAI provided by the NAS layer and defined in clause 5.15.5.2.1.

For all UEs that are allowed to use modes a), b) or c), the Access Stratum Connection Establishment NSSAI Inclusion Mode should be the same over the same Registration Areas.The UE shall store and comply to the required behaviour for a PLMN per Access Type as part of the network slicing configuration. The Serving PLMN AMF shall not instruct the UE to operate in any other mode than mode d) in 3GPP Access Type unless the HPLMN provides an indication that it is allowed to do so (i.e. if a PLMN allows behaviours a,b,c, then its UDM sends to the serving AMF an explicit indication that the NSSAI can be included in RRC as part of the subscription data).

The UE default mode of operation is the following:

• For 3GPP access the UE shall by default operate in mode d) unless it has been provided with an indication to operate in mode a), b) or c).
• For untrusted non-3GPP access the UE shall operate by default in mode b) unless it has been provided with an indication to operate in mode a), c) or d).
• For trusted non-3GPP access the UE shall operate by default in mode d) unless it has been provided with an indication to operate in mode a), b) or c).
• For W-5GAN access the 5G-RG shall operate by default in mode b) unless it has been provided with an indication to operate in mode a), c) or d).

An operator may pre-configure the UE to operate by default according to mode c) in the HPLMN (i.e. the UE by default includes NSSAI in the access stratum when it performs an Initial Registration and Mobility Registration Update with the HPLMN until the HPLMN changes the mode as described above).