4.6.2.1 General

Upon registration to a PLMN or SNPN (except for the registration procedure for periodic registration update, the initial registration for onboarding services in SNPN, and the registration procedure for mobility registration update when registered for onboarding services in SNPN), the UE shall send to the AMF the requested NSSAI which includes one or more S-NSSAIs of the allowed NSSAI for the PLMN or SNPN or the configured NSSAI for the PLMN or SNPN and corresponds to the network slice(s) to which the UE intends to register with, if:

• the UE has a configured NSSAI for the current PLMN or SNPN;
• the UE has an allowed NSSAI for the current PLMN or SNPN; or
• the UE has neither allowed NSSAI for the current PLMN or SNPN nor configured NSSAI for the current PLMN or SNPN and has a default configured NSSAI. In this case, the UE indicates to the AMF that the requested NSSAI is created from the default configured NSSAI.

If the PLMN code of the current PLMN is not the PLMN code derived from the IMSI and the mapped S-NSSAI(s) associated to the allowed NSSAI or the configured NSSAI are missing, the UE shall locally set the mapped S-NSSAI to the same value as the received S-NSSAI. Additionally, if the UE receives a Rejected NSSAI IE or an Extended rejected NSSAI IE without associated mapped S-NSSAI(s), and the rejected NSSAI is different from the rejected NSSAI for the failed or revoked NSSAA, the UE shall locally set the mapped S-NSSAI(s) to the same value as the received S-NSSAI.

NOTE 1: The above can occur a) when the UE is roaming or is in an EHPLMN and the AMF is compliant with earlier versions of the specification and does not provide a mapped S-NSSAI for one or more S-NSSAIs in, e.g. the allowed NSSAI or configured NSSAI to the UE; or b) when the UE is in an EHPLMN whose PLMN code is not the PLMN code derived from the IMSI and in which the AMF does not provide mapped S-NSSAIs as specified in clause 4.6.1.

Other than S-NSSAIs contained in the NSSAIs described above, the requested NSSAI can be formed based on the S-NSSAI(s) available in the UE (see clause 5.5.1.3.2 for further details). If the UE received mapped S-NSSAI(s) from the network, the UE shall also provide the mapped S-NSSAI(s) for the requested NSSAI.

NOTE 2: Void.

If the UE did not receive a mapped S-NSSAI for one or more S-NSSAIs in the allowed NSSAI or configured NSSAI, the UE shall use the S-NSSAI as received from the serving network (i.e. without the locally set mapped S-NSSAI) in any NAS message.

The AMF verifies if the requested NSSAI is permitted based on the subscribed S-NSSAIs in the UE subscription and the mapped S-NSSAI(s), if provided by the UE, and if so then the AMF shall provide the UE with the allowed NSSAI for the PLMN or SNPN, and shall also provide the UE with the mapped S-NSSAI(s) for the allowed NSSAI for the PLMN or SNPN as specified in clause 4.6.1. Additionally, if the AMF allows one or more subscribed S-NSSAIs for the UE, the AMF may include the allowed subscribed S-NSSAI(s) in the allowed NSSAI in the REGISTRATION ACCEPT message. The AMF shall ensure that there are not two or more S-NSSAIs of the allowed NSSAI which are mapped to the same S-NSSAI of the HPLMN or the subscribed SNPN. If:

• all the S-NSSAIs included in the requested NSSAI are rejected, or the requested NSSAI was not included by the UE;
• all default S-NSSAIs are not allowed; and
• the UE is neither registering nor registered for onboarding services in SNPN and the UE is neither registering nor registered for emergency services;

then the AMF may reject the registration request (see clauses 5.5.1.2.5 and 5.5.1.3.5 for further details).

In a network where mapped S-NSSAIs are required as specified in clause 4.6.1, if the mapped S-NSSAI(s) associated to requested NSSAI are missing, the AMF shall locally set the mapped S-NSSAI to the same value as the received S-NSSAI.

NOTE 3: E.g. in roaming scenarios, when the UE is compliant with earlier versions of the specification, and in scenarios where the serving network does not provide a mapped S-NSSAI for one or more S-NSSAIs in the allowed NSSAI or configured NSSAI, the UE can omit a mapped S-NSSAI for one or more S-NSSAIs in requested NSSAI.

The set of network slice(s) for a UE can be changed at any time while the UE is registered to a PLMN or SNPN, and the change may be initiated by the network or the UE. In this case, the allowed NSSAI and associated registration area may be changed during the registration procedure or the generic UE configuration update procedure. The configured NSSAI and the rejected NSSAI may be changed during the registration procedure or the generic UE configuration update procedure. The default configured NSSAI may be changed by sending a UE parameters update transparent container to the UE during the NAS transport procedure. The pending NSSAI may be changed during the registration procedure. In addition, using the generic UE configuration update procedure, the network may trigger the registration procedure in order to update the allowed NSSAI.

The UE in NB-N1 mode does not include the requested NSSAI during the registration procedure if the 5GS registration type IE indicates "mobility registration updating", procedure is not initiated to change the slice(s) that the UE is currently registered to, and the UE is still in the current registration area.

The AMF does not include the allowed NSSAI during a registration procedure with the 5GS registration type IE indicating "mobility registration updating" for the UE in NB-N1 mode, except if the allowed NSSAI has changed for the UE.

The UE does not include the requested NSSAI during the registration procedure if the 5GS registration type IE indicates "SNPN onboarding registration" or the UE is registered for onboarding services in SNPN. The AMF does not include the allowed NSSAI during a registration procedure with the 5GS registration type IE indicating "SNPN onboarding registration" or during a registration procedure when the UE is registered for onboarding services in SNPN.

The UE considers the last received allowed NSSAI as valid until the UE receives a new allowed NSSAI.