4.29 Support of indirect network sharing

A 5GS can support indirect network sharing between a hosting operator and participating operators as specified in 3GPP TS 23.501 [8]. The AMF may support indirect network sharing.

NOTE 1: In this version of the specification, the support of indirect network sharing has no UE impact.

NOTE 2: In indirect network sharing, the AMF of hosting operator acts towards to the UE as the AMF of the selected PLMN or the RPLMN.

NOTE 3: In order to support indirect network sharing deployment, when a UE of participating operator registers in the HPLMN, the HPLMN can include a PLMN ID representing the participating operator in the list of equivalent PLMNs.

NOTE 4: In indirect network sharing, if the UE is not allowed to access the selected PLMN which represents the participating operator, the AMF of hosting operator can reject the registration request using an existing cause value.

NOTE 5: In indirect network sharing, if the UE has registered to HPLMN 5GCN over 3GPP access and is registering to the HPLMN 5GCN over non-3GPP access, and the network determines that the UE cannot be registered to the HPLMN 5GCN over 3GPP access and non-3GPP access simultaneously, then the AMF of HPLMN can reject the registration request over non-3GPP access using 5GMM cause value #111 "protocol error, unspecified".

In indirect network sharing, during the generic UE configuration update procedure (see clause 5.4.4), the registration procedure for initial registration (see clause 5.5.1.2) or the registration procedure for mobility and periodic registration update (see clause 5.5.1.3), if the selected PLMN ID is the PLMN ID of the HPLMN or an EHPLMN of the UE, the AMF of hosting operator shall determine the available S-NSSAI(s) of hosting operator corresponding to the S-NSSAI(s) of participating operator if provided by the UE in the Requested NSSAI IE of the REGISTRATION REQUEST message. If the selected PLMN ID is the PLMN ID of an EHPLMN of the UE whose PLMN code is not derived from the IMSI:

• when the AMF determines the value(s) of the S-NSSAI(s) of hosting operator for network internal purposes, the AMF shall set value(s) of the mapped S-NSSAI(s) to the value(s) of the S-NSSAI(s) of the serving EHPLMN if provided by the UE in the Requested NSSAI IE of the REGISTRATION REQUEST message; and
• when the AMF determines the value(s) of the S-NSSAI(s) of the serving EHPLMN to be sent to the UE, the AMF shall set value(s) of the S-NSSAI(s) of the serving EHPLMN to value(s) of the mapped S-NSSAI(s) and the AMF shall only send the S-NSSAI(s) of the serving EHPLMN, i.e. S-NSSAI(s) of participating operator without mapped S-NSSAI(s) to the UE.

NOTE 5A: If the selected PLMN ID is the PLMN ID of an EHPLMN of the UE whose PLMN code is not derived from the IMSI and the UE provided S-NSSAI(s) of participating operator in the Requested mapped NSSAI IE of the REGISTRATION REQUEST message, the AMF of hosting operator determines the available S-NSSAI(s) of hosting operator corresponding to the S-NSSAI(s) of participating operator provided by the UE.

NOTE 6: If the selected PLMN ID is the PLMN ID of the HPLMN or the EHPLMN whose PLMN code is derived from the IMSI of the UE, the AMF sends only the HPLMN S-NSSAI(s), i.e. S-NSSAI(s) of participating operator, to the UE.

NOTE 6A: For a deployment requirement regarding network slicing for EHPLMNs in indirect network sharing see 3GPP TS 23.501 [8], clause 5.18.5.

In indirect network sharing, during the UE-requested PDU session establishment procedure, if the serving PLMN ID is the PLMN ID of the HPLMN or an EHPLMN of the UE, the AMF of hosting operator performs SMF selection using the determined S-NSSAI of hosting operator and the corresponding S-NSSAI of participating operator. If the serving PLMN ID is the PLMN ID of an EHPLMN of the UE whose PLMN code is not derived from the IMSI, the SMF of hosting operator shall only use the corresponding S-NSSAI of participating operator without mapped S-NSSAI towards the UE.

NOTE 7: If the serving PLMN ID is the PLMN ID of the HPLMN or the EHPLMN whose PLMN code is derived from the IMSI of the UE, the SMF of hosting operator sends only the HPLMN S-NSSAI, i.e. S-NSSAI of participating operator, to the UE.

NOTE 8: If the selected PLMN ID is the PLMN ID of the HPLMN or an EHPLMN of the UE, the AMF of hosting operator uses the determined S-NSSAI(s) of hosting operator and the corresponding S-NSSAI(s) of participating operator towards other core-network functions (e.g. SMF).

NOTE 9: If the selected PLMN ID is different from the PLMN ID of the HPLMN and EHPLMN(s) of the UE, the AMF and the SMF of hosting operator can use S-NSSAI(s) of hosting operator as S-NSSAI(s) of serving PLMN, and corresponding mapped S-NSSAI(s).