5.18.5 Network Sharing and Network Slicing

As defined in clause 5.15.1, a Network Slice is defined within a PLMN or SNPN. Network sharing is performed among different PLMNs and/or SNPNs.

In the case of 5G MOCN, each PLMN or SNPN sharing the NG-RAN defines and supports its PLMN- or SNPN- specific set of slices that are supported by the common NG-RAN.

In the case of Indirect Network Sharing, the differences of Network Slicing handling are performed as the follows:

• If, in an Indirect Network Sharing area, the selected PLMN ID representing the participating operator is the HPLMN ID or EHPLMN ID (which is not derived from UE's SUPI) of the UE, from the network side, the network slicing handling shall be performed as defined in clause 5.15.4 and clause 5.15.6. The changes compared to baseline operations are as follows:
• During Registration procedure, the UE includes S-NSSAI(s) of participating operator in the NAS Registration Request messages as described in TS 24.501 [47]. After receiving the Registration Request including the above information, the serving AMF determines the corresponding S-NSSAIs of hosting operator based on the Subscribed S-NSSAIs and slice mapping information from the HPLMN S-NSSAI(s) to the S-NSSAI(s) of the hosting operator locally or the slice mapping information received from the NSSF of hosting operator's network. The serving AMF further checks whether the corresponding S-NSSAIs of hosting operator are supported by the shared RAN. If none of the corresponding S-NSSAIs of hosting operator is supported, the serving AMF rejects the Registration Request. Otherwise the serving AMF continues the Registration procedure and sends to the UE Allowed NSSAI, Partially Allowed NSSAI, Rejected S-NSSAIs and Configured NSSAI only containing the S-NSSAI(s) of participating operator, i.e. HPLMN or EHPLMN S-NSSAI(s) without mapping information. The serving AMF creates a list of S-NSSAIs of the hosting operator corresponding to the S-NSSAIs included in the Allowed NSSAI sent to the UE and includes these S-NSSAIs in the Allowed NSSAI in the signalling to the shared RAN and to the PCF during the AM policy association establishment. The UE Context in the serving AMF shall retain the slice mapping information. The above AMF functionality is applied also during UE Configuration Update procedure.

NOTE 1: In the case of Indirect Network Sharing, to support EHPLMN ID broadcast option, as deployment requirement for the participating operator, the S-NSSAI value supported by the EHPLMN is the same as the HPLMN S-NSSAI value. The serving AMF sets the value(s) of the HPLMN S-NSSAI(s) to the value(s) of the EHPLMN S-NSSAI(s) when it determines the value(s) of S-NSSAI(s) of the hosting operator.

• During PDU Session Establishment procedure, the UE includes the S-NSSAI(s) of participating operator in the PDU Session Establishment Request as described in TS 24.501 [47]. After receiving the S-NSSAI of participating operator from UE, the serving AMF uses the slice mapping information stored in the UE Context to determine the S-NSSAI of hosting operator (i.e. VPLMN S-NSSAI) to be used as "the S-NSSAI belonging to the Allowed NSSAI" as defined in clause 5.15.6. The serving AMF sends the serving PLMN ID (i.e. the selected PLMN ID representing the participating operator), VPLMN S-NSSAI (i.e. the corresponding S-NSSAI of the hosting operator) and HPLMN S-NSSAI to the V-SMF. The V-SMF can identify the Indirect Network Sharing case based on the serving PLMN ID and then it sends the HPLMN S-NSSAI in the PDU Session Establishment Accept message to the UE and uses the VPLMN S-NSSAI for the user plane handling (NG-RAN, V-UPF) in hosting operator's network.

NOTE 2: If NSSF is involved in the above cases, the AMF will send HPLMN S-NSSAI(s) to the NSSF to retrieve the slice mapping information from the HPLMN S-NSSAI(s) to the VPLMN S-NSSAI(s).

NOTE 3: In the case of Indirect Network Sharing, HPLMN/EHPLMN S-NSSAI is corresponding to S-NSSAI of participating operator and VPLMN S-NSSAI is corresponding to S-NSSAI of hosting operator.

NOTE 4: In the case of Indirect Network Sharing, the shared RAN only needs to support the S-NSSAI of hosting operator and select the serving AMF as described in clause 5.15.5.2.1. Then, the shared RAN does not need to be provisioned with the slice mapping information. The serving AMF and the V-SMF in the hosting operator network can be configured to know whether the serving PLMN ID (i.e. the selected PLMN ID) is HPLMN ID/EHPLMN ID or not. The serving AMF and V-SMF with the above functionality will be selected in this case.

NOTE 5: At mobility between the AMF of the participating operator network and the AMF of the hosting operator network, the transferred UE Context information only includes S-NSSAIs of participating operator without S-NSSAIs of hosting operator.

• For other cases, i.e. the selected PLMN ID representing the participating operator is different from HPLMN ID and EHPLMN IDs of UE, the network slicing handling including UE and network shall comply with the roaming case as defined in clause 5.15.6. The applied S-NSSAI values for the PLMN ID selected by UE (i.e. the broadcast PLMN ID) are the S-NSSAI values of hosting operator.

NOTE 6: Which broadcast option to be used and whether to broadcast one or more PLMN ID(s) for each participating operator is determined based on the agreement between the hosting operator and the participating operator.