5.18.6 Indirect Network Sharing for Disaster Condition

Subject to operator policy and national/regional regulations, the Indirect Network Sharing can be used by UEs of the PLMN with the Disaster Condition to minimize the service interruption.

NOTE 1: In the case of Indirect Network Sharing for Disaster Condition, the UE is not aware of Disaster Condition and the UE behaviour is same as the normal case of Indirect Network Sharing as specified in clause 5.18.3.

NOTE 2: How the hosting PLMN is made aware that another PLMN (as the participating operator network) is a PLMN with Disaster Condition and how the hosting PLMN is made aware of the area where the Disaster Condition applies is out of scope of 3GPP.

When the Disaster Condition arises, the AMF of the hosting operator's network receives the NAS Registration Request message sent by the UE of the participating operator. The AMF identifies that the UE is registering to the network via the Indirect Network Sharing for Disaster Condition by checking that the UE is from a participating operator that can use Indirect Network Sharing for Disaster Condition and that the UE is registering to the network for the Indirect Network Sharing and the UE is in the area of Disaster Condition. If the above conditions are satisfied, comparing to the normal Indirect Network Sharing case, the AMF also provides the Disaster Roaming service indication to AUSF and UDM during the registration procedure. In addition, the AMF also provides this indication to V-SMF during the PDU session related procedure and the V-SMF provides it to the H-SMF. The NFs of the participating operator network (e.g. UDM and SMF) are able to identify which UE(s) are using the Indirect Network Sharing for Disaster Condition based on the Disaster Roaming service indication and the PLMN ID of the hosting operator.

NOTE 3: The Disaster Roaming service indication is specified in clause 5.40.4.

NOTE 4: Per-PLMN unified access control can be used to reduce load in the hosting operator's network and allow the access priority for the specific UEs during the Disaster Condition.

In the case that more than one hosting operators can provide the Indirect Network Sharing for Disaster Condition for the participating operator in the disaster area, in order to reduce the signalling load, the different hosting operators shall ensure their RANs broadcast different PLMN IDs all representing the participating operator toward the UEs of the participating operator.

NOTE 5: In the above case, even if inter-AMFs interface between the different hosting operators can be established, it is recommended that the different hosting operators enable their RANs to broadcast different PLMN IDs representing the participating operator toward the UEs of the participating operator.

NOTE 6: In the above case, how to achieve to broadcast different PLMN IDs all representing the participating operator is up to national/regional regulations and operator policy. For instance, if the participating PLMN is using a two digit MNC, e.g. MNC=XY, then the RANs of the hosting operators might be able to broadcast PLMN IDs using 3 digit MNCs, e.g. MNCs XY1 and XY2 for the UEs of the participating operator. Before the Disaster Condition arises, the PLMN IDs with MNCs XY1 and XY2 can be configured as the equivalent PLMN ID to the participating PLMN ID with MNC XY by participating operator (i.e. HPLMN).

When the Disaster Condition is no longer applicable, the RAN of the hosting operator stops broadcasting the PLMN ID representing the participating operator, then UEs of the participating operator in RRC_IDLE and RRC_INACTIVE state perform PLMN selection as described in TS 23.122 [17] and TS 24.501 [47] and return to the PLMN previously with Disaster Condition. For UEs of the participating operator in RRC_CONNECTED state, the hosting operator's network or the participating operator's network may (possibly after a delay to allow communications to finish) perform the Network-initiated Deregistration (as specified in the clause 4.2.2.3.3 of TS 23.502 [3]) or the hosting operator's network may perform the AN release procedure (as specified in clause 4.2.6 of TS 23.502 [3]) to move the UEs to RRC_IDLE mode. The hosting operator shall organize the return of the UEs of the participating operator in a manner that does not cause overload (e.g. of signalling) in the PLMN that previously had the Disaster Condition.

NOTE 7: In the above case, the existing mechanism of RFSP index (as specified in clause 5.3.4.3) can be used to redirect UEs of the participating operator in RRC_CONNECTED state to home network previously with Disaster Condition.