5.40 Support of Disaster Roaming with Minimization of Service Interruption

23.5013GPPRelease 18System architecture for the 5G System (5GS)TS

5.40.1 General

Subject to operator policy and national/regional regulations, 5GS provides Disaster Roaming service (e.g. voice call and data service) for the UEs from PLMN(s) with Disaster Condition. The UE shall attempt Disaster Roaming only if:

– there is no available PLMN which is allowable (see TS 23.122 [17]);

– the UE is not in RM-REGISTERED and CM-CONNECTED state over non-3GPP access connected to 5GCN;

– the UE cannot get service over non-3GPP access through ePDG;

– the UE supports Disaster Roaming service;

– the UE has been configured by the HPLMN with an indication of whether Disaster roaming is enabled in the UE set to "disaster roaming is enabled in the UE" as specified in clause 5.40.2; and

– a PLMN without Disaster Condition is able to accept Disaster Inbound Roamers from the PLMN with Disaster Condition.

In this Release of the specification, the Disaster Condition only applies to NG-RAN nodes, which means the rest of the network functions except one or more NG-RAN nodes of the PLMN with Disaster Condition can be assumed to be operational.

5.40.2 UE configuration and provisioning for Disaster Roaming

A UE supporting Disaster Roaming is configured with the following information:

– Optionally, indication of whether disaster roaming is enabled in the UE;

– Optionally, indication of ‘applicability of "lists of PLMN(s) to be used in disaster condition" provided by a VPLMN’;

– Optionally, list of PLMN(s) to be used in Disaster Condition.

The Activation of Disaster Roaming is performed by the HPLMN by setting the indication of whether Disaster roaming is enabled in the UE to "disaster roaming is enabled in the UE" using the UE Parameters Update Procedure as defined in TS 23.502 [3]. The UE shall only perform disaster roaming if the HPLMN has configured the UE with the indication of whether disaster roaming is enabled in the UE and set the indication to "disaster roaming is enabled in the UE". The UE, registered for Disaster Roaming service, shall deregister from the PLMN providing Disaster Roaming service if the received indication of whether disaster roaming is enabled in the UE is set to "disaster roaming is disabled in the UE".

The optional ‘list of PLMN(s) to be used in Disaster Condition’ may be pre-configured in USIM or provided by the HPLMN during and after a successful registration procedure over 3GPP access or non-3GPP access via Registration Request procedure or UE Configuration Update procedure as defined in TS 23.502 [3]. The ‘list of PLMN(s) to be used in Disaster Condition’ may be configured over non-3GPP access before disaster condition has occurred.

While roaming (i.e. not in HPLMN), the Registered PLMN may provide the ‘list of PLMN(s) to be used in Disaster Condition’ during and after a successful registration procedure to the UE via Registration Request procedure or UE Configuration Update procedure as specified in TS 23.502 [3]. This list shall not alter any list provided by the HPLMN and shall only be used if the UE is configured by the HPLMN using the UE Parameters Update Procedure as defined in TS 23.502 [3] with the indication of ‘applicability of "lists of PLMN(s) to be used in disaster condition" provided by a VPLMN’ set to "True".

The details of the UE behaviour regarding the usage of this list are described in TS 23.122 [17] and TS 24.501 [47]. If the UE is not configured with ‘list of PLMN(s) to be used in Disaster Condition’, the UE follows the procedure described in TS 23.122 [17] to select PLMN to be used in Disaster Condition.

The HPLMN may use UE Parameters Update Procedure as defined in TS 23.502 [3] to update the Disaster Roaming information configuration in UE, if the UDM has received MINT support indication as indicated in 5GMM capability from the AMF. The UE indicates the support of MINT in 5GMM capability as specified in clause 5.4.4a, during registration procedure as defined in TS 23.502 [3].

5.40.3 Disaster Condition Notification and Determination

The NG-RAN in the PLMN that provides Disaster Roaming service, broadcasts an indication of accessibility for Disaster Roaming service, and optionally, a ‘list of one or more PLMN(s) with Disaster Condition for which Disaster Roaming service is offered by the available PLMN’ in the impacted area as described in TS 38.304 [50] and TS 38.331 [28].

A UE determines the Disaster Condition based on the information broadcasted from the NG-RAN providing Disaster Roaming service, and performs the network selection and the access control for the Disaster Roaming as described in TS 23.122 [17] and TS 24.501 [47].

NOTE 1: How a PLMN is notified that another PLMN is a PLMN with Disaster Condition and how a PLMN is notified of the area where the associated Disaster Condition applies is managed by the government agencies or the authorities, and is out of scope of 3GPP.

NOTE 2: The broadcast for Disaster Roaming service from the NG-RAN occurs only during the Disaster Condition.

5.40.4 Registration for Disaster Roaming service

For a UE to receive Disaster Roaming service from a PLMN providing Disaster Roaming service, the UE sends a NAS Registration Request message with Registration Type value "Disaster Roaming Initial Registration" or "Disaster Roaming Mobility Registration Update":

– When the AMF in the PLMN providing Disaster Roaming service receives a NAS Registration Request with Registration Type set to "Disaster Roaming Initial Registration" or "Disaster Roaming Mobility Registration Update";

– the AMF controls if the UE is allowed to access Disaster Roaming service in the area with Disaster Condition as specified in clause 4.2.2.2.2 of TS 23.502 [3];

– the AMF may provide the Disaster Roaming service indication to AUSF and UDM as specified in clause 4.2.2.2.2 of TS 23.502 [3] and TS 33.501 [29]. The AMF may provide the Disaster Roaming service indication to SMF as specified in clause 4.3.2 of TS 23.502 [3].

NOTE 1: The AUSF and the UDM are configured with Disaster Condition via OAM based on operator policy and the request by the government agencies. Based on this local configuration and/or the Disaster Roaming service indication, the AUSF can execute authentication of the UE, and the UDM can provides the subscription data for a Disaster Roaming service to the AMF and/or the SMF.

To support the Disaster Roaming service, the PLMN providing Disaster Roaming service is configured to support communication with the network entities in the HPLMN of the UE, i.e. configurations related to roaming interfaces for communication between serving PLMN and HPLMN shall be deployed in the affected entities. This communication between the PLMNs need only be enabled during the Disaster Condition.

The Disaster Roaming service is limited to the impacted geographic area with Disaster Condition. The NG-RAN nodes and AMF in the PLMN providing Disaster Roaming service are configured with the area information, i.e. a list of TAIs which can be formulated by the PLMN providing the Disaster Roaming service based on the geographic area with Disaster Condition in the other PLMN(s).

The AMF in the PLMN providing Disaster Roaming service provides the mobility restriction list to the NG-RAN as specified in clause 5.3.4.1.1 considering the area with Disaster Condition, and also indicating that EPC is not an allowed core network.

NOTE 2: From the perspective of emergency services, a UE is following procedures as described in clause 4.24 of TS 24.501 [47] when registered for Disaster Roaming service.

5.40.5 Handling when a Disaster Condition is no longer applicable

When a UE detects a Disaster Condition is no longer applicable, the UE performs PLMN selection as described in TS 23.122 [17] and TS 24.501 [47] and may return to the PLMN previously with Disaster Condition.

A PLMN providing Disaster Roaming:

– May trigger the Disaster Inbound Roaming UEs to return to the PLMN previously with Disaster Condition when the Disaster Inbound Roamers attempt to transit to 5GMM-CONNECTED mode.

– May trigger the Disaster Inbound Roaming UEs to return to the PLMN previously with Disaster Condition by triggering Deregistration procedure.

– May trigger the Disaster Inbound Roaming UEs to return to the PLMN previously with Disaster Condition by rejecting Registration Request message.

– May trigger the Disaster Inbound Roaming UEs to return to the PLMN previously with Disaster Condition by rejecting Service Request message.

– Shall organise the return of the Disaster Roaming UEs in a manner that does not cause overload (e.g. of signalling) in the PLMN that previously had the Disaster Condition.

– Stop broadcasting of providing Disaster Roaming service as specified in clause 5.40.3.

– May determine that the disaster condition has ended and the UE which is registered for disaster roaming services has an emergency PDU session, the AMF initiates the UE configuration update procedure to indicate that the UE is registered for emergency services as described in TS 24.501 [47].

– May determine that the disaster condition has ended and inform the UE by initiating the UE configuration update procedure indicating re-registration from UE is required as specified in clause 5.4.4 of TS 24.501 [47] if the UE is in CM-CONNECTED mode.

NOTE: Whether and how long the PLMN waits before paging the Disaster Inbound Roamers upon being notified that a Disaster Condition no longer applies is up to operator’s policy.

The HPLMN i.e. the UDM may trigger the Disaster Inbound Roaming UEs to return to the PLMN previously with Disaster Condition by triggering Deregistration procedure.

5.40.6 Prevention of signalling overload related to Disaster Condition and Disaster Roaming service

The load control, congestion and overload control mechanism specified in clause 5.19 and access control and barring specified in clause 5.2.5 can be used to mitigate the load caused by UE requesting the Disaster Roaming service in the PLMN providing Disaster Roaming service and returning of UE to allowable PLMN when Disaster Condition is no longer applicable.

To prevent signalling overload in PLMN providing Disaster Roaming, the HPLMN or registered PLMN:

– may provide the UE in a prioritized manner with the list of PLMNs described in clause 5.40.2 for Disaster Roaming;

– may provide disaster roaming wait range information to control when the UE can initiate the registration for Disaster Roaming service upon arriving in the PLMN providing Disaster Roaming service as specified in TS 23.122 [17] and TS 24.501 [47]; and

– applies Access Identity 3 for Disaster Roaming service request as specified in TS 24.501 [47].

NOTE: The mechanisms available at the AMF and the SMF for mitigation of overload and congestion are used for 5GSM congestion mitigation during the Disaster Roaming.

To prevent signalling overload by returning UEs in PLMN previously with Disaster Condition which is no long applicable, the HPLMN or registered PLMN:

– may provide disaster return wait range information to control when the UE can initiate the registration upon returning to the PLMN previously with Disaster Condition as specified in TS 23.122 [17] and TS 24.501 [47].