4.24 Minimization of service interruption

24.5013GPPNon-Access-Stratum (NAS) protocol for 5G System (5GS)Release 18Stage 3TS

The UE and the network may support Minimization of service interruption (MINT). MINT aims to enable a UE to obtain service from a PLMN offering disaster roaming services when a disaster condition applies to the UE’s determined PLMN with disaster condition.

If the UE supports MINT, the indication of whether disaster roaming is enabled in the UE, the indication of ‘applicability of "lists of PLMN(s) to be used in disaster condition" provided by a VPLMN’, the one or more "list of PLMN(s) to be used in disaster condition", disaster roaming wait range and disaster return wait range provisioned by the network, if available, are stored in the non-volatile memory in the ME as specified in annex C and are kept when the UE enters 5GMM-DEREGISTERED state. Annex C specifies condition under which the indication of whether disaster roaming is enabled in the UE, the indication of ‘applicability of "lists of PLMN(s) to be used in disaster condition" provided by a VPLMN’, the one or more "lists of PLMN(s) to be used in disaster condition", disaster roaming wait range and disaster return wait range stored in the ME are deleted.

Upon selecting a PLMN for disaster roaming as specified in 3GPP TS 23.122 [6]:

a) if the UE does not have a stored disaster roaming wait range, the UE shall perform a registration procedure for disaster roaming services on the selected PLMN as described in clause 5.5.1; and

b) if the UE has a stored disaster roaming wait range, the UE shall generate a random number within the disaster roaming wait range and start a timer with the generated random number. While the timer is running, the UE shall not initiate registration on the selected PLMN except if the UE needs to request an emergency PDU session, in which case the UE shall initiate the registration procedure, set the 5GS registration type IE to "emergency registration" in the REGISTRATION REQUEST message and keep the timer running. Upon expiration of the timer, if the UE does not have an emergency PDU session, the UE shall perform a registration procedure for disaster roaming services as described in clause 5.5.1 if still camped on the selected PLMN. If the UE has an emergency PDU session when the timer expires, the registration procedure for disaster roaming services as described in clause 5.5.1 shall be performed after the release of the emergency PDU session, if the UE is still camped on the selected PLMN.

The timer started with a generated random number within the disaster roaming wait range is stopped and the UE shall perform a PLMN selection as described in 3GPP TS 23.122 [5], if:

a) the UE has successfully registered over non-3GPP access on another PLMN;

b) the UE has successfully registered with an allowable PLMN; or

c) an NG-RAN cell selected for camping of the selected PLMN broadcasts neither the disaster related indication nor a "list of one or more PLMN(s) with disaster condition for which disaster roaming services is offered by the available PLMN" including the determined PLMN with Disaster Condition (see 3GPP TS 23.122 [5]).

Upon determining that a disaster condition has ended and that the UE shall perform PLMN selection as specified in 3GPP TS 23.122 [6]:

a) if the UE does not have a stored disaster return wait range, the UE shall perform a registration procedure on the selected PLMN; and

b) if the UE has a stored disaster return wait range, the UE shall generate a random number within the disaster return wait range and start a timer with the generated random number value. While the timer is running, the UE shall not initiate registration on the selected PLMN except if the UE needs to request an emergency PDU session, in which case the UE shall initiate the registration procedure, set the 5GS registration type IE to "emergency registration" in the REGISTRATION REQUEST message and keep the timer running. Upon expiration of the timer, if the UE does not have an emergency PDU session, the UE shall perform a registration procedure if still camped on the selected PLMN. If the UE has an emergency PDU session when the timer expires, the registration procedure as described in clause 5.5.1 shall be performed after the release of the emergency PDU session, if the UE is still camped on the selected PLMN.

When the AMF assigns a registration area to the UE registered for disaster roaming services, the AMF shall only include TAIs covering the area with the disaster condition.

When the AMF determines that the disaster condition has ended and the UE which is registered for disaster roaming services has an emergency PDU session, the AMF shall initiate the generic UE configuration update procedure to indicate that the UE is registered for emergency services as described in subclause 5.4.4.2.

Interworking with EPS is not supported for UEs that are registered for disaster roaming services. When registering for disaster roaming services, the UE indicates to the network that S1 mode is not supported as described in subclause 5.5.1.2.2. While registered for disaster roaming services and upon a need to establish an emergency PDU session or perform emergency services fallback, the UE initiates the registration procedure for mobility and periodic registration update and indicates that S1 mode is supported as described in subclause 5.5.1.3.2.

If the UE is registered for disaster roaming services and the registered PLMN is removed from forbidden PLMN lists due to reasons specified in 3GPP TS 23.122 [5] subclause 4.4.6 or in 3GPP TS 23.122 [5] Annex C, then UE shall initiate the de-registration procedure and perform PLMN selection as specified in 3GPP TS 23.122 [5].