4.24 Minimization of service interruption

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 determined PLMN with disaster condition. The UE can receive disaster roaming services from a forbidden PLMN, from a TAI of allowable PLMN which is the list of "5GS forbidden tracking areas for roaming" or the list of "5GS forbidden tracking areas for regional provision of service", or from restricted access technology of allowable PLMN in list of "PLMNs with associated access technology restrictions", as as specified in 3GPP TS 23.122 [5]. The UE and the network may support MINT in allowable PLMN.

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.

If the UE supports MINT-EPS, the indication of whether disaster roaming in EPS is enabled in the UE, 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.

Upon selecting a PLMN for disaster roaming as specified in 3GPP TS 23.122 [5]:

• if:
• the UE does not have a stored disaster roaming wait range; or
• the UE is configured with access identity 1, 2, 12, 13, or 14 and the configured access identity is valid in the selected PLMN,

the UE shall perform a registration procedure for disaster roaming services on the selected PLMN as described in clause 5.5.1; and

• if the UE has a stored disaster roaming wait range; and
• the UE is configured with access identity 1, 2, 12, 13, or 14 and the configured access identity is invalid in the selected PLMN; or
• the UE is not configured with access identity 1, 2, 12, 13, or, 14,

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.

If the UE is switched off when the timer for disaster roaming wait range is running, the UE shall behave as follows when the UE is switched on, the USIM in the UE remains the same and the UE selects the PLMN for disaster roaming:

• let t1 be the time remaining for the timer for disaster roaming wait range timeout at switch off and let t be the time elapsed between switch off and switch on. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1.

Upon expiry of the timer for disaster roaming wait range, the UE shall not start a timer with the disaster roaming wait range value again until disaster condition has ended.

Upon determining that a disaster condition has ended as specified in 3GPP TS 23.122 [5]:

• the UE shall stop the timer started with a generated random number within the disaster roaming wait range, if running;
• the UE shall perform PLMN selection as specified in 3GPP TS 23.122 [5], except if the UE already selected an allowable PLMN as specified in 3GPP TS 23.122 [5]; and
• if the UE selects the UE determined PLMN with disaster condition and has a stored disaster return wait range, which is provided by the PLMN providing disaster roaming services or by the selected PLMN and:
• the UE is configured with access identity 1, 2, 11, 12, 13, 14, or 15 and the access identity is invalid in the selected PLMN; or
• the UE is not configured with access identity 1, 2, 11, 12, 13, 14, or 15,

the UE shall generate a random number within the disaster return wait range, start a timer with the generated random number value and enter 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION state or 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE state, if registered. 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.

Otherwise, the UE shall perform registration procedure in the selected PLMN.

If the UE is switched off when the timer for disaster return wait range is running, the UE shall behave as follows when the UE is switched on, the USIM in the UE remains the same and the UE selects the UE determined PLMN with disaster condition:

• let t1 be the time remaining for the timer for disaster return wait range timeout at switch off and let t be the time elapsed between switch off and switch on. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1.

Upon expiry of the timer for disaster return wait range, the UE shall not start a timer with the disaster return wait range value again until the UE selects a PLMN for disaster roaming services.

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. If the AMF is of an allowable PLMN of the UE, the AMF shall only include TAIs covering the area with the disaster condition, which are either forbidden tracking areas, are of tracking areas of restricted NG-RAN access technology or are of tracking areas of restricted satellite NG-RAN access technology.

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 clause 5.4.4.2.

Interworking with EPS is not supported for UEs that support MINT and are registered for disaster roaming services in 5GS. When registering for disaster roaming services, the UE indicates to the network that S1 mode is not supported as described in clause 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 clause 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 clause 4.4.6 or Annex C in 3GPP TS 23.122 [5], then UE shall initiate the de-registration procedure and perform PLMN selection as specified in 3GPP TS 23.122 [5].