Content for  TS 23.122  Word version:  18.6.0

The UE to the AMF: The UE initiates initial registration, emergency registration or registration procedure for mobility and periodic registration update (see TS 24.501) to the AMF by sending REGISTRATION REQUEST message with the 5GS registration type IE indicating "initial registration", "emergency registration" or "mobility registration updating";

Upon receiving the REGISTRATION REQUEST message, the AMF executes the registration procedure as defined in clause 4.2.2.2.2 of TS 23.502. As part of the registration procedure:

1. the AMF provides the registration type to the UDM using Nudm_UECM_Registration. As a consequence, in case of the 5GS registration type message indicates "initial registration" or "emergency registration" the UDM shall delete the stored "ME support of SOR-CMCI" indicator, if any, and the stored "ME support of SOR-SNPN-SI-LS" indicator, if any, in UDR using Nudr_DM_Update service operation (see TS 23.502).

In addition:

1. if the AMF does not have subscription data for the UE, the AMF invokes Nudm_SDM_Get service operation to the UDM to get amongst other information the Access and Mobility Subscription data for the UE (see step 14b in clause 4.2.2.2.2 of TS 23.502); or
2. if the AMF already has subscription data for the UE and:
   1. the 5GS registration type IE in the received REGISTRATION REQUEST message indicates "initial registration" and the "SoR Update Indicator for Initial Registration" field in the UE context is set to 'the UDM requests the AMF to retrieve SoR information when the UE performs NAS registration type "initial registration"' as specified in Table 5.2.2.2.2-1 of TS 23.502); or
   2. the 5GS registration type IE in the received REGISTRATION REQUEST message indicates "emergency registration" and the "SoR Update Indicator for Emergency Registration" field in the UE context is set to 'the UDM requests the AMF to retrieve SoR information when the UE performs NAS registration type "emergency registration"' as specified in Table 5.2.2.2.2-1 of TS 23.502);
   then the AMF invokes Nudm_SDM_Get service operation message to the UDM to retrieve the steering of roaming information (see step 14b in clause 4.2.2.2.2 of TS 23.502);
   otherwise the AMF sends a REGISTRATION ACCEPT message without the steering of roaming information to the UE and steps 3a, 3b, 3c, 3d, 4, 5, 6 are skipped;

If the user subscription information indicates to send the steering of roaming information due to initial registration in a non-subscribed SNPN, then the UDM shall store the "ME support of SOR-SNPN-SI" indicator and shall provide the steering of roaming information to the UE when the UE performs initial registration in a non-subscribed SNPN except if the UE supports equivalent SNPNs, it does not support SOR-SNPN-SI and it is in an equivalent SNPN of the subscribed SNPN. Otherwise:

1. If the UE is registering on the subscribed SNPN and the UE has not indicated support for SOR-SNPN-SI in the REGISTRATION REQUEST message, the UDM shall delete the stored "ME support of SOR-SNPN-SI" indicator, if any, and shall not provide the SOR-SNPN-SI to the UE; and
2. If:
   1. the UE is registering on the subscribed SNPN and the UE has indicated support for SOR-SNPN-SI in the REGISTRATION REQUEST message; or
   2. the UE is registering on a non-subscribed SNPN except if the UE supports equivalent SNPNs, it does not support SOR-SNPN-SI and it is in an equivalent SNPN of the subscribed SNPN;

the UDM shall store the "ME support of SOR-SNPN-SI" indicator and may provide the SOR-SNPN-SI to the UE based on the subscribed SNPN or HPLMN policy. If the UDM is to provide the steering of roaming information to the UE when the UE performs the registration in a non-subscribed SNPN and the subscribed SNPN or HPLMN policy for the SOR-AF invocation is absent then steps 3b and 3c are not performed and the UDM obtains the available SOR-SNPN-SI (i.e. all retrieved from the UDR). In addition, if the UDM obtains the SOR-SNPN-SI and

• the "ME support of SOR-CMCI" indicator is stored for the UE, then the UDM shall obtain the SOR-CMCI, if available, otherwise the UDM shall not obtain the SOR-CMCI. If the SOR-CMCI is provided then the UDM may indicate to the UE to store the SOR-CMCI in the ME by providing the "Store the SOR-CMCI in the ME" indicator; and
• the "ME support of SOR-SNPN-SI-LS" indicator is stored for the UE, then the UDM shall obtain the SOR-SNPN-SI-LS, if available, otherwise the UDM shall not obtain the SOR-SNPN-SI-LS.

If the UDM is to provide the steering of roaming information to the UE when the UE performs the registration in a non-subscribed SNPN and the subscribed SNPN or HPLMN policy for the SOR-AF invocation is present, then the UDM obtains the SOR-SNPN-SI, SOR-CMCI, if any, and SOR-SNPN-SI-LS, if any, from the SOR-AF using steps 3b and 3c;

The UDM to the SOR-AF: Nsoraf_SoR_Get request (SNPN identity, SUPI of the UE, access type (see TS 29.571)). The SNPN identity and the access type parameters, indicating where the UE is registering, are stored in the UDM;

The SOR-AF to the UDM: Nsoraf_SoR_Get response (the SOR-SNPN-SI, the SOR-CMCI, if any, the "Store the SOR-CMCI in the ME" indicator, if any, and the SOR-SNPN-SI-LS, if any); Based on the information received in step 3b and any subscribed SNPN or HPLMN specific criteria, the SOR-AF may include the SOR-SNPN-SI, the SOR-CMCI, if any, optionally the "Store the SOR-CMCI in the ME" indicator, if any, and the SOR-SNPN-SI-LS, if any. If the SOR-AF includes the SOR-SNPN-SI and the ME supports:

• the SOR-CMCI, the SOR-AF may provide the SOR-CMCI and optionally the "Store the SOR-CMCI in the ME" indicator, otherwise the SOR-AF shall provide neither the SOR-CMCI nor the "Store the SOR-CMCI in the ME" indicator;and
• the SOR-SNPN-SI-LS, the SOR-AF may provide the SOR-SNPN-SI-LS, otherwise the SOR-AF shall not provide SOR-SNPN-SI-LS.

The UDM forms the steering of roaming information as specified in TS 33.501 from the SOR-SNPN-SI, the SOR-CMCI, if any, the "Store the SOR-CMCI in the ME" indicator, if any, and SOR-SNPN-SI-LS, if any, obtained in step 3a or the SOR-SNPN-SI, the SOR-CMCI, if any, the "Store the SOR-CMCI in the ME" indicator, if any, and SOR-SNPN-SI-LS, if any, obtained in step 3c. If:

• the SOR-SNPN-SI was not obtained in steps 3a or 3c; or
• the SOR-AF has not sent to the UDM an Nsoraf_SoR_Get response (step 3c) within an operator defined time after the UDM sending to the SOR-AF an Nsoraf_SoR_Get request (step 3b);

and the UE is performing initial registration in a non-subscribed SNPN and the user subscription information indicates to send the steering of roaming information due to initial registration in a non-subscribed SNPN, then the UDM forms the steering of roaming information as specified in TS 33.501 from the subscribed SNPN or HPLMN indication that 'no change of the SOR-SNPN-SI stored in the UE is needed and thus no SOR-SNPN-SI is provided';

The UDM to the AMF: The UDM sends a response to the Nudm_SDM_Get service operation to the AMF, which includes the steering of roaming information within the Access and Mobility Subscription data. The Access and Mobility Subscription data type is defined in clause 5.2.3.3.1 of TS 23.502). If the UE is performing initial registration or emergency registration and the UDM supports SOR-CMCI or SOR-SNPN-SI-LS, the subscribed SNPN or HPLMN shall request the UE to acknowledge the successful security check of the received steering of roaming information, by providing the indication as part of the steering of roaming information in the Nudm_SDM_Get response service operation. Otherwise, the subscribed SNPN or HPLMN may request the UE to acknowledge the successful security check of the received steering of roaming information, by providing the indication as part of the steering of roaming information in the Nudm_SDM_Get response service operation;

The AMF to the UDM: As part of the registration procedure, the SNPN also invokes Nudm_SDM_Subscribe service operation to the UDM to subscribe to notification of changes of the subscription data (e.g. received in step 4) including notification of updates of the steering of roaming information included in the Access and Mobility Subscription data (see step 14c in clause 4.2.2.2.2 of TS 23.502);

The AMF to the UE: The AMF shall transparently send the received steering of roaming information to the UE in the REGISTRATION ACCEPT message;

If the steering of roaming information is received and the security check is successful, then:

1. if the UDM has not requested an acknowledgement from the UE, then the UE shall send the REGISTRATION COMPLETE message to the serving AMF without including an SOR transparent container; and
2. if the steering of roaming information contains the SOR-SNPN-SI, the ME shall replace the credentials holder controlled prioritized list of preferred SNPNs for the selected entry of the "list of subscriber data" or the selected PLMN subscription with the received credentials holder controlled prioritized list of preferred SNPNs, if any, and the ME shall replace the credentials holder controlled prioritized list of GINs for the selected entry of the "list of subscriber data" or the selected PLMN subscription with the received credentials holder controlled prioritized list of GINs, if any, and delete the SNPNs identified by the credentials holder controlled prioritized list of preferred SNPNs or the SNPN(s) stored along with GIN(s) identified by the credentials holder controlled prioritized list of GINs from the list of "temporarily forbidden SNPNs" and the list of "permanently forbidden SNPNs", if they are present in these lists. If the SOR information contains the SOR-SNPN-SI-LS, the ME shall replace the "credentials holder controlled prioritized list of preferred SNPNs for access for localized services in SNPN" for the selected entry of the "list of subscriber data" or the selected PLMN subscription with the received "credentials holder controlled prioritized list of preferred SNPNs for access for localized services in SNPN", if any, and the ME shall replace the "credentials holder controlled prioritized list of preferred GINs for access for localized services in SNPN" for the selected entry of the "list of subscriber data" or the selected PLMN subscription with the received "credentials holder controlled prioritized list of preferred GINs for access for localized services in SNPN", if any, and delete the SNPNs identified by the "credentials holder controlled prioritized list of preferred SNPNs for access for localized services in SNPN" or the SNPN(s) stored along with GIN(s) identified by the "credentials holder controlled prioritized list of preferred GINs for access for localized services in SNPN" from the list of "temporarily forbidden SNPNs for access for localized services in SNPN" and the list of "permanently forbidden SNPNs for access for localized services in SNPN", if they are present in these lists. Additionally, the UE may perform SNPN selection. If the UE decides to perform SNPN selection:
   1. if the UE has a list of available and allowable SNPN in the area and based on this list or any other implementation specific means the UE determines that there is a higher priority SNPN than the selected SNPN; or
   2. the UE does not have a list of available and allowable SNPN in the area and is unable to determine whether there is a higher priority SNPN than the selected SNPN using any other implementation specific means;
   and the UE is in automatic network selection mode:
   1. if the UE is configured with the SOR-CMCI or received the SOR-CMCI over N1 NAS signalling, the UE shall apply the actions in clause C.4.2. In this case steps 8 to 11 are skipped;
   2. otherwise, the UE shall:
      1. release the current N1 NAS signalling connection locally and then attempt to obtain service on a higher priority SNPN as specified in clause 4.9.3. In this case, steps 8 to 11 are skipped. The UE shall suspend the transmission of 5GSM messages until the N1 NAS signalling is released. The UE shall not initiate the establishment of a new N1 signalling connection, unless for the purpose of initiating a registration procedure for emergency services or establishing an emergency PDU session, until the attempts to obtain service on a higher priority SNPN are completed. If the UE has an established emergency PDU session (see TS 24.501), the receipt of the steering of roaming information shall not trigger the release of the N1 NAS signalling connection. The UE shall release the current N1 NAS signalling connection locally subsequently after the emergency PDU session is released. If the UE needs to disable the N1 mode capability (see TS 24.501) and there is no emergency service pending, the UE shall first attempt to obtain service on a higher priority SNPN as described in this step, and if no higher priority SNPN can be selected but the last registered SNPN is selected, then the UE shall disable the N1 mode capability; or
      2. not release the current N1 NAS signalling connection locally (e.g. if the UE has established PDU session(s)) and skip steps 8 to 10;

If the UE's ME is configured with an indication that the UE is to receive the steering of roaming information due to initial registration in a non-subscribed SNPN, but neither the SOR-SNPN-SI nor the subscribed SNPN or HPLMN indication that 'no change of the SOR-SNPN-SI stored in the UE is needed and thus no SOR-SNPN-SI is provided' is received in the REGISTRATION ACCEPT message, when the UE performs initial registration in a VPLMN or if the steering of roaming information is received but the security check is not successful, then the UE shall:

1. if the SOR transparent container is included in the REGISTRATION ACCEPT message, send the REGISTRATION COMPLETE message to the serving AMF without including an SOR transparent container;
2. if the current chosen non-subscribed SNPN is not contained in the list of "SNPNs where registration was aborted due to SOR" for the selected entry in the "list of subscriber data" or the selected PLMN subscription, and is not part of the user controlled prioritized list of preferred SNPNs for the selected entry in the "list of subscriber data" or the selected PLMN subscription, and the UE is not in manual mode of operation, release the current N1 NAS signalling connection locally and attempt to obtain service on a higher priority SNPN as specified in clause 4.9.3, with an exception that the current SNPN is considered as lowest priority, and skip steps 9 to 11. The UE shall suspend the transmission of 5GSM messages until the N1 NAS signalling is released. If the UE has an established emergency PDU session (see TS 24.501), the UE shall release the current N1 NAS signalling connection locally after the release of the emergency PDU session. If the UE needs to disable the N1 mode capability (see TS 24.501) and there is no emergency service pending, the UE shall first attempt to obtain service on a higher priority SNPN as described in this step, and if no higher priority SNPN can be selected but the last registered SNPN is selected, then the UE shall disable the N1 mode capability; and
3. if the current chosen non-subscribed SNPN is not contained in the list of "SNPNs where registration was aborted due to SOR" for the selected entry in the "list of subscriber data" or the selected PLMN subscription, store the SNPN identity in the list of "SNPNs where registration was aborted due to SOR" for the selected entry in the "list of subscriber data" or the selected PLMN subscription;

The UE to the AMF: If the UDM has requested an acknowledgement from the UE and the UE verified that the steering of roaming information has been provided by the subscribed SNPN or HPLMN in step 7, then: a. b. b1. c.

The AMF to the UDM: If an SOR transparent container is received in the REGISTRATION COMPLETE message, the AMF uses the Nudm_SDM_Info service operation to provide the received SOR transparent container to the UDM. If the subscribed SNPN or HPLMN decided that the UE is to acknowledge the successful security check of the received steering of roaming information in step 4, the UDM verifies that the acknowledgement is provided by the UE as specified in TS 33.501. If:

• the "ME support of SOR-CMCI" indicator in the header of the SOR transparent container is set to "supported", then the UDM shall store the "ME support of SOR-CMCI" indicator, otherwise the UDM shall delete the stored "ME support of SOR-CMCI" indicator, if any; and
• the "ME support of SOR-SNPN-SI-LS" indicator in the header of the SOR transparent container is set to "supported", then the UDM shall store the "ME support of SOR-SNPN-SI-LS" indicator, otherwise the UDM shall delete the stored "ME support of SOR-SNPN-SI-LS" indicator, if any

The UDM to the SOR-AF: Nsoraf_SoR_Info (SUPI of the UE, successful delivery, "ME support of SOR-CMCI" indicator, if any, "ME support of SOR-SNPN-SI-LS" indicator, if any). If the subscribed SNPN or HPLMN policy for the SOR-AF invocation is present and the UDM received and verified the UE acknowledgement in step 10, then the UDM informs the SOR-AF about successful delivery of the SOR-SNPN-SI to the UE. If:

• the "ME support of SOR-CMCI" indicator is stored for the UE, the UDM shall include the "ME support of SOR-CMCI" indicator; and
• the "ME support of SOR-SNPN-SI-LS" indicator is stored for the UE, the UDM shall include the "ME support of SOR-SNPN-SI-LS" indicator; and

If the UE has a list of available SNPNs in the area and based on this list the UE determines that there is a higher priority SNPN than the selected SNPN and the UE is in automatic network selection mode, then the UE may attempt to obtain service on a higher priority SNPN as specified in clause 4.9.3 after the release of the N1 NAS signalling connection. If within an implementation dependent time the N1 NAS signalling connection is not released, then the UE may locally release the N1 signalling connection except when the UE has an established emergency PDU session (see TS 24.501).