Content for  TS 24.502  Word version:  19.0.0

If the UE is connected to an N3IWF that is in the same country as the country in which the UE is currently in and the AMF has previously indicated support for emergency services over non-3GPP access (see TS 24.501), the UE shall use the existing N3IWF connection for emergency services. Otherwise, the UE shall perform the IKEv2 deletion procedure for the existing N3IWF connection and initiate N3AN node selection procedure for emergency services as described below. When the UE supports connectivity with N3IWF but does not support connectivity with ePDG, the UE shall perform the procedure in clause 7.2.6.2 for selecting an N3IWF for emergency services. When the UE supports connectivity with N3IWF and ePDG, the UE shall perform the procedure in clause 7.2.6.3 for selecting either an N3IWF or an ePDG for emergency services.

If the UE is in the home country, the UE shall follow the procedure in clause 7.2.4.3 bullet a). If the UE is in a visited country, the UE shall perform the DNS NAPTR query using Visited Country Emergency N3IWF FQDN as specified in TS 23.003 via the non-3GPP access network to determine PLMNs in the visited country that support emergency services in non-3GPP access via N3IWF. If the DNS response contains one or more records, the UE shall select a PLMN included in the DNS response that has highest PLMN priority (see TS 24.526) in the N3AN node selection information, excluding any PLMN in the list of "forbidden PLMNs for non-3GPP access to 5GCN". The UE shall construct an N3IWF FQDN based on the FQDN format of the selected PLMN's N3AN node selection information entry in the N3AN node selection information using the PLMN ID of the selected PLMN as specified in TS 23.003. If none of the PLMNs included in the DNS response figures in the N3AN node selection information or the N3AN node selection information is not provisioned, the UE shall select any of the PLMNs included in the DNS response and shall construct an N3IWF FQDN based on the Operator Identifier based N3IWF FQDN format. If the emergency registration procedure has failed for all attempted PLMNs, or the DNS response in the visited country does not contain any record, the UE shall abort the procedure. NOTE: The UE can notifiy the user that an emergency session cannot be established.

The UE operating in SNPN access operation mode with a selected entry of "list of subscriber data" shall perform following procedures:

1. if the selected entry is not considered as valid, the UE may:
   1. select another valid entry of "list of subscriber data", if any, such that the UE is in the country where the configured N3IWF of the entry is located, which has not been tried yet, and proceed to bullet b) 1);
   2. select another valid entry of "list of subscriber data", if any, such that the UE is not in the country where the configured N3IWF of the entry is located, which has not been tried yet, and proceed to bullet b) 2);
   3. stop operating in SNPN access operation mode and attempt to perform UE procedure as specified in clause 7.2.6.2; or
   4. abort the procedure; and
2. if the selected entry is considered as valid and:
   1. the UE is in the home country, i.e. in the country where the configured N3IWF of the selected entry of "list of subscriber data" is located, the UE shall follow the procedure in clause 7.2.5 bullet a). If the emergency registration procedure has failed, the UE may proceed to bullet a) 1), a) 2), a) 3) or a) 4); or
   2. the UE is in a visited country, i.e. in a country other than the country where the configured N3IWF of the selected entry of "list of subscriber data" is located, the UE shall perform the DNS NAPTR query using Visited Country Emergency SNPN FQDN as specified in TS 23.003 via the non-3GPP access network to determine SNPNs in the visited country that support emergency services in non-3GPP access via N3IWF:
      1. if the DNS response contains one or more records, the UE shall select an SNPN included in the DNS response via UE implementation means and construct an N3IWF FQDN based on the FQDN format of the selected SNPN as specified in TS 23.003 for N3IWF selection. The UE shall use the DNS server function to resolve the constructed SNPN N3IWF FQDN to the IP address(es) of the N3IWF:
         1. if the DNS response contains one or more IP addresses of N3IWF, the UE shall select an IP address of N3IWF with the same IP version as its local IP address, if any, and initiate the procedure as specified in clause 7.3; and
         2. if the DNS resolution of constructed SNPN N3IWF FQDN fails, or the emergency registration procedure in the bullet above has failed, the UE shall select another SNPN, if any, included in the DNS response and repeat the procedure as specified in bullet b) 2) i); and
      2. if the DNS response contains no record, or no DNS response is received, or the emergency registration procedure has failed for all the SNPNs included in the DNS response as specified bullet b) 2) i), the UE may proceed to bullet a) 1), a) 2) or a) 3).

If the UE is in the home country, the UE shall follow the steps in clause 7.2.4.4.2 bullet a), except that:

• in bullet a)1)i), if the emergency registration fails, the UE shall attempt to select an ePDG in the home country using the steps under bullet a)1)ii); and
• in bullet a)1)ii):
  • Emergency ePDG FQDN shall be used instead of home ePDG identifier; and
  • If the emergency registration fails, the UE shall attempt to select an N3IWF in the home country using the steps under bullet a)1)i).

If the UE is in a visited country, the UE shall perform the DNS NAPTR query using Visited Country Emergency N3IWF FQDN and Visited Country Emergency FQDN as specified in TS 23.003 via the non-3GPP access network to determine PLMNs in the visited country that support emergency services in non-3GPP access via N3IWF or ePDG. If the DNS response contains one or more records, the UE shall select a PLMN included in the DNS response that has highest PLMN priority (see TS 24.526) in the N3AN node selection information.

• If the N3AN node selection information for the PLMN is available the UE selects first an N3IWF or ePDG based on the preference parameter in the selected PLMN's N3AN node selection information entry of the N3AN node selection information. If N3IWF is preferred, the UE constructs the N3IWF FQDN based on the FQDN format of the selected PLMN's N3AN node selection information entry in the N3AN node selection information using the PLMN ID of the selected PLMN as specified in TS 23.003. If ePDG is preferred, the UE constructs either the Tracking/Location Area Identity based Emergency ePDG FQDN or the Operator Identifier based Emergency ePDG FQDN as indicated by the FQDN format in the N3AN node selection information for the selected PLMN.
• If the N3AN node selection information is not available, the UE shall follow the procedure in clause 7.2.6.2, except that, instead of aborting the procedure in case of a failure, the UE shall perform the procedure for ePDG selection for emergency services specified in TS 24.302, by constructing the Operator Identifier based Emergency ePDG FQDN.

If the emergency registration procedure has failed for all attempted PLMNs, the UE shall abort the procedure.