Content for  TS 23.003  Word version:  18.5.0

The N3IWF Fully Qualified Domain Name (N3IWF FQDN) shall be constructed using one of the following formats, as specified in clause 6.3.6 of TS 23.501:

• Operator Identifier based N3IWF FQDN;
• Tracking Area Identity based N3IWF FQDN;
• the N3IWF FQDN configured in the UE by the HPLMN.
• SNPN Identifier based N3IWF FQDN.

The Visited Country FQDN for N3IWF is used by a roaming UE to determine whether the visited country mandates the selection of an N3IWF in this country. The Visited Country FQDN for N3IWF shall be constructed as specified in clause 28.3.2.2.4. The Replacement field used in DNS-based Discovery of regulatory requirements shall be constructed as specified in clause 28.3.2.2.5.1. The Visited Country FQDN for SNPN N3IWF is used by a UE in the visited country to determine whether the visited country mandates the selection of an N3IWF in this country for the SNPN identified by the SNPN Identifier provided by the UE. The Visited Country FQDN for SNPN N3IWF shall be constructed as specified in clause 28.3.2.2.6. The Replacement field used in DNS-based Discovery of SNPN N3IWF for regulatory requirements shall be constructed as specified in clause 28.3.2.2.7.2. The Visited Country FQDN for N3IWF supporting Onboarding is used by a UE in the visited country to determine whether the visited country mandates the selection of an N3IWF in this country for onboarding services. The Visited Country FQDN with N3IWF supporting Onboarding shall be constructed as specified in clause 28.3.2.2.4.3. The Replacement field used in DNS-based Discovery of regulatory requirements shall be constructed as specified in clause 28.3.2.2.5.3. The Visited Country FQDN for SNPN N3IWF supporting Onboarding is used by a UE in the visited country to determine whether the visited country mandates the selection of an SNPN N3IWF in this country for onboarding services. The Visited Country FQDN with SNPN N3IWF supporting Onboarding shall be constructed as specified in clause 28.3.2.2.6.2. The Replacement field used in DNS-based Discovery of SNPN N3IWF for regulatory requirements shall be constructed as specified in clause 28.3.2.2.7.2

The N3IWF Fully Qualified Domain Name (N3IWF FQDN) contains an Operator Identifier that shall uniquely identify the PLMN where the N3IWF is located. The N3IWF FQDN is composed of seven labels. The last three labels shall be "pub.3gppnetwork.org". The third and fourth labels together shall uniquely identify the PLMN. The first two labels shall be "n3iwf.5gc". The N3IWF FQDN shall be constructed as follows: In the roaming case, the UE can utilise the services of the VPLMN or the HPLMN. In this case, the Operator Identifier based N3IWF FQDN shall be constructed as described above, but using the MNC and MCC of the VPLMN or the HPLMN. In order to guarantee inter-PLMN DNS translation, the <MNC> and <MCC> coding used in the "n3iwf.­5gc.­mnc<MNC>.­mcc<MCC>.­pub.­3gppnetwork.­org" format of the Operator Identifier based N3IWF FQDN shall be:

• <MNC> = 3 digits
• <MCC> = 3 digits

If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN. As an example, the Operator Identifier based N3IWF FQDN for MCC 345 and MNC 12 is coded in the DNS as:

The Tracking Area Identity based N3IWF FQDN is used to support location based N3IWF selection within a PLMN. There are two N3IWF FQDNs defined one based on a TAI with a 2 octet TAC and a 5GS one based on a 3 octet TAC.

1. The Tracking Area Identity based N3IWF FQDN using a 2 octet TAC shall be constructed respectively as:
   "tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org"
   where
   • the <MNC> and <MCC> shall identify the PLMN where the N3IWF is located and shall be encoded as
     • <MNC> = 3 digits
     • <MCC> = 3 digits
     If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN.
   • the <TAC>, together with the <MCC> and <MNC> shall identify the Tracking Area Identity the UE is located in.
     The TAC is a 16-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-high-byte> or <TAC-low-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digit coding;
   As examples,
   • the Tracking Area Identity based N3IWF FQDN for the TAC H'0B21, MCC 345 and MNC 12 is coded in the DNS as:
     "tac-lb21.tac-hb0b.tac.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org"
2. The 5GS Tracking Area Identity based N3IWF FQDN using a 3 octet TAC shall be constructed respectively as:
   "tac-lb<TAC-low-byte>.tac-mb<TAC-middle-byte>.tac-hb<TAC-high-byte>.5gstac.n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org"
   where
   • the <MNC> and <MCC> shall identify the PLMN where the N3IWF is located and shall be encoded as
     • <MNC> = 3 digits
     • <MCC> = 3 digits
     If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN.
   • the <TAC>, together with the <MCC> and <MNC> shall identify the 5GSTracking Area Identity the UE is located in.
     The 5GS TAC is a 24-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-low-byte>, <TAC-middle-byte> or <TAC-high-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digit coding;
   As examples,
   • the 5GS Tracking Area Identity based N3IWF FQDN for the 5GS TAC H'0B1A21, MCC 345 and MNC 12 is coded in the DNS as:
     "tac-lb21.tac-mb1a.tac-hb0b.5gstac.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org"

n3iwf.5gc.mcc345.visited-country.pub.3gppnetwork.org

; IN NAPTR order
;              pref.
;                  flag
;                     service
;                        regexp
;                          replacement

  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc013.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc014.mcc345.pub.3gppnetwork.org

sos.n3iwf.5gc.mcc345.visited-country.pub.3gppnetwork.org

; IN NAPTR order
;              pref.
;                  flag
;                     service
;                        regexp
;                          replacement

  IN NAPTR 100 999 "" ""   sos.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   sos.n3iwf.5gc.mnc013.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   sos.n3iwf.5gc.mnc014.mcc345.pub.3gppnetwork.org

onboarding.n3iwf.5gc.mcc345.visited-country.pub.3gppnetwork.org

; IN NAPTR order
;              pref.
;                  flag
;                     service
;                        regexp
;                          replacement

  IN NAPTR 100 999 "" ""   onboarding.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   onboarding.n3iwf.5gc.mnc013.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   onboarding.n3iwf.5gc.mnc014.mcc345.pub.3gppnetwork.org