Section: 19.4.2.9.3 Tracking/Location Area Identity based ePDG FQDN
Content: The Tracking/Location Area Identity based ePDG FQDN is used to support location based ePDG selection within a PLMN. There are two Tracking Area Identity based ePDG 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 ePDG FQDN using a 2 octet TAC and the Location Area Identity based ePDG FQDN shall be constructed respectively as: "tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" and "lac<LAC>.epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" where - the <MNC> and <MCC> shall identify the PLMN where the ePDG 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 ePDG 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; - the <LAC>, together with the <MCC> and <MNC> shall identify the Location Area Identity the UE is located in. The LAC> shall be hexadecimal coded digits representing the LAC; if there are less than 4 significant digits in <LAC>, one or more "0" digit(s) is/are inserted at the left side to fill the 4 digit coding; As examples, - the Tracking Area Identity based ePDG FQDN for the TAC H'0B21, MCC 345 and MNC 12 is coded in the DNS as: " tac-lb21.tac-hb0b.tac.epdg.epc.mnc012.mcc345.pub.3gppnetwork.org" - the Location Area Identity based ePDG FQDN for the LAC H'0B21, MCC 345 and MNC 12 is coded in the DNS as: " lac0b21.epdg.epc.mnc012.mcc345.pub.3gppnetwork.org" 2) The 5GS Tracking Area Identity based ePDG 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. epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" where - the <MNC> and <MCC> shall identify the PLMN where the ePDG 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 ePDG FQDN. - the <TAC>, together with the <MCC> and <MNC> shall identify the 5GS Tracking 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 digits coding; As examples, - the 5GS Tracking Area Identity based ePDG 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.epdg.epc.mnc012.mcc345.pub.3gppnetwork.org"