Section: 19.4.2.9.2 Operator Identifier based ePDG FQDN
Content: The ePDG Fully Qualified Domain Name (ePDG FQDN) contains an Operator Identifier that shall uniquely identify the PLMN where the ePDG is located. The ePDG 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 "epdg.epc". The ePDG FQDN shall be constructed as follows: "epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" In the roaming case, the UE can utilise the services of the VPLMN or the HPLMN (see 3GPP TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [68] and 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [77]). In this case, the Operator Identifier based ePDG 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 "epdg.epc. mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" format of the Operator Identifier based ePDG 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 ePDG FQDN. As an example, the Operator Identifier based ePDG FQDN for MCC 345 and MNC 12 is coded in the DNS as: "epdg.epc.mnc012.mcc345.pub.3gppnetwork.org".