Question: What is the correct format for constructing an Operator Identifier based Emergency ePDG Fully Qualified Domain Name (FQDN) according to 3GPP specifications?
Option 1: sos.epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org
Option 2: epdg.epc.sos.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org
Option 3: mnc<MNC>.mcc<MCC>.sos.epdg.epc.pub.3gppnetwork.org
Option 4: mcc<MCC>.mnc<MNC>.epdg.epc.sos.pub.3gppnetwork.org
Explanation: The correct format for constructing an Operator Identifier based Emergency ePDG FQDN is specified in the 3GPP TS 23.003 document, which requires the addition of the label "sos" before the labels "epdg.epc". This results in the correct format being "sos.epdg.epc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org", where <MNC> and <MCC> are replaced with the actual Mobile Network Code and Mobile Country Code values, respectively.