Question: What is the correct format for constructing an Operator Identifier based Emergency ePDG Fully Qualified Domain Name (FQDN) for a network with Mobile Country Code (MCC) 123 and Mobile Network Code (MNC) 456, according to 3GPP standards?
Option 1: epdg.epc.mnc456.mcc123.emergency.3gppnetwork.org
Option 2: sos.epdg.epc.mnc0456.mcc0123.pub.3gppnetwork.net
Option 3: emergency.epdg.epc.mnc456.mcc123.3gppnetwork.org
Option 4: sos.epdg.epc.mnc456.mcc123.pub.3gppnetwork.org
Explanation: The correct construction of an Operator Identifier based Emergency ePDG FQDN involves adding the 'sos' label before 'epdg.epc', followed by the Mobile Network Code (MNC) and Mobile Country Code (MCC) in the format .mnc<MNC>.mcc<MCC>, and ending with .pub.3gppnetwork.org. For MCC 123 and MNC 456, the correct FQDN is sos.epdg.epc.mnc456.mcc123.pub.3gppnetwork.org.