Question: What is the correct format for deriving a default HA-APN Operator Identifier from an IMSI, specifically when the Mobile Network Code (MNC) has only 2 significant digits?
Option 1: ha-apn.mnc12.mcc<MCC>.pub.3gppnetwork.org
Option 2: ha-apn.mnc012.mcc<MCC>.pub.3gppnetwork.org
Option 3: ha-apn.mnc<2-digit MNC>.mcc<MCC>.pub.3gppnetwork.org (no padding specified)
Option 4: ha-apn.mnc0<MNC>.mcc<MCC>.pub.3gppnetwork.org (implying variable padding)
Explanation: According to the specifications for HA-APN Operator Identifier formatting, when deriving from an IMSI and the MNC has fewer than 3 significant digits, a "0" is inserted at the left side to fill the required 3-digit coding. Thus, a 2-digit MNC (e.g., "12") would be formatted as "mnc012" in the HA-APN Operator Identifier string, making Option 2 the correct answer. This ensures consistency and uniqueness in DNS translations across different PLMNs.