Question: What is the correct format for constructing a Home Network Realm/Domain from an IMSI, considering the Mobile Country Code (MCC) and Mobile Network Code (MNC) lengths?
Option 1: epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org, where <MNC> is always 2 digits (padding with a zero if necessary) and <MCC> is always 3 digits.
Option 2: epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org, where <MNC> can be either 2 or 3 digits (without padding for 2-digit MNCs) and <MCC> is always 3 digits.
Option 3: mcc<MCC>.mnc<MNC>.epc.3gppnetwork.org, with <MNC> being 2 or 3 digits based on the PLMN's configuration (without padding for 2-digit MNCs) and <MCC> always being 3 digits.
Option 4: epc.mcc<MCC>.mnc<MNC>.org, where both <MNC> and <MCC> are fixed to 3 digits, with <MNC> padded with a zero if originally 2 digits.
Explanation: According to the specifications for constructing a Home Network Realm/Domain from an IMSI, the correct format is epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org. Specifically, it's mandated that if the MNC of the PLMN is 2 digits, then a zero shall be added at the beginning to make it 3 digits for consistency in the domain name format. This ensures uniformity across different configurations, making Option 1 the correct choice as it accurately reflects this requirement.