Question: What is the format of the home network domain name of the OCS if it is not known and needs to be derived from the subscriber's IMSI?
Option 1: ocs.<MCC>.mnc<MNC>.gppnetwork.org
Option 2: ocs.mnc<MNC>.mcc<MCC>.3gppnetwork.org
Option 3: mnc<MNC>.mcc<MCC>.ocs.3gppnetwork.org
Option 4: mcc<MCC>.mnc<MNC>.ocs.gppnetwork.org
Explanation: According to the specification, if the home network domain of the OCS is not known, it shall be in the form of "ocs.mnc<MNC>.mcc<MCC>.3gppnetwork.org", where "<MNC>" and "<MCC>" fields correspond to the MNC and MCC of the operator's PLMN to which the OCS belongs. This format ensures that the domain name is unique and can be derived from the subscriber's IMSI.