Question: In a roaming scenario where the GGSN/PGW from the Visited PLMN (VPLMN) is to be selected, how is the APN Operator Identifier (APN-OI) for the User Equipment (UE) constructed?
Option 1: Derived from the UE's International Mobile Subscriber Identity (IMSI) with the format "mnc<MNC>.mcc<MCC>.gprs"
Option 2: Constructed from the serving network PLMN ID, ignoring any received APN-OI replacement field
Option 3: Determined by the Home PLMN's (HPLMN) default APN Operator Identifier
Option 4: Based on the UE's location, using a combination of cell ID and Location Area Code (LAC)
Explanation: In roaming scenarios where the GGSN/PGW from the VPLMN is to be selected, the APN-OI for the UE is constructed based on the serving network's PLMN ID. This approach ensures seamless connectivity in visited networks by utilizing local network identifiers for DNS translations, rather than relying on the home network's identifiers or other static configurations.