Question: What is the purpose of the APN Operator Identifier in a GPRS/EPS PLMN?
Option 1: To uniquely identify the UE and provide DNS translations for human-readable APNs.
Option 2: To select the GGSN/PGW for non-roaming and home routed scenarios only.
Option 3: To guarantee inter-PLMN DNS translation and provide a default APN Operator Identifier.
Option 4: To determine the labels that precede the "mnc<MNC>.mcc<MCC>.gprs" trailing labels in the APN-OI replacement field.
Explanation: The APN Operator Identifier is used to uniquely identify the GPRS/EPS PLMN and provide DNS translations for human-readable APNs, as well as to guarantee inter-PLMN DNS translation. It is composed of three labels, with the last label being "gprs", and the first and second labels together identifying the PLMN.