Question: What is the primary function of the APN Network Identifier in a GGSN/PGW setup, and what part of the APN structure is it?
Option 1: Defines the PLMN GPRS/EPS backbone location; Mandatory part
Option 2: Specifies the requested service by the MS; Optional part
Option 3: Identifies the external network connected to the GGSN/PGW and optionally a requested service by the MS; Mandatory part
Option 4: Determines the DNS name encoding scheme; Optional part
Explanation: The APN Network Identifier is crucial for identifying the external network to which the GGSN/PGW is connected. Additionally, it may optionally specify a requested service by the Mobile Station (MS). This part of the APN structure is mandatory, ensuring proper routing and service provision in telecom networks.