Question: In a UMTS network, when is the 'Successful MS-initiated session conclusions, per APN' performance measurement incremented on the GGSN (Gateway GPRS Support Node: serves as gateway for Wireless Packet Core)?
Option 1: On transmission by the GGSN of a DELETE PDP CONTEXT RESPONSE to the SGSN (Serving GPRS Support Node) with cause 'Request Accepted'
Option 2: Upon receipt of a DELETE PDP CONTEXT REQUEST from the SGSN with a valid APN (Access Point Name)
Option 3: After a successful PDP context activation procedure initiated by the User Equipment (UE: User Equipment)
Option 4: When the GGSN detects inactivity for a predefined period on an established PDP context
Explanation: This is correct because the measurement increments upon the GGSN's transmission of a DELETE PDP CONTEXT RESPONSE with 'Request Accepted', indicating successful session conclusion initiated by the Mobile Station (MS).