Question: What triggers the measurement of 'Number of subscribers in the SGSN in STANDBY state' as defined in Telecommunication management Performance Management (PM) specifications?
Option 1: Periodic polling of all subscribers by the SGSN.
Option 2: Transition of a GPRS subscriber registered in the SGSN into/from the operational state 'STANDBY'.
Option 3: Receipt of a specific measurement request from the Network Management System (NMS).
Option 4: Scheduled system maintenance of the SGSN.
Explanation: The correct answer is based on understanding how the measurement for subscribers in a STANDBY state is triggered. This transition prompts the measurement, making it directly related to the dynamic change in a subscriber's state rather than periodic checks or external requests.