Question: In the context of Performance Management (PM) for Core Network (CN) Circuit Switched (CS) domain, what triggers the collection of 'Attempted calls for calling party number' measurement based on Observed Destination?
Option 1: Receipt of a 'RELEASE' message from the UE at the MSC-S.
Option 2: Successful call setup between two UEs in the same network.
Option 3: Receipt by the MSC-S of an 'IAM' message or 'SETUP' from UE, prompting extraction of the calling party number.
Option 4: Periodic polling of the VLR for subscriber MSISDN numbers.
Explanation: This is correct because the trigger for collecting this measurement is the receipt by the MSC-S of either an 'IAM' from another MSC-S or a 'SETUP' message directly from the UE. This event prompts extraction of the observed destination number (the calling party's number), crucial for accurately counting attempted calls in circuit-switched domains of GSM/UMTS networks for performance management purposes.