Question: At what point is the 'Attempted calls for called party numbers' measurement triggered in a UMTS/Circuit Switched (CS) Core Network domain?
Option 1: Upon receipt of an 'Alerting' message from the User Equipment (UE)
Option 2: When the Mobile Switching Center - Server (MSC-S) sends a 'Connect' message to the UE
Option 3: On transmission by the MSC-S of a 'SETUP' message to the called UE or an 'IAM' message to an adjacent MSC-S
Option 4: After the UE responds with a 'Connect Acknowledge' message
Explanation: This measurement is triggered at the initiation of call setup, specifically when the MSC-S sends out either a 'SETUP' message (for calls directed to a UE) or an 'IAM' for inter-MSC connections, marking the attempt to establish a connection with the specified called party number.