Question: For the 'Attempted mobile terminating calls' measurement in a UMTS network, at what point is the attempt counted from the MSC-S's perspective?
Option 1: Upon receipt of a 'SETUP ACKNOWLEDGE' message from the called mobile.
Option 2: On transmission by the MSC-S of an 'ALERTING' message to the calling party.
Option 3: When the called mobile user answers the call (i.e., call is established).
Option 4: On transmission by the MSC-S of a 'SETUP' message to the called mobile.
Explanation: This is correct because the attempt is counted when the MSC-S transmits a 'SETUP' message to the called mobile for the requested mobile terminating call. This marks the initiation of the call setup process from the network's perspective, hence counting as an attempted call.