Question: In a scenario where two Mission Critical (MC) service users, subscribed to different MC systems, engage in a private call via interconnection, which MC system assumes the controlling function for the call?
Option 1: The MC system of the called MC service user
Option 2: A neutral third-party MC system not associated with either user
Option 3: Both MC systems share the controlling function equally
Option 4: The MC system providing MC service to the calling MC service user
Explanation: This is because, as per the defined architecture for Mission Critical services, when private calls are facilitated through interconnection between users of different MC systems, the controlling function for the call is provided by the MC system that serves the initiating (calling) MC service user. This ensures streamlined management and coordination of the private call, leveraging the existing service provision framework of the calling user's MC system.