Question: Upon receiving a Floor Release message with the first bit in the subtype set to '1' (Acknowledgment required), what action does the IWF floor control server take towards the MCPTT client?
Option 1: Sends a Floor Ack message with Message Type set to '4' and Source field set to '2', then enters the 'U: not permitted and Floor Taken' state.
Option 2: Forwards the Floor Release message to the floor control server arbitration logic without sending an acknowledgment.
Option 3: Sends a Floor Taken message including the granted MCPTT user's ID, only if privacy is not requested, and remains in the 'U: pending Floor Revoke' state.
Option 4: Enters the 'G: Idle' state and sends a Floor Idle message with appropriate floor indications for specific group calls.
Explanation: When the first bit in the subtype of the Floor Release message is set to '1', indicating that an acknowledgment is required, the IWF floor control server must respond with a Floor Ack message. This message specifically includes details such as setting the Message Type field to '4' (indicating Floor Release) and the Source field to '2' (signifying the controlling MCPTT function as the source). The state transition mentioned in Option 1 is not directly related to the acknowledgment requirement but since it's the only option that correctly identifies the sending of a Floor Ack message upon receiving a Floor Release with an acknowledgment required, it stands as the correct choice based on the provided context.