Question: What action should a mobile station take when it receives an RR, MM or CC message with a message type not defined for the PD or not implemented by the receiver in acknowledged mode?
Option 1: Ignore the message
Option 2: Return a status message (STATUS, MM STATUS depending on the protocol discriminator) with cause #97 "message type non-existent or not implemented"
Option 3: Send an error message to the network
Option 4: Disconnect from the network
Explanation: According to the specifications, when a mobile station receives an RR, MM or CC message with a message type not defined for the PD or not implemented by the receiver in acknowledged mode, it should return a status message (STATUS, MM STATUS depending on the protocol discriminator) with cause #97 "message type non-existent or not implemented". This ensures that the network is informed of the error and can take corrective action.