Question: What action does a mobile station take when it receives a message containing an unknown IE encoded as "comprehension required"?
Option 1: The mobile station ignores the message and returns a status message (STATUS, MM STATUS depending on the protocol discriminator) with cause # 96 "Invalid mandatory information".
Option 2: The mobile station tries to process the message and only returns an error if it cannot understand the IE.
Option 3: The mobile station sends an error message to the network indicating that it does not support the unknown IE.
Option 4: The mobile station terminates the connection with the network.
Explanation: According to the 3GPP specification, when a mobile station receives a message containing an unknown IE encoded as "comprehension required", it shall ignore the message except for returning a status message (STATUS, MM STATUS depending on the protocol discriminator) with cause # 96 "Invalid mandatory information". This ensures that the mobile station does not attempt to process the unknown IE and instead notifies the network of the error.