Question: What happens when a UE encounters an error with a mandatory information element in a DEACTIVATE EPS BEARER CONTEXT REQUEST message?
Option 1: A DEACTIVATE EPS BEARER CONTEXT REJECT message is sent to the network.
Option 2: A DEACTIVATE EPS BEARER CONTEXT ACCEPT message is returned, and all resources associated with that EPS bearer are released.
Option 3: The UE sends a PDN DISCONNECT REQUEST message to the network.
Option 4: The UE releases all resources associated with the EPS bearer without sending any response.
Explanation: According to the specified procedure, when a UE encounters an error with a mandatory information element in a DEACTIVATE EPS BEARER CONTEXT REQUEST message, it returns a DEACTIVATE EPS BEARER CONTEXT ACCEPT message and releases all resources associated with that EPS bearer. This ensures that the network is informed of the deactivation and can release its own resources accordingly.