Question: What action does the UE take when it encounters an error with a mandatory information element in a PDU SESSION ESTABLISHMENT ACCEPT message?
Option 1: The UE sends a PDU SESSION RELEASE COMPLETE message.
Option 2: The UE initiates a PDU session release procedure by sending a PDU SESSION RELEASE REQUEST message with 5GSM cause #96 "invalid mandatory information".
Option 3: The UE ignores the error and continues with the existing PDU session.
Option 4: The UE sends a PDU SESSION ESTABLISHMENT REJECT message.
Explanation: According to the specified procedures, when the UE encounters an error with a mandatory information element in a PDU SESSION ESTABLISHMENT ACCEPT message, it initiates a PDU session release procedure by sending a PDU SESSION RELEASE REQUEST message with 5GSM cause #96 "invalid mandatory information". This ensures that the UE and the network can recover from the error and maintain a valid PDU session state.