Question: In E-UTRAN S1AP, if a receiving node supports a procedure but cannot perform requested functionality marked as 'shall' in the procedure text, how should it respond?
Option 1: Respond with a successful outcome message, omitting the unsupported functionality.
Option 2: Proceed with the execution of the Elementary Procedure (EP), informing the requesting node about the unsupported functionality.
Option 3: Respond with the message used to report an unsuccessful outcome for this procedure, containing an appropriate cause value.
Option 4: Ignore the request and do not send a response.
Explanation: According to specification principles, if a receiving node supports a procedure but cannot perform 'shall' functionality, it must respond with a message indicating an unsuccessful outcome, providing transparency about unexecuted functionalities with an appropriate cause value for the failure.