Question: In E-UTRAN X2 Application Protocol (X2AP), when a receiving eNB supports a procedure but cannot perform requested functionality marked as 'shall' due to a specific condition, how must it respond?
Option 1: Ignore the request and continue with existing operations.
Option 2: Respond with a success message, assuming an alternative action.
Option 3: Proceed with partial execution of the procedure, omitting the unsupported functionality.
Option 4: Respond with a message reporting an unsuccessful outcome, containing an appropriate cause value.
Explanation: According to the specified principles for procedure logic in E-UTRAN X2AP, if a receiving node (eNB) supports a procedure but cannot perform a 'shall' functionality due to a certain condition, it must respond with a message indicating an unsuccessful outcome, including a relevant cause value to inform the originating eNB about the reason for the failure.