A scheduler performs a plurality of scheduler operations each scheduling an output queue selected from a plurality of output queues associated with an egress port. The scheduler includes a candidate decision logic and a final decision logic. The candidate decision logic is arranged to decide a plurality of candidate output queues for a current scheduler operation, regardless of a resultant status of packet transmission of at least one scheduled output queue decided by at least one previous scheduler operation. The final decision logic is arranged to select one of the candidate output queues as a scheduled output queue decided by the current scheduler operation after obtaining the resultant status of packet transmission of the at least one scheduled output queue decided by the at least one previous scheduler operation.