A timeslot interchange switch has a three stage pipelined construction. A cross-connect stage identifies egress timeslots for which there is a corresponding data source. The cross connect stage has a set of flags which indicate whether or not there is a data source for each of a plurality of egress timeslots. The cross connect stage takes the flags in groups. If one or more flags in a group indicates an egress timeslot has a corresponding data source then information identifying the egress timeslot is passed to a connection scheduler via a FIFO. The connection scheduler looks up the data source for each the egress timeslot.