PURPOSE: To improve the TDMA frame utilizing efficiency by allowing a center station to receive a reference burst(RB) once for several frames and receiving a line connection element burst (CSC) from other frames.

CONSTITUTION: The system is a demand assign TDMA system employing plural carriers in which a burst of a required length is allocated to a proper location in a TDMA frame under the control of a center station based on a line connection request from plural peripheral stations. Then a time slot for a line connection request burst is provided to other carriers f1-fn at a same time as a burst RB, a center station receives the RB once for several frames and receives a line connection element burst (CSC) for other frames. In this case, the synchronization is taken by allowing the center station not to receive the RB for each frame but to receive the RB once for several frames. Thus, a peripheral station sends the CSC to the center station to other carrier at the same time as the RB, the center station receives it in place of the RB and accepts a line connection request to improve the frame utilizing efficiency.