Abstract: As shown in FIG. 2 an ATD multiplexer (1-i) comprises a congestion detector (34) for detecting internal traffic congestion when a data cell stream is transferred from one of the two data inputs (4, 5) to the data output (6). If internal traffic congestion occurs, congestion signal transmitter (36) will supply a congestion signal. An upstream ATD multiplexer (1-j) will receive this congestion signal as an external congestion signal through congestion signal receiver (37) and in response thereto blocks one of its two data inputs (4, 5). In this fashion the data supply to ATD multiplexer (1-i) will be restricted.If the data supply to ATD multiplexer (1-i) is restricted to such an extent that internal traffic congestion no longer occurs in ATD multiplexer (1-i), the blocking of the blocked data input in ATD multiplexer (1-j) will be removed in a delayed manner.