that they all send their packets simultaneously after sending a packet a queuing means may receive an acknowledge signal as from one of the address checking means 40 0 to 40 7 via the self routing switching network 1 when a queing means receives such an acknowledge signal as it deletes the front packet from its queue if a queuing means does not receive such an acknowledge signal it does not delete its front packet hence the same packet is sent again at the next timing signal ts each of the address checking means 40 0 to 40 7 checks the address of packet received from the self routing switching network 1 if a packet has been routed to the correct address i e to the address checking means connected to the external output terminal of the address of the packet the address checking means sends it on to the external output terminal and returns an acknowledge signal as through the self routing switching network 1 indicating that the packet has been correctly received since the switching elements of the self routing switching network 1 are still in the same state at this point the acknowledge signal retraces the route of the packet in reverse reaching the queuing means one of 30 0 to 30 7 from which the packet originated if a packet.