Abstract: For connecting external wiring to a circuit board (1), which is inserted in a housing arrangement (7), there is conventional backpanel (13) having connector elements (15) for receiving corresponding connector elements (3) on the circuit board. The external wiring is connected to contacts (29) on an exchangeable and removable connector unit (21). The unit is inserted in the housing in a similar way as a circuit board but is not connected to the backpanel (13) and comprises connector contacts (27) for connection with corresponding connectors (5) on the circuit board (1). When the circuit board (1) is inserted into the housing (7) thus electrical contact is obtained both with the contacts (15) on the backpanel (13) and with the contacts (27) on the wiring connector unit (21). From the contacts (27) on the connector unit (21) leads extend to the various contact pins (29), which are located easily accessible from the front of the housing (7).

Abstract: A method and apparatus for transmitting message information between a plurality of transmission units includes a plurality of data transmission channels on a bus system which are each permanently assigned to a respective transmission unit and adapted to transmit message information only to the transmission unit to which it is assigned from any one of the other transmisstion units. In addition, a plurality of status transmission channels on the bus system are each assigned to one of the transmission units and adapted to transmit status information from any one of the transmission units. This status information indicates whether the data transmission channel assigned to the same transmission unit as the respective status transmission channel is engaged or unoccupied for transmitting message information. The method and apparatus are particularly suited for switching nodes in packet-switched communications.