a circuit arrangement is provided for testing a passive bus network system which comprises stations which are connectible to a coaxial cable segment via media adapter units , the stations realizing the data packet exchange via the coaxial cable segment with carrier sense multiple access with collision detection access method . in conjunction with a status receiving device which monitors the transmitted data packets , the passive bus network system is monitored by the data transmitter and the data receiver in view of the presence of the line terminating impedances , the proper connection of the media adapter units to the transmission medium , as well as the transmitting and receiving functions and the collision recognition and state of the collision recognition circuit .