Abstract: A method of analysing a communication system to locate the source of a fault. The communication system comprises a signal carrying medium (9) coupled to a series of end station ports (2-6) which enable respective end stations (24) to transmit signals onto and receive signals from the medium and a controller (8) to control connection of end stations (24) to the medium via the ports (2-6). The method comprises disconnecting end stations (24) in series from the medium (9) in response to detection of a fault and then detecting whether the fault still exists. A fault analyzer (10) adapted to respond to the detection of a fault causes the controller (8) firstly to disconnect an end station (24) which has previously been characterised as the most likely source of a fault. The controller (8) may disconnect groups of end stations (24) and reconnect subgroups if no fault is present in the group which was not disconnected until the faulty end station is identified.