Communication system with master, slave and repeater units

A communication system is formed with a master unit (30) and at least one slave unit (40a-40e) connected by a network including a bus (31-33). Repeater units (50a,50b) are inserted on the network between the master unit and the slave unit in one or more stages. As the master unit transmits broadcast request frames downstream through the network to the slave units, each slave unit controls the timing of transmitting the response frames successively such that the master unit receives the response frames without waiting in between regardless of repeater delay times of each of the returned response frames determined by the number of stages of the repeater units. Each communication frame that is transmitted through the network contains identification data indicative of its type and each repeater unit serves to repeat certain types of received frames only in the upstream direction.