Abstract: Information originating at a plurality of terminal units is transmitted to a common information sink via a concentrator coupled between a plurality of terminal units and the common information sink. In one embodiment, used in a time reporting system, the information originates at a token reader at each of the terminals which is arranged to read pre-recorded information on an identification badge or time card. Each terminal is connected to the concentrator over a dedicated duplex communication link, and when the terminal has information to transmit, a first word is transmitted to the concentrator, the concentrator, in addition to being coupled to each of the terminals, is coupled to the information sink via a dedicated duplex communication link. Assuming the concentrator is idle, when a first word is received at a concentrator from a terminal, the concentrator attempts to seize the link between it and the common information sink.