Abstract: An unslotted radio frequency multiple access bus communications system employing a contention listen-while-talk (LWT) protocol. The system includes a plurality of remotely located terminals coupled to a communications bus. The bus includes a pair of oppositely directed, unidirectional signal paths which are connected at one end so that one path is an inbound path to that end and the second is an outbound path from that end. Each of the remote terminals includes a bus interface unit (BIU) coupled to both the inbound and outbound paths at the remote location. Each BIU is adapted to transmit and receive modulated carrier signals on the inbound and outbound paths, respectively.When a terminal wishes to send a message to another terminal, the terminal's BIU initially performs an rf carrier sensing operation to make an initial determination as to whether or not any other subscriber is transmitting on the inbound path.

Abstract: A time division multiple access communications system includes a plurality of terminals coupled to a common signal path, or bus. In one form of the invention, time slots are allocated on a relatively static basis to various requesting terminals to establish communication links over the bus. Control of bus access and communication link formation is distributed over the entire system, wherein at least one terminal having the slot allocation capability may address selected other terminals and allocate the capability among those other terminals. In a second form, subscriber terminals contend for access to the bus. In a third form, a dual mode communication system is provided incorporating both the allocation and contention modes of operation.