Abstract: A multipoint access data communication system which includes a communication bus, a plurality of transceivers connected to the bus for communication, and a remote collision detector associated with each transceiver for detecting collisions between communications on the medium, has improvements which adapt the transceivers for connection to a plurality of network interface units, and local access arbitrators associated with the transceivers for preventing collisions between transmissions simultaneously attempted by two or more network interface units connected to a transceiver.