Abstract: With the growing trend towards distributed hard real time systems, the ability of computer networks to handle hard real time message traffic is becoming more important. Ethernet is a kind of non deterministic network. In this paper, an Ethernet based protocol called RTCC is presented, that provides hard real time performance guarantees to distributed hard real time applications without requiring any modifications to the existing Ethernet hardware. Command/response multiplex transmission and bus table are introduced in RTCC in order to schedule the channel. So two problems that real time communication faces, an access arbitration process and a transmission control process, can be solved well. Performance measurements from experiments on a 10 Mbps Ethernet indicate that determinism of RTCC is good.