Communication subsystem is a major factor that affects the overall performance of a workstation cluster system. In this paper, the authors analyzed and compared the performance of three popular networks, and pointed out that the high level protocol processing is the bottleneck of communication in workstation cluster system. A user level high performance protocol, called RCP(reduced communication protocol), had been built on a cluster of 8 Sun SPARC workstations connected with 640Mbps Myrinet. Low overhead and high efficiency of the protocol are achieved by simplifying the protocol's redundant functions, reducing the times of data copying, and operating directly on hardware buffer. The round trip latency of RCP is much lower than TCP/IP(200μs vs 1 540μs), the application available bandwidth is much improved(178Mbps vs 34 Mbps) and the bandwidth usage of Myrinet on RCP reaches to 80.5%. A very simple interface to application or PVM is provided as well.