Performance evaluation of an off-host communications architecture

The Computer Networks Laboratory at the University of Virginia has implemented the SAFENET lightweight protocol suite on the Navy’s Desktop Tactical Computer (DTC2). The software delivered includes the Xpress Transfer Protocol, a new transport and network layer protocol to support high-throughput, low-latency, priority-sensitive communications. One of our research questions was whether to embed XTP in the DTC-2’s UNIX kernel or run XTP on an attached processor on the DTC-2’s VMEbus. We implemented both strategies and the attached processor approach proved to have somewhat higher performance. In this paper we survey the hardware and software system environment, report the performance achieved at the MAC, transport, and user levels, and develop an analytic model for predicting throughput and latency as a function of vendor-provided or easily-measured system parameters. Our conclusions identifr both the advantages and perSormance concerns inherent to of-host protocol execution.