Performance analysis of a CSMA/CD bus based multiprocessor system

The authors present a detailed analysis of the CSMA/CD (carrier-sense-multiple-access-with-collision-detection) bus that forms the backbone of a multiprocessor-based communications system. Fiber-optic implementations of the Ethernet protocol (based on the IEEE 802.3 standard) and the Enet II protocol (proposed by M.K. Molloy in 1984) are modeled with the SIMAN simulation language. The primary difference between the two protocols is in the collision resolution scheme with subtle differences in the access mechanism. The communications system consists of multiple MicroVAX II and III processors, used primarily in this study to provide loading to the CSMA/CD bus. Various performance metrics are investigated, including bus utilization and queuing, packet and message response times, and pertinent collision statistics. It is found that both protocols meet the criteria for successful performance within the proposed system. Owing to the light input loading and corresponding low bus utilization, minimal impact to total system performance results when changing from protocol to protocol. However, it is evident from the results that the performance of the Enet II protocol is degrading more rapidly than that of the Ethernet