On transparent bridging of CSMA/CD networks

The authors study the interconnection of CSMA/CD (carrier sense multiple access with collision detection) local area networks (LANs) or LAN segments using a transparent bridge. The main concern was to study the performance and the implementation of a transparent bridge employing a novel bridging technique called cut-through bridging. The authors developed an approximate performance model of a multisegment CSMA/CD LAN whose segments are connected by a transparent bridge (cut-through or store-and-forward variety). It is found that, at light loads, the cut-through bridged system provided a lower average frame delay than a normal-bridged system, whereas at heavy loads, it achieved the same maximum throughput as the latter. Also, the normalized channel capacity of a bridged system could exceed unity because of the availability of multiple channels for parallel frame transmissions. The analysis was found to be quite accurate upon verification by simulation. Also, implementation of a normal transparent bridge requiring two Ethernet Etherlink interfaces and bridge software for interconnecting CSMA/CD LAN segments is reported