Ethernet: distributed packet switching for local computer networks
Communications of the ACM
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The builder of a local area network is immediately confronted with the selection of a communications architecture to interconnect the elements (hosts and terminals) of the network. This choice must often be made in the presence of great uncertainty regarding the available alternatives and their capabilities, and a dearth of comparative information. This was the situation confronting NASA upon seriously considering local area networks as an architecture for mission support operations. As a result, a comparative study was performed in which alternative communication architectures were evaluated under similar operating conditions and system configurations. Considered were: (1) the ring, (2) the cable-bus, (3) a circuit-switching system, and (4) a shared memory system. The principle performance criterion used was the mean time required to move a message from one host processor to another host processor. Local operations within each host, such as interrupt service time, were considered to be part of this overall time. The performance of each alternative was evaluated through simulation models and is summarized in this paper.