next up previous

2.5 Local Network Technology

The predominant technology for local networks is ethernet, developed at Xerox PARC in the 1970s. The key innovation in ethernet was building a system in which a network node could sense when the network was in use. An earlier network known as the AlohaNet used radio to link terminals in the Hawaiian islands to a mainframe at the University of Hawaii. The organization of the network was a success, but performance suffered because a node could not tell when another node was transmitting. When two nodes transmitted at the same time their messages were garbled. Researchers at Xerox designed their system around a medium (the ether) which had the property that nodes could detect transmissions in progress and thus postpone their own transmissions. Analytical models predicted that a very high percentage of the network bandwidth could be exploited by a packet-switched network based on carrier-sense technology.