metcalfe76ethernet - 1. Background C omputer Systems G....

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Computer Systems G. Bell, S. Fuller and D. Siewiorek, Editors Ethernet: Distributed Packet Switching for Local Computer Networks Robert M. Metcalfe and David R. Boggs Xerox Palo Alto Research Center Ethernet is a branching broadcast communication system for carrying digital data packets among locally distributed computing stations. The packet transport mechanism provided by Ethernet has been used to build systems which can be viewed as either local computer networks or loosely coupled multiprocessors. An Ether- net's shared communication facility, its Ether, is a pas- sive broadcast medium with no central control. Coordi- nation of access to the Ether for packet broadcasts is distributed among the contending transmitting stations using controlled statistical arbitration. Switching of packets to their destinations on the Ether is distributed among the receiving stations using packet address recognition. Design principles and implementation are described, based on experience with an operating Ether- net of 100 nodes along a kilometer of coaxial cable. A model for estimating performance under heavy loads and a packet protocol for error controlled communica- tion are included for completeness. Key Words and Phrases: computer networks, packet switching, multiprocessing, distributed control, dis- tributed computing, broadcast communication, statisti- cal arbitration CR Categories: 3.81, 4.32, 6.35 Copyright © 1976, Association for Computing Machinery, Inc. General permission to republish, but not for profit, all or part of this material is granted provided that ACM's copyright notice is given and that reference is made to the publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Computing Machinery. Author's present addresses: R.M. Metcalfe, Transaction Tech- nology, Inc., 10880 Wilshire Boulevard, Los Angeles, CA 94304; D. Boggs, Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304. 395 1. Background One can characterize distributed computing as a spectrum of activities varying in their degree of decen- tralization, with one extreme being remote computer networking and the other extreme being multiprocess- ing. Remote computer networking is the loose intercon- nection of previously isolated, widely separated, and rather large computing systems. Multiprocessing is the construction of previously monolithic and serial com- puting systems from increasingly numerous and smaller pieces computing in parallel. Near the middle of this spectrum is local networking, the interconnection of computers to gain the resource sharing of computer networking and the parallelism of multiprocessing. The separation between computers and the associ- ated bit rate of their communication can be used to di- vide the distributed computing spectrum into broad activities. The product of separation and bit rate, now about 1 gigabit-meter per second (1 Gbmps), is an in- dication of the limit of current communication tech- nology and can be expected to increase with time: Activity Separation
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metcalfe76ethernet - 1. Background C omputer Systems G....

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