Absfract-Radio communicationis considered as a method for providing remote terminal access to computers. Digital byte streams from each terminal are partitioned into packets (blocks) and transmitted in a burst mode over a shared radio channel. When many terminals operate in this fashion, transmissions may conflict with and destroy each other. A means for controlling this is for the terminal to sense the presence of other transmissions; this leads to a new method for multiplexing in a packet radio environment: carrier sense multiple access (CSMA). Two protocols are described for CSMA and their throughput-delay characteristics are given. These results show the large advantage CSMA provides as compared to the random ALOHA access modes.

In multihop packet radio networks with randomly distributed terminals, the optimal transmission radii to maximize the expected progress of packets in desired directions are determined with a variety of transmission protocols and network configurations. It is shown that the FM capture phenomenon with slotted ALOHA greatly improves the expected progress over the system without capture due to the more limited area of possibly interfering terminals around the receiver. The (mini)slotted nonpersistent carrier-sense-multiple-access (CSMA) only slightly outperforms ALOHA, unlike the single-hop case (where a large improvement is available), because of a large area of "hidden" terminals and the long vulnerable period generated by them. As an example of an inhomogeneous terminal distribution, the effect of a gap in an otherwise randomly distributed terminal population on the expected progress of packets crossing the gap is considered. In this case, the disadvantage of using a large transmission radius is demonstrated.

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This paper was first published online by the Internet Society in December 20031 and is being re-published in ACM SIGCOMM Computer Communication Review because of its historic import. It was written at the urging of its primary editor, the late Barry Leiner. He felt that a factual rendering of the events and activities associated with the development of the early Internet would be a valuable contribution. The contributing authors did their best to incorporate only factual material into this document. There are sure to be many details that have not been captured in the body of the document but it remains one of the most accurate renderings of the early period of development available.

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mo problems reZevant t o the design of a store-and-forward communication network ( t h e message routing problem and the chan FinaZ l y , two i n t e r e s t i n g applications