File:ALOHA PACKET SYSTEM With and Without Slots.pdf

Summary

https://disco.ethz.ch/alumni/pascalv/refs/rn_1975_roberts.pdf This paper was originally distributed informally as ARPA Satellite System Note 8 on June 26, 1972 . The paper i s an important one and since its initial limited distribution, th e paper has been frequently referenced in the open literature, but the paper itself has been unavailable in the open literature . Publication here is meant to correct the previous gap in the literature . As the paper was originally distributed only to other researchers intimately familiar with the area covered by t e paper, the paper makes few concessions to the reader along the lines of introductory or tutorial material . Therefore, a bit o f background material follows . ALOHA packet systems were originally described by Abramson ("The ALOHA System--Another Alternative for Compute r Communication," Proceedings of the AFIPS Fall Joint Compute r Conference, Vol . 37, 1970, pp . 281-285) . In an ALOHA a single broadcast channel is shared by a number of communicating devices . In the version originally described by Abramson, every device transmits its packets independent of any other device or an y specific time . That is, the device transmits the whole packet a t a random point in time ; the device then times out for receiving an acknowledgment . If an acknowledgment is not received, it i s assumed that a collision occured with a packet transmitted b y some other device and the packet is retransmitted after a rando m additional waiting time (to avoid repeated collisions) . Under a certain set of assumptions, Abramson showed that the effective capacity of such a channel is l/(2e) .