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University of Hawaii

Electrical Engineering

ALOHAnet

There was a time before the internet and cellphones!

Back in 1968, professors in the Electrical Engineering department at the University of Hawaii at Manoa, Prof. Norman Abramson Prof. Thomas Gaarder, Prof. Franklin Kuo, Prof. Shu Lin, Prof. Wesley Peterson, and Prof. Edward ("Ned") Weldon, started working on the ALOHA network protocol.

The goal was to connect users at the Mānoa campus on the island of Oʻahu with users at other University of Hawaiʻi campuses on other islands using low-cost commercial radio equipment. The first broadcast was made in 1971.

ALOHAnet is an important part of telecommunication development because it demonstrated the viability of random access protocols. Unlike existing protocols at the time in which users directly communicated to one another to avoid collisions between user traffics, ALOHAnet proposed the wild idea of letting all the client nodes communicate with each other on the same frequency. How then did ALOHAnet avoid user collisions?

The control mechanism of ALOHAnet was simple: each user would send its data without controlling when it was sent; if there was no traffic, the data got through. If there was traffic, then the user waited a random amount of time before resending. Such a simple control scheme meant a huge decrease in protocol complexity as well as in the cost of networking hardware. The random-access channel was the basis for Ethernet development and later Wi-Fi networks. Later advancements of the ALOHA protocol also appeared in satellite communications and GSM networks.

Why did they think that such a simple control scheme would work? With math! (See Wikipedia page for detail.) They showed that the probability of collision on a random-access channel is small enough that the ALOHAnet is an efficient way of transmitting data.

The College of Engineering at the University of Hawaii at Manoa was presented with an IEEE MILESTONE plaque in October 2020.

Plaque mounted on the Dole street facing wall of Holmes Hall