The story of our first MAC starts out in pristine Hawaii in the early 1970s.
The story of our first MAC starts out in pristine Hawaii in the early 1970s. Inthis case, ‘‘pristine’’ can be interpreted as ‘‘not havinga workingtelephone sys-tem.’’ This did not make life more pleasant for researcher Norman Abramson and his colleagues at the University of Hawaii whowere trying toconnect userson re-mote islands to the main computer in Honolulu. Stringing their own cables under the Pacific Ocean was notin the cards, so they looked for a different solution.
The one they found usedshort-range radios, witheach userterminal sharing the same upstream frequency to send frames to the central computer. It included a simple and elegant method to solve the channel allocation problem. Their work has been extended by many researchers since then (Schwartz and Abramson, 2009). Although Abramson’s work, called the ALOHA system, used ground-based radio broadcasting, the basic idea is applicable to any system in which uncoordinated users are competing for the use of a single shared channel.
We will discuss two versions of ALOHA here: pure and slotted. They differ with respect to whether time is continuous, as in the pure version, or divided into discrete slots into which all frames must fit.