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Where did it come from?
Influenced by Norman Abramson's "Aloha Net" Satellite radio link between the Hawaiian islands.
The Aloha network pioneered common channel, multiple access network arbitration
If traffic waiting, transmit. If no ack, assume collision, use random backoff and retry
Notes:
From http://en.wikipedia.org/wiki/ALOHA_network
Metcalf discussed the issues explored in the Aloha network in his memo first describing ethernet. Norman Abramson's group developed an inter-island communication system to experiment with mechanisms for sharing a common channel. The Alohanet was a shared radio channel, but the theory was applicable to other shared channels.
Aloha protocol was to transmit and await acknowledgement. If no acknowledgement, assume a collision and wait a random interval and try again. There was no check before transmitting, so collisions predictably went up as traffic increased. Abramson calculated a theoretical maximum channel utilization of 18% for "pure aloha" due to rapidly increasing collision rates.
Slotted Aloha (time division multiplexed) with a master clock got utilization up to 37%. Abramson received the 1995 IEEE Koji Kobayashi award "for the development of the concept of the Aloha System, which led to modern local area networks".
Metcalf recognized Aloha could be improved by arbitrating access to the communication channel. His new concept included both a "listen before you talk" or "carrier sense" and a method of reliably detecting collision so you didn't have to wait an arbitrary time for an acknowledgement. The resulting system was called Carrier Sense Multiple Access with Collision Detect (CSMA/CD). He also settled on truncated binary exponential backoff (stops after 16 attempts)