Notes:
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)
As earlier stated, ethernet was originally clocked using the internal clock from the Altos at 2.94 Mb/s and was ussed to connect Altos graphical workstations, laser printers and servers together on the same network. In July 1976 Bob Metcalf and David Boggs published the paper “Ethernet: Distributed Packet Switching For Local Computer Networks” in the Communications of the ACM. In late 1977 Bob Metcalf, David Boggs, Charles Thacker, and Butler Lampson received the US patent on ethernet, a “Multipoint Data Communication System With Collision Detection”. The ethernet repeater was patented in 1978.
The original 10Mb/s standard was published in 1980 by the DEC-Intel-Xerox (DIX) consortium. The DIX standard was based on a thick coax cable. Around the same time the IEEE formed sub-committees to standardize different networking technologies (the 802 branch). The ethernet group was 802.3 and the token-ring group was 802.5. The official title of the 802.3 standard was “IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Later Specifications”. They didn’t use the “ethernet” term to avoid endorsing any particular company or companies. The current 802.3 standard is 1,268 pages.