So, to get a little retro on everybody, I thought I’d take a step back in time and have a fun look at the history of Ethernet. A couple of months ago, Ethernet actually celebrated its 44th anniversary. That’s right. Ethernet was developed back in 1973 and today, 44 years later, it is becoming THE ubiquitous local area networking (LAN) technology in addition to wide area networking (WAN) and now even infiltrating storage area networking (SAN).
Back in 1970, Bob Metcalf was fresh out of the Massachusetts Institute of Technology (MIT) and working at Xerox Corp. in Palo Alto, California. His team was charged on figuring out how to connect a PC to a Xerox printer. Doing research on networking, he remembered a paper he had seen in his studies at MIT. In the 1960s, Norman Abramson and fellow students at the University of Hawaii worked on a radio network communications mechanism between the Hawaiian Islands.
It was a simple concept: A radio station could send a transmission whenever it liked. If no response was received, it assumed that the other station did not receive the information in the first place because that station had also sent a transmission and caused a “collision.” Using that assumption, each station would chose a random back-off time, retransmit the signal again and there was a pretty good chance of receiving the second send. It was calculated that with this protocol, called Pure Aloha, channel utilization would max out at about 18 percent. To increase channel utilization, Abramson devised “Slotted Aloha” in which they assigned transmission slot times for each station and used a master clock for timeslot synchronization. Is any of this sounding familiar to you?
Metcalf took this theory and added mechanisms for collision detection, “carrier sensing” which created a way to listen for a transmission before sending anything and supported access to a shared channel by multiple sending devices or “multiple access” creating the CSMA/CD protocol. He also developed a more sophisticated backoff algorithm, which, in combination with the CSMA/CD protocol, enabled communications channel operate at 100 percent load vs the 37 percent Aloha Net was maxing out at.
To read more Ethernet blogs from Ronen Isaac, click here.
In late 1972, Metcalf tested the first experimental network on the Xerox Alto computer. In 1973 he presented his first paper on it and changed the name from Aloha Alto to Ethernet to emphasize the evolution of the technology. The name “Ethernet” represented how a single cable could carry transmissions to all stations on a network just as aluminiferous ether could propagate electromagnetic waves in space. In 1976 Bob and his team published their first paper on Ethernet. In the 1980s Ethernet was published as a standard by the IEEE and assigned the IEEE number of 802 for dealing with local area networking technology. Specifically, 803.2 was assigned to Ethernet. Numerous versions of 802 standards exist today depending on the on the medium connected. 802.3 is assigned to wireless LANs, 802.16 is assigned to broadband access (WiMAX) and 802.15.1 is assigned to Bluetooth networking.
Today, Bob Metcalf is still working in networking and influencing and mentoring young under and post-graduates from all over the world as a Professor of Electrical Engineering and Director of Innovation at The University of Texas at Austin.
So, that’s a fun little look back at where Ethernet came from. In my next blog, I’ll talk about where Ethernet is going.
This article was originally published on Military Embedded Systems – http://mil-embedded.com/guest-blogs/aloha-ethernet-the-history-of-ethernet/
