2026-08-25
On March 31, 1975, four Xerox PARC researchers — Robert M. Metcalfe, David R. Boggs, Charles P. Thacker, and Butler W. Lampson — filed US Patent 4,063,220. The title was clinical: "Multipoint data communication system with collision detection." The invention was not. In eleven claims, it defined how computers should share a single wire without a traffic cop — and every packet you send, wired or wireless, still follows those rules.
The problem was simple and vicious. If you connect 100 computers to one cable, and any of them can talk whenever it wants, they will inevitably talk at the same time and garble each other. The old telephone solution was a central switch. The old radio solution was assigning each station a frequency. Both required expensive coordination.
Metcalfe had spent 1972 studying ALOHAnet, Norman Abramson's radio network in Hawaii that let terminals on outer islands transmit whenever they liked to a receiver on Oahu — collisions and all. If two packets clashed, both sides waited a random interval and retried. Simple. Wasteful. It topped out around 18% channel utilization.
The patent's insight, developed with Boggs at PARC, was to add two moves:
The whole protocol — CSMA/CD — needed no central controller, no scheduling, no addresses assigned by a master. Nodes were peers. Add or remove a computer by physically tapping the coaxial cable. The network figured itself out.
Boggs and Metcalfe prototyped it on the Xerox Alto at 2.94 Mbps, wiring PARC's offices together. They named it "Ethernet" after the discredited 19th-century "luminiferous ether" that was supposed to carry light waves — the joke being that their coax cable was the ether that carried bits. By 1980, DEC, Intel, and Xerox published the "DIX" standard; in 1983 it became IEEE 802.3.
The direct legacy is obvious: every RJ-45 jack, every switched Gigabit Ethernet port in every data center rack, every 10G/100G/400G backbone. Modern switched Ethernet has largely engineered collisions out of existence, but the frame format, MAC addresses, and preamble timing are Metcalfe and Boggs's design.
The surprising legacy is Wi-Fi. IEEE 802.11 could not literally copy CSMA/CD, because a radio can't reliably hear its own signal while transmitting (the outgoing signal drowns out any collision). So Wi-Fi uses CSMA/CA — collision avoidance: listen, wait a random contention window, then transmit, and expect an ACK. Same philosophy: distributed, peer-based, randomized backoff, no central conductor. Every 802.11 frame you send negotiates airtime the way 1975 PARC nodes negotiated coax.
You'll also find its DNA in Bluetooth adaptive frequency hopping, LoRaWAN's ALOHA-style uplinks, and even the retry-and-backoff logic in TCP congestion control. Metcalfe went on to found 3Com and coined Metcalfe's Law — a network's value grows with the square of its users — a claim you can only make if your network protocol is trivially cheap to join, which is exactly what patent 4,063,220 guaranteed.
The patent expired in 1994, right as the internet went commercial. The timing was accidental. The consequence was that nobody had to license the protocol to sell a network card, and Ethernet ate the world.