01Overview

In 1973 Metcalfe designed Ethernet at Xerox PARC, running at 2.94 Mbps. It used CSMA/CD: listen before sending, back off and retry on collision. In 1980 DEC, Intel and Xerox published the DIX standard; in 1983 IEEE 802.3 standardised it.

In the 1990s switches replaced the shared medium, collision domains disappeared, and speeds rose from 10M to 100M, 1G and 10G. Ethernet’s real victory was simplicity: a fixed frame format, and upgrades confined to the physical layer. Today it is not only the LAN but the default interconnect inside data centres.

02History

  1. 1973

    Metcalfe designs Ethernet

    CSMA/CD on a shared bus.

  2. 1980

    The DIX standard

    Three companies agree on one specification.

  3. 1983

    IEEE 802.3

    The international standard.

  4. 1990

    Switched Ethernet

    Collision domains disappear.

  5. 2000

    10 Gigabit and the datacentre

    Ethernet moves into the backbone.

03Core concepts

CSMA/CD

Listen before talking, listen while talking, back off after a collision.

Frame

Ethernet’s unit of transmission, carrying source and destination MAC addresses.

Switch

Forwards frames by MAC address and splits collision domains.

04Hands-on

Do it once — it beats reading it ten times

Capture your own traffic and list the MAC addresses in the first 20 frames, marking broadcasts

05Self-check

Say it in your own words first, then open the answer. Whatever you cannot explain is what to review next.

Can you explain "CSMA/CD"?

Listen before talking, listen while talking, back off after a collision.

Can you explain "Frame"?

Ethernet’s unit of transmission, carrying source and destination MAC addresses.

Can you explain "Switch"?

Forwards frames by MAC address and splits collision domains.

What problem did it solve, and why was there nothing better at the time?

Go back to the history section: how was this done before, and what did it cost?

If you had to build it today, how would you break it down?

Use the hands-on task above: write a plan of at most three steps before you start.

06Key people

R

Robert Metcalfe

1946 –

Inventor of Ethernet.

R

Radia Perlman

1951 –

Spanning tree protocol, which lets Ethernet be redundant.

07Further reading

  • Ethernet: The Definitive GuideCharles Spurgeon · 2000
  • Computer NetworksTanenbaum & Wetherall · 1981