Ethernet: The Humble Protocol That Conquered the World
How a simple frame format and CSMA/CD became the foundation for literally every wired network on Earth
Look around you right now. Every computer, printer, router, switch, and smart device connected to a wired network is using Ethernet. Your laptop’s WiFi? It converts to Ethernet when it hits the access point. That fancy fiber optic connection to your ISP? Ethernet frames running over light.
Ethernet has become so universally dominant that we don’t even think about it anymore. It’s like electrical outlets - just basic infrastructure that we expect to work everywhere.
But here’s the crazy part: Ethernet started as a scrappy underdog fighting against IBM’s Token Ring and other “superior” networking technologies. It won not because it was the best technical solution, but because it was simple, cheap, and good enough.
The Ethernet frame - this simple structure carries literally every piece of data on every wired network
The Birth of Ethernet: A Hawaiian Inspiration
Ethernet was invented at Xerox PARC in 1973 by Bob Metcalfe and David Boggs. The inspiration came from an unlikely source: ALOHAnet, a radio-based packet network in Hawaii that connected the islands.
ALOHAnet’s approach was beautifully simple: just transmit whenever you have data. If two stations transmitted at the same time and their signals collided, they’d both detect the collision and try again later with a random delay.
Metcalfe realized this same approach could work for coaxial cable networks. He called it “Ethernet” because the original coax cable acted like the old scientific concept of “luminiferous ether” - a shared medium that carried signals.
CSMA/CD: Polite Conversation on a Shared Medium
Early Ethernet used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) - essentially a set of polite conversation rules for a shared network cable:
Carrier Sense: “Is anyone else talking?”
Before transmitting, listen to see if the cable is busy. If someone else is transmitting, wait your turn.
Multiple Access: “Everyone can talk”
Any device can use the shared medium when it appears to be free.
Collision Detection: “Oops, we both started talking”
If two devices start transmitting simultaneously, they detect the collision and both stop immediately.
Exponential Backoff: “Let’s not do that again right away”
After a collision, each device waits a random amount of time before trying again. If collisions keep happening, the wait times increase exponentially.
This created a surprisingly fair system where busy networks naturally self-regulated, and devices with urgent data got it through eventually.
The Frame: Ethernet’s Universal Container
The genius of Ethernet is its simple frame format. Every piece of data - whether it’s a web page, email, video stream, or IoT sensor reading - gets wrapped in the same basic structure:
Preamble: “Pay attention, here comes a frame”
Destination MAC: “This data is for device XX:XX:XX:XX:XX:XX”
Source MAC: “This data came from device YY:YY:YY:YY:YY:YY”
EtherType: “The payload is IP traffic” (or whatever protocol)
Payload: The actual data (46-1500 bytes)
Frame Check Sequence: “Here’s a checksum to verify integrity”
This universal wrapper means Ethernet can carry any higher-level protocol without caring what’s inside.
MAC Addresses: Every Device’s Unique Fingerprint
Every Ethernet device has a MAC address (Media Access Control) - a supposedly unique 48-bit identifier burned into the hardware. These look like 00:1B:44:11:3A:B7 and serve as the physical address for Ethernet communication.
The first 24 bits identify the manufacturer (called the OUI - Organizationally Unique Identifier). You can tell if a device was made by Intel, Apple, or Cisco just by looking at its MAC address.
MAC addresses only matter locally - they identify devices on the same Ethernet segment. When data needs to travel across routers to different networks, the MAC addresses get rewritten at each hop while the IP addresses stay the same.
The Evolution: From Collisions to Switches
Early Ethernet used shared coax cable where everyone competed for the same medium. This worked fine for small networks, but performance degraded badly as more devices were added.
The breakthrough came with Ethernet switches in the 1990s. Instead of everyone sharing one cable, switches created dedicated point-to-point links between each device and the switch.
This eliminated collisions entirely and created full-duplex communication - devices could send and receive simultaneously. A modern switched Ethernet network is actually thousands of individual point-to-point links managed by intelligent switches.
Speed Evolution: From 3 Mbps to 800 Gbps
Ethernet’s speed evolution is mind-blowing:
1973: Original Ethernet - 3 Mbps over coax
1985: 10BASE-T - 10 Mbps over twisted pair
1995: Fast Ethernet - 100 Mbps
1999: Gigabit Ethernet - 1 Gbps
2002: 10 Gigabit Ethernet - 10 Gbps
2010: 40/100 Gigabit Ethernet
2017: 200/400 Gigabit Ethernet
2024: 800 Gigabit Ethernet
That’s a 250,000x speed increase over 50 years, while maintaining backward compatibility with the basic frame format. You can still plug a 1985 Ethernet device into a modern network (with the right adapters) and it will work.
Why Ethernet Won the Standards War
In the 1980s and 1990s, Ethernet competed against several “technically superior” alternatives:
Token Ring: More predictable performance, but complex and expensive
FDDI: Faster and more reliable, but required expensive fiber optic infrastructure
ATM: Promised to unify voice, video, and data, but was incredibly complex
Ethernet won because it was:
Simple: Easy to understand, implement, and troubleshoot
Cheap: Used commodity parts and simple manufacturing
Flexible: Worked over different cable types and at different speeds
Open: Standardized by IEEE, not controlled by a single vendor
Good Enough: Met most networking needs without overengineering
Modern Ethernet: Way Beyond Simple Networking
Today’s Ethernet does things the original designers never imagined:
Power over Ethernet (PoE)
Ethernet cables can now carry both data and power, eliminating the need for separate power supplies for IP phones, security cameras, and access points.
Ethernet Storage Networks
High-speed Ethernet has largely replaced expensive Fibre Channel in storage area networks. Your “cloud storage” is probably running over Ethernet.
Automotive Ethernet
Modern cars use Ethernet for high-speed communication between computers controlling everything from entertainment to autonomous driving systems.
Time-Sensitive Networking (TSN)
Industrial Ethernet can now provide microsecond-precise timing for factory automation and real-time control systems.
Single Pair Ethernet
New standards allow Ethernet over just two wires, enabling IoT devices and automotive applications with minimal cabling.
The Hidden Ethernet Everywhere
Most people think of Ethernet as “that cable that plugs into my computer,” but it’s actually everywhere:
- WiFi access points convert wireless to Ethernet
- Cell phone towers use Ethernet for backhaul connections
- Smart TVs and streaming devices often prefer Ethernet over WiFi
- Game consoles use Ethernet for low-latency online gaming
- Industrial control systems run on specialized Ethernet variants
- Data centers are entirely built on high-speed Ethernet fabrics
A Personal Note
I’ve worked with Ethernet since the 10BASE-2 coax days with vampire taps and terminating resistors. Watching it evolve from a collision-prone shared medium to today’s 400+ Gbps switched fabrics has been incredible.
What I love most about Ethernet is its democratic nature. It’s not controlled by any single company, it’s implemented by everyone, and it just works. The basic frame format from 1973 is still carrying this blog post to your device right now.
Ethernet succeeded not because it was perfect, but because it was adaptable. Every time it faced a new challenge (speed, distance, power, timing), the networking community found ways to extend it while preserving its essential simplicity.
That’s the mark of a truly great standard.
Want to explore more foundational protocols? Check out our deep dives into TCP (reliable transport), IP (internet layer), and DNS (name resolution). Or browse our complete protocol library.
