Field Guide · concept

Also known as: IEEE 802.3

Ethernet is the dominant family of wired local-area networking standards, defining the cabling, signaling, and frame format that carry data between computers on a LAN.1

Preamble SFD Dest MAC Src MAC Type Payload (data) FCS 7 B 1 B 6 B 6 B 2 B 46–1500 B 4 B MAC addresses steer the frame; the FCS is a CRC that catches corruption in transit
An Ethernet frame: a preamble and start delimiter mark its beginning, destination and source MAC addresses say who it is for and from, a type field names the payload's protocol, and a frame check sequence (a CRC) at the tail lets the receiver detect corruption.

Overview

Standardized as IEEE 802.3, Ethernet packages data into frames tagged with source and destination MAC addresses and sends them over twisted-pair copper (terminated in the familiar 8-pin RJ45 plug) or over fiber-optic cable for longer runs and higher speeds. Each 48-bit MAC address is globally unique to a network interface, so a switch can learn which port each device sits behind and forward frames only where they need to go.

Speeds have climbed from the original 10 Mb/s through Fast and Gigabit Ethernet to 10, 100, and 400 Gb/s, each grade reusing the same frame format so old and new gear interoperate. Devices attach through a NIC and connect to a switch; the same cabling can also carry power via Power over Ethernet.

A tail frame check sequence — a cyclic redundancy check — lets the receiver discard any frame that arrived corrupted, so upper layers see a clean byte stream or nothing at all. That reliability, plus predictable latency, is why wired Ethernet remains the default for anything that must not drop.

Speed grades

The family has scaled by three orders of magnitude while keeping one frame format:

Name Rate Typical medium Era
Ethernet 10 Mb/s Twisted pair / coax 1980s
Fast Ethernet 100 Mb/s Cat 5 twisted pair 1990s
Gigabit 1 Gb/s Cat 5e/6 twisted pair 2000s
10 GigE 10 Gb/s Cat 6a copper / fiber 2000s–10s
100–400 GigE 100–400 Gb/s Fiber Data centers

Where it fits

Ethernet is the default for fixed, performance-sensitive connections where a cable is practical — servers, desktops, and infrastructure — while Wi-Fi handles mobility. A wired Ethernet link gives a GopherTrunk capture node a stable, low-jitter path to stream decoded calls to a server, avoiding the contention and interference of a shared radio channel; paired with PoE, a single cable can both feed and power a mast-mounted node.

Sources

  1. Ethernet — Wikipedia, on the wired LAN standard family, the 802.3 frame format, and its speed grades. 

See also