What Is Ethernet?

Ethernet is a family of wired networking technologies that defines the physical and data link layer specifications for local area network (LAN) communication. Originally developed at Xerox PARC by Robert Metcalfe and colleagues in 1973, it was first standardized commercially in 1980 through the DIX specification produced by Digital Equipment Corporation, Intel, and Xerox, and then adopted in 1983 as the IEEE 802.3 standard. Over the subsequent four decades, Ethernet has evolved from a 10 Mbps coaxial cable technology to a family of specifications supporting speeds from 10 Mbps through 400 Gbps over copper twisted pair, multimode fiber, and single-mode fiber media.

Ethernet operates by framing data into variable-length packets called frames, each carrying a destination MAC address, a source MAC address, an EtherType field identifying the encapsulated protocol, a payload of 46 to 1500 bytes, and a 32-bit CRC for error detection. Devices on a shared segment originally contended for channel access using carrier-sense multiple access with collision detection (CSMA/CD), but the near-universal adoption of switched Ethernet eliminated shared-medium collisions and made CSMA/CD operationally vestigial in modern deployments.

IEEE 802.3 Standard and Physical Layers

The IEEE 802.3 standard, maintained by the IEEE 802.3 working group, specifies physical layer signaling, medium attachment unit interfaces, and MAC sublayer operation across a large number of physical media variants. Each variant is named using a convention that encodes speed and medium type: 10BASE-T denotes 10 Mbps over twisted pair, 1000BASE-LX denotes 1 Gbps over long-wavelength single-mode fiber, and 100GBASE-SR4 denotes 100 Gbps over four short-range multimode fiber lanes. Power over Ethernet (PoE), specified in IEEE 802.3af, 802.3at, and 802.3bt, adds DC power delivery over data cables to support IP cameras, wireless access points, and IoT devices. The 2022 revision of the standard, IEEE Std 802.3-2022, consolidated numerous amendments spanning speeds from 10 Mbps to 400 Gbps into a single document exceeding 7,000 pages, reflecting the breadth of the technology family.

Local Area Network Architecture

In local area network deployments, Ethernet is the dominant layer-2 technology interconnecting end stations, switches, and routers within a building or campus. Layer-2 switches use MAC address tables to forward frames only to the destination port, eliminating collision domains and enabling full-duplex operation on each link. Virtual LANs (VLANs), specified in IEEE 802.1Q, partition a single physical switched infrastructure into isolated broadcast domains, allowing a single Ethernet plant to carry traffic for multiple logically separate networks. Spanning Tree Protocol (STP) and its rapid variant RSTP prevent forwarding loops in topologies with redundant paths between switches. The IEEE 802 family of networking standards milestone traces how the 802.3 working group's standardization decisions in the 1980s and 1990s established Ethernet's technical architecture and enabled the interoperability ecosystem that made it the dominant wired LAN technology by the mid-1990s.

Time-sensitive and Industrial Extensions

Time-sensitive networking (TSN), a set of amendments to the IEEE 802.1 standard series, adds deterministic latency guarantees and time synchronization to standard Ethernet infrastructure. TSN enables Ethernet to carry safety-critical traffic in automotive (IEEE 802.1Q profiles for automotive), industrial automation (IEC/IEEE 60802), and avionics environments. Virtual links, a concept used in AFDX (Avionics Full-Duplex Switched Ethernet), define pre-allocated, bandwidth-limited unidirectional paths across an Ethernet network, providing determinism for flight-critical data exchange without the variability of standard switched forwarding. Industrial fieldbuses such as EtherNet/IP and PROFINET adapt standard Ethernet hardware for real-time process control applications, adding application-layer protocols that impose timing and redundancy requirements beyond the base IEEE 802.3 specification. An overview of the Ethernet and IEEE 802.3 standards evolution covers the progression of physical layer speeds and encoding schemes from 10BASE-T through the 400 Gbps specifications ratified in recent years.

Applications

Ethernet has applications across a wide range of environments, including:

• Enterprise and campus local area networks interconnecting computers, servers, and storage
• Data center fabrics linking servers at speeds of 25, 100, and 400 Gbps
• Industrial automation networks using PROFINET and EtherNet/IP over standard Ethernet hardware
• Avionics systems using AFDX virtual links for deterministic flight-critical data distribution
• Home networking via Power over Ethernet for IP cameras, VoIP phones, and access points