Ethernet

Ethernet is a family of computer networking technologies for local area networks (LANs). It defines both the physical media and the data-link layer protocols used to place data on a shared communication medium and to receive it. The term originates from the early Ethernet work at Xerox PARC and was standardized as IEEE 802.3, with ongoing amendments to cover new speeds, media, and features.

Original Ethernet used thick or thin coax (10BASE5, 10BASE2) and CSMA/CD on a shared bus. Since the 1990s, Ethernet has evolved to use star topologies with switches, eliminating collisions in full-duplex operation. It relies on copper twisted-pair and fiber-optic cables, supporting distances from a few meters to several kilometers depending on the standard.

Ethernet frames contain destination and source MAC addresses, EtherType or length, payload (up to 1500 bytes for standard frames), and a Frame Check Sequence. Minimum frame size is 64 bytes; maximum is 1518 bytes, though some variants add extra headers (VLAN tags, jumbo frames).

Speeds have progressed from 10 Mbps (10BASE-T) to 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit Ethernet), 10 Gbps, 40 Gbps, and beyond. Copper variants include 10BASE-T, 100BASE-TX, 1000BASE-T, 10GBASE-T. Fiber variants include 100BASE-FX, 1000BASE-LX/SX, 10GBASE-SR/LR. Auto-negotiation allows devices to agree on speed and duplex.

Today Ethernet is the dominant LAN technology, featuring low cost, high reliability, and broad interoperability. It remains defined within IEEE 802.3 with numerous amendments; Ethernet frames and switching underpin most enterprise networks, data centers, and the internet's access infrastructure.