What Is Ethernet?

Ethernet is the IEEE 802.3 family of standards that defines wired local area networking, covering the cables, connectors, frame format, and signaling that carry data between devices on a single network. Ethernet moves data as electrical or optical signals over a physical cable rather than radio waves, which separates Ethernet from Wi-Fi. The standard was first published by the Institute of Electrical and Electronics Engineers in 1983 as IEEE 802.3 and has grown from 10 megabits per second to 400 gigabits per second across later revisions.

This article defines Ethernet, explains how Ethernet works through frames and MAC addressing, lists the Ethernet speed grades from Fast Ethernet to 10 Gigabit Ethernet, describes the cables and RJ45 connectors Ethernet uses, and compares Ethernet against Wi-Fi on latency and reliability. Each section names the relevant IEEE 802.3 designation so the speed, cable, and connector match a defined standard rather than a marketing label. The order moves from the definition of Ethernet to the mechanism, then to the physical media, and ends with the wired-versus-wireless comparison.

What Is Ethernet?

Ethernet is the IEEE 802.3 standard for wired local area networks that defines how devices frame, address, and transmit data over a physical cable. Ethernet specifies the cabling, the connector, the frame structure, and the access method that let computers, switches, and routers exchange data on the same network. The Institute of Electrical and Electronics Engineers maintains Ethernet under the 802.3 working group, which assigns a designation such as 802.3ab for Gigabit Ethernet over copper.

Ethernet operates at the physical layer and the data link layer of the OSI model. The physical layer covers the cable, the connector, and the signaling.

The data link layer covers the frame and the Media Access Control address that identifies each network interface. A single Ethernet network connects through a switch, which forwards each frame to the port holding the destination device.

How Does Ethernet Work?

Ethernet works by packaging data into frames, addressing each frame with MAC addresses, and forwarding the frame through a switch to the destination device. The frame is the unit of transmission, and the MAC address is the identifier that directs each frame to one network interface.

The Ethernet Frame

An Ethernet frame holds the destination MAC address, the source MAC address, an optional VLAN tag, a type field, the data payload, and a frame check sequence. The standard payload ranges from 46 to 1500 bytes, and a jumbo frame extends the payload to 9000 bytes on networks that support it. The frame check sequence uses a cyclic redundancy check so the receiver detects a corrupted frame and discards it.

MAC Addressing and Switching

A MAC address is a 48-bit hardware identifier assigned to each network interface, written as six hexadecimal pairs such as 00:1A:2B:3C:4D:5E. An Ethernet switch reads the source MAC address of each incoming frame and builds a table that maps every MAC address to a physical port. The switch then forwards a frame only to the port that holds the destination address rather than flooding every port.

Full-Duplex Transmission

Modern Ethernet runs in full-duplex mode, which lets a device send and receive data at the same time over separate wire pairs. Full-duplex switching removed the collisions that the original shared-medium Ethernet handled through Carrier Sense Multiple Access with Collision Detection. A full-duplex link between a device and a switch dedicates the full rated bandwidth to that single connection.

What Are the Ethernet Speed Standards?

Ethernet defines six common speed grades, each tied to a specific IEEE 802.3 designation. The speed standards below list the rate and the designation for each grade.

• Fast Ethernet reaches 100 megabits per second. The 100BASE-TX standard under IEEE 802.3u carries 100 Mbps over two pairs of copper.
• Gigabit Ethernet reaches 1000 megabits per second. The 1000BASE-T standard under IEEE 802.3ab carries 1 Gbps over four pairs of copper to 100 meters.
• 2.5 Gigabit Ethernet reaches 2500 megabits per second. The 2.5GBASE-T standard under IEEE 802.3bz runs over existing Cat5e cable to 100 meters.
• 5 Gigabit Ethernet reaches 5000 megabits per second. The 5GBASE-T standard under IEEE 802.3bz runs over Cat6 cable to 100 meters.
• 10 Gigabit Ethernet reaches 10000 megabits per second. The 10GBASE-T standard under IEEE 802.3an runs over Cat6a cable to 100 meters.
• Higher grades reach 25, 40, 100, and 400 gigabits per second. These standards serve data centers over fiber and Cat8 copper rather than home networks.

The speed a link reaches depends on the slowest component in the path. A Gigabit switch port connected through Cat5e cable negotiates 1 Gbps, while the same port over Cat3 cable falls back to 100 Mbps. The cable category that each speed requires is detailed in the breakdown of Ethernet cable types.

What Cables and Connectors Does Ethernet Use?

Ethernet over copper uses twisted-pair cable terminated with an 8P8C connector, known as RJ45, while higher-speed Ethernet uses fiber optic cable with LC or SC connectors. The twisted-pair design pairs and twists each wire to cancel electromagnetic interference.

• Twisted-pair copper carries most Ethernet. Four pairs of copper wire inside one jacket carry the signal for Fast, Gigabit, and 10 Gigabit Ethernet.
• The RJ45 connector terminates copper Ethernet. The 8-position 8-contact connector seats into a switch, router, or network card port.
• Fiber optic carries long-distance and high-speed Ethernet. Glass or plastic strands carry light pulses for runs beyond 100 meters or speeds above 10 Gbps.
• The cable category sets the maximum speed. Categories from Cat5e to Cat8 rate each cable for a bandwidth in megahertz and a top supported speed.

The RJ45 connector follows the TIA-568 wiring standard, which defines the T568A and T568B pin arrangements for the eight conductors. The role of the physical port on a computer is covered in the overview of types of computer ports.

Ethernet vs Wi-Fi: How Do They Differ?

Ethernet sends data over a physical cable, which gives lower latency and steadier throughput than Wi-Fi, while Wi-Fi sends data over radio waves, which removes the cable but adds interference and variable latency. The transmission medium is the core difference between the two.

• Latency is lower on Ethernet. A wired link adds under 1 millisecond of latency, while Wi-Fi adds variable latency from contention and retransmission.
• Reliability is higher on Ethernet. A cable carries a steady signal free of the interference that walls, distance, and other networks add to Wi-Fi.
• Mobility is higher on Wi-Fi. Wi-Fi connects devices without a cable, which suits phones, tablets, and laptops that move between rooms.
• Throughput is more consistent on Ethernet. A Gigabit Ethernet link holds near its rated speed, while Wi-Fi throughput drops with distance and obstacles.

The full set of trade-offs between the two transmission methods appears in the comparison of wired versus wireless networking. The radio-based alternative is defined in the overview of what Wi-Fi is.

What Is Power over Ethernet?

Power over Ethernet, defined under IEEE 802.3af, 802.3at, and 802.3bt, carries electrical power and data over the same Ethernet cable, so a device runs without a separate power adapter. The standard supplies power through the unused or data pairs of the twisted-pair cable.

• 802.3af supplies up to 15.4 watts. The original PoE standard powers IP phones, basic access points, and small cameras over one cable.
• 802.3at supplies up to 30 watts. The PoE+ standard powers pan-tilt-zoom cameras and dual-band access points that draw more current.
• 802.3bt supplies up to 90 watts. The PoE++ standard powers video phones, displays, and devices that need higher draw across all four pairs.
• A PoE switch or injector adds the power. A PoE-capable switch supplies the voltage, or an inline injector adds it to a standard switch port.

Power over Ethernet removes the need for a power outlet at the device, which suits access points and cameras mounted away from an outlet. The access point that PoE commonly powers relays Wi-Fi to wireless devices on the same network.

What Is the History of Ethernet?

Ethernet was invented at Xerox PARC in 1973 by Robert Metcalfe and standardized as IEEE 802.3 in 1983, growing from 10 megabits per second to 400 gigabits per second across later revisions. The standard replaced competing local network technologies through the 1980s and 1990s.

The original Ethernet ran at 10 Mbps over a shared coaxial cable and used Carrier Sense Multiple Access with Collision Detection to manage access. Fast Ethernet raised the rate to 100 Mbps in 1995 under IEEE 802.3u, and Gigabit Ethernet reached 1000 Mbps in 1999 under 802.3ab.

The move from shared coaxial cable to switched twisted-pair links removed collisions and let each connection run in full-duplex at its full rated speed. Ethernet outlasted rival standards such as Token Ring and remains the dominant wired local network technology.

Ethernet Speed Standard Comparison

Key Takeaways

• Ethernet is IEEE 802.3. The standard defines wired local networking, including cables, connectors, frames, and MAC addressing.
• Frames carry the data. Each Ethernet frame holds source and destination MAC addresses plus a payload of 46 to 1500 bytes.
• Switches forward by MAC address. A switch maps each MAC address to a port and sends each frame only to its destination.
• Speed grades range from 100 Mbps to 10 Gbps. Fast, Gigabit, 2.5G, 5G, and 10G Ethernet each match a defined cable category.
• RJ45 terminates copper Ethernet. The 8P8C connector wired to TIA-568 seats into every switch, router, and network card port.

Last Thoughts on Ethernet

Ethernet is the IEEE 802.3 standard that defines wired local area networking through frames, MAC addressing, full-duplex switching, twisted-pair or fiber cable, and the RJ45 connector. Ethernet speed grades run from 100 Mbps Fast Ethernet to 10 Gbps 10GBASE-T, with each grade tied to a cable category and an IEEE designation. The cable category that a given speed requires is detailed in the guide to Ethernet cable types, and the choice between a cable and a radio link is weighed in the comparison of wired versus wireless networking.

The way framed data reaches the wider internet beyond the local network is explained in the overview of how data travels on the internet. The full set of networking topics sits on the how networks work hub.