Definition

Ethernet

Contributor(s): Alissa Irei and John Burke

Ethernet is the traditional technology for connecting wired local area networks (LANs), enabling devices to communicate with each other via a protocol -- a set of rules or common network language.

As a data-link layer protocol in the TCP/IP stack, Ethernet describes how network devices can format and transmit data packets so other devices on the same local or campus area network segment can recognize, receive and process them. An Ethernet cable is the physical, encased wiring over which the data travels.

Any device accessing a geographically localized network using a cable -- i.e., with a wired rather than wireless connection -- likely uses Ethernet -- whether in a home, school or office setting. From businesses to gamers, diverse end users depend on the benefits of Ethernet connectivity, including reliability and security.

Compared to wireless LAN technology, Ethernet is typically less vulnerable to disruptions -- whether from radio wave interference, physical barriers or bandwidth hogs. It can also offer a greater degree of network security and control than wireless technology, as devices must connect using physical cabling -- making it difficult for outsiders to access network data or hijack bandwidth for unsanctioned devices.

How Ethernet works

The Institute of Electrical and Electronics Engineers Inc. (IEEE) specifies in the family of standards called IEEE 802.3 that the Ethernet protocol touches both Layer 1 -- the physical layer -- and Layer 2 -- the data link layer -- on the OSI network protocol model. Ethernet defines two units of transmission: packet and frame. The frame includes not just the payload of data being transmitted, but also:

  • the physical media access control (MAC) addresses of both the sender and receiver;
  • VLAN tagging and quality of service information; and
  • error correction information to detect transmission problems.

Each frame is wrapped in a packet that contains several bytes of information to establish the connection and mark where the frame starts.

Engineers at Xerox first developed Ethernet in the 1970s. Ethernet initially ran over coaxial cables, while a typical Ethernet LAN today uses special grades of twisted pair cables or fiber optic cabling. Early Ethernet connected multiple devices into network segments through hubs -- Layer 1 devices responsible for transporting network data -- using either a daisy chain or star topology.

Ethernet cable history image
Evolution of Ethernet

If two devices that share a hub try to transmit data at the same time, however, the packets can collide and create connectivity problems. To alleviate these digital traffic jams, the IEEE developed the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, which allows devices to check whether a given line is in use before initiating new transmissions.

Later, Ethernet hubs largely gave way to network switches, their more sophisticated and modern counterparts. Because a hub cannot discriminate between points on a network segment, it can't send data directly from point A to point B. Instead, whenever a network device sends a transmission via an input port, the hub copies the data and distributes it to all the available output ports.

In contrast, a switch intelligently sends any given port only the traffic intended for its devices rather than copies of any and all the transmissions on the network segment -- improving security and efficiency.

Types of Ethernet cables

The IEEE 802.3 working group approved the first Ethernet standard in 1983. Since then, the technology has continued to evolve and embrace new media, higher transmission speeds and changes in frame content -- e.g., 802.3ac to accommodate VLAN and priority tagging -- and functional requirements -- e.g., 802.3af to define Power over Ethernet (POE), which is crucial to most Wi-Fi and IP telephony deployments. Wi-Fi standards -- IEEE 802.11a, b, g, n, ac and ax -- define the equivalent of Ethernet for Wireless LANs.

Ethernet standard IEEE 802.3u ushered in 100BASE-T -- also known as Fast Ethernet -- with data transmission speeds of up to 100 megabits per second (Mbps). The term BASE-T indicates the use of twisted-pair cabling.

Gigabit Ethernet boasts speeds of 1,000 Mbps -- 1 gigabit or 1 billion bits per second -- 10-Gigabit Ethernet (GbE), up to 10 Gbps, and so on. Network engineers use 100BASE-T largely to connect end-user computers, printers and other devices; to manage servers and storage; and to achieve higher speeds for network backbone segments. Over time, the typical speed of each connection tends to increase.

Ethernet cables connect network devices to the appropriate routers or modems, with different cables working with different standards and speeds. The Category 5 (CAT5) cable supports traditional and 100BASE-T Ethernet, for example, while Category 5e (CAT5e) can handle Gigabit Ethernet and Category 6 (CAT6) works with 10 GbE.

This was last updated in September 2018

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What kind of multiplexing is CSMA/CD most like?
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Tough to answer. Statistical?
It is not time division nor frequency division. No "token ring" for sequencing.
What are the odds of two devices transmitting at the same time resulting in a collision?
Also If a collision occurs, is it bad ?
For streaming video a lost packet might be a few pixels. For a data transfer it could be a corrupted file.

Perhaps its better to say "Monte Carlo" multiplexing because the odds are also determined by the number of players.
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How do you think the role of Ethernet in networking will evolve?
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I'm not computer sabby like most people but lately I can appreciate technology like Wi-Fi and recently ethernet. Question, if I'm sharing my friends' Wi-Fi, is ethernet private browsing or open for all to see? Privacy is important to me.
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Hello there - What is the difference between Broadcast domain and Collision domain?
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If two computers send data at the same time, a collision will occur. When this happens, the data sent is not usable. In general, both computers will stop sending, and wait a random amount of time, before they try again. A special protocol was developed to deal with such problems. It is called Carrier sense multiple access with collision detection or CSMA/CD.
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If a computer boots up and needs and IP address, how can it reach the server and how can the server send the info back? (assuming that the computer and server are on the same ethernet)
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