Ethernet as a LAN technology family
Ethernet is a family of wired networking technologies used mainly in Local Area Networks (LAN), and also in access and Metropolitan Area Networks (MAN). In Wide Area Networks (WAN), it is used in services provided by network operators. Ethernet prototypes were developed at Xerox PARC during the 1970s, including work by Robert Metcalfe. Metcalfe and David Boggs published their Ethernet description in 1976, and IEEE later standardized the technology in the 802.3 family. Its adoption is linked to a simple structure, low deployment cost, and a broad choice of transmission media.
Ethernet's scope also reflects standardization. The 802.3 working group defines Ethernet specifications for the Physical Layer and the MAC sublayer. Compliance with the relevant PHY and MAC parameters allows devices from different manufacturers to interoperate.
Reading Ethernet standard names
Ethernet standards use a naming convention such as 10Base-T. Its elements can be read as follows:
- 10: Indicates the nominal transmission rate in megabits per second (Mbps), in this case 10 Mbps.
- Base: Stands for signaling, meaning the standard uses digital signaling over the entire channel.
- T: Indicates the medium. 'T' stands for Twisted Pair, while '2' and '5' identify historical coaxial variants. Letters such as 'F', 'S', 'L', and 'E' occur in names for different fiber PHYs, depending on the standard.
Classic Ethernet at 10 Mbps
The first Ethernet standards operated at 10 Mbps and used a shared medium in which devices participated in one communication domain.
Coaxial standards, bus topology
- 10Base-5 (Thicknet):This early Ethernet standard used thick, rigid coaxial cable as a shared backbone. Devices connected using "vampire taps" that pierced the insulation to make contact. The maximum segment length was 500 meters.
- 10Base-2 (Thinnet): A less expensive and more flexible successor used thinner coaxial cable. Devices were connected in a daisy-chain fashion using BNC T-connectors. The maximum segment length was 185 meters. Both standards created a single , meaning collisions were a normal part of operation, managed by the CSMA/CD protocol.
10BASE-T, star topology
The introduction of 10Base-T promoted physical star wiring in place of a bus. Each device used its own cable to a central device.
- Medium: Used Unshielded Twisted Pair (UTP) Category 3 or 5 cable, commonly terminated with an 8P8C connector called RJ-45.
- Central device: Initially, devices were connected to a . A hub acts as a simple multiport repeater, meaning it copies incoming data to all other ports. Logically, the network still behaved like a bus, with all devices in the same collision domain. Later, hubs were replaced by switches that selectively forward frames.
- Benefits: A failure on one cable usually affected one link, which simplified troubleshooting and limited the impact on other devices.
Fast Ethernet: 100 Mbps
As applications grew more demanding, higher speeds led to Fast Ethernet, standardized as IEEE 802.3u. The standard increased the nominal rate tenfold to 100 Mbps.
- 100Base-TX: The dominant standard for Fast Ethernet over copper. It requires two pairs of wires in a Category 5 (or better) UTP cable. It became the de facto standard for LAN connections for many years.
- 100Base-FX: The fiber optic version of Fast Ethernet. It uses two strands of (one for transmitting, one for receiving). Under specified conditions and full-duplex operation, the reach can be up to 2 km.
Gigabit Ethernet: 1 Gbps
The next tenfold increase brought Gigabit Ethernet (1000 Mbps), used for high-performance server connections and network backbones.
Gigabit over copper, 1000BASE-T
Standardized as IEEE 802.3ab, 1000Base-T uses all four pairs of a Category 5e or better cable to transmit in both directions at the same time (). This requires signal processing and echo cancellation.
Gigabit over fiber, 1000BASE-X
Standardized as IEEE 802.3z, this family includes fiber optic versions for backbone connectivity:
- 1000Base-SX: Uses short-wavelength (S) lasers, around 850 nm, over multimode fiber. Reach up to 550 meters depends on the fiber grade.
- 1000Base-LX: Uses long-wavelength (L) lasers, around 1310 nm, over multimode fiber (typically up to 550 m) and (typically up to 5 km).
10 Gigabit Ethernet and Higher Rates
10 Gigabit Ethernet (10 Gbps) extended Ethernet use to access links, data centers, and selected metropolitan connections.
- 10GBASE-T: Provides 10 Gbps over copper. A full 100-meter channel requires Category 6A or better, including Category 7, with the installation meeting the specified parameters.
- 10GBASE-SR/LR/ER: A family of fiber standards for different distances: Short Reach (about 300 m on MMF), Long Reach (10 km on SMF), and Extended Reach (40 km on SMF).
- 10GBASE-LX4: A standard that uses Coarse WDM (CWDM) to transmit four wavelengths over a single pair of multimode fibers to achieve 10 Gbps.
40 Gbps and 100 Gbps Ethernet
Standardized in IEEE 802.3ba, 40 and 100 Gbps interfaces use parallel transmission lanes. The part of the standard defining the physical-medium details is the sublayer.
Standards and technologies
- 40GBASE-SR4 and 100GBASE-SR10: These are short-reach standards over parallel multimode fiber. 40G uses 4 lanes of 10 Gbps each, typically 8 fibers for both directions. 100G uses 10 lanes of 10 Gbps each, typically 20 fibers.
- 40GBASE-LR4 and 100GBASE-LR4: These are long-reach standards over a single pair of single-mode fibers. They use to transmit 4 separate wavelengths ("colors"). For 40G, each wavelength carries 10 Gbps; for 100G, each carries 25 Gbps.
- 100GBASE-ER4: An Extended Reach variant defined in the 100G standards family, capable of transmitting 100 Gbps up to 40 km over single-mode fiber.
IEEE P802.3df completed with IEEE Std 802.3df-2024 for 400 Gbps and 800 Gbps Ethernet. IEEE P802.3dj covers further rates, including 1.6 Tbps, and remains a project whose status depends on its stage of standardization.