+ Ethernet physical layer A standard 8P8C (often called RJ45) connector used most commonly on category 5 cable, one of the types of cabling used in Ethernet networks Standard IEEE 802.3 (1983 onwards) Physical media Twisted pair, optical fiber, coaxial cable Network topology Point-to-point, star, bus Major variants 10BASE5, 10BASE2, 10BASE-T, 100BASE-TX, 1000BASE-T, 10GBASE-R Maximum distance 100 m (328 ft) over twisted pair, up to 100 km over optical fiber Mode of operation optical, differential (balanced), single-ended Maximum bit rate to Voltage levels ± 2.5 V (over twisted pair) Common connector types 8P8C, LC, SC, ST, MPO
The physical-layer specifications of the Ethernet family of computer network standards are published by the Institute of Electrical and Electronics Engineers (IEEE), which defines the electrical or optical properties and the transfer speed of the physical connection between a device and the network or between network devices. It is complemented by the MAC layer and the logical link layer. An implementation of a specific physical layer is commonly referred to as PHY.
The Ethernet physical layer has evolved over its existence starting in 1980 and encompasses multiple physical media interfaces and several orders of magnitude of speed from to . The physical medium ranges from bulky coaxial cable to twisted pair and optical fiber with a standardized reach of up to 80 km. In general, network protocol stack software will work similarly on all physical layers.
Many Ethernet adapters and switch ports support multiple speeds by using autonegotiation to set the speed and duplex for the best values supported by both connected devices. If autonegotiation fails, some multiple-speed devices sense the speed used by their partner, but this may result in a duplex mismatch. With rare exceptions, a 100BASE-TX port (10/100) also supports 10BASE-T while a 1000BASE-T port (10/100/1000) also supports 10BASE-T and 100BASE-TX. Most 10GBASE-T ports also support 1000BASE-T, some even 100BASE-TX or 10BASE-T. While autonegotiation can practically be relied on for Ethernet over twisted pair, few optical-fiber ports support multiple speeds. In any case, even multi-rate fiber interfaces only support a single wavelength (e.g. 850 nm for 1000BASE-SX or 10GBASE-SR).
10 Gigabit Ethernet was already used in both enterprise and carrier networks by 2007, with and 100 Gigabit Ethernet ratified. In 2024, the fastest additions to the Ethernet family were variants.
Naming conventions
Generally, layers are named by their specifications:IEEE 802.3 1.2.3 Physical layer and media notation 10, 100, 1000, 10G, ... – the nominal, usable speed at the top of the physical layer (no suffix = , G = ), excluding line codes but including other physical layer overhead (preamble, SFD, IPG); some WAN PHYs (W) run at slightly reduced bitrates for compatibility reasons; encoded PHY sublayers usually run at higher bitrates BASE, BROAD, PASS – indicates baseband, broadband, or passband signaling respectively -T, -T1, -S, -L, -E, -Z, -C, -K, -H ... – medium (PMD): T = twisted pair, -T1 = single-pair twisted pair, S = 850 nm short wavelength (multi-mode fiber), L = 1300 nm long wavelength (mostly single-mode fiber), E or Z = 1500 nm extra long wavelength (single-mode), B = bidirectional fiber (mostly single-mode) using WDM, P = passive optical (PON), C = copper/twinax, K = backplane, 2 or 5 or 36 = coax with 185/500/3600 m reach (obsolete), F = fiber, various wavelengths, H = plastic optical fiber X, R – PCS encoding method (varying with the generation): X for 8b/10b block encoding (4B5B for Fast Ethernet), R for large block encoding (64b/66b) 1, 2, 4, 10 – for LAN PHYs indicates number of lanes used per link; for WAN PHYs indicates reach in kilometers For , no encoding is indicated as all variants use Manchester code. Most twisted pair layers use unique encoding, so most often just -T is used.
The reach, especially for optical connections, is defined as the maximum achievable link length that is guaranteed to work when all channel parameters are met (modal bandwidth, attenuation, insertion losses etc.). With better channel parameters, often a longer, stable link length can be achieved. Vice versa, a link with worse channel parameters can also work but only over a shorter distance. Reach and maximum distance have the same meaning.
Physical layers The following sections provide a brief summary of official Ethernet media types. In addition to these official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling.
Early implementations and
Early Ethernet standards used Manchester coding so that the signal was self-clocking and not adversely affected by high-pass filters.
NameStandard (Clause)Common connectorsLink reachRequired cableDescription Coaxial cableXerox experimental EthernetProprietary (1976)Vampire tap1 km75 Ω coaxialThe original Ethernet implementation had eight-bit addresses and other differences in frame format.10BASE5 (8)AUI, N, vampire tap500 mRG-8/UOriginal standard uses a single coaxial cable in which a connection is made by tapping into the single cable, drilling in to make contact with the core and the screen. Widespread deployment in the early 1980s. Was known also as DIX Standard (pre 802.3) and later as Thick-Ethernet (in contrast to 10BASE2, thinnet). over expensive 50 Ω coaxial cabling, electrical bus topology with collision detection. Deprecated 2003.10BASE2 (10)BNC, 185 mRG-5850 Ω coaxial cable connects machines together, each machine using a T-connector to connect to its NIC. Requires terminators at each end. For many years during the mid to late 1980, this was the dominant Ethernet standard. Also called Thin Ethernet, Thinnet or Cheapernet. over RG-58 coaxial cabling, bus topology with collision detection. Deprecated 2011.10BROAD36 (11)F1800 m @VF0.87IEEE 802.3 11.5.3 Delay requirements75 Ω coaxialAn early standard supporting Ethernet over longer distances. It utilized broadband modulation techniques, similar to those employed in cable modem systems, and operated over coaxial cable. , scrambled NRZ signaling modulated (PSK) over high-frequency carrier, broad bandwidth coaxial cabling, bus topology with collision detection. Deprecated 2003. Twisted-pair cable1BASE5 (12)8P8C ()250 mvoice-gradeAlso called StarLAN. Operated at over twisted pair to an active hub, star topology. Although a commercial failure, 1BASE5 pioneered the use of twisted-pair cabling and defined the architecture for all subsequent Ethernet evolution on that medium. Deprecated 2003.StarLAN 10Proprietary (1988)8P8C100 mvoice-grade over copper twisted pair cabling, star topologyevolved into 10BASE-TLattisNet UTPProprietary (1987)8P8C100 mvoice-grade over copper twisted pair cabling, star topologyevolved into 10BASE-T (14) 8P8C ()100 m Cat-3 Runs over four wires (two twisted pairs). A repeater hub or switch sits in the middle and has a port for each node. This is also the configuration used for . Copper twisted pair cabling, star topologydirect evolution of . , still widely supported. (14)100 mCat-5Energy-Efficient Ethernet variant of 10BASE-T using a reduced amplitude signal over Category 5 cable, completely interoperable with 10BASE-T nodes. (146)IEC 63171-1, IEC 63171-61000 mEthernet over a single twisted pair - long reach, for industrial applications (147)25 mEthernet over a single twisted pair - short reach, for automotive applications with shared medium support, including PoDL802.3da-2026 (188)50 mEthernet over a single twisted pair - medium reach, for automotive applications with shared medium support, including PoDL Fiber-optical cableFOIRL (9.9)ST1000 mFDDI-style MMF Fiber-optic inter-repeater link; the original standard for Ethernet over fiber, superseded by , deprecated 2011 (15) A generic term for the family of Ethernet standards using fiber optic cable: , and . Of these only gained widespread use. over fiber pair (15&18) ST2000 m FDDI-style MMF An updated version of the FOIRL standard for end nodes, 2 km reach over FDDI-style multi-mode fiber, 850 nm wavelength (15&17)2000 m Intended for backbones connecting a number of hubs or switches as a direct successor to FOIRL; deprecated 2011. (15&16)1000 m A passive star network that required no repeater, it was never implemented. Deprecated 2003.
All Fast Ethernet variants use a star topology and generally use 4B5B line coding.
NameStandard (Clause)Common connectorsDescription Twisted-pair cable100BASE‑T (21) A term for any of the three standards for Ethernet over twisted pair cable. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2. , 100BASE-TX has totally dominated the market, and may be considered synonymous with 100BASE-T in informal usage.100BASE-TX (24, 25) 8P8C (FDDI TP-PMD standard, ANSI INCITS 263-1995) 4B5B MLT-3 coded signaling, Category 5 cable using two twisted pairs. The specifications are largely borrowed from FDDI's TP-PMD."The 100BASE-TX PMD (and MDI) is specified by incorporating the FDDI TP-PMD standard, ANSI X3.263: 1995 (TP-PMD), by reference, with the modifications noted below." (section 25.2 of IEEE802.3-2002). , still very popular.100BASE-T4 (23)8P8C ()8B6T PAM-3 coded signaling, Category 3 cable (as used for 10BASE-T installations) using four twisted pairs. Limited to half-duplex. Deprecated 2003.100BASE-T2 (32) 8P8C () PAM-5 coded signaling, CAT3 copper cabling with two twisted pairs, star topology. Supports full-duplex. It is functionally equivalent to 100BASE-TX, but supports old telephone cable. However, special sophisticated digital signal processors are required to handle the encoding schemes it uses, making this option fairly expensive at the time. It arrived well after 100BASE-TX was established in the market. 100BASE-T2 and 100BASE-T4 were not widely adopted but some of the technology developed for them is used in 1000BASE-T. Deprecated 2003.100BASE-T1 (96) none specified Uses PAM-3 modulation at 66.7 MBd over a single, bi-directional twisted pair of up to 15 m; three bits are encoded as two ternary symbols. It is intended for automotive applications.100BaseVG8P8CStandardized by a different IEEE 802 subgroup, 802.12, because it used a different, more centralized form of media access (demand priority). Proposed by Hewlett-Packard. Inherently half-duplex, it needed four pairs in a Cat-3 cable. Now obsolete, the standard has been withdrawn in 2001.HDMI Ethernet Channel (2009)HDMIHEC uses a hybrid to mix and separate 100BASE-TX's transmit and receive signals through a single twisted pair. Fiber-optical cable100BASE‑FX (24, 26)ST, SC4B5B NRZI coded signaling, two strands of multi-mode optical fiber using 1300 nm wavelength. Maximum length is 400 meters for half-duplex connections (to ensure collisions are detected) or 2 kilometers for full-duplex. The specifications are largely borrowed from FDDI.100BASE‑SX (2000)ST, SC Ethernet over multi-mode fiber. Maximum length is 300 meters. 100BASE-SX used short wavelength (850 nm) optics that was sharable with 10BASE-FL, thus making an autonegotiation scheme possible with 10/100 fiber adapters.100BASE‑BX10 (58, 66)ST, SC, LC Ethernet bidirectionally over a single strand of single-mode optical fiber. An optical multiplexer is used to split transmit and receive signals into different wavelengths (1530 and 1310 nm) allowing them to share the same fiber. Supports up to 10 km, full-duplex only.IEEE 802.3 66. Extensions of the Reconciliation Sublayer (RS), 100BASE-X PHY, and 1000BASE-X PHY for unidirectional transport100BASE-LX10 (58)ST, SC, LC Ethernet up to 10 km over a pair of single-mode fibers, using 1310 wavelength, full-duplex only.