Ethernet physical layer

Electrical or optical properties between network devices

+ 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 Coaxial cable, twisted pair, optical fiber Network topology Point to point, star, bus Major variants 10BASE5, 10BASE2, 10BASE T, 100BASE TX, 1000BASE T, 10GBASE T Maximum distance 100 m (328 ft) over twisted pair, up to 100 km over optical fiber Mode of operation differential (balanced), optical, single ended Maximum bit rate 1 Mbit/s to 400 Gbit/s Voltage levels ± 2.5 V (over twisted pair) Common connector types 8P8C, LC, SC, ST

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 1 Mbit/s to 400 Gbit/s. 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 40 Gbit/s and 100 Gigabit Ethernet ratified. In 2017, the fastest additions to the Ethernet family were 200 and 400 Gbit/s. Development of 800 Gbit/s and 1.6 Tbit/s Ethernet standards started in 2021.

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.

Some fiber connections have minimum cable lengths due to maximum level constraints on received signals. Fiber ports designed for long haul wavelengths may require a signal attenuator if used within a building. 10BASE2 installations, running on RG 58 coaxial cable, require a minimum of 0.5 m between stations tapped into the network cable to minimize reflections. 10BASE T, 100BASE T, and 1000BASE T installations running on twisted pair cable use a star topology. No minimum cable length is required for these networks.

Some networking standards are not part of the IEEE 802.3 Ethernet standard, but support the Ethernet frame format, and are capable of interoperating with it. LattisNet—A SynOptics pre standard twisted pair 10 Mbit/s variant. 100BaseVG—An early contender for 100 Mbit/s Ethernet. It runs over four pairs of Category 3 cable but was not commercially successful. TIA 100BASE SX—Promoted by the Telecommunications Industry Association. 100BASE SX is an alternative implementation of 100 Mbit/s Ethernet over fiber; it is incompatible with the official 100BASE FX standard. Its main feature is interoperability with 10BASE FL, supporting autonegotiation between 10 and 100 Mbit/s operation – a feature lacking in the official standards due to the use of differing LED wavelengths. It was targeted at the installed base of 10 Mbit/s fiber networks. TIA 1000BASE TX—Promoted by the Telecommunications Industry Association, it was a commercial failure. 1000BASE TX uses a simpler protocol than the official 1000BASE T standard so the electronics can be cheaper, but requires Category 6 cable. G. hn—A standard developed by ITU T and promoted by HomeGrid Forum for high speed (up to 1 Gbit/s) local area networks over existing home wiring (coaxial cables, power lines and phone lines). G. hn defines an Application Protocol Convergence (APC) layer that accepts Ethernet frames and encapsulates them into G. hn MSDUs. Other networking standards do not use the Ethernet frame format but can still be connected to Ethernet using MAC based bridging. 802.11—Standards for wireless local area networks (LANs), sold as Wi Fi
802.16—Standards for wireless metropolitan area networks (MANs), sold as WiMAX

Other special purpose physical layers include Avionics Full Duplex Switched Ethernet and TTEthernet.