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,[1] 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,[2] 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[3][4] and 100 Gigabit Ethernet[5] ratified.[6] In 2017, the fastest additions to the Ethernet family were 200 and 400 Gbit/s.[7] Development of 800 Gbit/s and 1.6 Tbit/s Ethernet standards started in 2021.[8]
^"Configuring and Troubleshooting Ethernet 10/100/1000Mb Half/Full Duplex Auto-Negotiation". Cisco Systems. Retrieved 2016-08-09. ...it is possible for a link partner to detect the speed at which the other link partner operates, even though the other link partner is not configured for auto-negotiation. In order to detect the speed, the link partner senses the type of electrical signal that arrives and sees if it is 10 Mb or 100 Mb.
^"Characteristics of 10GBASE-T Technology". fiber-optical-networking.com. 2017-11-08. Retrieved 2018-04-09.
^"Consideration for 40 Gigabit Ethernet" (PDF). IEEE HSSG. May 2007.
^"40 gigabit Ethernet answers" (PDF). IEEE HSSG. May 2007.
^"HECTO: High-Speed Electro-Optical Components for Integrated Transmitter and Receiver in Optical Communication". Hecto.eu. Retrieved December 17, 2011.
^"IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force". IEEE. 2010-06-19.
^802.3bs-2017 - IEEE Standard for Ethernet - Amendment 10: Media Access Control Parameters, Physical Layers, and Management Parameters for 200 Gb/s and 400 Gb/s Operation. IEEE 802.3. 2017-12-12. doi:10.1109/IEEESTD.2017.8207825. ISBN 978-1-5044-4450-7.
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