Ethernet physical layer

Generally, layers are named by their specifications: • 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. All Fast Ethernet variants use a star topology and generally use 4B5B line coding. ====== All Gigabit Ethernet variants use a star topology. 1000BASE-X variants use 8b/10b PCS encoding. Initially, half-duplex mode was included in the standard but has since been abandoned. Very few devices support gigabit speed in half-duplex. 2.5 and 2.5GBASE-T and 5GBASE-T are scaled-down variants of 10GBASE-T and provide longer reach over pre-Cat 6A cabling. These physical layers support twisted-pair copper cabling and backplanes only. ====== 10 Gigabit Ethernet is a version of Ethernet with a nominal data rate of , ten times as fast as Gigabit Ethernet. The first 10 Gigabit Ethernet standard, IEEE Std 802.3ae-2002, was published in 2002. Subsequent standards encompass media types for single-mode fiber (long haul), multi-mode fiber (up to 400 m), copper backplane (up to 1 m) and copper twisted pair (up to 100 m). All 10-gigabit standards were consolidated into IEEE Std 802.3-2008. Most 10-gigabit variants use 64b/66b PCS code (-R). 10 Gigabit Ethernet, specifically 10GBASE-LR and 10GBASE-ER, enjoys significant market shares in carrier networks. ====== Single-lane 25-gigabit Ethernet is based on one 25.78125 GBd lane of the four from the 100 Gigabit Ethernet standard developed by the P802.3by task force. 25GBASE-T over twisted pair was approved alongside 40GBASE-T within IEEE 802.3bq. ====== This class of Ethernet was standardized in June 2010 as IEEE 802.3ba. The work also included the first generation, published in March 2011 as IEEE 802.3bg. A twisted-pair standard was published in 2016 as IEEE 802.3bq-2016. ====== The IEEE 802.3cd task force developed along with next-generation 100 and standards using lanes. ====== The first generation of 100 Gigabit Ethernet using 10 and lanes was standardized in June 2010 as IEEE 802.3ba alongside 40 Gigabit Ethernet. ====== First generation have been defined by the IEEE 802.3bs task force and standardized in 802.3bs-2017. may be a further goal. In May 2018, IEEE 802.3 started the 802.3ck task force to develop standards for 100, 200, and PHYs and attachment unit interfaces (AUI) using lanes. It was predicted this would be followed rapidly by a scaling to 100 Terabit, possibly as early as 2020. These were theoretical predictions of technological ability, rather than estimates of when such speeds would actually become available at a practical price point. ====== The Ethernet Technology Consortium proposed an Ethernet PCS variant based on tightly bundled 400GBASE-R in April 2020. In February 2024, the IEEE 802.3df Task Force defined variants for Ethernet over twinaxial copper, electrical backplanes, single-mode and multi-mode optical fiber along with new 200 and variants using lanes. 1.6 Tbit/s In December 2022, IEEE started the P802.3dj Task Force to define variants for 200, 400, 800 and over twinaxial copper, electrical backplanes, single-mode and multi-mode optical fiber along with new variants using lanes. First mile Ethernet in the first mile provides Internet access service directly from providers to homes and small businesses. ==Sublayers==

Starting with Fast Ethernet, the physical layer specifications are divided into three sublayers in order to simplify design and interoperability: • PCS (Physical Coding Sublayer) - This sublayer performs auto-negotiation and basic encoding (e.g., 8b/10b), lane separation and recombination. For Ethernet, the bit rate at the top of the PCS is the nominal bit rate, e.g. for classic Ethernet or for Gigabit Ethernet. • PMA (Physical Medium Attachment sublayer) - This sublayer performs PMA framing, octet synchronization/detection, and polynomial scrambling/descrambling. • PMD (Physical Medium Dependent sublayer) - This sublayer consists of a transceiver for the physical medium. ==Twisted-pair cable==

Several varieties of Ethernet were specifically designed to run over 4-pair copper structured cabling already installed in many locations. In a departure from both 10BASE-T and 100BASE-TX, 1000BASE-T and above use all four cable pairs for simultaneous transmission in both directions through the use of echo cancellation. Using point-to-point copper cabling provides the opportunity to deliver electrical power along with the data. This is called power over Ethernet and there are several variations defined in IEEE 802.3 standards. Combining 10BASE-T (or 100BASE-TX) with Mode A allows a hub or a switch to transmit both power and data over only two pairs. This was designed to leave the other two pairs free for analog telephone signals. The pins used in Mode B supply power over the spare pairs not used by 10BASE-T and 100BASE-TX. 4PPoE defined in IEEE 802.3bt can use all four pairs to supply up to 100 W. The cable requirements depend on the transmission speed and the employed encoding method. Generally, faster speeds require both higher-grade cables and more sophisticated encoding. ==Minimum cable lengths==

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. ==Related standards==

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 variant. • 100BaseVG—An early contender for 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 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 operation – a feature lacking in the official standards due to the use of differing LED wavelengths. It was targeted at the installed base of 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 ) 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. ==References==