computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

ing, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common. Fast Ethernet was introduced in 1995 as the IEEE 802.3u standard and remained the fastest version of Ethernet for three years before the introduction of

Gigabit Ethernet In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use i ...

. The acronym ''GE/FE'' is sometimes used for devices supporting both standards.

Nomenclature

The "100" in the media type designation refers to the transmission speed of 100 Mbit/s, while the "BASE" refers to

baseband In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...

signaling. The letter following the dash ("T" or "F") refers to the physical medium that carries the signal (twisted pair or fiber, respectively), while the last character ("X", "4", etc.) refers to the

line code In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained c ...

method used. Fast Ethernet is sometimes referred to as 100BASE-X, where "X" is a placeholder for the FX and TX variants.

General design

Fast Ethernet is an extension of the 10-megabit

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

standard. It runs on

twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted ba ...

optical fiber cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...

in a star wired bus topology, similar to the IEEE standard 802.3i called

10BASE-T 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...

, itself an evolution of 10BASE5 (802.3) and 10BASE2 (802.3a). Fast Ethernet devices are generally backward compatible with existing 10BASE-T systems, enabling plug-and-play upgrades from 10BASE-T. Most switches and other networking devices with ports capable of Fast Ethernet can perform

autonegotiation Autonegotiation is a signaling mechanism and procedure used by Ethernet over twisted pair by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control. In this process, the connected devices ...

, sensing a piece of 10BASE-T equipment and setting the port to 10BASE-T half duplex if the 10BASE-T equipment cannot perform auto negotiation itself. The standard specifies the use of

CSMA/CD Carrier-sense multiple access with collision detection (CSMA/CD) is a medium access control (MAC) method used most notably in early Ethernet technology for local area networking. It uses carrier-sensing to defer transmissions until no other statio ...

for media access control. A

full-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

mode is also specified and in practice, all modern networks use

Ethernet switch A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A netw ...

es and operate in full-duplex mode, even as legacy devices that use half duplex still exist. A Fast Ethernet adapter can be logically divided into a

media access control In IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublay ...

ler (MAC), which deals with the higher-level issues of medium availability, and a physical layer interface (

PHY PHY is an abbreviation for the physical layer of the OSI model and refers to the circuitry required to implement physical layer functions. PHY or Phy may also refer to: * Phy, the drug methadone * Phetchabun Airport (IATA code), Thailand See ...

). The MAC is typically linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a

media-independent interface The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet (i.e., ) media access control (MAC) block to a PHY#Ethernet physical transceiver, PHY chip. The MII is standardized by IEEE 802.3u and ...

(MII), or by a two-bit 50 MHz variant called

reduced media independent interface The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet (i.e., ) media access control (MAC) block to a PHY chip. The MII is standardized by IEEE 802.3u and connects different types of PHYs ...

(RMII). In rare cases, the MII may be an external connection but is usually a connection between ICs in a network adapter or even two sections within a single IC. The specs are written based on the assumption that the interface between MAC and PHY will be an MII but they do not require it. Fast Ethernet or

Ethernet hub An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/out ...

s may use the MII to connect to multiple PHYs for their different interfaces. The MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s. The

information rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

actually observed on real networks is less than the theoretical maximum, due to the necessary header and trailer (addressing and error-detection bits) on every

Ethernet frame In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload. ...

, and the required

interpacket gap In computer networking, the interpacket gap (IPG), also known as interframe spacing, or interframe gap (IFG), is a pause which may be required between network packets or network frames. Depending on the physical layer protocol or encoding used, ...

between transmissions.

Copper

100BASE-T is any of several Fast Ethernet standards for

twisted pair cable Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted ba ...

s, including: 100BASE-TX (100 Mbit/s over two-pair Cat5 or better cable), 100BASE-T4 (100 Mbit/s over four-pair

Cat3 Cat 3 or CAT3 may refer to: * Category 3 cable, an unshielded twisted pair cable * Nanaimo/Long Lake Water Airport (ICAO airport code), Canada * Cognitive Abilities Test 3, a test of reasoning abilities undertaken by students in the UK and Canada ...

or better cable, defunct), 100BASE-T2 (100 Mbit/s over two-pair Cat3 or better cable, also defunct). The segment length for a 100BASE-T cable is limited to (the same limit as

and

gigabit Ethernet In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use i ...

). All are or were standards under

IEEE 802.3 IEEE 802.3 is a working group and a collection standards defining the physical layer and data link layer's media access control (MAC) of wired Ethernet. The standards are produced by the working group of Institute of Electrical and Electronics Eng ...

(approved 1995). Almost all 100BASE-T installations are 100BASE-TX.

100BASE-TX

100BASE-TX is the predominant form of Fast Ethernet, and runs over two wire-pairs inside a category 5 or above cable. Each

network segment A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations. Ethernet According to the defining IEEE 802.3 standards ...

can have a maximum cabling distance of . One pair is used for each direction, providing

operation with 100 Mbit/s of throughput in each direction. Like

, the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6. Since a typical category 5 cable contains 4 pairs, it can support two 100BASE-TX links with a wiring adaptor. Cabling is conventional wired to

ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...

's termination standards, T568A or T568B. This places the active pairs on the orange and green pairs (canonical second and third pairs). The configuration of 100BASE-TX networks is very similar to 10BASE-T. When used to build a

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...

, the devices on the network (computers, printers etc.) are typically connected to a hub or

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

, creating a

star network A star network is an implementation of a spoke–hub distribution paradigm in computer networks. In a star network, every host is connected to a central hub. In its simplest form, one central hub acts as a conduit to transmit messages. The ...

. Alternatively, it is possible to connect two devices directly using a

crossover cable A crossover cable connects two devices of the same type, for example DTE-DTE or DCE-DCE, usually connected asymmetrically (DTE-DCE), by a modified cable called a crosslink. Such a distinction between devices was introduced by IBM. The cross ...

. With today's equipment, crossover cables are generally not needed as most equipment supports auto-negotiation along with

auto MDI-X A medium dependent interface (MDI) describes the interface (both physical and electrical/optical) in a computer network from a physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also d ...

to select and match speed, duplex and pairing. With 100BASE-TX hardware, the raw bits, presented 4 bits wide clocked at 25 MHz at the MII, go through

4B5B In telecommunication, 4B5B is a form of data communications line code. 4B5B maps groups of 4 bits of data onto groups of 5 bits for transmission. These 5-bit words are pre-determined in a dictionary and they are chosen to ensure that there will be ...

binary encoding to generate a series of 0 and 1 symbols clocked at a 125 MHz

symbol rate In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in ''b ...

. The 4B5B encoding provides DC equalization and spectrum shaping. Just as in the 100BASE-FX case, the bits are then transferred to the physical medium attachment layer using NRZI encoding. However, 100BASE-TX introduces an additional, medium-dependent sublayer, which employs

MLT-3 MLT-3 encoding (Multi-Level Transmit) is a line code (a signaling method used in a telecommunication system for transmission purposes) that uses three voltage levels. An MLT-3 interface emits less electromagnetic interference and requires less band ...

as a final encoding of the data stream before transmission, resulting in a maximum

fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. In ...

of 31.25 MHz. The procedure is borrowed from the ANSI X3.263

FDDI Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case it m ...

specifications, with minor changes."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).

100BASE-T1

In 100BASE-T1 the data is transmitted over a single copper pair, 3 bits per symbol, each transmitted as code pair using PAM3. It supports full-duplex transmission. The twisted-pair cable is required to support 66 MHz, with a maximum length of 15 m. No specific connector is defined. The standard is intended for automotive applications or when Fast Ethernet is to be integrated into another application. It was developed as BroadR-Reach before IEEE standardization.

100BASE-T2

In 100BASE-T2, standardized in IEEE 802.3y, the data is transmitted over two copper pairs, but these pairs are only required to be category 3 rather than the category 5 required by 100BASE-TX. Data is transmitted and received on both pairs simultaneously thus allowing full-duplex operation. Transmission uses 4 bits per symbol. The 4-bit symbol is expanded into two 3-bit symbols through a non-trivial scrambling procedure based on a

linear-feedback shift register In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a sh ...

. This is needed to flatten the bandwidth and emission spectrum of the signal, as well as to match transmission line properties. The mapping of the original bits to the symbol codes is not constant in time and has a fairly large period (appearing as a pseudo-random sequence). The final mapping from symbols to

PAM-5 Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier puls ...

line modulation levels obeys the table on the right. 100BASE-T2 was not widely adopted but the technology developed for it is used in 1000BASE-T.

100BASE-T4

100BASE-T4 was an early implementation of Fast Ethernet. It requires four twisted copper pairs of voice grade twisted pair, a lower-performing cable compared to

category 5 cable Category 5 cable (Cat 5) is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is ...

used by 100BASE-TX. Maximum distance is limited to 100 meters. One pair is reserved for transmit, one for receive, and the remaining two switch direction. The fact that 3 pairs are used to transmit in each direction makes 100BASE-T4 inherently half-duplex. A very unusual 8B6T code is used to convert 8 data bits into 6 base-3 digits (the signal shaping is possible as there are nearly three times as many 6-digit base-3 numbers as there are 8-digit base-2 numbers). The two resulting 3-digit base-3 symbols are sent in parallel over 3 pairs using 3-level

pulse-amplitude modulation Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulse ...

(PAM-3). 100BASE-T4 was not widely adopted but some of the technology developed for it is used in

1000BASE-T In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use i ...

. Very few hubs were released with 100BASE-T4 support. Some examples include the

3com 3Com Corporation was an American digital electronics manufacturer best known for its computer network products. The company was co-founded in 1979 by Robert Metcalfe, Howard Charney and others. Bill Krause joined as President in 1981. Metcalfe ex ...

3C250-T4 Superstack II HUB 100, IBM 8225 Fast Ethernet Stackable Hub and

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...

LinkBuilder FMS 100 T4. The same applies to

network interface controller A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network. Ear ...

cards. Bridging 100BASE-T4 with 100BASE-TX required additional network equipment.

100BaseVG

Proposed and marketed by

Hewlett Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...

, 100BaseVG was an alternative design using category 3 cabling and a token concept instead of CSMA/CD. It was slated for standardization as IEEE 802.12 but it quickly vanished when switched 100BASE-TX became popular.

Fiber optics

Fast Ethernet SFP ports

Fast Ethernet speed is not available on all SFP ports, but supported by some devices. An SFP port for

should not be assumed to be backwards compatible with Fast Ethernet.

Optical interoperability

To have interoperable there is some criteria that have to be meet: *

Line encoding In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained co ...

Wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

* Duplex mode * Media count * Media type and dimension 100BASE-X Ethernet is not backward compatible with

10BASE-F Classic Ethernet is a family of 10 Mbit/s Ethernet standards, which is the first generation of Ethernet standards. In 10BASE-X, the 10 represents its maximum throughput of 10 Mbit/s, BASE indicates its use of baseband transmission, and ...

and is not forward compatible with

1000BASE-X In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use i ...

100BASE-FX

100BASE-FX is a version of Fast Ethernet over

optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...

. The 100BASE-FX

physical medium dependent Physical medium dependent sublayers or PMDs further help to define the physical layer of computer network protocols. They define the details of transmission and reception of individual bits on a physical medium. These responsibilities encompass b ...

(PMD) sublayer is defined by

's PMD, so 100BASE-FX is not compatible with

10BASE-FL Classic Ethernet is a family of 10 Mbit/s Ethernet standards, which is the first generation of Ethernet standards. In 10BASE-X, the 10 represents its maximum throughput of 10 Mbit/s, BASE indicates its use of baseband transmission, and ...

, the 10 Mbit/s version over optical fiber. 100BASE-FX is still used for existing installation of

multimode fiber Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large ...

where more speed is not required, like industrial automation plants.

100BASE-LFX

100BASE-LFX is a non-standard term to refer to Fast Ethernet transmission. It is very similar to 100BASE-FX but achieves longer distances up to 4-5 km over a pair of multi-mode fibers through the use of Fabry–Pérot laser transmitter running on 1310 nm wavelength. The signal attenuation per km at 1300 nm is about half the loss of 850nm.

100BASE-SX

100BASE-SX is a version of Fast Ethernet over optical fiber standardized in TIA/EIA-785-1-2002. It is a lower-cost, shorter-distance alternative to 100BASE-FX. Because of the shorter wavelength used (850 nm) and the shorter distance supported, 100BASE-SX uses less expensive optical components (LEDs instead of lasers). Because it uses the same wavelength as

, the 10 Mbit/s version of Ethernet over optical fiber, 100BASE-SX can be backward-compatible with 10BASE-FL. Cost and compatibility makes 100BASE-SX an attractive option for those upgrading from 10BASE-FL and those who do not require long distances.

100BASE-LX10

100BASE-LX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah-2004 clause 58. It has a 10 km reach over a pair of single-mode fibers.

100BASE-BX10

100BASE-BX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah-2004 clause 58. It uses an optical multiplexer to split TX and RX signals into different wavelengths on the same fiber. It has a 10 km reach over a single strand of single-mode fiber.

100BASE-EX

100BASE-EX is very similar to 100BASE-LX10 but achieves longer distances up to 40 km over a pair of single-mode fibers due to higher quality optics than a LX10, running on 1310 nm wavelength lasers. 100BASE-EX is not a formal standard but industry-accepted term. It is sometimes referred to as 100BASE-LH (long haul), and is easily confused with 100BASE-LX10 or 100BASE-ZX because the use of -LX(10), -LH, -EX, and -ZX is ambiguous between vendors.

100BASE-ZX

100BASE-ZX is a non-standard but multi-vendor term to refer to Fast Ethernet transmission using 1,550 nm wavelength to achieve distances of at least 70 km over single-mode fiber. Some vendors specify distances up to 160 km over single-mode fiber, sometimes called 100BASE-EZX. Ranges beyond 80 km are highly dependent upon the path loss of the fiber in use, specifically the attenuation figure in dB per km, the number and quality of connectors/patch panels and splices located between transceivers.

Notes

References

External links

Common 100 Mbit/s Hardware Variations

Origins and History of Ethernet

IEEE802.3 standards free download

ProCurve Networking 100BASE-FX Technical Brief
{{Ethernet Ethernet