In computer networking, 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 [1] and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet. [2] The acronym GE/FE is sometimes used for devices supporting both standards. [3]
The 100 in the media type designation refers to the transmission speed of 100 Mbit/s, while the BASE refers to baseband 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 method used. Fast Ethernet is sometimes referred to as 100BASE-X, where X is a placeholder for the FX and TX variants. [4]
Fast Ethernet is an extension of the 10-megabit Ethernet standard. It runs on twisted pair or optical fiber cable in a star wired bus topology, similar to the IEEE standard 802.3i called 10BASE-T, 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, sensing a piece of 10BASE-T equipment and setting the port to 10BASE-T half duplex if the 10BASE-T equipment cannot perform autonegotiation itself. The standard specifies the use of CSMA/CD for media access control. A full-duplex mode is also specified and in practice, all modern networks use Ethernet switches 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 controller (MAC), which deals with the higher-level issues of medium availability, and a physical layer interface (PHY). The MAC is typically linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a media-independent interface (MII), or by a two-bit 50 MHz variant called reduced media independent interface (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 hubs 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 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, and the required interpacket gap between transmissions.
100BASE-T is any of several Fast Ethernet standards for twisted pair cables,[ dubious – discuss ] including: 100BASE-TX (100 Mbit/s over two-pair Cat5 or better cable), 100BASE-T4 (100 Mbit/s over four-pair Cat3 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 100 metres (328 ft) (the same limit as 10BASE-T and gigabit Ethernet). All are or were standards under IEEE 802.3 (approved 1995). Almost all 100BASE-T installations are 100BASE-TX.
Name | Standard | Status | Speed (Mbit/s) | Pairs required | Lanes per direction | Bits per hertz | Line code | Symbol rate per lane (MBd) | Bandwidth (MHz) | Max distance (m) | Cable | Cable rating (MHz) | Usage |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
100BASE-TX | 802.3u-1995 | current | 100 | 2 | 1 | 3.2 | 4B5B MLT-3 NRZI | 125 | 31.25 | 100 | Cat 5 | 100 | LAN |
100BASE-T1 | 802.3bw-2015 (CL96) | current | 100 | 1 | 1 | 2.66 | PAM-3 4B/3B | 75 | 37.5 | 15 | Cat 5e | 66 | Automotive, IoT, M2M |
100BASE-T2 | 802.3y-1997 | obsolete | 100 | 2 | 2 | 4 | LFSR PAM-5 | 25 | 12.5 | 100 | Cat 3 | 16 | Market failure |
100BASE-T4 | 802.3u-1995 | obsolete | 100 | 4 | 3 | 2.66 | 8B6T PAM-3 Half-duplex only | 25 | 12.5 | 100 | Cat 3 | 16 | Market failure |
100BaseVG | 802.12-1995 | obsolete | 100 | 4 | 4 | 1.66 | 5B6B Half-duplex only | 30 | 15 | 100 | Cat 3 | 16 | Market failure |
Pin | Pair | Wire | Color |
---|---|---|---|
1 | 3 | +/tip | white/green |
2 | 3 | −/ring | green |
3 | 2 | +/tip | white/orange |
4 | 1 | +/ring | blue |
5 | 1 | -/tip | white/blue |
6 | 2 | −/ring | orange |
7 | 4 | +/tip | white/brown |
8 | 4 | −/ring | brown |
Pin | Pair | Wire | Color |
---|---|---|---|
1 | 2 | +/tip | white/orange |
2 | 2 | −/ring | orange |
3 | 3 | +/tip | white/green |
4 | 1 | +/ring | blue |
5 | 1 | -/tip | white/blue |
6 | 3 | −/ring | green |
7 | 4 | +/tip | white/brown |
8 | 4 | −/ring | brown |
100BASE-TX is the predominant form of Fast Ethernet, and runs over two pairs of wire inside a Category 5 or above cable. Cable distance between nodes can be up to 100 metres (328 ft). One pair is used for each direction, providing full-duplex operation at 100 Mbit/s in each direction.
Like 10BASE-T, the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6. Since a typical Category 5 cable contains four pairs and the performance requirements of 100BASE-TX do not exceed the capabilities of even the worst-performing pair, one typical cable can carry two 100BASE-TX links with a simple wiring adaptor on each end. [6] Cabling is conventionally wired to one of ANSI/TIA-568's termination standards, T568A or T568B. 100BASE-TX uses pairs 2 and 3 (orange and green).
The configuration of 100BASE-TX networks is very similar to 10BASE-T. When used to build a local area network, the devices on the network (computers, printers etc.) are typically connected to a hub or switch, creating a star network. Alternatively, it is possible to connect two devices directly using a crossover cable. With today's equipment, crossover cables are generally not needed as most equipment supports auto-negotiation along with auto MDI-X 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 binary encoding to generate a series of 0 and 1 symbols clocked at a 125 MHz symbol rate. 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 as a final encoding of the data stream before transmission, resulting in a maximum fundamental frequency of 31.25 MHz. The procedure is borrowed from the ANSI X3.263 FDDI specifications, with minor changes. [7]
In 100BASE-T1 [8] 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 Open Alliance BroadR-Reach (OABR) before IEEE standardization. [9]
Symbol | Line signal level |
---|---|
000 | 0 |
001 | +1 |
010 | −1 |
011 | −2 |
100 (ESC) | +2 |
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 [10] 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. [11] 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 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. [5]
100BASE-T4 was an early implementation of Fast Ethernet. It required four twisted copper pairs of voice grade twisted pair, a lower-performing cable compared to Category 5 cable used by 100BASE-TX. Maximum distance was limited to 100 meters. One pair was reserved for transmit and one for receive, and the remaining two switched direction. The fact that three pairs were used to transmit in each direction made 100BASE-T4 inherently half-duplex. Using three cable pairs allowed it to reach 100 Mbit/s while running at lower carrier frequencies, which allowed it to run on older cabling that many companies had recently installed for 10BASE-T networks.
A very unusual 8B6T code was 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 were sent in parallel over three pairs using 3-level pulse-amplitude modulation (PAM-3).
100BASE-T4 was not widely adopted but some of the technology developed for it is used in 1000BASE-T. [5] Very few hubs were released with 100BASE-T4 support. Some examples include the 3com 3C250-T4 Superstack II HUB 100, IBM 8225 Fast Ethernet Stackable Hub [12] and Intel LinkBuilder FMS 100 T4. [13] [14] The same applies to network interface controllers. Bridging 100BASE-T4 with 100BASE-TX required additional network equipment.
Proposed and marketed by Hewlett-Packard, 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. The IEEE standard was later withdrawn. [15]
VG was similar to T4 in that it used more cable pairs combined with a lower carrier frequency to allow it to reach 100 Mbit/s on voice-grade cables. It differed in the way those cables were assigned. Whereas T4 would use the two extra pairs in different directions depending on the direction of data exchange, VG instead used two transmission modes. In one, control, two pairs are used for transmission and reception as in classic Ethernet, while the other two pairs are used for flow control. In the second mode, transmission, all four are used to transfer data in a single direction. The hubs implemented a token passing scheme to choose which of the attached nodes were allowed to communicate at any given time, based on signals sent to it from the nodes using control mode. When one node was selected to become active, it would switch to transfer mode, send or receive a packet, and return to control mode. [15]
This concept was intended to solve two problems. The first was that it eliminated the need for collision detection and thereby reduced contention on busy networks. While any particular node may find itself throttled due to heavy traffic, the network as a whole would not end up losing efficiency due to collisions and the resulting rebroadcasts. Under heavy use, the total throughput was increased compared to the other standards. The other was that the hubs could examine the payload types and schedule the nodes based on their bandwidth requirements. For instance, a node sending a video signal may not require much bandwidth but will require it to be predictable in terms of when it is delivered. A VG hub could schedule access on that node to ensure it received the transmission timeslots it needed while opening up the network at all other times to the other nodes. This style of access was known as demand priority. [15]
Fiber variants use fiber-optic cable with the listed interface types. Interfaces may be fixed or modular, often as small form-factor pluggable (SFP).
Fibre type | Introduced | Performance |
---|---|---|
MMF FDDI 62.5/125 µm | 1987 | MHz·km @ 850 nm | 160
MMF OM1 62.5/125 µm | 1989 | MHz·km @ 850 nm | 200
MMF OM2 50/125 µm | 1998 | MHz·km @ 850 nm | 500
MMF OM3 50/125 µm | 2003 | 1500 MHz·km @ 850 nm |
MMF OM4 50/125 µm | 2008 | 3500 MHz·km @ 850 nm |
MMF OM5 50/125 µm | 2016 | 3500 MHz·km @ 850 nm + 1850 MHz·km @ 950 nm |
SMF OS1 9/125 µm | 1998 | 1.0 dB/km @ 1300/1550 nm |
SMF OS2 9/125 µm | 2000 | 0.4 dB/km @ 1300/1550 nm |
Name | Standard | Status | Media | Connector | Transceiver Module | Reach in m | # Media (⇆) | # Lambdas (→) | # Lanes (→) | Notes |
---|---|---|---|---|---|---|---|---|---|---|
Fast Ethernet – (Data rate: 100 Mbit/s – Line code: 4B5B × NRZI – Line rate: 125 MBd – Full-Duplex / Half-Duplex) | ||||||||||
100BASE‑FX | 802.3u-1995 (CL24/26) | current | fiber 1300 nm | ST SC MT-RJ MIC (FDDI) | — | FDDI: 2k (FDX) | 2 | 1 | 1 | max. 412 m for half-duplex connections to ensure collision detection; specification largely derived from FDDI. Modal bandwidth: 800 MHz·km [16] [17] |
OM1: 4k | ||||||||||
50/125: 5k | ||||||||||
100BASE‑LFX | proprietary (non IEEE) | current | fiber 1310 nm | LC (SFP) ST SC | SFP | OM1: 2k | 2 | 1 | 1 | vendor-specific FP laser transmitter Full-duplex Modal bandwidth: 800 MHz·km [18] |
OM2: 2k | ||||||||||
62.5/125: 4k | ||||||||||
50/125: 4k | ||||||||||
OSx: 40k [17] | ||||||||||
100BASE-SX | TIA-785 (2000) | legacy | fiber 850 nm | ST SC LC | — | OM1: 300 | 2 | 1 | 1 | optics sharable with 10BASE-FL, thus making it possible to have an auto-negotiation scheme and use 10/100 fiber adapters. |
OM2: 300 | ||||||||||
100BASE-LX10 | 802.3ah-2004 (CL58) | phase-out | fiber 1310 nm | LC | SFP | OSx: 10k | 2 | 1 | 1 | full-duplex only |
100BASE-BX10 | phase-out | fiber TX: 1310 nm RX: 1550 nm | OSx: 40k | 1 | full-duplex only; optical multiplexer used to split TX and RX signals into different wavelengths. | |||||
Fast Ethernet speed is not available on all SFP ports, [19] but supported by some devices. [20] [21] An SFP port for Gigabit Ethernet should not be assumed to be backwards compatible with Fast Ethernet.
To have interoperability there are some criteria that have to be met: [22]
100BASE-X Ethernet is not backward compatible with 10BASE-F and is not forward compatible with 1000BASE-X.
100BASE-FX is a version of Fast Ethernet over optical fiber. The 100BASE-FX physical medium dependent (PMD) sublayer is defined by FDDI's PMD, [24] so 100BASE-FX is not compatible with 10BASE-FL, the 10 Mbit/s version over optical fiber.
100BASE-FX is still used for existing installation of multimode fiber where more speed is not required, like industrial automation plants. [17]
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 [25] running on 1310 nm wavelength. The signal attenuation per km at 1300 nm is about half the loss of 850 nm. [26] [27]
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 10BASE-FL, 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 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 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 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. [28] 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 is a non-standard but multi-vendor [29] [ better source needed ] 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. [30]
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 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.
100BaseVG is a 100 Mbit/s Ethernet standard specified to run over four pairs of Category 3 cable. It is also called 100VG-AnyLAN because it was defined to carry both Ethernet and Token Ring frame types.
10BASE2 is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network. During the mid to late 1980s, this was the dominant 10 Mbit/s Ethernet standard.
Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.
In computer networking, Gigabit Ethernet 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 in 1999, and has replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards. The first standard for faster 10 Gigabit Ethernet was approved in 2002. Full saturation is only achieved with 2 gigabit per second, as full duplex nature allows it to send and receive bytes on each wire simultaniously, 1 up and 1 down.
In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer: the layer most closely associated with the physical connection between devices. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes and properties of the electrical connectors, the frequencies to transmit on, the line code to use and similar low-level parameters, are specified by the physical layer.
Category 3 cable, commonly known as Cat 3 or station wire, and less commonly known as VG or voice-grade, is an unshielded twisted pair (UTP) cable used in telephone wiring. It is part of a family of standards defined jointly by the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) and published in TIA/EIA-568-B.
Small Form-factor Pluggable (SFP) is a compact, hot-pluggable network interface module format used for both telecommunication and data communications applications. An SFP interface on networking hardware is a modular slot for a media-specific transceiver, such as for a fiber-optic cable or a copper cable. The advantage of using SFPs compared to fixed interfaces is that individual ports can be equipped with different types of transceivers as required, with the majority including optical line terminals, network cards, switches and routers.
The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet medium access control (MAC) block to a PHY chip. The MII is standardized by IEEE 802.3u and connects different types of PHYs to MACs. Being media independent means that different types of PHY devices for connecting to different media can be used without redesigning or replacing the MAC hardware. Thus any MAC may be used with any PHY, independent of the network signal transmission medium.
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/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer. A repeater hub also participates in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.
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 first share their capabilities regarding these parameters and then choose the highest-performance transmission mode they both support.
A medium-dependent interface (MDI) describes the interface in a computer network from a physical-layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also defines a medium-dependent interface – crossover (MDI-X) interface. Auto–MDI-X ports on newer network interfaces detect if the connection would require a crossover and automatically choose the MDI or MDI-X configuration to complement the other end of the link.
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 800 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.
An Ethernet crossover cable is a crossover cable for Ethernet used to connect computing devices together directly. It is most often used to connect two devices of the same type, e.g. two computers or two switches to each other. By contrast, straight through patch cables are used to connect devices of different types, such as a computer to a network switch.
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.
Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from the access network's point of view it is known as the last mile.
The Cisco Catalyst 1900 is a 19" rack mountable, managed (configurable) 10BASE-T Ethernet switch with 100BASE-TX/100BASE-FX uplink ports. This product was popular in small office networks because of its features and price.
10 Gigabit Ethernet is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlike previous Ethernet standards, 10GbE defines only full-duplex point-to-point links which are generally connected by network switches; shared-medium CSMA/CD operation has not been carried over from the previous generations of Ethernet standards so half-duplex operation and repeater hubs do not exist in 10GbE. The first standard for faster 100 Gigabit Ethernet links was approved in 2010.
The OPEN Alliance is a non-profit, special interest group (SIG) of mainly automotive industry and technology providers collaborating to encourage wide scale adoption of Ethernet-based communication as the standard in automotive networking applications.