In computer networking A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general, Fast Ethernet is a collective term for a number of Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks . The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the fast Ethernet standards 100BASE-TX is by far the most common and is supported by the vast majority of Ethernet hardware currently produced. Fast Ethernet was introduced in 1995[1] and remained the fastest version of Ethernet for three years before being superseded by gigabit Ethernet Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2008 standard. Half-duplex gigabit links connected through hubs are allowed by the specification but in the marketplace full-duplex with switches are normal.[2]

Contents

General Design

A fast Ethernet adapter can be logically divided into a Media Access Controller The Media Access Control data communication protocol sub-layer, also known as the Medium Access Control, is a sublayer of the Data Link Layer specified in the seven-layer OSI model (layer 2). It provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multi-point (MAC) which deals with the higher level issues of medium availability and a Physical Layer Interface (PHY A PHY connects a link layer device to a physical medium such as an optical fibre or copper cable. A PHY typically includes a PCS and a PMD layer. The PCS encodes and decodes the data that is transmitted and received. The purpose of the encoding is to make it easier for the receiver to recover the signal). The MAC may be linked to the PHY by a 4 bit 25 MHz synchronous parallel interface known as a Media Independent Interface (MII) or a 2 bit 50 MHz variant Reduced Media Independent Interface (RMII). Repeaters (hubs A network hub or repeater hub is a device for connecting multiple twisted pair or fiber optic Ethernet devices together and making them act as a single network segment. Hubs work at the physical layer of the OSI model. The device is a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all) are also allowed and connect to multiple PHYs for their different interfaces.

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

The MII fixes the theoretical maximum data bit rate for all versions of fast Ethernet to 100 Mbit/s. The data signaling rate In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission path of a data transmission system 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 frame In computer networking, a frame is a digital data transmission unit on the Layer 2 of the OSI model, the occasional "lost frame" due to noise, and time waiting after each sent frame for other devices on the network to finish transmitting.

Copper

3Com 3c905-TX 100BASE-TX PCI Conventional PCI is a computer bus for attaching hardware devices in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification, or an expansion card that fits into a slot. The name PCI is an initialism formed from Peripheral Component Interconnect network interface card

100BASE-T is any of several Fast Ethernet standards for twisted pair cables, including: 100BASE-TX (100 Mbit/s over two-pair Cat5 Category 5 cable is a twisted pair high signal integrity cable type often referred to as Cat5 or Cat-5. Most Category-5 cables are unshielded, relying on the twisted pair design for noise rejection. Some, however, are shielded. Category 5 has been superseded by the Category 5e specification structured cabling for computer networks such as Ethernet, or better cable), 100BASE-T4 (100 Mbit/s over four-pair Cat3 Category 3 cable, commonly known as Cat 3, is an unshielded twisted pair cable designed to reliably carry data up to 10 Mbit/s, with a possible bandwidth of 16 MHz. It is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance and the Telecommunications Industry Association 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) (as with 10BASE-T Ethernet over twisted pair refers to the use of cables that contain insulated copper wires twisted together in pairs for the physical layer of an Ethernet network—that is, a network in which the Ethernet protocol provides the data link layer. Other Ethernet cable standards use coaxial cable or optical fiber. There are several different standards and gigabit Ethernet Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2008 standard. Half-duplex gigabit links connected through hubs are allowed by the specification but in the marketplace full-duplex with switches are normal). All are or were standards under IEEE 802.3 IEEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control sublayer of wired Ethernet. This is generally a LAN technology with some WAN applications. Physical connections are made between nodes and/or infrastructure devices (hubs, switches, routers) by various types of copper or fiber cable (approved 1995). Almost all 100BASE-T installations are 100BASE-TX.

In the early days of Fast Ethernet, much vendor advertising centered on claims by competing standards that "ours will work better with existing cables than theirs." In practice, it was quickly discovered that few existing networks actually met the assumed standards, because 10-megabit Ethernet was very tolerant of minor deviations from specified electrical characteristics and few installers ever bothered to make exact measurements of cable and connection quality; if Ethernet worked over a cable, it was deemed acceptable. Thus most networks had to be rewired for 100-megabit speed whether or not there had supposedly been CAT3 or CAT5 cable runs.[citation needed]

100BASE-TX

RJ-45 Wiring (TIA/EIA-568-B T568B)
Pin Pair Wire Color
1 2 1 white/orange
2 2 2 orange
3 3 1 white/green
4 1 2 blue
5 1 1 white/blue
6 3 2 green
7 4 1 white/brown
8 4 2 brown

100BASE-TX is the predominant form of Fast Ethernet, and runs over two wire-pairs inside a category 5 Category 5 cable is a twisted pair high signal integrity cable type often referred to as Cat5 or Cat-5. Most Category-5 cables are unshielded, relying on the twisted pair design for noise rejection. Some, however, are shielded. Category 5 has been superseded by the Category 5e specification structured cabling for computer networks such as Ethernet, or above cable (a typical category 5 cable contains 4 pairs and can therefore support two 100BASE-TX links). Like 10BASE-T Ethernet over twisted pair refers to the use of cables that contain insulated copper wires twisted together in pairs for the physical layer of an Ethernet network—that is, a network in which the Ethernet protocol provides the data link layer. Other Ethernet cable standards use coaxial cable or optical fiber. There are several different standards, the proper pairs are the orange and green pairs (canonical Canonical is an adjective derived from canon. Canon comes from the Greek word kanon, "rule" , and is used in various meanings second and third pairs) in TIA/EIA-568-B's termination standards, T568A or T568B. These pairs use pins 1, 2, 3 and 6.

In T568A and T568B, wires are in the order 1, 2, 3, 6, 4, 5, 7, 8 on the modular jack at each end. The color-order would be green/white, green, orange/white, blue, blue/white, orange, brown/white, brown for T568A, and orange/white, orange, green/white, blue, blue/white, green, brown/white, brown for T568B.

Each network segment A network segment is a portion of a computer network wherein every device communicates using the same physical layer. Devices that extend the physical layer, such as repeaters or network hubs, are also considered to extend the segment. However, devices that operate at the data link layer level or higher create new physical layers and thus create can have a maximum distance of 100 metres (328 ft). In its typical configuration, 100BASE-TX uses one pair of twisted wires in each direction, providing 100 Mbit/s of throughput in each direction (full-duplex A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions). See IEEE 802.3 IEEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control sublayer of wired Ethernet. This is generally a LAN technology with some WAN applications. Physical connections are made between nodes and/or infrastructure devices (hubs, switches, routers) by various types of copper or fiber cable for more details.

The configuration of 100BASE-TX networks is very similar to 10BASE-T. When used to build a local area network A local area network is a computer network covering a small physical area, like a home, office, or small groups of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased, the devices on the network (computers, printers etc.) are typically connected to a hub A network hub or repeater hub is a device for connecting multiple twisted pair or fiber optic Ethernet devices together and making them act as a single network segment. Hubs work at the physical layer of the OSI model. The device is a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all or switch A network switch or switching hub is a computer networking device that connects network segments, creating a star network Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. If the central node is passive,. Alternatively it is possible to connect two devices directly using a crossover cable.

With 100BASE-TX hardware, the raw bits (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 four bits onto groups of 5 bits, with a minimum density of 1 bits in the output. When NRZI-encoded, the 1 bits provide necessary clock transitions for the receiver. For example, a run of 4 bits such as 0000 contains no transitions and that causes clocking binary encoding to generate a series of 0 and 1 symbols clocked at 125 MHz symbol rate In digital communications, symbol rate is the number of symbol changes (signalling events) made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud (Bd) or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second. Each symbol can. The 4B5B encoding provides DC equalization and spectrum shaping (see the standard for details). Just as in the 100BASE-FX case, the bits are then transferred to the physical medium attachment layer using NRZI In telecommunication, a non-return-to-zero line code is a binary code in which "1s" are represented by one significant condition (usually a positive voltage) and "0s" are represented by some other significant condition (usually a negative voltage), with no other neutral or rest condition. The pulses have more energy than a RZ 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 Fiber Distributed Data Interface provides a 100 Mbit/s optical standard for data transmission in a local area network that can extend in range up to 200 kilometers (124 miles). Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its protocol is derived from the specifications, with minor discrepancies.[3]

100BASE-T4

100BASE-T4 was an early implementation of Fast Ethernet. It requires four twisted copper pairs, but those pairs were only required to be category 3 rather than the category 5 required by TX. One pair is reserved for transmit, one for receive, and the remaining two will switch direction as negotiated. 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 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, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses (PAM-3). The fact that 3 pairs are used to transmit in each direction makes 100BASE-T4 inherently half-duplex. This standard can be implemented with CAT 3, 4, 5 UTP cables, or STP if needed against interference. Maximum distance is limited to 100 meters. 100BASE-T4 was not widely adopted but the technology developed for it is used in 1000BASE-T.

100BASE-T2

Symbol Line signal level
000 0
001 +1
010 -1
011 -2
100(ESC) +2

In 100BASE-T2, the data is transmitted over two copper pairs, 4 bits per symbol. It uses these two pairs for simultaneously transmitting and receiving on both pairs[5] thus allowing full-duplex operation. First, a 4 bit symbol is expanded into two 3-bit symbols through a non-trivial scrambling procedure based on a linear feedback shift register A linear feedback shift register is a shift register whose input bit is a linear function of its previous state; see the standard for details. 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, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses 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.

Fiber

100BASE-FX

100BASE-FX is a version of Fast Ethernet over optical fiber An optical fiber is made up of the core , the cladding (reflecting the light pulses back into the core) and the buffer coating (protecting the core and cladding from moisture, damage, etc). Together, all of this creates a fiber optic which can carry up to 10 million messages at any time using light pulses. Fiber optics is the overlap of applied. It uses a 1300 nm A nanometre (Greek: νάνος, nanos, "dwarf"; μέτρον, metrοn, "unit of measurement") is a unit of length in the metric system, equal to one billionth of a metre near-infrared Infrared light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz (NIR) light wavelength In physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats. It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a characteristic of both traveling waves and transmitted via two strands of optical fiber, one for receive(RX) and the other for transmit(TX). Maximum length is 400 metres (1,310 ft) for half-duplex A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions connections (to ensure collisions are detected), 2 kilometres (6,600 ft) for full-duplex over multimode optical fiber, or 10,000 meters (32,808 feet) for full-duplex single mode optical fiber In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single ray of light (mode). This ray of light often contains a variety of different wavelengths. Although the ray travels parallel to the length of the fiber, it is often called the transverse mode since its electromagnetic vibrations occur. 100BASE-FX uses the same 4B5B encoding and NRZI line code that 100BASE-TX does. 100BASE-FX should use SC, ST, or MIC connectors An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so that light can pass. Most optical fiber connectors are spring-loaded: The fiber endfaces of the two connectors are pressed together, resulting in a with SC being the preferred option.[6]

100BASE-FX is not compatible with 10BASE-FL, the 10 MBit/s version over optical fiber.

100BASE-SX

100BASE-SX is a version of Fast Ethernet over optical fiber. It uses two strands of multi-mode optical fiber for receive and transmit. It is a lower cost alternative to using 100BASE-FX, because it uses short wavelength optics which are significantly less expensive than the long wavelength optics used in 100BASE-FX. 100BASE-SX can operate at distances up to 550 metres (1,800 ft).

100BASE-SX uses the same wavelength as 10BASE-FL, the 10 MBit/s version over optical fiber. Unlike 100BASE-FX, this allows 100BASE-SX to be backwards-compatible with 10BASE-FL.

Because of the shorter wavelength used (850 nm) and the shorter distance it can support, 100BASE-SX uses less expensive optical components (LEDs instead of lasers) which makes it an attractive option for those upgrading from 10BASE-FL and those who do not require long distances.

100BASE-BX

100BASE-BX is a version of Fast Ethernet over a single strand of optical fiber (unlike 100BASE-FX, which uses a pair of fibers). Single-mode fiber is used, along with a special multiplexer which splits the signal into transmit and receive wavelengths. The two wavelengths used for transmit and receive is 1310/1550 nm. The terminals on each side of the fiber are not equal, as the one transmitting "downstream" (from the center of the network to the outside) uses the 1550 nm wavelength, and the one transmitting "upstream" uses the 1310 nm wavelength. Distances can be 10, 20 or 40 km.

100BASE-LX10

100BASE-LX10 is a version of Fast Ethernet over two single-mode optical fibers In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single ray of light (mode). This ray of light often contains a variety of different wavelengths. Although the ray travels parallel to the length of the fiber, it is often called the transverse mode since its electromagnetic vibrations occur. It has a nominal reach of 10 km and a nominal wavelength In physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats. It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a characteristic of both traveling waves and of 1310 nm. It is described in IEEE 802.3 IEEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control sublayer of wired Ethernet. This is generally a LAN technology with some WAN applications. Physical connections are made between nodes and/or infrastructure devices (hubs, switches, routers) by various types of copper or fiber cable-2005 Section 5 chapter 58.

See also

References

  1. ^ IEEE 802.3u-1995
  2. ^ [1] The 802.3z Gigabit Ethernet Standard was published
  3. ^ "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).
  4. ^ Charles Spurgeon (2000). Ethernet the Definitive Guide. O'Reilly Media. p. 156.
  5. ^ Robert Breyer and Sean Riley (1999). Switched, Fast, and Gigabit Ethernet. Macmillan Technical Publishing. p. 107.
  6. ^ 802.3-2008 section 26.4.1

This article was originally based on material from the Free On-line Dictionary of Computing The Free On-line Dictionary of Computing is an online, searchable, encyclopedic dictionary of computing subjects. It was founded in 1985 by Denis Howe and is hosted by Imperial College London. Howe has served as the editor-in-chief since the dictionary's inception, with visitors to the website able to make suggestions for additions or corrections, which is licensed under the GFDL The GNU Free Documentation License is a copyleft license for free documentation, designed by the Free Software Foundation (FSF) for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute, and modify a work and requires all copies and derivatives to be available under the same license.

External links

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