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Ethernet () is a family of wired
computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically wired, optical, and wire ...
ing technologies commonly used in
local area network A local area network (LAN) is a that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a (WAN) not only covers a larger geographic distance, but also ge ...
s (LAN),
metropolitan area network A metropolitan area network (MAN) is a computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up o ...
s (MAN) and
wide area network A wide area network (WAN) is a telecommunications network A telecommunications network is a group of nodes interconnected by links that are used to exchange messages between the nodes. The links may use a variety of technologies based on t ...
s (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 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 Data rate units, bit per second unit (symbol: ''bit/s'' ...
s, a greater number of nodes, and longer link distances, but retains much
backward compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of a system, product, or technology that allows for interoperability Interoperability is a characteristic of a product or system, whose interfaces are completely ...
. Over time, Ethernet has largely replaced competing wired LAN technologies such as
Token Ring Token Ring network IBM hermaphroditic connector with locking clip. Screen connectors are prominently visible, gold-plated signal connectors less so. Token Ring is a computer network A computer network is a set of s sharing resources lo ...

Token Ring
,
FDDI Dual-attach FDDI board for SBus Fiber Distributed Data Interface (FDDI) is a standard for data transmission Data transmission and data reception (or, more broadly, data communication or digital communications) is the transfer and reception ...
and
ARCNET Attached Resource Computer NETwork (ARCNET or ARCnet) is a communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A communications sys ...
. The original
10BASE5 10BASE5 (also known as thick Ethernet or thicknet) was the first commercially available variant of . The technology was standardized in 1982 as . 10BASE5 uses a thick and stiff coaxial cable up to in length. Up to 100 stations can be connected ...
Ethernet uses
coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable An electrical cable is an assembly of one or more wires running side by side or bundled, which is used to carry electric current. A cable assembly is the composition of one ...
as a
shared medium In telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads or el ...
, while the newer Ethernet variants use twisted pair and
fiber optic An optical fiber (or fibre in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...

fiber optic
links in conjunction with
switches In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an ident ...

switches
. Over the course of its history, Ethernet data transfer rates have been increased from the original 2.94 
megabits per second In telecommunications, data-transfer rate is the average number of bits (bitrate), characters or symbols (baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are multip ...
(Mbit/s) to the latest 400 gigabits per second (Gbit/s). The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. Systems communicating over Ethernet divide a stream of data into shorter pieces called
frames A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Arts and media Film and television *Frame (film), one of ...
. Each frame contains source and destination addresses, and error-checking data so that damaged frames can be detected and discarded; most often, higher-layer protocols trigger retransmission of lost frames. Per the
OSI model The Open Systems Interconnection model (OSI model) is a that characterises and standardises the communication functions of a or computing system without regard to its underlying internal structure and technology. Its goal is the interoperabil ...

OSI model
, Ethernet provides services up to and including the
data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a that characterises and standardises the communication functions of a or computing system without r ...
. The 48-bit
MAC address A media access control address (MAC address) is a unique identifier A unique identifier (UID) is an identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, ...
was adopted by other
IEEE 802 IEEE 802 is a family of Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association for electronic engineering and electrical engineering (and associated disciplin ...

IEEE 802
networking standards, including
IEEE 802.11 IEEE 802.11 is part of the IEEE 802 IEEE 802 is a family of Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association for electronic engineering and electr ...
(
Wi-Fi Wi-Fi () is a family of wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installa ...

Wi-Fi
), as well as by
FDDI Fiber Distributed Data Interface (FDDI) is a standard for data transmission Data transmission and data reception (or, more broadly, data communication or digital communications) is the transfer and reception of data (a Digital data, digital ...
.
EtherType EtherType is a two-octet Octet may refer to: Music * Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble ** String octet, a piece of music written for eight string instruments *** Octet ...
values are also used in
Subnetwork Access Protocol The Subnetwork Access Protocol (SNAP) is a mechanism for multiplexing, on networks using IEEE 802.2 LLC, more protocols than can be distinguished by the 8-bit 802.2 Service Access PointA Service Access Point (SAP) is an identifying label for netwo ...
(SNAP) headers. Ethernet is widely used in homes and industry, and interworks well with wireless Wi-Fi technologies. The
Internet Protocol The Internet Protocol (IP) is the network layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a conceptual model A conceptual model is a representation of a system, made of the composition of concept C ...
is commonly carried over Ethernet and so it is considered one of the key technologies that make up the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consist ...

Internet
.


History

Ethernet was developed at
Xerox PARC PARC (Palo Alto Research Center; formerly Xerox PARC) is a research and development company in Palo Alto, California. Founded in 1969 by Jack Goldman, Jacob E. "Jack" Goldman, Xerox Corporation's chief scientist, the company was originally a divis ...
between 1973 and 1974. It was inspired by
ALOHAnet ALOHAnet, also known as the ALOHA System, or simply ALOHA, was a pioneering computer networking system developed at the University of Hawaii. ALOHAnet became operational in June 1971, providing the first public demonstration of a wireless packet ...
, which
Robert Metcalfe Robert (Bob) Melancton Metcalfe (born April 7, 1946) is an engineer and entrepreneur from the United States who helped pioneer the Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) t ...
had studied as part of his PhD dissertation. The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the
luminiferous aether Luminiferous aether or ether ("luminiferous", meaning "light-bearing") was the postulated medium Medium may refer to: Science and technology Aviation *Medium bomber, a class of war plane *Tecma Medium, a French hang glider design Communic ...
once postulated to exist as an "omnipresent, completely-passive medium for the propagation of electromagnetic waves." In 1975,
Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document An electronic document is any electronic media content (other than computer program A computer program is a collectio ...
filed a patent application listing Metcalfe,
David Boggs David Reeves Boggs (born 1950) is an electrical and radio engineer from the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily lo ...
,
Chuck Thacker Charles Patrick "Chuck" Thacker (February 26, 1943 – June 12, 2017) was an United States, American pioneer computer designer. He designed the Xerox Alto, which is the first computer that used a Computer mouse, mouse-driven graphical user int ...
, and
Butler Lampson Butler W. Lampson, ForMemRS, (born December 23, 1943) is an American computer scientist best known for his contributions to the development and implementation of distributed personal computing. Education and early life After graduating from the L ...
as inventors. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper.
Yogen Dalal Instead of a single "inventor", the Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, academic ...
, Ron Crane, Bob Garner, and Roy Ogus facilitated the upgrade from the original 2.94 Mbit/s protocol to the 10 Mbit/s protocol, which was released to the market in 1980. Metcalfe left Xerox in June 1979 to form
3Com 3Com Corporation was a digital electronics manufacturer best known for its computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. Th ...
. He convinced
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights ...
(DEC),
Intel Intel Corporation is an American multinational corporation A multinational company (MNC) is a corporate A corporation is an organization—usually a group of people or a company A company, abbreviated as co., is a Legal personalit ...

Intel
, and Xerox to work together to promote Ethernet as a standard. As part of that process Xerox agreed to relinquish their 'Ethernet' trademark. The first standard was published on September 30, 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications". This so-called DIX standard (Digital Intel Xerox) specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit
Ethertype EtherType is a two-octet Octet may refer to: Music * Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble ** String octet, a piece of music written for eight string instruments *** Octet ...
-type field. Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time and resulted in the publication of IEEE 802.3 on June 23, 1983. Ethernet initially competed with
Token Ring Token Ring network IBM hermaphroditic connector with locking clip. Screen connectors are prominently visible, gold-plated signal connectors less so. Token Ring is a computer network A computer network is a set of s sharing resources lo ...

Token Ring
and other
proprietary protocol In telecommunications, a proprietary protocol is a communications protocol owned by a single organization or individual. Intellectual property rights and enforcement Ownership by a single organization gives the owner the ability to place restrictio ...
s. Ethernet was able to adapt to market needs and with 10BASE2, shift to inexpensive thin coaxial cable and from 1990, to the now-ubiquitous
twisted pair Twisted pair cabling is a type of wiring in which two conductors of a single circuitCircuit may refer to: Science and technology Electrical engineering * Electrical circuit, a complete electrical network with a closed-loop giving a retu ...

twisted pair
with 10BASE-T. By the end of the 1980s, Ethernet was clearly the dominant network technology. In the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, and that year started selling adapters for
PDP-11 The PDP-11 is a series of 16-bit 16-bit microcomputer A microcomputer is a small, relatively inexpensive computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically ...
s and
VAX VAX is a series of computers featuring a 32-bit 32-bit microcomputers are computers in which 32-bit microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrate ...
es, as well as
Multibus Multibus is a computer bus In computer architecture In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer A computer is a machine t ...
-based Intel and
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. M ...
computers. This was followed quickly by DEC's
Unibus The Unibus was the earliest of several computer bus trolleybus in Toronto Toronto is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a recorded population of 2,731,571 in 2016, it is the ...

Unibus
to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. An Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. In the 1980s, IBM's own PC Network product competed with Ethernet for the PC, and through the 1980s, LAN hardware, in general, was not common on PCs. However, in the mid to late 1980s, PC networking did become popular in offices and schools for printer and fileserver sharing, and among the many diverse competing LAN technologies of that decade, Ethernet was one of the most popular.
Parallel port In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware a ...
based Ethernet adapters were produced for a time, with drivers for DOS and Windows. By the early 1990s, Ethernet became so prevalent that Ethernet ports began to appear on some PCs and most
workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating ...

workstation
s. This process was greatly sped up with the introduction of 10BASE-T and its relatively small
modular connector A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...
, at which point Ethernet ports appeared even on low-end motherboards. Since then, Ethernet technology has evolved to meet new bandwidth and market requirements. In addition to computers, Ethernet is now used to interconnect appliances and other personal devices. As
Industrial Ethernet Industrial Ethernet (IE) is the use of Ethernet in an industrial environment with protocols that provide determinism and real-time control. Protocols for industrial Ethernet include EtherCAT, EtherNet/IP, PROFINET, Ethernet Powerlink, POWERLIN ...
it is used in industrial applications and is quickly replacing legacy data transmission systems in the world's telecommunications networks. By 2010, the market for Ethernet equipment amounted to over $16 billion per year.


Standardization

In February 1980, the
Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association A professional association (also called a professional body, professional organization, or professional society) usually seeks to further Further or F ...
(IEEE) started project
802 Year 802 (Roman numerals, DCCCII) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. Events By place Byzantine Empire * October 31 – Empress Irene of Athens, Irene is deposed aft ...

802
to standardize local area networks (LAN). The "DIX-group" with Gary Robinson (DEC), Phil Arst (Intel), and Bob Printis (Xerox) submitted the so-called "Blue Book"
CSMA/CD Carrier-sense multiple access with collision detection (CSMA/CD) is a media access control In IEEE 802, IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware ...
specification as a candidate for the LAN specification. In addition to CSMA/CD, Token Ring (supported by IBM) and Token Bus (selected and henceforward supported by
General Motors General Motors Company (GM) is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinat ...

General Motors
) were also considered as candidates for a LAN standard. Competing proposals and broad interest in the initiative led to strong disagreement over which technology to standardize. In December 1980, the group was split into three subgroups, and standardization proceeded separately for each proposal. Delays in the standards process put at risk the market introduction of the
Xerox Star The Xerox Star workstation A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network A local area net ...
workstation and 3Com's Ethernet LAN products. With such business implications in mind,
David LiddleDavid Liddle is co-founder of Interval Research Corporation, consulting professor of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practi ...
(General Manager, Xerox Office Systems) and Metcalfe (3Com) strongly supported a proposal of Fritz Röscheisen (
Siemens Siemens AG ( ) is a German multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, ...

Siemens
Private Networks) for an alliance in the emerging office communication market, including Siemens' support for the international standardization of Ethernet (April 10, 1981). Ingrid Fromm, Siemens' representative to IEEE 802, quickly achieved broader support for Ethernet beyond IEEE by the establishment of a competing Task Group "Local Networks" within the European standards body ECMA TC24. In March 1982, ECMA TC24 with its corporate members reached an agreement on a standard for CSMA/CD based on the IEEE 802 draft. Because the DIX proposal was most technically complete and because of the speedy action taken by ECMA which decisively contributed to the conciliation of opinions within IEEE, the IEEE 802.3 CSMA/CD standard was approved in December 1982. IEEE published the 802.3 standard as a draft in 1983 and as a standard in 1985. Approval of Ethernet on the international level was achieved by a similar, cross- partisan action with Fromm as the
liaison officer A liaison officer is a person who liaises between two organizations to communicate and coordinate their activities. Generally, liaison officers are used to achieve the best utilization of resources or employment of services of one organization by ...
working to integrate with
International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization A standards organization, standards body, standards developing organization (SDO), or s ...
(IEC) Technical Committee 83 and
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm Norm, the Norm or NORM may refer to: In academic discipline ...
(ISO) Technical Committee 97 Sub Committee 6. The ISO 8802-3 standard was published in 1989.


Evolution

Ethernet has evolved to include higher bandwidth, improved
medium 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 A transmission ...
methods, and different physical media. The coaxial cable was replaced with point-to-point links connected by Ethernet repeaters or
switches In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an ident ...

switches
. Ethernet stations communicate by sending each other
data packet In telecommunications and computer networking, a network packet is a formatted unit of Data (computing), data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''Payload ...
s: blocks of data individually sent and delivered. As with other IEEE 802 LANs, adapters come programmed with globally unique 48-bit
MAC address A media access control address (MAC address) is a unique identifier A unique identifier (UID) is an identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, ...
so that each Ethernet station has a unique address. The MAC addresses are used to specify both the destination and the source of each data packet. Ethernet establishes link-level connections, which can be defined using both the destination and source addresses. On reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. A network interface normally does not accept packets addressed to other Ethernet stations. An EtherType field in each frame is used by the operating system on the receiving station to select the appropriate protocol module (e.g., an
Internet Protocol The Internet Protocol (IP) is the network layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a conceptual model A conceptual model is a representation of a system, made of the composition of concept C ...
version such as
IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the network layer communications protocol A communication protocol is a system of rules that allows two or more entities of a ...

IPv4
).
Ethernet frame In computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically ...

Ethernet frame
s are said to be ''self-identifying'', because of the EtherType field. Self-identifying frames make it possible to intermix multiple protocols on the same physical network and allow a single computer to use multiple protocols together. Despite the evolution of Ethernet technology, all generations of Ethernet (excluding early experimental versions) use the same frame formats. Mixed-speed networks can be built using Ethernet switches and repeaters supporting the desired Ethernet variants. Due to the ubiquity of Ethernet, and the ever-decreasing cost of the hardware needed to support it, most manufacturers now build Ethernet interfaces directly into
PC motherboard A motherboard (also called mainboard, main circuit board, system board, baseboard, planar board, logic board, or mobo) is the main printed circuit board A printed circuit board (PCB) mechanically supports and electrically connects electrica ...
s, eliminating the need for a separate network card.


Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. The method used was similar to those used in radio systems, with the common cable providing the communication channel likened to the ''Luminiferous aether'' in 19th-century physics, and it was from this reference that the name "Ethernet" was derived. Original Ethernet's shared coaxial cable (the shared medium) traversed a building or campus to every attached machine. A scheme known as
carrier sense multiple access with collision detection Carrier-sense multiple access with collision detection (CSMA/CD) is a media access control In IEEE 802, IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware ...
(CSMA/CD) governed the way the computers shared the channel. This scheme was simpler than competing Token Ring or
Token Bus Image:Token-bus.PNG, Token passing in a Token bus network Token bus is a network implementing a Token Ring protocol over a ''virtual ring'' on a coaxial cable. A token is passed around the network nodes and only the node possessing the token may ...
technologies. Computers are connected to an
Attachment Unit Interface The Attachment Unit Interface (AUI) is a physical and logical interface defined in the original IEEE 802.3 standard for 10BASE5 10BASE5 (also known as thick Ethernet or thicknet) was the first commercially available variant of . The techn ...
(AUI)
transceiver In radio communication, a transceiver is an electronic device which is a combination of a radio transmitter, ''trans''mitter and a Radio receiver, re''ceiver'', hence the name. It can both transmit and receive radio waves using an antenna (radio) ...

transceiver
, which is in turn connected to the cable (with thin Ethernet the transceiver is usually integrated into the network adapter). While a simple passive wire is highly reliable for small networks, it is not reliable for large extended networks, where damage to the wire in a single place, or a single bad connector, can make the whole Ethernet segment unusable. Through the first half of the 1980s, Ethernet's
10BASE5 10BASE5 (also known as thick Ethernet or thicknet) was the first commercially available variant of . The technology was standardized in 1982 as . 10BASE5 uses a thick and stiff coaxial cable up to in length. Up to 100 stations can be connected ...
implementation used a coaxial cable in diameter, later called "thick Ethernet" or "thicknet". Its successor,
10BASE2 10BASE2 (also known as cheapernet, thin Ethernet, thinnet, and thinwire) is a variant of Ethernet Ethernet () is a family of wired computer network A computer network is a set of s sharing resources located on or provided by . ...
, called "thin Ethernet" or "thinnet", used the
RG-58 RG-58/U is a type of coaxial cable Coaxial cable, or coax (pronounced ) is a type of consisting of an inner surrounded by a concentric conducting , with the two separated by a ( material); many coaxial cables also have a protective outer ...
coaxial cable. The emphasis was on making installation of the cable easier and less costly. Since all communication happens on the same wire, any information sent by one computer is received by all, even if that information is intended for just one destination. The network interface card interrupts the
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuit File:PExdcr01CJC.jpg, 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of ...

CPU
only when applicable packets are received: the card ignores information not addressed to it. Use of a single cable also means that the data bandwidth is shared, such that, for example, available data bandwidth to each device is halved when two stations are simultaneously active. A collision happens when two stations attempt to transmit at the same time. They corrupt transmitted data and require stations to re-transmit. The lost data and re-transmission reduces throughput. In the worst case, where multiple active hosts connected with maximum allowed cable length attempt to transmit many short frames, excessive collisions can reduce throughput dramatically. However, a
Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document An electronic document is any electronic media content (other than computer program A computer program is a collectio ...
report in 1980 studied performance of an existing Ethernet installation under both normal and artificially generated heavy load. The report claimed that 98% throughput on the LAN was observed. This is in contrast with
token passingOn a local area network, token passing is a channel access method where a signal called a ''token'' is passed between nodes to authorize that node to communicate. In contrast to Polling (computer science), polling access methods, there is no pre-defi ...
LANs (Token Ring, Token Bus), all of which suffer throughput degradation as each new node comes into the LAN, due to token waits. This report was controversial, as modeling showed that collision-based networks theoretically became unstable under loads as low as 37% of nominal capacity. Many early researchers failed to understand these results. Performance on real networks is significantly better. In a modern Ethernet, the stations do not all share one channel through a shared cable or a simple
repeater 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/outpu ...

repeater hub
; instead, each station communicates with a switch, which in turn forwards that traffic to the destination station. In this topology, collisions are only possible if station and switch attempt to communicate with each other at the same time, and collisions are limited to this link. Furthermore, the
10BASE-T 1 (one, also called unit, and unity) is a number and a numerical digit used to represent that number in numeral system, numerals. It represents a single entity, the unit (measurement), unit of counting or measurement. For example, a line segmen ...
standard introduced a
full duplex A duplex communication system 400px, Communication system A communications system or communication system is a collection of individual telecommunications network A telecommunications network is a group of nodes interconnected by links ...
mode of operation which became common with
Fast Ethernet In computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically ...
and the de facto standard with
Gigabit Ethernet In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (netwo ...
. In full duplex, switch and station can send and receive simultaneously, and therefore modern Ethernets are completely collision-free. File:Bustopologie.png, The original Ethernet implementation: shared medium, collision-prone. All computers trying to communicate share the same cable, and so compete with each other. File:HUB SWITCH 6.jpg, Modern Ethernet implementation: switched connection, collision-free. Each computer communicates only with its own switch, without competition for the cable with others.


Repeaters and hubs

For signal degradation and timing reasons, coaxial Ethernet segments have a restricted size. Somewhat larger networks can be built by using an Ethernet repeater. Early repeaters had only two ports, allowing, at most, a doubling of network size. Once repeaters with more than two ports became available, it was possible to wire the network in a
star topology A star network is an implementation of a spoke–hub distribution paradigm in computer networks. In a star network, every Host (network), host is connected to a central Hub (network science), hub. In its simplest form, one central hub acts as ...

star topology
. Early experiments with star topologies (called "Fibernet") using
optical fiber An optical fiber (or fibre in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...

optical fiber
were published by 1978. Shared cable Ethernet is always hard to install in offices because its bus topology is in conflict with the star topology cable plans designed into buildings for telephony. Modifying Ethernet to conform to twisted pair telephone wiring already installed in commercial buildings provided another opportunity to lower costs, expand the installed base, and leverage building design, and, thus, twisted-pair Ethernet was the next logical development in the mid-1980s. Ethernet on unshielded twisted-pair cables (UTP) began with StarLAN at 1 Mbit/s in the mid-1980s. In 1987
SynOptics SynOptics Communications was a Santa Clara, California-based early computer network equipment vendor from 1985 until 1994. SynOptics popularized the concept of the modular Ethernet hub and high-speed Ethernet networking over copper twisted-pair and ...
introduced the first twisted-pair Ethernet at 10 Mbit/s in a star-wired cabling topology with a central hub, later called
LattisNet LattisNet was a family of computer networking hardware and software products built and sold by SynOptics, SynOptics Communications (also rebranded by Western Digital) during the 1980s. Examples were the 1000, 2500 and 3000 series of LattisHub networ ...
. These evolved into 10BASE-T, which was designed for point-to-point links only, and all termination was built into the device. This changed repeaters from a specialist device used at the center of large networks to a device that every twisted pair-based network with more than two machines had to use. The tree structure that resulted from this made Ethernet networks easier to maintain by preventing most faults with one peer or its associated cable from affecting other devices on the network. Despite the physical star topology and the presence of separate transmit and receive channels in the twisted pair and fiber media, repeater-based Ethernet networks still use half-duplex and CSMA/CD, with only minimal activity by the repeater, primarily generation of the
jam signal Carrier-sense multiple access with collision detection (CSMA/CD) is a media access control In IEEE 802, IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware ...
in dealing with packet collisions. Every packet is sent to every other port on the repeater, so bandwidth and security problems are not addressed. The total throughput of the repeater is limited to that of a single link, and all links must operate at the same speed.


While repeaters can isolate some aspects of Ethernet segments, such as cable breakages, they still forward all traffic to all Ethernet devices. The entire network is one collision domain, and all hosts have to be able to detect collisions anywhere on the network. This limits the number of repeaters between the farthest nodes and creates practical limits on how many machines can communicate on an Ethernet network. Segments joined by repeaters have to all operate at the same speed, making phased-in upgrades impossible. To alleviate these problems, bridging was created to communicate at the data link layer while isolating the physical layer. With bridging, only well-formed Ethernet packets are forwarded from one Ethernet segment to another; collisions and packet errors are isolated. At initial startup, Ethernet bridges work somewhat like Ethernet repeaters, passing all traffic between segments. By observing the source addresses of incoming frames, the bridge then builds an address table associating addresses to segments. Once an address is learned, the bridge forwards network traffic destined for that address only to the associated segment, improving overall performance. Broadcasting (networking), Broadcast traffic is still forwarded to all network segments. Bridges also overcome the limits on total segments between two hosts and allow the mixing of speeds, both of which are critical to the incremental deployment of faster Ethernet variants. In 1989, Vanguard Managed Solutions, Motorola Codex introduced their 6310 EtherSpan, and Kalpana (company), Kalpana introduced their EtherSwitch; these were examples of the first commercial Ethernet switches. Early switches such as this used cut-through switching where only the header of the incoming packet is examined before it is either dropped or forwarded to another segment. This reduces the forwarding latency. One drawback of this method is that it does not readily allow a mixture of different link speeds. Another is that packets that have been corrupted are still propagated through the network. The eventual remedy for this was a return to the original store and forward approach of bridging, where the packet is read into a buffer on the switch in its entirety, its frame check sequence verified and only then the packet is forwarded. In modern network equipment, this process is typically done using application-specific integrated circuits allowing packets to be forwarded at wire speed. When a twisted pair or fiber link segment is used and neither end is connected to a repeater, full-duplex Ethernet becomes possible over that segment. In full-duplex mode, both devices can transmit and receive to and from each other at the same time, and there is no collision domain. This doubles the aggregate bandwidth of the link and is sometimes advertised as double the link speed (for example, 200 Mbit/s for Fast Ethernet). The elimination of the collision domain for these connections also means that all the link's bandwidth can be used by the two devices on that segment and that segment length is not limited by the constraints of collision detection. Since packets are typically delivered only to the port they are intended for, traffic on a switched Ethernet is less public than on shared-medium Ethernet. Despite this, switched Ethernet should still be regarded as an insecure network technology, because it is easy to subvert switched Ethernet systems by means such as ARP spoofing and MAC flooding. The bandwidth advantages, the improved isolation of devices from each other, the ability to easily mix different speeds of devices and the elimination of the chaining limits inherent in non-switched Ethernet have made switched Ethernet the dominant network technology.


Advanced networking

Simple switched Ethernet networks, while a great improvement over repeater-based Ethernet, suffer from single points of failure, attacks that trick switches or hosts into sending data to a machine even if it is not intended for it, scalability and security issues with regard to switching loops, broadcast radiation, and multicast traffic. Advanced networking features in switches use shortest path bridging (SPB) or the spanning-tree protocol (STP) to maintain a loop-free, meshed network, allowing physical loops for redundancy (STP) or load-balancing (SPB). Shortest path bridging includes the use of the link-state routing protocol IS-IS to allow larger networks with shortest path routes between devices. Advanced networking features also ensure port security, provide protection features such as MAC lockdown and broadcast radiation filtering, use virtual LANs to keep different classes of users separate while using the same physical infrastructure, employ multilayer switching to route between different classes, and use link aggregation to add bandwidth to overloaded links and to provide some redundancy. In 2016, Ethernet replaced InfiniBand as the most popular system interconnect of TOP500 supercomputers.


Varieties

The Ethernet physical layer evolved over a considerable time span and encompasses coaxial, twisted pair and fiber-optic physical media interfaces, with speeds from to . The first introduction of twisted-pair CSMA/CD was StarLAN, standardized as 802.3 1BASE5. While 1BASE5 had little market penetration, it defined the physical apparatus (wire, plug/jack, pin-out, and wiring plan) that would be carried over to 10BASE-T through 10GBASE-T. The most common forms used are Ethernet over twisted pair, 10BASE-T, 100BASE-TX, and 1000BASE-T. All three use twisted-pair cables and 8P8C modular connectors. They run at , , and , respectively. Optical fiber, Fiber optic variants of Ethernet (that commonly use Small form-factor pluggable transceiver, SFP modules) are also very popular in larger networks, offering high performance, better electrical isolation and longer distance (tens of kilometers with some versions). In general, network protocol stack software will work similarly on all varieties.


Frame structure

In IEEE 802.3, a datagram is called a ''packet'' or ''frame''. ''Packet'' is used to describe the overall transmission unit and includes the preamble (communication), preamble, start frame delimiter (SFD) and carrier extension (if present). The ''frame'' begins after the start frame delimiter with a frame header featuring source and destination MAC addresses and the EtherType field giving either the protocol type for the payload protocol or the length of the payload. The middle section of the frame consists of payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a 32-bit cyclic redundancy check, which is used to detect corruption of data in transit. Notably, Ethernet packets have no hop count, time-to-live field, leading to possible problems in the presence of a switching loop.


Autonegotiation

Autonegotiation is the procedure by which two connected devices choose common transmission parameters, e.g. speed and duplex mode. Autonegotiation was initially an optional feature, first introduced with 100BASE-TX, while it is also backward compatible with 10BASE-T. Autonegotiation is mandatory for 1000BASE-T and faster.


Error conditions


Switching loop

A switching loop or bridge loop occurs in
computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically wired, optical, and wire ...
s when there is more than one Layer 2 (
OSI model The Open Systems Interconnection model (OSI model) is a that characterises and standardises the communication functions of a or computing system without regard to its underlying internal structure and technology. Its goal is the interoperabil ...

OSI model
) path between two endpoints (e.g. multiple connections between two network switches or two ports on the same switch connected to each other). The loop creates broadcast radiation, broadcast storms as broadcasts and multicasts are forwarded by switches out every Computer port (hardware), port, the switch or switches will repeatedly rebroadcast the broadcast messages flooding the network. Since the Layer 2 header does not support a ''time to live'' (TTL) value, if a frame is sent into a looped topology, it can loop forever. A physical topology that contains switching or bridge loops is attractive for redundancy reasons, yet a switched network must not have loops. The solution is to allow physical loops, but create a loop-free logical topology using the shortest path bridging (SPB) protocol or the older spanning tree protocols (STP) on the network switches.


Jabber

A node that is sending longer than the maximum transmission window for an Ethernet packet is considered to be ''jabbering''. Depending on the physical topology, jabber detection and remedy differ somewhat. * An Medium Attachment Unit, MAU is required to detect and stop abnormally long transmission from the Data terminal equipment, DTE (longer than 20–150 ms) in order to prevent permanent network disruption. * On an electrically shared medium (10BASE5, 10BASE2, 1BASE5), jabber can only be detected by each end node, stopping reception. No further remedy is possible. * A repeater/repeater hub uses a jabber timer that ends retransmission to the other ports when it expires. The timer runs for 25,000 to 50,000 bit times for 1 Mbit/s, 40,000 to 75,000 bit times for 10 and 100 Mbit/s, and 80,000 to 150,000 bit times for 1 Gbit/s. Jabbering ports are partitioned off the network until a carrier is no longer detected. * End nodes utilizing a MAC layer will usually detect an oversized Ethernet frame and cease receiving. A bridge/switch will not forward the frame. * A non-uniform frame size configuration in the network using jumbo frames may be detected as jabber by end nodes. * A packet detected as jabber by an upstream repeater and subsequently cut off has an invalid frame check sequence and is dropped.


Runt frames

* ''Ethernet frame#Runt frames, Runts'' are packets or frames smaller than the minimum allowed size. They are dropped and not propagated.


See also

* 5-4-3 rule * Chaosnet * Ethernet crossover cable * Fiber media converter * ISO/IEC 11801 * Link Layer Discovery Protocol * List of device bit rates * LocalTalk * PHY * Point-to-point protocol over Ethernet (PPPoE) * Sneakernet * Wake-on-LAN (WoL)


Notes


References


Further reading

* Version 1.0 of the DIX specification. * *


External links


IEEE 802.3 Ethernet working group




{{Authority control Ethernet, American inventions IEEE standards Computer-related introductions in 1980