1.
Apple Attachment Unit Interface
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Apple Attachment Unit Interface is a mechanical re-design by Apple of the standard Attachment Unit Interface used to connect Ethernet transceivers to computer equipment. AUI was popular in the era before the dominance of 10BASE-T networking that started in the early 1990s, AAUI was an attempt to make the much smaller. AAUI was part of a system of Ethernet peripherals that tried to make connecting to Ethernet much easier, at the time, Ethernet systems usually were 10BASE2, also known as thinnet. A FriendlyNet 10BASE2 system did not use BNC T-connectors or separate 50 Ω terminators, instead of a single BNC connector that was inserted into a T-connector placed inline in the cable, the AAUI transceiver had two BNC connectors, one on each side to which the cables were attached. The transceiver would automatically terminate the network if a cable was not attached to one of the sides, additionally, Apple 10BASE2 cables would terminate the network if no device was attached to them. Thus the number of mistakes that could be made hooking up a network was reduced considerably. Since any of these mistakes would disable the network in an area this was a significant improvement, FriendlyNet equipment was quite expensive and even third party AAUI transceivers were rather expensive. Additionally, AAUI held no advantage for any other than 10BASE2. Apple eventually abandoned the system and sold off the name, Macintosh Quadra, Centris, PowerBook 500, Duo Dock II and early Power Macintoshes had an AAUI port, which requires an external transceiver. Later models included both an AAUI and modular connector port for directly connecting 10BASE-T, either could be used, AAUI connectors were also present on some Processor Direct Slot Ethernet adapter cards used in Macintosh LC and Performa machines. AAUI had disappeared by the late 1990s, when all new Apple machines starting with the beige Power Macintosh G3 series included only 10BASE-T, many third parties also created AAUI transceivers. Most made simplifications to the connectors and cables, presumably to reduce costs, most third parties, as well as any non-Apple equipment would use standard 10BASE2 cabling, including T-connectors and manual termination. Additionally, Apples 10BASE2 cables were not really feasible for all uses since they came in fixed lengths. AUI used a full-sized 15-pin D connector that used a clip for mechanical connections in place of thumbscrews. AAUI replaced these with a small 14-position,0. 050-inch-spaced ribbon contact connector, the connector may have been changed to avoid confusion with the monitor port on early Macintoshes, which also used a 15-pin D connector. 3rd party AAUI devices often omitted this sheath, requiring the user to directly squeeze small tabs on the sides of the housing to detach the hooks
2.
Apple Inc.
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Apple is an American multinational technology company headquartered in Cupertino, California that designs, develops, and sells consumer electronics, computer software, and online services. Apples consumer software includes the macOS and iOS operating systems, the media player, the Safari web browser. Its online services include the iTunes Store, the iOS App Store and Mac App Store, Apple Music, Apple was founded by Steve Jobs, Steve Wozniak, and Ronald Wayne in April 1976 to develop and sell personal computers. It was incorporated as Apple Computer, Inc. in January 1977, Apple joined the Dow Jones Industrial Average in March 2015. In November 2014, Apple became the first U. S. company to be valued at over US$700 billion in addition to being the largest publicly traded corporation in the world by market capitalization. The company employs 115,000 full-time employees as of July 2015 and it operates the online Apple Store and iTunes Store, the latter of which is the worlds largest music retailer. Consumers use more than one billion Apple products worldwide as of March 2016, Apples worldwide annual revenue totaled $233 billion for the fiscal year ending in September 2015. This revenue accounts for approximately 1. 25% of the total United States GDP.1 billion, the corporation receives significant criticism regarding the labor practices of its contractors and its environmental and business practices, including the origins of source materials. Apple was founded on April 1,1976, by Steve Jobs, Steve Wozniak, the Apple I kits were computers single-handedly designed and hand-built by Wozniak and first shown to the public at the Homebrew Computer Club. The Apple I was sold as a motherboard, which was less than what is now considered a personal computer. The Apple I went on sale in July 1976 and was market-priced at $666.66, Apple was incorporated January 3,1977, without Wayne, who sold his share of the company back to Jobs and Wozniak for $800. Multimillionaire Mike Markkula provided essential business expertise and funding of $250,000 during the incorporation of Apple, during the first five years of operations revenues grew exponentially, doubling about every four months. Between September 1977 and September 1980 yearly sales grew from $775,000 to $118m, the Apple II, also invented by Wozniak, was introduced on April 16,1977, at the first West Coast Computer Faire. It differed from its rivals, the TRS-80 and Commodore PET, because of its character cell-based color graphics. While early Apple II models used ordinary cassette tapes as storage devices, they were superseded by the introduction of a 5 1/4 inch floppy disk drive and interface called the Disk II. The Apple II was chosen to be the platform for the first killer app of the business world, VisiCalc. VisiCalc created a market for the Apple II and gave home users an additional reason to buy an Apple II. Before VisiCalc, Apple had been a distant third place competitor to Commodore, by the end of the 1970s, Apple had a staff of computer designers and a production line
3.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 gigabits per second. 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. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, an Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
4.
Coaxial cable
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Coaxial cable, or coax, is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an outer sheath or jacket. The term coaxial comes from the conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network connections, digital audio and this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference, the cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor, the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer, other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, the inner conductor might be solid or stranded, stranded is more flexible. To get better performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the conductor may be solid plastic, a foam plastic. The properties of control some electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables, solid Teflon is also used as an insulator. Some coaxial lines use air and have spacers to keep the conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield and this allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat
5.
BNC connector
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The BNC connector is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. It features two bayonet lugs on the connector, mating is fully achieved with a quarter turn of the coupling nut. BNC connectors are used with coaxial cable in radio, television, and other radio-frequency electronic equipment, test instruments. The BNC was commonly used for computer networks, including ARCnet, the IBM PC Network. BNC connectors are made to match the impedance of cable at either 50 ohms or 75 ohms. They are usually applied for frequencies below 4 GHz and voltages below 500 volts, similar connectors using the bayonet connection principle exist, and a threaded connector is also available. The BNC was originally designed for use and has gained wide acceptance in video. The BNC uses a slotted outer conductor and some plastic dielectric on each gender connector and this dielectric causes increasing losses at higher frequencies. Above 4 GHz, the slots may radiate signals, so the connector is usable, both 50 ohm and 75 ohm versions are available. The BNC connector is used for signal connections such as, analog, the BNC connector is used for composite video on commercial video devices. Consumer electronics devices with RCA connector jacks can be used with BNC-only commercial video equipment by inserting an adapter, BNC connectors were commonly used on 10base2 thin Ethernet network cables and network cards. BNC connections can also be found in recording studios, digital recording equipment uses the connection for synchronization of various components via the transmission of word clock timing signals. Typically the male connector is fitted to a cable, and the female to a panel on equipment, cable connectors are often designed to be fitted by crimping using a special power or manual tool. Wire strippers which strip outer jacket, shield braid, and inner dielectric to the lengths in one operation are used. The connector was named the BNC after its bayonet mount locking mechanism and its inventors, Paul Neill, Neill worked at Bell Labs and also invented the N connector, Concelman worked at Amphenol and also invented the C connector. A backronym has been applied to it, British Naval Connector. Another common incorrectly attributed origin is Berkeley Nucleonics Corporation, the basis for the development of the BNC connector was largely the work of Octavio M. Salati, a graduate of the Moore School of Electrical Engineering of the University of Pennsylvania. In 1945, while working at Hazeltine Electronics Corporation, he filed a patent for a connector for coaxial cables that would minimize wave reflection/loss, the patent was granted in 1951
6.
Category 5 cable
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Category 5 cable, commonly referred to as Cat 5, is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet, the cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX, 1000BASE-T, and 2. 5GBASE-T. Cat 5 is also used to other signals such as telephony. This cable is connected using punch-down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the balanced twisted pair design. Category 5 was superseded by the Category 5e specification, and later category 6 cable, the specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specify performance characteristics and test requirements for frequencies up to 100 MHz, cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C modular connectors are used for connecting category 5 cable, the cable is terminated in either the T568A scheme or the T568B scheme. The two schemes work equally well and may be mixed in an installation so long as the scheme is used on both ends of each cable. Each of the four pairs in a Cat 5 cable has differing precise number of twists per meter to minimize crosstalk between the pairs, although cable assemblies containing 4 pairs are common, category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs and this use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs. The cable is available in both stranded and solid conductor forms, the stranded form is more flexible and withstands more bending without breaking. Permanent wiring is solid-core, while patch cables are stranded, the specific category of cable in use can be identified by the printing on the side of the cable. Most Category 5 cables can be bent at any radius exceeding approximately four times the diameter of the cable. The maximum length for a segment is 100 m per TIA/EIA 568-5-A. If longer runs are required, the use of hardware such as a repeater or switch is necessary. The specifications for 10BASE-T networking specify a 100-meter length between active devices and this allows for 90 meters of solid-core permanent wiring, two connectors and two stranded patch cables of 5 meters, one at each end. The category 5e specification improves upon the category 5 specification by revising and introducing new specifications to further mitigate the amount of crosstalk
7.
IEEE 802.11
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They are created and maintained by the Institute of Electrical and Electronics Engineers LAN/MAN Standards Committee. The base version of the standard was released in 1997, and has had subsequent amendments, the standard and amendments provide the basis for wireless network products using the Wi-Fi brand. As a result, in the marketplace, each tends to become its own standard. The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the basic protocol. 802. 11-1997 was the first wireless networking standard in the family, but 802. 11b was the first widely accepted one, followed by 802. 11a,802. 11g,802. 11n, and 802. 11ac. Other standards in the family are service amendments that are used to extend the current scope of the existing standard, which may also include corrections to a previous specification. 802. 11b and 802. 11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the U. S. Federal Communications Commission Rules and Regulations. Because of this choice of band,802. 11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones. Better or worse performance with higher or lower frequencies may be realized,802. 11n can use either the 2.4 GHz or the 5 GHz band,802. 11ac uses only the 5 GHz band. The segment of the frequency spectrum used by 802.11 varies between countries. In the US,802. 11a and 802. 11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by one through six of 802. 11b and 802. 11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802. 11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption. 802.11 technology has its origins in a 1985 ruling by the U. S. Federal Communications Commission that released the ISM band for unlicensed use, in 1991 NCR Corporation/AT&T invented a precursor to 802.11 in Nieuwegein, the Netherlands. The inventors initially intended to use the technology for cashier systems, the first wireless products were brought to the market under the name WaveLAN with raw data rates of 1 Mbit/s and 2 Mbit/s. Vic Hayes, who held the chair of IEEE802.11 for 10 years, in 1999, the Wi-Fi Alliance was formed as a trade association to hold the Wi-Fi trademark under which most products are sold. The original version of the standard IEEE802.11 was released in 1997 and clarified in 1999 and it specified two net bit rates of 1 or 2 megabits per second, plus forward error correction code. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz, some earlier WLAN technologies used lower frequencies, such as the U. S.900 MHz ISM band
8.
10BASE5
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10BASE5 was the first commercially available variant of Ethernet. 10BASE5 uses a thick and stiff coaxial cable up to 500 metres in length, up to 100 stations can be connected to the cable using vampire taps and share a single collision domain with 10 Mbit/s of bandwidth shared among them. The system is difficult to install and maintain, as of 2003, IEEE802.3 has deprecated this standard for new installations. The name 10BASE5 is derived from several characteristics of the physical medium, the 10 refers to its transmission speed of 10 Mbit/s. The BASE is short for baseband signalling, and the 5 stands for the segment length of 500 metres. For its physical layer 10BASE5 uses cable similar to RG-8/U coaxial cable and this is a stiff,0. 375-inch diameter cable with an impedance of 50 ohms, a solid center conductor, a foam insulating filler, a shielding braid, and an outer jacket. The outer jacket is often yellow-to-orange fluorinated ethylene propylene so it often is called yellow cable, orange hose, 10BASE5 coaxial cables had a maximum length of 500 metres. Up to 100 nodes could be connected to a 10BASE5 segment, transceiver nodes can be connected to cable segments with N connectors, or via a vampire tap, which allows new nodes to be added while existing connections are live. Transceivers should be installed only at precise 2. 5-metre intervals and this distance was chosen to not correspond to the wavelength of the signal, this ensures that the reflections from multiple taps are not in phase. These suitable points are marked on the cable with black bands, the cable is required to be one continuous run, T-connections are not allowed. As is the case with most other high-speed buses, segments must be terminated at each end, for coaxial-cable-based Ethernet, each end of the cable has a 50 ohm resistor attached. Typically this resistor is built into a male N connector and attached to the end of the cable just past the last device. With termination missing, or if there is a break in the cable and this reflected signal is indistinguishable from a collision, and prevents communication. Adding new stations to network is complicated by the need to pierce the cable. The cable is stiff and difficult to bend around corners, one improper connection could take down the whole network and finding the source of the trouble is difficult.3 or later
9.
Obsolescence
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Obsolescence is the state of being which occurs when an object, service, or practice is no longer wanted even though it may still be in good working order. Obsolescence frequently occurs because a replacement has become available that has, in sum, obsolete refers to something that is already disused or discarded, or antiquated. Typically, obsolescence is preceded by a decline in popularity. Driven by rapid changes, new components are developed and launched on the market with increasing speed. The result is a change in production methods of all components. A growing industry sector is facing issues where life cycles of products no longer fit together with life cycles of required components and this issue is known as obsolescence, the status given to a part when it is no longer available from its original manufacturer. However, obsolescence extends beyond electronic components to other items, such as materials, textiles, in addition, obsolescence has been shown to appear for software, specifications, standards, processes, and soft resources, such as human skills. It is highly important to implement and operate a management of obsolescence to mitigate. Technical obsolescence usually occurs when a new product or technology supersedes the old, on a smaller scale, particular products may become obsolete due to replacement by a newer version of the product. Many products in the industry become obsolete in this manner, for example. Singularly, rapid obsolescence of data formats along with their hardware and software can lead to loss of critical information. Another complementary reason for obsolescence can be that supporting technologies may no longer be available to produce or even repair a product and it is rarely worth redeveloping a product to get around these issues since its overall functionality and price/performance ratio has usually been superseded by that time as well. Some products are rendered obsolete due to changes in complementary products which results in the function of the first product being made unnecessary. For example, buggy whips became obsolete when people started to travel in cars rather than in horse-drawn buggies, items become functionally obsolete when they can no longer adequately perform the function for which they were created. This causes scarcity of parts and skilled technicians for repairs. This ultimately leads to prohibitive expense in keeping old technology functioning, the term obsolescence was first applied to the built environment in 1910 in an attempt to explain American skyscrapers sudden loss of value. For example, he suggested that hotels obsolescence will occur faster than banks due to their ever-changing functions, sometimes marketers deliberately introduce obsolescence into their product strategy, with the objective of generating long-term sales volume by reducing the time between repeat purchases. One example might be producing an appliance which is designed to wear out within five years of its purchase
10.
Baseband
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Baseband is a signal that has a very narrow and near-zero frequency range, i. e. a spectral magnitude that is nonzero only for frequencies in the vicinity of the origin and negligible elsewhere. In telecommunications and signal processing, baseband signals are transmitted without modulation, baseband has a low-frequency—contained within the bandwidth frequency close to 0 hertz up to a higher cut-off frequency. Baseband can be synonymous with lowpass or non-modulated, and is differentiated from passband, bandpass, carrier-modulated, intermediate frequency, or radio frequency. A baseband bandwidth is equal to the highest frequency of a signal or system, or a bound on such frequencies. By contrast, passband bandwidth is the difference between a highest frequency and a nonzero lowest frequency, a baseband channel or lowpass channel is a communication channel that can transfer frequencies that are very near zero. Examples are serial cables and local networks, as opposed to passband channels such as radio frequency channels. Frequency division multiplexing allows an analog telephone wire to carry a telephone call. Passband transmission makes communication possible over a bandpass filtered channel, such as the telephone network local-loop or a wireless channel. The word BASE in Ethernet physical layer standards, for example 10BASE5, 100BASE-TX and 1000BASE-SX, a baseband processor also known as BP or BBP is used to process the down-converted digital signal to retrieve essential data for the wireless digital system. The baseband processing block in receivers is usually responsible for providing data, code pseudo-ranges and carrier phase measurements. A baseband signal or lowpass signal is a signal that can include frequencies that are very near zero, the equivalent baseband signal is Z = I + j Q where I is the inphase signal, Q the quadrature phase signal, and j the imaginary unit. In a digital method, the I and Q signals of each modulation symbol are evident from the constellation diagram. The frequency spectrum of this includes negative as well as positive frequencies. The physical passband signal corresponds to I cos − Q sin = R e where ω is the angular frequency in rad/s. A signal at baseband is often used to modulate a higher frequency signal in order that it may be transmitted via radio. Modulation results in shifting the signal up to higher frequencies than it originally spanned. A key consequence of the usual double-sideband amplitude modulation is that the range of frequencies the signal spans is doubled, thus, the RF bandwidth of a signal is twice its baseband bandwidth. Steps may be taken to reduce this effect, such as single-sideband modulation, some transmission schemes such as frequency modulation use even more bandwidth
11.
Manchester code
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In telecommunication and data storage, Manchester coding is a line code in which the encoding of each data bit is either low then high, or high then low, of equal time. It therefore has no DC bias, and is self-clocking, which means that it may be inductively or capacitively coupled, as a result, electrical connections using a Manchester code are easily galvanically isolated using a network isolator—a simple one-to-one isolation transformer. The name comes from its development at the University of Manchester, according to Cisco, Manchester encoding introduces some difficult frequency-related problems that make it unsuitable for use at higher data rates. Manchester code ensures frequent line voltage transitions, directly proportional to the clock rate, extracting the original data from the received encoded bit, Summary, Each bit is transmitted in a fixed time. A0 is expressed by a transition, a 1 by high-to-low transition. The transitions which signify 0 or 1 occur at the midpoint of a period, transitions at the start of a period are overhead and dont signify data. Manchester code always has a transition at the middle of each bit period, the direction of the mid-bit transition indicates the data. Transitions at the boundaries do not carry information. They exist only to place the signal in the state to allow the mid-bit transition. The price of these benefits is a doubling of the bandwidth requirement compared to simpler NRZ coding schemes, Manchester encoding is a special case of binary phase-shift keying, where the data controls the phase of a square wave carrier whose frequency is the data rate. Such a signal is easy to generate, there are two opposing conventions for the representations of data. The first of these was first published by G. E. Thomas in 1949 and is followed by numerous authors. It specifies that for a 0 bit the signal levels will be low-high - with a low level in the first half of the bit period, for a 1 bit the signal levels will be high-low. The second convention is followed by numerous authors as well as by IEEE802.4. It states that a logic 0 is represented by a signal sequence. If a Manchester encoded signal is inverted in communication, it is transformed from one convention to the other and this ambiguity can be overcome by using differential Manchester encoding
12.
Medium Attachment Unit
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A Medium Attachment Unit is a transceiver which converts signals on an Ethernet cable to and from Attachment Unit Interface signals. On original 10BASE5 Ethernet, the MAU was typically clamped to the Ethernet cable, for backwards compatibility with equipment which still has external AUI interfaces, MAUs are still available with 10BASE2 or 10BASET connections. The following standard, Fast Ethernet introduces division onto Media Access Controller, some early Fast Ethernet hardware had a physical external MII connectors, functionally similar to AUI connector. Objectives of MAU, Provide the physical means for communication between local network data link entities, Provide a communication channel capable of high bandwidth and low bit error ratio performance. Provide for ease of installation and service, MAU Characteristics, Enables coupling the Physical Layer Signalling by way of the AUI to the explicit baseband coaxial transmission system. Supports message traffic at a rate of 10,100. Provides for driving up to 500m of coaxial cable without the use of a repeater. Permits the DTE to test the MAU and the medium itself, supports system configurations using the CSMA/CD access mechanism defined with baseband signaling. Collision detection and Loop-back functions direct transfer through the MAU and it removes equipment from the network whenever it continuously transmits for periods significantly longer than required for a maximum-length packet, indicating a possible problem with the NIC. The signal quality error test detects silent failures in the circuitry, Link integrity functions detects breaks in the wire pairs. Both Signal quality error test and Link integrity functions assist in fault isolation, two modes of operation, Normal mode, The MAU functions as a direct connection between the baseband medium and the DTE. Data output from the DTE is output to the coaxial trunk medium and this mode is the “normal” mode of operation for the intended message traffic between stations. Monitor mode or Isolated mode, The MAU functions as a connection between the baseband medium and the DTE. Data output from the DTE is suppressed and only data on the coaxial trunk medium is input to the DTE and this mode is for observing message traffic. Receive function The ability to receive serial data bit streams over the baseband medium, collision Presence function The ability to detect the presence of two or more stations concurrent transmissions. Monitor function The ability to inhibit the normal transmit data stream to the medium at the time the normal receive function and collision presence function remain operational. Jabber function The ability to interrupt the transmit function and inhibit an abnormally long output data stream. It removes equipment from the network whenever it continuously transmits for periods longer than required for a maximum-length packet
13.
Transmission line
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This article covers two-conductor transmission line such as parallel line, coaxial cable, stripline, and microstrip. Ordinary electrical cables suffice to carry low frequency alternating current, such as power, which reverses direction 100 to 120 times per second. However, they cannot be used to carry currents in the frequency range, above about 30 kHz, because the energy tends to radiate off the cable as radio waves. Radio frequency currents tend to reflect from discontinuities in the cable such as connectors and joints. These reflections act as bottlenecks, preventing the signal power from reaching the destination, Transmission lines use specialized construction, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. Types of transmission line include parallel line, coaxial cable, and planar transmission lines such as stripline, the higher the frequency of electromagnetic waves moving through a given cable or medium, the shorter the wavelength of the waves. Transmission lines become necessary when the length of the cable is longer than a significant fraction of the transmitted frequencys wavelength. At microwave frequencies and above, power losses in transmission lines become excessive, and waveguides are used instead, some sources define waveguides as a type of transmission line, however, this article will not include them. At even higher frequencies, in the terahertz, infrared and light range, waveguides in turn become lossy, mathematical analysis of the behaviour of electrical transmission lines grew out of the work of James Clerk Maxwell, Lord Kelvin and Oliver Heaviside. In 1855 Lord Kelvin formulated a model of the current in a submarine cable. The model correctly predicted the performance of the 1858 trans-Atlantic submarine telegraph cable. In 1885 Heaviside published the first papers that described his analysis of propagation in cables, in many electric circuits, the length of the wires connecting the components can for the most part be ignored. That is, the voltage on the wire at a time can be assumed to be the same at all points. Stated another way, the length of the wire is important when the signal frequency components with corresponding wavelengths comparable to or less than the length of the wire. A common rule of thumb is that the cable or wire should be treated as a line if the length is greater than 1/10 of the wavelength. If the transmission line is uniform along its length, then its behaviour is described by a single parameter called the characteristic impedance. This is the ratio of the voltage of a given wave to the complex current of the same wave at any point on the line. Typical values of Z0 are 50 or 75 ohms for a cable, about 100 ohms for a twisted pair of wires
14.
Electrical termination
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Electrical termination is an electrical industry term used to describe the specific point at which a conductive device, such as wire or cable, ends or starts. The conductive device may or may not pass the carried electricity or signal onto another conductive device at this point, a common point of electrical termination is at a terminal block. A wire typically ends, or terminates, at the terminal block, ordinary electrical cables suffice to carry low frequency alternating current, such as mains power, which reverses direction 100 to 120 times per second, and audio signals. However, they cannot be used to carry currents in the frequency range, above about 30 kHz, because the energy tends to radiate off the cable as radio waves. The higher the frequency of waves moving through a given cable or medium. Transmission lines become necessary when the length of the cable is longer than a significant fraction of the transmitted frequencys wavelength, types of transmission line cables include parallel line, and coaxial cable. and these require high frequency signal termination. The terminator is usually placed at the end of a line or daisy chain bus, and is designed to match the AC impedance of the cable and hence minimize signal reflections. Less commonly, a terminator is also placed at the end of the wire or cable. Radio frequency currents tend to reflect from discontinuities in the such as connectors and joints. Secondary reflections can also occur at the start, allowing interference to persist as repeated echoes of old data. These reflections also act as bottlenecks, preventing the signal power from reaching the destination, transmission line cables require impedance matching to carry electromagnetic signals with minimal reflections and power losses. Signal terminators are designed to match the characteristic impedances at both cable ends. Types of transmission line cables include balanced line such as line, and twisted pairs. Passive terminators often consist of a resistor, however significantly reactive loads may require other passive components such as inductors, capacitors. Active terminators consist of a regulator that keeps the voltage used for the terminating resistor at a constant level. Forced Perfect Termination Forced Perfect Termination can be used on single ended buses where diodes remove over, the signal is locked between two actively regulated voltage levels, which results in superior performance over a standard active terminator. All parallel SCSI units use terminators, SCSI is primarily used for storage and backup. Controller area network, commonly known as CAN Bus, uses terminators consisting of a 120 ohm resistor, dummy loads are commonly used in HF to EHF frequency circuits
15.
Resistor
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A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of power as heat may be used as part of motor controls, in power distribution systems. Fixed resistors have resistances that only slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements, or as sensing devices for heat, light, humidity, force, Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds, Resistors are also implemented within integrated circuits. The electrical function of a resistor is specified by its resistance, the nominal value of the resistance falls within the manufacturing tolerance, indicated on the component. Two typical schematic diagram symbols are as follows, The notation to state a resistors value in a circuit diagram varies, one common scheme is the letter and digit code for resistance values following IEC60062. It avoids using a separator and replaces the decimal separator with a letter loosely associated with SI prefixes corresponding with the parts resistance. For example, 8K2 as part marking code, in a diagram or in a bill of materials indicates a resistor value of 8.2 kΩ. Additional zeros imply a tighter tolerance, for example 15M0 for three significant digits, when the value can be expressed without the need for a prefix, an R is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω, for example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 /300 =0.04 amperes flows through that resistor. Practical resistors also have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits, the ohm is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere, since resistors are specified and manufactured over a very large range of values, the derived units of milliohm, kilohm, and megohm are also in common usage. The total resistance of resistors connected in series is the sum of their resistance values. R e q = R1 + R2 + ⋯ + R n, the total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. 1 R e q =1 R1 +1 R2 + ⋯ +1 R n. For example, a 10 ohm resistor connected in parallel with a 5 ohm resistor, a resistor network that is a combination of parallel and series connections can be broken up into smaller parts that are either one or the other
16.
Ohm
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The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. The definition of the ohm was revised several times, today the definition of the ohm is expressed from the quantum Hall effect. In many cases the resistance of a conductor in ohms is approximately constant within a range of voltages, temperatures. In alternating current circuits, electrical impedance is also measured in ohms, the siemens is the SI derived unit of electric conductance and admittance, also known as the mho, it is the reciprocal of resistance in ohms. The power dissipated by a resistor may be calculated from its resistance, non-linear resistors have a value that may vary depending on the applied voltage. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Two different methods of establishing a system of units can be chosen. Various artifacts, such as a length of wire or a standard cell, could be specified as producing defined quantities for resistance, voltage. This latter method ensures coherence with the units of energy, defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. Some early definitions of a unit of resistance, for example, the absolute-units system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the advantage of simplifying the equations used in the solution of electromagnetic problems. However, the CGS units turned out to have impractical sizes for practical measurements, various artifact standards were proposed as the definition of the unit of resistance. In 1860 Werner Siemens published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie and he proposed a column of pure mercury, of one square millimetre cross section, one metre long, Siemens mercury unit. However, this unit was not coherent with other units, one proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out experiments to the required precision. The BAAS in 1861 appointed a committee including Maxwell and Thomson to report upon Standards of Electrical Resistance, in the third report of the committee,1864, the resistance unit is referred to as B. A. unit, or Ohmad. By 1867 the unit is referred to as simply Ohm, the B. A. ohm was intended to be 109 CGS units but owing to an error in calculations the definition was 1. 3% too small. The error was significant for preparation of working standards, on September 21,1881 the Congrès internationale délectriciens defined a practical unit of Ohm for the resistance, based on CGS units, using a mercury column at zero deg
17.
Alternating current
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Alternating current, is an electric current which periodically reverses direction, whereas direct current flows only in one direction. A common source of DC power is a cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, the usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves, audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information encoded onto the AC signal and these currents typically alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer, use of a higher voltage leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current and this means that when transmitting a fixed power on a given wire, if the current is halved, the power loss will be four times less. Power is often transmitted at hundreds of kilovolts, and transformed to 100–240 volts for domestic use, high voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, energy is generated at a convenient voltage for the design of a generator, near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world, high-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. HVDC systems, however, tend to be expensive and less efficient over shorter distances than transformers. Three-phase electrical generation is very common, the simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other, if coils are added opposite to these, they generate the same phases with reverse polarity and so can be simply wired together. In practice, higher pole orders are commonly used, for example, a 12-pole machine would have 36 coils. The advantage is that lower rotational speeds can be used to generate the same frequency, for example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency, the lower speed is preferable for larger machines. If the load on a system is balanced equally among the phases. Even in the worst-case unbalanced load, the current will not exceed the highest of the phase currents
18.
Ground loop (electricity)
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In an electrical system, a ground loop or earth loop is an equipment and wiring configuration in which there are multiple paths for electricity to flow to ground. Ground loops are a cause of noise, hum, and interference in audio, video. In any case the difference between the ground terminals of each item of equipment is small. A severe risk of electric shock occurs when equipment grounds are removed in an attempt to cure the problems thought to be caused by ground loops. This only becomes a problem when one or more cables are then connected between A and B, to pass data or audio signals from one to the other. The shield of the cable is typically connected to the grounded equipment chassis of both A and B. There is now a ground loop, the ground loop will be carrying some current at the local supply frequency, typically 50 Hz or 60 Hz, due to electromagnetic induction from current-carrying conductors nearby. There is an AC magnetic field everywhere in developed areas, however, its magnitude and this influences the current induced in the ground loop, which is also dependent on the area enclosed by the ground loop and its orientation. The impedance of the loop, basically just its resistance at low frequencies and it is important to realise that for a ground loop to cause problems, there must be a local magnetic field produced by power frequency or other systems. It is the combination of radiated field and receptive ground loop that causes problems, in effect, the ground loop is the secondary of a very loosely coupled transformer, the primary being the summation of all current carrying conductors nearby. Transformer action limits the voltage in the loop, and the weak coupling limits the maximum current that will flow. Again, the voltage is not relevant, inside a building, the wiring may include radiating loops, e. g. It has been alleged that a significant cause of current in the loop is voltage drop along the equipment protective ground conductors. This is rarely significant, because safety regulations place strict limits on ground leakage current, the current arising due to magnetic induction is liable to be at least one or two orders of magnitude greater. So, when a current is induced in the loop, there will be a drop along the signal ground return. This is directly additive to the signal, and will result in objectionable hum. This is a significant fraction of the voltage of a moving coil pickup cartridge. Therefore there is no current loop, and no hum problem due directly to the grounding arrangements, careless interconnection is virtually guaranteed to result in hum problems
19.
Ground (electricity)
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Electrical circuits may be connected to ground for several reasons. In mains powered equipment, exposed parts are connected to ground to prevent user contact with dangerous voltage when electrical insulation fails. In electrical power systems, a protective ground conductor is an essential part of the safety Earthing system. Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices, in some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor. For measurement purposes, the Earth serves as a constant potential reference against which other potentials can be measured, an electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a ground is usually idealized as a source or sink for charge. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid, stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard. This is usually a large conductor attached to one side of the power supply which serves as the return path for current from many different components in the circuit. Long-distance electromagnetic telegraph systems from 1820 onwards used two or more wires to carry the signal and return currents. During dry weather, the ground connection often developed a high resistance, an electrical connection to earth can be used as a reference potential for radio frequency signals for certain kinds of antennas. The part directly in contact with the earth - the earth electrode - can be as simple as a rod or stake driven into the earth. Because high frequency signals can flow to earth due to capacitative effects, because of this, a complex system of buried rods and wires can be effective. An ideal signal ground maintains a fixed potential regardless of how much current flows into ground or out of ground. Some types of transmitting antenna systems in the VLF, LF, MF, sometimes a counterpoise is used as a ground plane, supported above the ground. Electrical power distribution systems are connected to ground to limit the voltage that can appear on distribution circuits. A distribution system insulated from ground may attain a high potential due to transient voltages caused by arcing, static electricity, a ground connection of the system dissipates such potentials and limits the rise in voltage of the grounded system. In a mains electricity wiring installation, the ground conductor typically refers to three different conductors or conductor systems as listed below. Equipment earthing conductors provide a connection between non-current-carrying metallic parts of equipment and the earth
20.
Time-domain reflectometer
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A time-domain reflectometer is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables. It can also be used to locate discontinuities in a connector, printed circuit board, the equivalent device for optical fiber is an optical time-domain reflectometer. A TDR measures reflections along a conductor, in order to measure those reflections, the TDR will transmit an incident signal onto the conductor and listen for its reflections. If the conductor is of a uniform impedance and is terminated, then there will be no reflections. Instead, if there are variations, then some of the incident signal will be reflected back to the source. A TDR is similar in principle to radar, generally, the reflections will have the same shape as the incident signal, but their sign and magnitude depend on the change in impedance level. If there is a increase in the impedance, then the reflection will have the same sign as the incident signal, if there is a step decrease in impedance. The magnitude of the reflection depends not only on the amount of the impedance change, the reflections are measured at the output/input to the TDR and displayed or plotted as a function of time. Alternatively, the display can be read as a function of length because the speed of signal propagation is almost constant for a given transmission medium. Because of its sensitivity to variations, a TDR may be used to verify cable impedance characteristics, splice and connector locations and associated losses. Some TDRs transmit a pulse along the conductor, the resolution of such instruments is often the width of the pulse, narrow pulses can offer good resolution, but they have high frequency signal components that are attenuated in long cables. The shape of the pulse is often a half cycle sinusoid, for longer cables, wider pulse widths are used. Fast rise time steps are also used, instead of looking for the reflection of a complete pulse, the instrument is concerned with the rising edge, which can be very fast. A 1970s technology TDR used steps with a time of 25 ps. Still other TDRs transmit complex signals and detect reflections with correlation techniques and these traces were produced by a time-domain reflectometer made from common lab equipment connected to approximately 100 feet of coaxial cable having a characteristic impedance of 50 ohms. The propagation velocity of this cable is approximately 66 % of the speed of light in a vacuum and these traces were produced by a commercial TDR using a step waveform with a 25 ps risetime, a sampling head with a 35 ps risetime, and an 18-inch SMA cable. The far end of the SMA cable was left open or connected to different adapters and it takes about 3 ns for the pulse to travel down the cable, reflect, and reach the sampling head. A second reflection can be seen in some traces, it is due to the reflection seeing a small mismatch at the sampling head, consider the case where the far end of the cable is shorted
21.
Ethernet over twisted pair
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Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Early Ethernet had used various grades of coaxial cable, but in 1984 and this led to the development of 10BASE-T and its successors 100BASE-TX and 1000BASE-T, supporting speeds of 10,100 and 1,000 Mbit/s respectively. All these three standards define both full-duplex and half-duplex communication, however, half-duplex operation for gigabit speed isnt supported by any existing hardware. All these standards use 8P8C connectors, and the cables from Cat3 to Cat8 have four pairs of wires, though 10BASE-T, the Institute of Electrical and Electronics Engineers standards association ratified several versions of the technology. The first two designs were StarLAN, standardized in 1986, at one megabit per second, and LattisNet, developed in January 1987. Both were developed before the 10BASE-T standard and used different signalling, in 1988 AT&T released StarLAN10, named for working at 10 Mbit/s. The StarLAN10 signalling was used as the basis of 10BASE-T, the centralized star topology was a more common approach to cabling than the bus in earlier standards and easier to manage. Using point-to-point links instead of a shared bus greatly simplified troubleshooting and was prone to failure. Exchanging cheap repeater hubs for more advanced switching hubs provided an upgrade path. Mixing different speeds in a single network became possible with the arrival of Fast Ethernet, depending on cable grades, subsequent upgrading to Gigabit Ethernet or faster may be as easy as replacing the network switches. The common names for the standards derive from aspects of the physical media, the leading number refers to the transmission speed in Mbit/s. BASE denotes that baseband transmission is used, the T designates twisted pair cable, where the pair of wires for each signal is twisted together to reduce radio frequency interference and crosstalk between pairs. Where there are standards for the same transmission speed, they are distinguished by a letter or digit following the T, such as TX, referring to the encoding method. Twisted-pair Ethernet standards are such that the majority of cables can be wired straight-through and it is conventional to wire cables for 10- or 100-Mbit/s Ethernet to either the T568A or T568B standards. The terms used in the explanations of the 568 standards, tip and ring, refer to older communication technologies, and equate to the positive and negative parts of the connections. A 10BASE-T or 100BASE-TX node such as a PC uses a connector wiring called medium dependent interfaces, transmitting on pin 1 and 2, an infrastructure node accordingly uses a connector wiring called MDI-X, transmitting on pin 3 and 6 and receiving on pin 1 and 2. These ports are connected using a cable, so each transmitter talks to the receiver on the other side. Nodes can have two types of ports, MDI or MDI-X, hubs and switches have regular ports
22.
Fast Ethernet
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In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s. Of the Fast Ethernet standards, 100BASE-TX is by far the most common, Fast Ethernet was introduced in 1995 as the IEEE802. 3u standard and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet. The acronym GE/FE is sometimes used for supporting both standards. Fast Ethernet is an extension of the 10-megabit Ethernet standard and it runs on UTP data or optical fiber cable in a star wired bus topology, similar to 10BASE-T where all cables are attached to a hub. Fast Ethernet devices are backward compatible with existing 10BASE-T systems. Fast Ethernet is sometimes referred to as 100BASE-X, where X is a placeholder for the FX, the standard specifies the use of CSMA/CD for media access control. A full-duplex mode is also specified and in all modern networks use Ethernet switches. The 100 in the type designation refers to the transmission speed of 100 Mbit/s. The letter following the dash refers to the medium that carries the signal. A Fast Ethernet adapter can be divided into a media access controller, which deals with the higher-level issues of medium availability. The MAC may be linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a media-independent interface, in rare cases the MII may be an external connection but is usually a connection between ICs in a network adapter or even within a single IC. The specs are based on the assumption that the interface between MAC and PHY will be a MII but they do not require it. Repeaters 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. 100BASE-T is any of several Fast Ethernet standards for twisted pair cables, including, 100BASE-TX, 100BASE-T4, the segment length for a 100BASE-T cable is limited to 100 metres. All are or were standards under IEEE802.3, 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 said vendors standards will work better with existing cables than other standards. Thus most networks had to be rewired for 100 Megabit speed whether or not there had supposedly been CAT3 or CAT5 cable runs, 100BASE-TX is the predominant form of Fast Ethernet, and runs over two wire-pairs inside a category 5 or above cable. Like 10BASE-T, the pairs in a standard connection are terminated on pins 1,2,3 and 6
23.
EAD socket
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An EAD socket was a network connection socket used in the early 1990s. Ethernet networking of this period used thin coax or 10BASE2, all devices on a network segment connected to the same electrical section of RG-58 coaxial cable. Intermediate devices were connected via a T piece, the two ends of the segment were terminated with a resistive network terminator. Although these networks were reliable when connected, they were prone to accidental misconnection by non-technical office staff and this was particularly an issue when devices, such as desktop computers, were being added or removed from the network. Although a rare need at this time, the situation was worse for portable laptops. With the obsolescence of 10BASE2 networks, from the mid 1990s, in favour of Ethernet over twisted pair, EAD is an abbreviation for German Ethernet-Anschlussdose. The EAD standard defines wall mounted Ethernet connection outlets that are more reliable than standard BNC T-connectors, EAD outlets have been developed from TAE connectors for telephony applications but they are intended for connecting coaxial network cables like 10BASE2. A different mechanical encoding prevents mix-up with phone plugs, EAD cables are duplex connections replacing two thin-wire cables, the T-connector is integrated into the BNC end. The contacts of an EAD outlet are closed if no connector is plugged in, when a cable is plugged in, the normally closed contacts in the socket are opened so that signals pass through the loop cable. Worn out connectors or outlets can cause the problems that haunted the simpler connectors. Description of the EAD system at itwissen. info
24.
Computer network
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A computer network or data network is a telecommunications network which allows nodes to share resources. In computer networks, networked computing devices exchange data with other using a data link. The connections between nodes are established using either cable media or wireless media, the best-known computer network is the Internet. Network computer devices that originate, route and terminate the data are called network nodes, nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the networks size, topology and organizational intent. In most cases, application-specific communications protocols are layered over other more general communications protocols and this formidable collection of information technology requires skilled network management to keep it all running reliably. The chronology of significant computer-network developments includes, In the late 1950s, in 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. Licklider developed a group he called the Intergalactic Computer Network. In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of computer systems. The same year, at Massachusetts Institute of Technology, a group supported by General Electric and Bell Labs used a computer to route. Throughout the 1960s, Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network, in 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network. This was an precursor to the ARPANET, of which Roberts became program manager. Also in 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control, in 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks. In July 1976, Robert Metcalfe and David Boggs published their paper Ethernet, Distributed Packet Switching for Local Computer Networks, in 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s, by 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added, the ability of Ethernet to scale easily is a contributing factor to its continued use. Providing access to information on shared storage devices is an important feature of many networks, a network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network
25.
Network interface controller
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A network interface controller is a computer hardware component that connects a computer to a computer network. Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard. The network controller implements the electronic circuitry required to communicate using a physical layer and data link layer standard such as Ethernet, Fibre Channel. The NIC allows computers to communicate over a network, either by using cables or wirelessly. Although other network technologies exist, IEEE802 networks including the Ethernet variants have achieved near-ubiquity since the mid-1990s, newer server motherboards may even have dual network interfaces built-in. The Ethernet capabilities are integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip. A separate network card is not required unless additional interfaces are needed or some type of network is used. The NIC may use one or more of the techniques to indicate the availability of packets to transfer. Interrupt-driven I/O is where the peripheral alerts the CPU that it is ready to transfer data, also, NICs may use one or more of the following techniques to transfer packet data, Programmed input/output is where the CPU moves the data to or from the NIC to memory. Direct memory access is where some other device other than the CPU assumes control of the bus to move data to or from the NIC to memory. This removes load from the CPU but requires more logic on the card, in addition, a packet buffer on the NIC may not be required and latency can be reduced. There are two types of DMA, third-party DMA in which a DMA controller other than the NIC performs transfers, an Ethernet network controller typically has an 8P8C socket where the network cable is connected. Older NICs also supplied BNC, or AUI connections, a few LEDs inform the user of whether the network is active, and whether or not data transmission occurs. Ethernet network controllers typically support 10 Mbit/s Ethernet,100 Mbit/s Ethernet, such controllers are designated as 10/100/1000, meaning that they can support a notional maximum transfer rate of 10,100 or 1000 Mbit/s. 10 Gigabit Ethernet NICs are also available, and, as of November 2014, are beginning to be available on computer motherboards, multiqueue NICs provide multiple transmit and receive queues, allowing packets received by the NIC to be assigned to one of its receive queues. The hardware-based distribution of the interrupts, described above, is referred to as receive-side scaling, purely software implementations also exist, such as the receive packet steering and receive flow steering. Examples of such implementations are the RFS and Intel Flow Director, with multiqueue NICs, additional performance improvements can be achieved by distributing outgoing traffic among different transmit queues. By assigning different transmit queues to different CPUs/cores, various operating systems internal contentions can be avoided and those NICs support, Accessing local and remote memory without involving the remote CPU
26.
Attachment Unit Interface
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The Attachment Unit Interface is a physical and logical interface defined in the original IEEE802.3 standard for 10BASE5 Ethernet. In the OSI Model, this serves as the demarcation point between the Physical and Data-Link layers. The physical interface consists 15 pin connection that provides a path between an Ethernet nodes Physical Signalling and the Medium Attachment Unit, sometimes known as a transceiver. An AUI cable may be up to 50 meters long, although frequently the cable is omitted altogether, the electrical AUI connection was still present inside the equipment. By the mid-1990s AUI had all but disappeared as Fast Ethernet became more common, Gigabit Ethernet and 10 Gigabit Ethernet have respectively the GMII and XGMII standards which are equivalent to AUI. A modified form using a connector called the AAUI was introduced on Apple Macintosh computers in 1991. An AUI connector is a DA-15 and it has a sliding clip in place of the thumbscrews normally found on a D-connector to hold two connectors together. This clip permits the MAU and MAC to be attached to one another even when their size. This clip is however found to be awkward and/or unreliable.3 or later
27.
Local area network
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By contrast, a wide area network, not only covers a larger geographic distance, but also generally involves leased telecommunication circuits or Internet links. An even greater contrast is the Internet, which is a system of globally connected business, Ethernet and Wi-Fi are the two most common transmission technologies in use for local area networks. Historical technologies include ARCNET, Token ring, and AppleTalk, the increasing demand and use of computers in universities and research labs in the late 1960s generated the need to provide high-speed interconnections between computer systems. A1970 report from the Lawrence Radiation Laboratory detailing the growth of their Octopus network gave an indication of the situation. A number of experimental and early commercial LAN technologies were developed in the 1970s, Cambridge Ring was developed at Cambridge University starting in 1974. Ethernet was developed at Xerox PARC in 1973–1975, and filed as U. S, in 1976, after the system was deployed at PARC, Robert Metcalfe and David Boggs published a seminal paper, Ethernet, Distributed Packet-Switching for Local Computer Networks. ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977 and it had the first commercial installation in December 1977 at Chase Manhattan Bank in New York. The initial driving force for networking was generally to share storage and printers, there was much enthusiasm for the concept and for several years, from about 1983 onward, computer industry pundits would regularly declare the coming year to be, “The year of the LAN”. In practice, the concept was marred by proliferation of incompatible physical layer and network protocol implementations, typically, each vendor would have its own type of network card, cabling, protocol, and network operating system. Netware dominated the personal computer LAN business from early after its introduction in 1983 until the mid-1990s when Microsoft introduced Windows NT Advanced Server, of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. During the same period, Unix workstations were using TCP/IP networking, early LAN cabling had generally been based on various grades of coaxial cable. This led to the development of 10BASE-T and structured cabling which is still the basis of most commercial LANs today, while fiber-optic cabling is common for links between switches, use of fiber to the desktop is rare. Many LANs use wireless technologies that are built into Smartphones, tablet computers, in a wireless local area network, users may move unrestricted in the coverage area. Wireless networks have become popular in residences and small businesses, because of their ease of installation, guests are often offered Internet access via a hotspot service. Network topology describes the layout of interconnections between devices and network segments, at the data link layer and physical layer, a wide variety of LAN topologies have been used, including ring, bus, mesh and star. At the higher layers, NetBEUI, IPX/SPX, AppleTalk and others were once common, simple LANs generally consist of cabling and one or more switches. A switch can be connected to a router, cable modem, a LAN can include a wide variety of other network devices such as firewalls, load balancers, and network intrusion detection. LANs can maintain connections with other LANs via leased lines, leased services, depending on how the connections are established and secured, and the distance involved, such linked LANs may also be classified as a metropolitan area network or a wide area network
28.
Free On-line Dictionary of Computing
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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 was hosted by Imperial College London, in May 2015, the site was updated to state that it was no longer supported by Imperial College Department of Computing. Howe has served as the editor-in-chief since the inception, with visitors to the website able to make suggestions for additions or corrections to articles. The dictionary incorporates the text of other resources, such as the Jargon File. Due to its availability under the GNU Free Documentation License, a license, it has in turn been incorporated in whole or part into other free content projects
29.
GNU Free Documentation License
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The GNU Free Documentation License is a copyleft license for free documentation, designed by the Free Software Foundation for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute, copies may also be sold commercially, but, if produced in larger quantities, the original document or source code must be made available to the works recipient. The GFDL was designed for manuals, textbooks, other reference and instructional materials, however, it can be used for any text-based work, regardless of subject matter. For example, the online encyclopedia Wikipedia uses the GFDL for all of its text. The GFDL was released in form for feedback in September 1999. After revisions, version 1.1 was issued in March 2000, version 1.2 in November 2002, the current state of the license is version 1.3. The first discussion draft of the GNU Free Documentation License version 2 was released on September 26,2006, material licensed under the current version of the license can be used for any purpose, as long as the use meets certain conditions. All previous authors of the work must be attributed, all changes to the work must be logged. All derivative works must be licensed under the same license, the full text of the license, unmodified invariant sections as defined by the author if any, and any other added warranty disclaimers and copyright notices from previous versions must be maintained. Technical measures such as DRM may not be used to control or obstruct distribution or editing of the document, the license explicitly separates any kind of Document from Secondary Sections, which may not be integrated with the Document, but exist as front-matter materials or appendices. Secondary sections can contain information regarding the authors or publishers relationship to the subject matter, if the material is modified, its title has to be changed. The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for History, Acknowledgements, Dedications and Endorsements sections. These features were added in part to make the more financially attractive to commercial publishers of software documentation. Endorsements sections are intended to be used in official standard documents, the GFDL requires the ability to copy and distribute the Document in any medium, either commercially or noncommercially and therefore is incompatible with material that excludes commercial re-use. Material that restricts commercial re-use is incompatible with the license and cannot be incorporated into the work, one example of such liberal and commercial fair use is parody. Although the two work on similar copyleft principles, the GFDL is not compatible with the Creative Commons Attribution-ShareAlike license. These exemptions allow a GFDL-based collaborative project with multiple authors to transition to the CC BY-SA3, if it was not originally published on an MMC, it can only be relicensed if it were added to an MMC before November 1,2008. To prevent the clause from being used as a general compatibility measure, at the release of version 1.3, the FSF stated that all content added before November 1,2008 to Wikipedia as an example satisfied the conditions
30.
Gigabit Ethernet
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In computer networking, Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE802. 3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks, the cables and equipment are very similar to previous standards and have been very common and economical since 2010. Ethernet was the result of the research done at Xerox PARC in the early 1970s, Ethernet later evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased speed from 10 to 100 megabits per second, Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE802. 3z,802. 3z is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or -ZX. For the history behind the X see Fast Ethernet, IEEE802. 3ab, ratified in 1999, defines Gigabit Ethernet transmission over unshielded twisted pair category 5, 5e or 6 cabling, and became known as 1000BASE-T. With the ratification of 802. 3ab, Gigabit Ethernet became a desktop technology as organizations could use their existing copper cabling infrastructure, IEEE802. 3ah, ratified in 2004 added two more gigabit fiber standards, 1000BASE-LX10 and 1000BASE-BX10. This was part of a group of protocols known as Ethernet in the First Mile. Initially, Gigabit Ethernet was deployed in high-capacity backbone network links, in 2000, Apples Power Mac G4 and PowerBook G4 were the first mass-produced personal computers featuring the 1000BASE-T connection. It quickly became a feature in many other computers. There are five physical layer standards for Gigabit Ethernet using optical fiber, twisted pair cable and these standards use 8b/10b encoding, which inflates the line rate by 25%, from 1000 Mbit/s to 1250 Mbit/s, to ensure a DC balanced signal. The symbols are sent using NRZ. Optical fiber transceivers are most often implemented as modules in SFP form or GBIC on older devices. IEEE802. 3ab, which defines the widely used 1000BASE-T interface type, uses a different encoding scheme in order to keep the rate as low as possible. IEEE802. 3ap defines Ethernet Operation over Electrical Backplanes at different speeds, Ethernet in the First Mile later added 1000BASE-LX10 and -BX10. 1000BASE-CX is a standard for Gigabit Ethernet connections with maximum distances of 25 meters using balanced shielded twisted pair. The short segment length is due to high signal transmission rate. 1000BASE-KX is part of the IEEE802. 3ap standard for Ethernet Operation over Electrical Backplanes and this standard defines one to four lanes of backplane links, one RX and one TX differential pair per lane, at link bandwidth ranging from 100Mbit to 10Gbit per second
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10 Gigabit Ethernet
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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 IEEE802. 3ae-2002 standard, half duplex operation and repeater hubs do not exist in 10GbE. Like previous versions of Ethernet, 10GbE can use either copper or fiber cabling, however, because of its bandwidth requirements, higher-grade copper cables are required, category 6a or Class F/Category 7 cables for lengths up to 100 meters. The 10 Gigabit Ethernet standard encompasses a number of different physical layer standards, a networking device, such as a switch or a network interface controller may have different PHY types through pluggable PHY modules, such as those based on SFP+. At the time that the 10 Gigabit Ethernet standard was developed, the WAN PHY encapsulates Ethernet packets in SONET OC-192c frames and operates at a slightly slower data-rate than the local area network PHY. Over the years the Institute of Electrical and Electronics Engineers 802.3 working group has published several standards relating to 10GbE, to implement different 10GbE physical layer standards, many interfaces consist of a standard socket into which different PHY modules may be plugged. Physical layer modules are not specified in a standards body. Relevant MSAs for 10GbE include XENPAK, XFP and SFP+, when choosing a PHY module, a designer considers cost, reach, media type, power consumption, and size. A single point-to-point link can have different MSA pluggable formats on either end as long as the 10GbE optical or copper port type inside the pluggable is identical, XENPAK was the first MSA for 10GE and had the largest form factor. X2 and XPAK were later competing standards with smaller form factors, X2 and XPAK have not been as successful in the market as XENPAK. XFP came after X2 and XPAK and it is also smaller, the newest module standard is the enhanced small form-factor pluggable transceiver, generally called SFP+. Based on the small form-factor pluggable transceiver and developed by the ANSI T11 fibre channel group, it is smaller still, SFP+ has become the most popular socket on 10GE systems. SFP+ modules do only optical to electrical conversion, no clock and data recovery, SFP+ modules share a common physical form factor with legacy SFP modules, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19 rack width blade. Optical modules are connected to a host by either a XAUI, XENPAK, X2, and XPAK modules use XAUI to connect to their hosts. XAUI uses a data channel and is specified in IEEE802.3 Clause 48. XFP modules use a XFI interface and SFP+ modules use an SFI interface, XFI and SFI use a single lane data channel and the 64b/66b encoding specified in IEEE802.3 Clause 49. SFP+ modules can further be grouped into two types of host interfaces, linear or limiting, limiting modules are preferred except when using old fiber infrastructure which requires the use of the linear interface provided by 10GBASE-LRM modules. There are two classifications for optical fiber, single-mode and multi-mode, in SMF light follows a single path through the fiber while in MMF it takes multiple paths resulting in differential mode delay
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100 Gigabit Ethernet
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40 Gigabit Ethernet and 100 Gigabit Ethernet are groups of computer networking technologies for transmitting Ethernet frames at rates of 40 and 100 gigabits per second, respectively. The technology was first defined by the IEEE802. 3ba-2010 standard and later by the 802. 3bg-2011,802. 3bj-2014, the standards define numerous port types with different optical and electrical interfaces and different numbers of optical fiber strands per port. Short distances over twinaxial cable are supported, 40GBASE-T uses twisted pair cabling for 40 Gbit/s over up to 30 m. On July 18,2006, a call for interest for a High Speed Study Group to investigate new standards for high speed Ethernet was held at the IEEE802.3 plenary meeting in San Diego. The first 802.3 HSSG study group meeting was held in September 2006, in June 2007, a trade group called Road to 100G was formed after the NXTcomm trade show in Chicago. The project is to provide for the interconnection of equipment satisfying the requirements of the intended applications. The 802. 3ba task force met for the first time in January 2008 and this standard was approved at the June 2010 IEEE Standards Board meeting under the name IEEE Std 802. 3ba-2010. On June 17,2010, the IEEE802. 3ba standard was approved In March 2011 the IEEE802. 3bg standard was approved, on September 10,2011, the P802. 3bj 100 Gbit/s Backplane and Copper Cable task force was approved. The scope of project is to specify additions to and appropriate modifications of IEEE Std 802. On May 10,2013, the P802. 3bm 40 Gbit/s and 100 Gbit/s Fiber Optic Task Force was approved and this project is to specify additions to and appropriate modifications of IEEE Std 802. In addition, to add 40 Gb/s Physical Layer specifications and management parameters for operation on extended reach single-mode fiber optic cables, also on May 10,2013, the P802. 3bq 40GBASE-T Task Force was approved. On June 12,2014, the IEEE802. 3bj standard was approved, on February 16,2015, the IEEE802. 3bm standard was approved. On May 12,2016, the IEEE P802. 3cd Task Force started working to define next generation two-lane 100 Gbit/s PHY, the IEEE802.3 working group is concerned with the maintenance and extension of the Ethernet data communications standard. Additions to the 802.3 standard are performed by forces which are designated by one or two letters. For example, the 802. 3z task force drafted the original Gigabit Ethernet standard,802. 3ba is the designation given to the higher speed Ethernet task force which completed its work to modify the 802.3 standard to support speeds higher than 10 Gbit/s in 2010. The speeds chosen by 802. 3ba were 40 and 100 Gbit/s to support both end-point and link aggregation needs and this was the first time two different Ethernet speeds were specified in a single standard. The decision to include both speeds came from pressure to support the 40 Gbit/s rate for local applications and the 100 Gbit/s rate for internet backbones. The standard was announced in July 2007 and was ratified on June 17,2010, the 40/100 Gigabit Ethernet standards encompass a number of different Ethernet physical layer specifications
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Ethernet physical layer
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The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 1 Mbit/s to 100 Gbit/s, while the medium can range from bulky coaxial cable to twisted pair. In general, network protocol stack software will work similarly on all physical layers,10 Gigabit Ethernet was already used in both enterprise and carrier networks by 2007, with 40 Gbit/s and 100 Gigabit Ethernet ratified. Robert Metcalfe, one of the co-inventors of Ethernet, in 2008 said he believed commercial applications using Terabit Ethernet may occur by 2015, though it might require new Ethernet standards. Many Ethernet adapters and switch ports support multiple speeds, using autonegotiation to set the speed, while this can practically be taken for granted for ports supporting twisted-pair cabling, only few optical-fiber ports support multiple speeds. If auto-negotiation fails, some multiple-speed devices sense the speed used by their partner, a 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T, generally, layers are named by their specifications,10,100,1000, 10G. – the nominal, usable speed for the MAC layer, encoded PHY sublayers usually run higher bitrates BASE, BROAD, PASS – indicates baseband, broadband, or passband signaling -T, -S, -L, -C, -K. g. X for 8b/10b block encoding, R for large blocks 1,2,4,10 – number of lanes used per link or reach for WAN PHYs For 10 Mbit/s, most twisted pair layers use unique encoding, so most often just -T is used. The following sections provide a summary of official Ethernet media types. In addition to official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling. Early Ethernet standards used Manchester coding so that the signal was self-clocking, all Fast Ethernet variants use a star topology. All Gigabit Ethernet variants use a star topology, initially, half-duplex mode was included in the standard but has been abandoned since. Very few devices support gigabit speed in half-duplex,2. 5GBASE-T and 5GBASE-T are scaled-down variants of 10GBASE-T. These physical layers support twisted pair copper cabling only,10 Gigabit Ethernet defines a version of Ethernet with a nominal data rate of 10 Gbit/s, ten times as fast as Gigabit Ethernet. In 2002, the first 10 Gigabit Ethernet standard was published as IEEE Std 802. 3ae-2002, subsequent standards encompass media types for single-mode fibre, multi-mode fibre, copper backplane and copper twisted pair. All 10-gigabit standards were consolidated into IEEE Std 802. 3-2008, as of 2009,10 Gigabit Ethernet is predominantly deployed in carrier networks, where 10GBASE-LR and 10GBASE-ER enjoy significant market shares. Single-lane 25-gigabit Ethernet is based on one 25.78125 GBd lane of the four from the 100 Gigabit Ethernet standard developed by task force P802. 3by, 25GBASE-T over twisted pair was approved alongside 40GBASE-T within IEEE802. 3bq
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Autonegotiation
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Autonegotiation is an Ethernet procedure by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control. In this process, the devices first share their capabilities regarding these parameters. In the OSI model, autonegotiation resides in the physical layer, for Ethernet over twisted pair it is defined in clause 28 of IEEE802.3. Autonegotiation was originally defined as an component in the fast Ethernet standard. It is backwards compatible with the normal link pulses used by 10BASE-T, the protocol was significantly extended in the gigabit Ethernet standard, and is mandatory for 1000BASE-T gigabit Ethernet over twisted pair. In 1995, a standard was released to allow connected network adapters to negotiate the best possible shared mode of operation, the initial autonegotiation standard contained a mechanism for detecting the speed but not the duplex setting of Ethernet peers that did not use autonegotiation. Autonegotiation can be used by devices that are capable of different transmission rates, different duplex modes, parallel detection is used when a device that is capable of autonegotiation is connected to one that is not. This happens if the device does not support autonegotiation or autonegotiation is administratively disabled. In this condition, the device that is capable of autonegotiation can determine and this procedure cannot determine the presence of full duplex, so half duplex is always assumed. The standards for 1000BASE-T, 1000BASE-TX and 10GBASE-T require autonegotiation to be always present, other than speed and duplex mode, autonegotiation is used to communicate the port type and the master-slave parameters. Auto-negotiation is based on similar to those used by 10BASE-T devices to detect the presence of a connection to another device. These connection present pulses are sent by Ethernet devices when they are not sending or receiving any frames and they are unipolar positive-only electrical pulses of a nominal duration of 100 ns, with a maximum pulse width of 200 ns, generated at a 16 ms time interval. These pulses are called link integrity test pulses in the 10BASE-T terminology, a device detects the failure of a link if neither a frame nor two of the LIT pulses is received for 50-150 ms. For this scheme to work, devices must send LIT pulses regardless of receiving any, auto-negotiation uses similar pulses labeled as NLP. NLP are still unipolar, positive-only, and of the duration of 100 ns. Each such pulse burst is called a fast link pulse burst, the time interval between the start of each FLP burst is the same 16 milliseconds as between normal link pulses. The FLP burst consists of 17 NLP at a 125 µs time interval, between each pair of two consecutive NLP an additional positive pulse may be present. The presence of this additional pulse indicates a logical 1, its absence a logical 0, as a result, every FLP contains a data word of 16 bits
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EtherType
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EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the payload of the frame, the same field is also used to indicate the size of some Ethernet frames. EtherType was first defined by the Ethernet II framing standard, in modern implementations of Ethernet, the field within the Ethernet frame used to describe the EtherType also can be used to represent the size of the payload of the Ethernet Frame. Historically, depending on the type of Ethernet framing that was in use on an Ethernet segment, Ethernet II framing considered these octets to represent EtherType while the original IEEE802.3 framing considered these octets to represent the size of the payload in bytes. That value was chosen because the length of the data field of an Ethernet 802.3 frame is 1500 bytes. The interpretation of values 1501–1535, inclusive, is undefined, with 802. 1Q VLAN tagging and QinQ the sparse 16-bit EtherType is being completely used. The 16-bit EtherType not only tags the payload class, it serves to help end any VLAN tagging or QinQ stacking. Via look-ahead peeking in streams, the 16-bit EtherType can help to confirm or package a QinQ 32+32+16=80-bit header between the 48-bit MAC addresses and the payload, of those 80-bits only 32-bits are used for dynamic information. For a full 66-bit addressing system,18 bits are needed beyond the MAC, thus, additional EtherType values are required and used for Triple Tagging QinQinQ. Vendor implementations may avoid wasting bandwidth sending those 48-bits in proprietary link compression schemes, the EtherType usually does not contain any CRC or FCS information. The size of the payload of non-standard jumbo frames, typically ~9000 Bytes long, falls within the range used by EtherType, the proposition to resolve this conflict was to substitute the special EtherType value when a length would otherwise be used. However, the proposition was not accepted and it is defunct, the chair of IEEE802.3 at the time, Geoff Thompson, responded to the draft outlining IEEE802. 3s official position and the reasons behind the position. The draft authors also responded to the letter, but no subsequent answer from the IEEE802.3 has been recorded. However, for Ethernet, the Ethernet II header is still used, not all well known de facto uses of EtherTypes are always recorded in the IEEE list of EtherType values. For example, EtherType 0x0806 appears in the IEEE list only as Symbolics, however, the IEEE Registration Authority lists all the accepted EtherTypes, including the 0x0806. IEEE Registration Authority Tutorials IEEE EtherType Registration Authority
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Ethernet flow control
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Ethernet flow control is a mechanism for temporarily stopping the transmission of data on Ethernet family computer networks. The first flow control mechanism, the frame, was defined by the IEEE802. 3x standard. The goal of this mechanism is to zero loss under congestion in data center bridging networks. Ethernet is a family of computer network protocols. Flow control can be implemented at the link layer. A sending station may be transmitting data faster than the end of the link can accept it. The first flow control mechanism, the frame, was defined by the Institute of Electrical. The IEEE standard 802. 3x was issued in 1997, an overwhelmed network node can send a pause frame, which halts the transmission of the sender for a specified period of time. A media access control frame is used to carry the pause command, only stations configured for full-duplex operation may send PAUSE frames. The use of a well-known address makes it unnecessary for a station to discover, another advantage of using this multicast address arises from the use of flow control between network switches. The particular multicast address used is selected from a range of address which have been reserved by the IEEE802. 1D standard which specifies the operation of switches used for bridging. Normally, a frame with a multicast destination sent to a switch will be forwarded out to all ports of the switch. However, this range of multicast address is special and will not be forwarded by an 802. 1D-compliant switch, instead, frames sent to this range are understood to be frames meant to be acted upon only within the switch. A pause frame includes the period of time being requested. This number is the duration of the pause. The pause time is measured in units of pause quanta, where each unit is equal to 512 bit times, by 1999, several vendors supported receiving pause frames, but fewer implemented sending them. One original motivation for the frame was to handle network interface controllers that did not have enough buffering to handle full-speed reception. This problem is not as common with advances in bus speeds, a more likely scenario is network congestion within a switch
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Ethernet frame
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A data packet on an Ethernet link is called an Ethernet packet, which transports an Ethernet frame as its payload. An Ethernet frame is preceded by a preamble and start frame delimiter, each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols carried in the frame, the frame ends with a frame check sequence, which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data. A data packet on the wire and the frame as its payload consist of binary data, Ethernet transmits data with the most-significant octet first, within each octet, however, the least-significant bit is transmitted first. The internal structure of an Ethernet frame is specified in IEEE802.3, the table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets. Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, the optional 802. 1Q tag consumes additional space in the frame. Field sizes for this option are indicated parenthetically in the table above, IEEE802. 1ad allows for multiple tags in each frame. This option is not illustrated here, an Ethernet packet starts with a seven-octet preamble and one-octet start frame delimiter. The preamble consists of a 56-bit pattern of alternating 1 and 0 bits, allowing devices on the network to easily synchronize their receiver clocks and it is followed by the SFD to provide byte-level synchronization and to mark a new incoming frame. The SFD is the value that marks the end of the preamble, which is the first field of an Ethernet packet. The SFD is designed to break the bit pattern of the preamble, the SFD is immediately followed by the destination MAC address, which is the first field in an Ethernet frame. SFD has the value of 171, which is transmitted with least-significant bit first as 213, physical layer transceiver circuitry is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the medium and uses a bus from the media independent interface family. Fast Ethernet transceiver chips utilize the MII bus, which is a wide bus, therefore the preamble is represented as 14 instances of 0x5. Gigabit Ethernet transceiver chips use the GMII bus, which is a wide interface. The header features destination and source MAC addresses, the EtherType field and, optionally, the EtherType field is two octets long and it can be used for two different purposes. When used as EtherType, the length of the frame is determined by the location of the interpacket gap, the IEEE802. 1Q tag, if present, is a four-octet field that indicates virtual LAN membership and IEEE802. 1p priority. The minimum payload is 42 octets when an 802. 1Q tag is present and 46 octets when absent, the maximum payload is 1500 octets
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Ethernet Alliance
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The Ethernet Alliance was incorporated in the US state of California in August 2005 and officially launched in January 2006 as a non-profit industry consortium to promote and support Ethernet. The Ethernet Alliance work groups are called subcommittees and these subcommittees are focused on efforts around specific standards-based Ethernet initiatives. As of March 2011, the working subcommittees within the Ethernet Alliance included,802. 3av-2009 that extended the speed of EPON networks to 10 Gbit/s. 802. 3an-2006 which defined a specification for running 10 Gigabit Ethernet over twisted-pair copper designated 10GBASE-T, Carrier Ethernet helps guide work being done to support the specific, evolving and growing demands of Ethernet from carriers and service providers. Energy Efficient Ethernet work is based up EEE Standard 802. 3az-2010. Ethernet in the Data Center focus includes protocols such as Data Center Bridging, Fibre Channel over Ethernet, iSCSI, Remote direct memory access over Converged Ethernet, higher Speed Ethernet encompasses all aspects of 40 Gbit/s and 100 Gbit/s Ethernet largely based op the work of IEEE Std. High Speed Modular Interconnects helps drive the adoption through demonstrating interoperability of compliant HS Modular Interconnect devices and ports including optical modules, in previous Ethernet technology iterations, an alliance was formed to support the adoption of that new technology into the market. The Ethernet Alliance was preceded by the Fast Ethernet Alliance, the Gigabit Ethernet Alliance, the 10 Gigabit Ethernet Alliance, and these alliances would dissolve a few years after the completion of the standards effort they supported. Unfortunately, this was long before the technology would reach volume adoption. He worked with others in the industry and the bodies to create an alliance that would exist as long as Ethernet technology existed. The Road to 100G Alliance was formally announced on June 19,2007 at the NXTcomm 2007 show in Chicago, the founding members were Bay Microsystems, Enigma Semiconductor, Integrated Device Technology, IP Infusion, and Lattice Semiconductor. It was headquartered in the Silicon Valley area of California, with the expanded charter and the formation of the HSE and Carrier Ethernet subcommittees, the Road to 100G alliance merged with the Ethernet Alliance on December 31,2008. The Ethernet Alliance offers white papers, presentations, frequently asked questions and these materials are available on the Ethernet Alliance public website and are available free of charge. These papers provide educational materials with an industry-based perspective and they may be based upon the work of Ethernet Alliance subcommittees or support the activities inside Ethernet standards bodies. TEFs offer face-to-face events to bring members of the various Ethernet communities to discuss. The Ethernet Alliance offers an opportunity for academic institutions to become involved in the organization for no fee
