Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but one using the electromagnetic spectrum, in a one-to-many model. Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of electronic communication were one-to-one, with the message intended for a single recipient; the term broadcasting evolved from its use as the agricultural method of sowing seeds in a field by casting them broadly about. It was adopted for describing the widespread distribution of information by printed materials or by telegraph. Examples applying it to "one-to-many" radio transmissions of an individual station to multiple listeners appeared as early as 1898. Over the air broadcasting is associated with radio and television, though in recent years, both radio and television transmissions have begun to be distributed by cable; the receiving parties may include the general public or a small subset.
The field of broadcasting includes both government-managed services such as public radio, community radio and public television, private commercial radio and commercial television. The U. S. Code of Federal Regulations, title 47, part 97 defines "broadcasting" as "transmissions intended for reception by the general public, either direct or relayed". Private or two-way telecommunications transmissions do not qualify under this definition. For example and citizens band radio operators are not allowed to broadcast; as defined, "transmitting" and "broadcasting" are not the same. Transmission of radio and television programs from a radio or television station to home receivers by radio waves is referred to as "over the air" or terrestrial broadcasting and in most countries requires a broadcasting license. Transmissions using a wire or cable, like cable television, are considered broadcasts but do not require a license. In the 2000s, transmissions of television and radio programs via streaming digital technology have been referred to as broadcasting as well.
The earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code, a system developed in the 1830s by Samuel F. B. Morse, physicist Joseph Henry and Alfred Vail, they developed an electrical telegraph system which sent pulses of electric current along wires which controlled an electromagnet, located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, the silence between them. Morse therefore developed the forerunner to modern International Morse code; this was important for ship-to-ship and ship-to-shore communication, but it became important for business and general news reporting, as an arena for personal communication by radio amateurs. Audio broadcasting began experimentally in the first decade of the 20th century. By the early 1920s radio broadcasting became a household medium, at first on the AM band and on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, using VHF and UHF spectrum.
Satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS emerging in the 1980s. All broadcasting was composed of analog signals using analog transmission techniques but in the 2000s, broadcasters have switched to digital signals using digital transmission. In general usage, broadcasting most refers to the transmission of information and entertainment programming from various sources to the general public. Analog audio vs. HD Radio Analog television vs. Digital television WirelessThe world's technological capacity to receive information through one-way broadcast networks more than quadrupled during the two decades from 1986 to 2007, from 432 exabytes of information, to 1.9 zettabytes. This is the information equivalent of 55 newspapers per person per day in 1986, 175 newspapers per person per day by 2007. There have been several methods used for broadcasting electronic media audio and video to the general public: Telephone broadcasting: the earliest form of electronic broadcasting.
Telephone broadcasting began with the advent of Théâtrophone systems, which were telephone-based distribution systems allowing subscribers to listen to live opera and theatre performances over telephone lines, created by French inventor Clément Ader in 1881. Telephone broadcasting grew to include telephone newspaper services for news and entertainment programming which were introduced in the 1890s located in large European cities; these telephone-based subscription services were the first examples of electrical/electronic broadcasting and offered a wide variety of programming. Radio broadcasting. Radio stations can be linked in radio networks to broadcast common radio programs, either in broadcast syndication, simulcast or subchannels. Television broadcasting, experimentally from 1925, commercially from t
Texas Instruments Inc. is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, United States. TI is one of the top ten semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which accounts for more than 80% of their revenue. TI produces TI digital light processing technology and education technology products including calculators and multi-core processors. To date, TI has more than 43,000 patents worldwide. Texas Instruments emerged in 1951 after a reorganization of Geophysical Service Incorporated, a company founded in 1930 that manufactured equipment for use in the seismic industry, as well as defense electronics. TI produced the world's first commercial silicon transistor in 1954, designed and manufactured the first transistor radio in 1954. Jack Kilby invented the integrated circuit in 1958 while working at TI's Central Research Labs.
TI invented the hand-held calculator in 1967, introduced the first single-chip microcontroller in 1970, which combined all the elements of computing onto one piece of silicon. In 1987, TI invented the digital light processing device, which serves as the foundation for the company's award-winning DLP technology and DLP Cinema. In 1990, TI came out with the popular TI-81 calculator which made them a leader in the graphing calculator industry. In 1997, its defense business was sold to Raytheon, which allowed TI to strengthen its focus on digital solutions. After the acquisition of National Semiconductor in 2011, the company had a combined portfolio of nearly 45,000 analog products and customer design tools, making it the world's largest maker of analog technology components. Texas Instruments was founded by Cecil H. Green, J. Erik Jonsson, Eugene McDermott, Patrick E. Haggerty in 1951. McDermott was one of the original founders of Geophysical Service Inc. in 1930. McDermott and Jonsson were GSI employees who purchased the company in 1941.
In November, 1945, Patrick Haggerty was hired as general manager of the Laboratory and Manufacturing division, which focused on electronic equipment. By 1951, the L&M division, with its defense contracts, was growing faster than GSI's Geophysical division; the company was reorganized and renamed General Instruments Inc. Because there existed a firm named General Instrument, the company was renamed Texas Instruments that same year. From 1956 to 1961, Fred Agnich of Dallas a Republican member of the Texas House of Representatives, was the Texas Instruments president. Geophysical Service, Inc. became a subsidiary of Texas Instruments. Early in 1988 most of GSI was sold to the Halliburton Company. Texas Instruments exists to create and market useful products and services to satisfy the needs of its customers throughout the world. In 1930, J. Clarence Karcher and Eugene McDermott founded Geophysical Service, an early provider of seismic exploration services to the petroleum industry. In 1939, the company reorganized as Coronado Corp. an oil company with Geophysical Service Inc, now as a subsidiary.
On December 6, 1941, McDermott along with three other GSI employees, J. Erik Jonsson, Cecil H. Green, H. B. Peacock purchased GSI. During World War II, GSI expanded their services to include electronics for the U. S. Army, Signal Corps, the U. S. Navy. In 1951, the company changed its name to Texas Instruments, with GSI becoming a wholly owned subsidiary of the new company. An early success story for TI-GSI came in 1965 when GSI was able to monitor the Soviet Union's underground nuclear weapons testing under the ocean in Vela Uniform, a subset of Project Vela, to verify compliance of the Partial Nuclear Test Ban Treaty. Texas Instruments continued to manufacture equipment for use in the seismic industry, GSI continued to provide seismic services. After selling GSI, TI sold the company to Halliburton in 1988, at which point GSI ceased to exist as a separate entity. In early 1952, Texas Instruments purchased a patent license to produce germanium transistors from Western Electric Co. the manufacturing arm of AT&T, for $25,000, beginning production by the end of the year.
On January 1, 1953, Haggerty brought Gordon Teal to the company as a research director. Gordon brought with him his expertise in growing semiconductor crystals. Teal's first assignment was to organize what became TI's Central Research Laboratories, which Teal based on his prior experience at Bell Labs. Among his new hires was Willis Adcock who joined TI early in 1953. Adcock, who like Teal was a physical chemist, began leading a small research group focused on the task of fabricating "grown-junction silicon single-crystal small-signal transistors. Adcock became the first TI Principal Fellow. In January 1954 Morris Tanenbaum at Bell Labs created the first workable silicon transistor; this work was reported in the spring of 1954, at the IRE off-the-record conference on Solid State Devices, was published in the Journal of Applied Physics. Working independently in April 1954, Gordon Teal at TI created the first commercial silicon transistor and tested it on April 14, 1954. On May 10, 1954, at the Institute of Radio Engineers National Conference on Airborne Electronics in Dayton, OH,Teal presented a paper: "Some Recent Developments in Silicon and Germanium Materials and Devices,".
In 1954, Texas Instruments manufactured the first transistor radio. The Regency TR-1 used germanium transistors, as silicon transistors were much more expensive at the time; this was an effort b
Token Ring local area network technology is a communications protocol for local area networks. It uses a special three-byte frame called a "token" that travels around a logical "ring" of workstations or servers; this token passing is a channel access method providing fair access for all stations, eliminating the collisions of contention-based access methods. Introduced by IBM in 1984, it was standardized with protocol IEEE 802.5 and was successful in corporate environments, but eclipsed by the versions of Ethernet. A wide range of different local area network technologies were developed in the early 1970s, of which one, the Cambridge Ring had demonstrated the potential of a token passing ring topology, many teams worldwide began working on their own implementations. At the IBM Zurich Research Laboratory Werner Bux and Hans Müller in particular worked on the design and development of IBM's Token Ring technology, while early work at MIT led to the Proteon 10 Mbit/s ProNet-10 Token Ring network in 1981 – the same year that workstation vendor Apollo Computer introduced their proprietary 12 Mbit/s Apollo Token Ring network running over 75-ohm RG-6U coaxial cabling.
Proteon evolved a 16 Mbit/s version that ran on unshielded twisted pair cable. IBM launched their own proprietary Token Ring product on October 15, 1985, it ran at 4 Mbit/s, attachment was possible from IBM PCs, midrange computers and mainframes. It used a convenient star-wired physical topology, ran over shielded twisted-pair cabling, shortly thereafter became the basis for the /IEEE standard 802.5. During this time, IBM argued that Token Ring LANs were superior to Ethernet under load, but these claims were fiercely debated. In 1988 the faster 16 Mbit/s Token Ring was standardized by the 802.5 working group, an increase to 100 Mbit/s was standardized and marketed during the wane of Token Ring's existence. However it was never used, while a 1000 Mbit/s standard was approved in 2001, no products were brought to market and standards activity came to a standstill as Fast Ethernet and Gigabit Ethernet dominated the local area networking market. Ethernet and Token Ring have some notable differences: Token Ring access is more deterministic, compared to Ethernet's contention-based CSMA/CD Ethernet supports a direct cable connection between two network interface cards by the use of a crossover cable or through auto-sensing if supported.
Token Ring does not inherently support this feature and requires additional software and hardware to operate on a direct cable connection setup. Token Ring eliminates collision by the use of a single-use token and early token release to alleviate the down time. Ethernet alleviates collision by carrier sense multiple access and by the use of an intelligent switch. Token Ring network interface cards contain all of the intelligence required for speed autodetection and can drive themselves on many Multistation Access Units that operate without power. Ethernet network interface cards can theoretically operate on a passive hub to a degree, but not as a large LAN and the issue of collisions is still present. Token Ring employs ` access priority'. Unswitched Ethernet does not have provisioning for an access priority system as all nodes have equal contest for traffic. Multiple identical MAC addresses are supported on Token Ring. Switched Ethernet cannot support duplicate MAC addresses without reprimand.
Token Ring was more complex than Ethernet, requiring a specialized processor and licensed MAC/LLC firmware for each interface. By contrast, Ethernet included both the lower licensing cost in the MAC chip; the cost of a token Ring interface using the Texas Instruments TMS380C16 MAC and PHY was three times that of an Ethernet interface using the Intel 82586 MAC and PHY. Both networks used expensive cable, but once Ethernet was standardized for unshielded twisted pair with 10BASE-T and 100BASE-TX, it had a distinct advantage and sales of it increased markedly. More significant when comparing overall system costs was the much-higher cost of router ports and network cards for Token Ring vs Ethernet; the emergence of Ethernet switches may have been the final straw. Stations on a Token Ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to the next with a control token circulating around the ring controlling access. Similar token passing mechanisms are used by ARCNET, token bus, 100VG-AnyLAN and FDDI, they have theoretical advantages over the CSMA/CD of early Ethernet.
A Token Ring network can be modeled as a polling system where a single server provides service to queues in a cyclic order. The data transmission process goes as follows: Empty information frames are continuously circulated on the ring; when a computer has a message to send, it seizes the token. The computer will be able to send the frame; the frame is examined by each successive workstation. The workstation that identifies itself to be the destination for the message copies it from the frame and changes the token back to 0; when the frame gets back to the originat
Ethernet is a family of computer networking technologies used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, has since retained a good deal of backward compatibility and been refined to support higher bit rates and longer link distances. Over time, Ethernet has replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET; the original 10BASE5 Ethernet uses coaxial cable as a shared medium, while the newer Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original 2.94 megabits per second to the latest 400 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; each frame contains source and destination addresses, error-checking data so that damaged frames can be detected and discarded.
As per the OSI model, Ethernet provides services up including the data link layer. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols including Wi-Fi wireless networking technology. Ethernet is used in home and industry; the Internet Protocol is carried over Ethernet and so it is considered one of the key technologies that make up the Internet. Ethernet was developed at Xerox PARC between 1973 and 1974, it was inspired by ALOHAnet. The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the luminiferous aether once postulated to exist as an "omnipresent, completely-passive medium for the propagation of electromagnetic waves." In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, Butler Lampson as inventors. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper; that same year, Ron Crane, Bob Garner, Roy Ogus facilitated the upgrade from the original 2.94 Mbit/s protocol to the 10 Mbit/s protocol, released to the market in 1980.
Metcalfe left Xerox in June 1979 to form 3Com. He convinced Digital Equipment Corporation and Xerox to work together to promote Ethernet as a standard; as part of that process Xerox agreed to relinquish their'Ethernet' trademark. The first standard was published on September 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications"; this so-called DIX standard specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field. Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time and resulted in the publication of IEEE 802.3 on June 23, 1983. Ethernet competed with Token Ring and other proprietary protocols. Ethernet was able to adapt to market realities and shift to inexpensive thin coaxial cable and ubiquitous twisted pair wiring. By the end of the 1980s, Ethernet was the dominant network technology. In the process, 3Com became a major company.
3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed by DEC's Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. An Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced with drivers for DOS and Windows. By the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, Ethernet ports began to appear on some PCs and most workstations; this process was sped up with the introduction of 10BASE-T and its small modular connector, at which point Ethernet ports appeared on low-end motherboards. Since Ethernet technology has evolved to meet new bandwidth and market requirements.
In addition to computers, Ethernet is now used to interconnect appliances and other personal devices. As Industrial Ethernet it is used in industrial applications and is replacing legacy data transmission systems in the world's telecommunications networks. By 2010, the market for Ethernet equipment amounted to over $16 billion per year. In February 1980, the Institute of Electrical and Electronics Engineers started project 802 to standardize local area networks; the "DIX-group" with Gary Robinson, Phil Arst, Bob Printis submitted the so-called "Blue Book" CSMA/CD specification as a candidate for the LAN specification. In addition to CSMA/CD, Token Ring and Token Bus were considered as candidates for a LAN standard. Competing proposals and broad interest in the initiative led to strong disagreement over which technology to standardize. In December 1980, the group was split into three subgroups, standardization proceeded separately for each proposal. Delays in the standards process put at risk the market introduction of the Xerox Star workstation and 3Com's Ethernet LAN products.
With such business implications in mind, David Liddle an
Network topology is the arrangement of the elements of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial fieldbusses, computer networks. Network topology is the topological structure of a network and may be depicted physically or logically, it is an application of graph theory wherein communicating devices are modeled as nodes and the connections between the devices are modeled as links or lines between the nodes. Physical topology is the placement of the various components of a network, while logical topology illustrates how data flows within a network. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two different networks, yet their topologies may be identical. A network’s physical topology is a particular concern of the physical layer of the OSI model. Examples of network topologies are found in local area networks, a common computer network installation.
Any given node in the LAN has one or more physical links to other devices in the network. A wide variety of physical topologies have been used in LANs, including ring, bus and star. Conversely, mapping the data flow between the components determines the logical topology of the network. In comparison, Controller Area Networks, common in vehicles, are distributed control system networks of one or more controllers interconnected with sensors and actuators over, invariably, a physical bus topology. Two basic categories of network topologies exist, logical topologies; the transmission medium layout used to link devices is the physical topology of the network. For conductive or fiber optical mediums, this refers to the layout of cabling, the locations of nodes, the links between the nodes and the cabling; the physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, the cost associated with cabling or telecommunication circuits.
In contrast, logical topology is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology carried on a physical star topology. Token ring is wired as a physical star from the media access unit. Physically, AFDX can be a cascaded star topology of multiple dual redundant Ethernet switches. Logical topologies are closely associated with media access control methods and protocols; some networks are able to dynamically change their logical topology through configuration changes to their routers and switches. The transmission media used to link devices to form a computer network include electrical cables, optical fiber, radio waves. In the OSI model, these are defined at layers 2 -- the physical layer and the data link layer.
A adopted family of transmission media used in local area network technology is collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Ethernet transmits data over both fiber cables. Wireless LAN standards use radio waves. Power line communication uses a building's power cabling to transmit data; the orders of the following wired technologies are from slowest to fastest transmission speed. Coaxial cable is used for cable television systems, office buildings, other work-sites for local area networks; the cables consist of copper or aluminum wire surrounded by an insulating layer, which itself is surrounded by a conductive layer. The insulation helps minimize distortion. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second. ITU-T G.hn technology uses existing home wiring to create a high-speed local area network. Signal traces on printed circuit boards are common for board-level serial communication between certain types integrated circuits, a common example being SPI.
Ribbon cable has been a cost-effective media for serial protocols within metallic enclosures or rolled within copper braid or foil, over short distances, or at lower data rates. Several serial network protocols can be deployed without shielded or twisted pair cabling, that is, with "flat" or "ribbon" cable, or a hybrid flat/twisted ribbon cable, should EMC, bandwidth constraints permit: RS-232, RS-422, RS-485, CAN, GPIB, SCSI, etc. Twisted pair wire is the most used medium for all telecommunication. Twisted-pair cabling consist of copper wires. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cablin
International Business Machines Corporation is an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the Computing-Tabulating-Recording Company and was renamed "International Business Machines" in 1924. IBM produces and sells computer hardware and software, provides hosting and consulting services in areas ranging from mainframe computers to nanotechnology. IBM is a major research organization, holding the record for most U. S. patents generated by a business for 26 consecutive years. Inventions by IBM include the automated teller machine, the floppy disk, the hard disk drive, the magnetic stripe card, the relational database, the SQL programming language, the UPC barcode, dynamic random-access memory; the IBM mainframe, exemplified by the System/360, was the dominant computing platform during the 1960s and 1970s. IBM has continually shifted business operations by focusing on higher-value, more profitable markets.
This includes spinning off printer manufacturer Lexmark in 1991 and the sale of personal computer and x86-based server businesses to Lenovo, acquiring companies such as PwC Consulting, SPSS, The Weather Company, Red Hat. In 2014, IBM announced that it would go "fabless", continuing to design semiconductors, but offloading manufacturing to GlobalFoundries. Nicknamed Big Blue, IBM is one of 30 companies included in the Dow Jones Industrial Average and one of the world's largest employers, with over 380,000 employees, known as "IBMers". At least 70% of IBMers are based outside the United States, the country with the largest number of IBMers is India. IBM employees have been awarded five Nobel Prizes, six Turing Awards, ten National Medals of Technology and five National Medals of Science. In the 1880s, technologies emerged that would form the core of International Business Machines. Julius E. Pitrap patented the computing scale in 1885. On June 16, 1911, their four companies were amalgamated in New York State by Charles Ranlett Flint forming a fifth company, the Computing-Tabulating-Recording Company based in Endicott, New York.
The five companies had offices and plants in Endicott and Binghamton, New York. C.. They manufactured machinery for sale and lease, ranging from commercial scales and industrial time recorders and cheese slicers, to tabulators and punched cards. Thomas J. Watson, Sr. fired from the National Cash Register Company by John Henry Patterson, called on Flint and, in 1914, was offered a position at CTR. Watson joined CTR as General Manager 11 months was made President when court cases relating to his time at NCR were resolved. Having learned Patterson's pioneering business practices, Watson proceeded to put the stamp of NCR onto CTR's companies, he implemented sales conventions, "generous sales incentives, a focus on customer service, an insistence on well-groomed, dark-suited salesmen and had an evangelical fervor for instilling company pride and loyalty in every worker". His favorite slogan, "THINK", became a mantra for each company's employees. During Watson's first four years, revenues reached $9 million and the company's operations expanded to Europe, South America and Australia.
Watson never liked the clumsy hyphenated name "Computing-Tabulating-Recording Company" and on February 14, 1924 chose to replace it with the more expansive title "International Business Machines". By 1933 most of the subsidiaries had been merged into one company, IBM. In 1937, IBM's tabulating equipment enabled organizations to process unprecedented amounts of data, its clients including the U. S. Government, during its first effort to maintain the employment records for 26 million people pursuant to the Social Security Act, the tracking of persecuted groups by Hitler's Third Reich through the German subsidiary Dehomag. In 1949, Thomas Watson, Sr. created IBM World Trade Corporation, a subsidiary of IBM focused on foreign operations. In 1952, he stepped down after 40 years at the company helm, his son Thomas Watson, Jr. was named president. In 1956, the company demonstrated the first practical example of artificial intelligence when Arthur L. Samuel of IBM's Poughkeepsie, New York, laboratory programmed an IBM 704 not to play checkers but "learn" from its own experience.
In 1957, the FORTRAN scientific programming language was developed. In 1961, IBM developed the SABRE reservation system for American Airlines and introduced the successful Selectric typewriter. In 1963, IBM employees and computers helped. A year it moved its corporate headquarters from New York City to Armonk, New York; the latter half of the 1960s saw IBM continue its support of space exploration, participating in the 1965 Gemini flights, 1966 Saturn flights and 1969 lunar mission. On April 7, 1964, IBM announced the first computer system family, the IBM System/360, it spanned the complete range of commercial and scientific applications from large to small, allowing companies for the first time to upgrade to models with greater computing capability without having to rewrite their applications. It was followed by the IBM System/370 in 1970. Together the
IEEE 802.11 is part of the IEEE 802 set of LAN protocols, specifies the set of media access control and physical layer protocols for implementing wireless local area network Wi-Fi computer communication in various frequencies, including but not limited to 2.4, 5, 60 GHz frequency bands. They are the world's most used wireless computer networking standards, used in most home and office networks to allow laptops and smartphones to talk to each other and access the Internet without connecting wires, 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, has had subsequent amendments; the standard and amendments provide the basis for wireless network products using the Wi-Fi brand. While each amendment is revoked when it is incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products.
As a result, in the marketplace, each revision tends to become its own standard. The protocols are used in conjunction with IEEE 802.2, are designed to interwork seamlessly with Ethernet, are often used to carry Internet Protocol traffic. Although IEEE 802.11 specifications list channels that might be used, the radio frequency spectrum availability allowed varies by regulatory domain. The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The 802.11 protocol family employ carrier-sense multiple access with collision avoidance whereby equipment listens to a channel for other users before transmitting each packet. 802.11-1997 was the first wireless networking standard in the family, but 802.11b was the first accepted one, followed by 802.11a, 802.11g, 802.11n, 802.11ac. Other standards in the family are service amendments that are used to extend the current scope of the existing standard, which may 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 frequency band, 802.11b/g/n equipment may suffer interference in the 2.4 GHz band from microwave ovens, cordless telephones, Bluetooth devices etc. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum and orthogonal frequency-division multiplexing signaling methods, respectively. 802.11a uses the 5 GHz U-NII band, for much of the world, offers at least 23 non-overlapping 20 MHz-wide channels rather than the 2.4 GHz ISM frequency band offering only three non-overlapping 20 MHz-wide channels, where other adjacent channels overlap—see list of WLAN channels. Better or worse performance with higher or lower frequencies may be realized, depending on the environment. 802.11 n can use either the 5 GHz band. The segment of the radio 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 channels 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 the Netherlands. The inventors 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 IEEE 802.11 for 10 years, has been called the "father of Wi-Fi", was involved in designing the initial 802.11b and 802.11a standards within the IEEE. 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 major commercial breakthrough came with Apple Inc. adopting Wi-Fi for their iBook series of laptops in 1999. It was the first mass consumer product to offer Wi-Fi network connectivity, branded by Apple as AirPort. One year IBM followed with its ThinkPad 1300 series in 2000; the original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is now obsolete. It specified two net bit rates of 2 megabits per second, plus forward error correction code, it specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s. 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. Legacy 802.11 with direct-sequence spread spectrum was supplanted and popularized by 802.11b. 802.11a, published in 1999, uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface.
It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20