1.
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
2.
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
3.
Cisco Systems
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Through its numerous acquired subsidiaries, such as OpenDNS, WebEx, and Jasper, Cisco specializes into specific tech markets, such as Internet of Things, domain security, and energy management. Cisco is the largest networking company in the world, the stock was added to the Dow Jones Industrial Average on June 8,2009, and is also included in the S&P500 Index, the Russell 1000 Index, NASDAQ-100 Index and the Russell 1000 Growth Stock Index. By the time the company went public in 1990, when it was listed on the NASDAQ, Cisco was the most valuable company in the world by 2000, with a more than $500 billion market capitalization. Despite founding Cisco in 1984, Bosack, along with Kirk Lougheed, continued to work at Stanford on Ciscos first product and it consisted of exact replicas of Stanfords Blue Box router and a stolen copy of the Universitys multiple-protocol router software. The software was written some years earlier at Stanford medical school by research engineer William Yeager. Bosack and Lougheed adapted it into what became the foundation for Cisco IOS, in 1987, Stanford licensed the router software and two computer boards to Cisco. In addition to Bosack, Lerner and Lougheed, Greg Satz, a programmer, and Richard Troiano, the companys first CEO was Bill Graves, who held the position from 1987 to 1988. In 1988, John Morgridge was appointed CEO, the name Cisco was derived from the city name San Francisco, which is why the companys engineers insisted on using the lower case cisco in its early years. The logo is intended to depict the two towers of the Golden Gate Bridge, on February 16,1990, Cisco Systems went public and was listed on the NASDAQ stock exchange. On August 28,1990, Lerner was fired, upon hearing the news, her husband Bosack resigned in protest. The couple walked away from Cisco with $170 million, 70% of which was committed to their own charity, although Cisco was not the first company to develop and sell dedicated network nodes, it was one of the first to sell commercially successful routers supporting multiple network protocols. Classical, CPU-based architecture of early Cisco devices coupled with flexibility of operating system IOS allowed for keeping up with evolving technology needs by means of frequent software upgrades, some popular models of that time managed to stay in production for almost a decade virtually unchanged—a rarity in high-tech industry. This philosophy dominated the companys product lines throughout the 1990s, in 1995, John Morgridge was succeeded by John Chambers. The phenomenal growth of the Internet in mid-to-late 1990s quickly changed the telecom landspe, as the Internet Protocol became widely adopted, the importance of multi-protocol routing declined. In late March 2000, at the height of the bubble, Cisco became the most valuable company in the world. In July 2014, with a cap of about US$129 billion. One of them, Juniper Networks, shipped their first product in 1999, Cisco answered the challenge with homegrown ASICs and fast processing cards for GSR routers and Catalyst 6500 switches. In 2004, Cisco also started migration to new high-end hardware CRS-1, as part of a massive rebranding campaign in 2006, Cisco Systems adopted the shortened name Cisco and created The Human Network advertising campaign
4.
Token ring
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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 ring of workstations or servers. This token passing is an access method providing fair access for all stations. Proteon later 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, and attachment was possible from IBM PCs, midrange computers and it used a convenient star-wired physical topology, and ran over shielded twisted-pair cabling, and shortly thereafter became the basis for the /IEEE standard 802.5. During this time, IBM argued strongly that token ring LANs were superior to Ethernet, especially 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, 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, Token ring network interface cards contain all of the intelligence required for speed autodetection, routing and can drive themselves on many Multistation Access Units that operate without power. Ethernet network interface cards can operate on a passive hub to a degree, but not as a large LAN. Token ring employs access priority in which certain nodes can have priority over the token, 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, by contrast, Ethernet included both the firmware and the lower licensing cost in the MAC chip. The cost of a token ring interface using the Texas Instruments TMS380C16 MAC, even 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, similar token passing mechanisms are used by ARCNET, token bus, 100VG-AnyLAN and FDDI, and they have theoretical advantages over the CSMA/CD of early Ethernet. A token ring network can be modeled as a 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 then be able to send the frame, the frame is then examined by each successive workstation. The workstation that identifies itself to be the destination for the copies it from the frame
5.
Power over Ethernet
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Power over Ethernet or PoE describes any of several standardized or ad-hoc systems which pass electric power along with data on twisted pair Ethernet cabling. This allows a single cable to provide both data connection and electric power to such as wireless access points, IP cameras. There are several techniques for transmitting power over Ethernet cabling. Two of them have been standardized by IEEE802.3 since 2003 and these standards are known as Alternative A and Alternative B. For 10BASE-T and 100BASE-TX, only two of the four pairs in typical CAT-5 cable are used. Alternative B separates the data and the conductors, making troubleshooting easier. It also makes use of all four twisted pair, copper wires. The positive voltage runs along pins 4 and 5, and the negative along pins 7 and 8, Alternative A transports power on the same wires as data for 10 and 100 Mbit/s. This is similar to the phantom power technique commonly used for powering condenser microphones, Power may be transmitted on the data conductors by applying a common voltage to each pair. Because twisted-pair Ethernet uses differential signalling, this does not interfere with data transmission, the common mode voltage is easily extracted using the center tap of the standard Ethernet pulse transformer. For Gigabit Ethernet and faster, all four pairs are used for data transmission and this signaling allows the presence of a conformant device to be detected by the power source, and allows the device and source to negotiate the amount of power required or available. Up to 25.5 W is available for a device, the IEEE standards for PoE require category 5 cable or better for high power levels but allow using category 3 cable if less power is required. A midspan power supply, also known as a PoE power injector, is an additional PoE power source that can be used in combination with a non-PoE switch, the original IEEE802. 3af-2003 PoE standard provides up to 15.4 W of DC power on each port. Only 12.95 W is assured to be available at the device as some power dissipates in the cable. The updated IEEE802. 3at-2009 PoE standard also known as PoE+ or PoE plus, the 2009 standard prohibits a powered device from using all four pairs for power. Both of these amendments have since incorporated into the IEEE802. 3-2012 publication. Standards body IEEE is currently looking at ways of increasing the amount of power transmitted, the upcoming IEEE802. 3bt aka 4PPoE standard will introduce two new levels of power,55 W and 90-100 W. Each twisted pair can handle a current of up to one ampere, additionally, support for 2. 5GBASE-T, 5GBASE-T and 10GBASE-T is planned
6.
Uninterruptible power supply
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The on-battery runtime of most uninterruptible power sources is relatively short but sufficient to start a standby power source or properly shut down the protected equipment. UPS units range in size from units designed to protect a computer without a video monitor to large units powering entire data centers or buildings. The worlds largest UPS, the 46-megawatt Battery Electric Storage System, in Fairbanks, Alaska, powers the entire city, the primary role of any UPS is to provide short-term power when the input power source fails. The three general categories of modern UPS systems are on-line, line-interactive and standby, a line-interactive UPS maintains the inverter in line and redirects the batterys DC current path from the normal charging mode to supplying current when power is lost. In a standby system the load is powered directly by the input power, most UPS below 1 kVA are of the line-interactive or standby variety which are usually less expensive. For large power units, Dynamic Uninterruptible Power Supplies are sometimes used, a synchronous motor/alternator is connected on the mains via a choke. Energy is stored in a flywheel, when the mains power fails, an eddy-current regulation maintains the power on the load as long as the flywheels energy is not exhausted. DUPS are sometimes combined or integrated with a generator that is turned on after a brief delay. A fuel cell UPS has been developed in recent years using hydrogen, the offline/standby UPS offers only the most basic features, providing surge protection and battery backup. The protected equipment is connected directly to incoming utility power. When the incoming voltage falls below or rises above a level the SPS turns on its internal DC-AC inverter circuitry. The UPS then mechanically switches the connected equipment on to its DC-AC inverter output, the switchover time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be designed to power equipment, such as a personal computer. The line-interactive UPS is similar in operation to a standby UPS and this is a special type of transformer that can add or subtract powered coils of wire, thereby increasing or decreasing the magnetic field and the output voltage of the transformer. This may also be performed by a buck–boost transformer which is distinct from an autotransformer and this type of UPS is able to tolerate continuous undervoltage brownouts and overvoltage surges without consuming the limited reserve battery power. It instead compensates by automatically selecting different power taps on the autotransformer, depending on the design, changing the autotransformer tap can cause a very brief output power disruption, which may cause UPSs equipped with a power-loss alarm to chirp for a moment. This has become popular even in the cheapest UPSs because it takes advantage of components already included, the difference between the two voltages is because charging a battery requires a delta voltage. Furthermore, it is easier to do the switching on the side of the transformer because of the lower currents on that side
7.
Computer port (hardware)
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In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. In computer terms, a port generally refers to the part of connection. Computer ports have many uses, to connect a monitor, webcam, speakers, on the physical layer, a computer port is a specialized outlet on a piece of equipment to which a plug or cable connects. Electronically, the several conductors where the port and cable contacts connect, Port connectors may be male or female, but female connectors are much more common. Bent pins are easier to replace on a cable than on an attached to a computer. Computer ports in common use cover a variety of shapes such as round, rectangular, square, trapezoidal. There is some standardization to physical properties and function, for instance, most computers have a keyboard port, into which the keyboard is connected. The original IBM PC also had two identical 5 pin DIN connectors, one used for the keyboard, the second for a cassette recorder interface, the two were not interchangeable. Electronically, hardware ports can almost always be divided into two based on the signal transfer, Serial ports send and receive one bit at a time via a single wire pair. Parallel ports send multiple bits at the time over several sets of wires. After ports are connected, they typically require handshaking, where transfer type, transfer rate, hot-swappable ports can be connected while equipment is running. Almost all ports on personal computers are hot-swappable, plug-and-play ports are designed so that the connected devices automatically start handshaking as soon as the hot-swapping is done. USB ports and FireWire ports are plug-and-play, auto-detect or auto-detection ports are usually plug-and-play, but they offer another type of convenience. An auto-detect port may automatically determine what kind of device has been attached, the users response determines the purpose of the port, which is physically a 1/8 tip-ring-sleeve mini jack. Some auto-detect ports can even switch between input and output based on context, as of 2006, manufacturers have nearly standardized colors associated with ports on personal computers, although there are no guarantees. The two extra conductors in the 6-pin connection carry electrical power and this is why a self-powered device such as a camcorder often connects with a cable that is 4-pins on the camera side and 6-pins on the computer side, the two power conductors simply being ignored. This is also why laptop computers usually have only 4-pin FireWire ports, optical fiber, microwave, and other technologies have different kinds of connections, as metal wires are not effective for signal transfers with these technologies. Optical connections are usually a glass or plastic interface, possibly with an oil that lessens refraction between the two interface surfaces
8.
ERS 3500 and ERS 2500 series
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Ethernet Routing Switch 3500 Series and Ethernet Routing Switch 2500 Series or in data computer networking terms are stackable routing switches designed and manufactured by Avaya. The Switches can be stacked up to eight units high through a stacking configuration and these Switches are all covered by Avayas Lifetime warranty. In 2008 Layer 3 routing support, secure web access with https, in January 2008 another detailed evaluation of this systems was performed by Tolly Enterprises, LLC. comparing the 2500 systems to Catalyst 2960-24T and HP ProCurve 2626 and 2650 systems. Later in November 2010 IGMP multicast and IPv6 management was added in version 4.3, as of February 2012 the software version 4.4 is the latest software released for the product which was currently published in August 2011. The ERS3500 Series consists or four gigabit Ethernet models the 3510GT, 3510GT-PWR+, 3524GT, and 3524GT-PWR+ along with 2 fast Ethernet models 35265T, and 3526T-PWR+. The switch can be installed initially as standalone and then field-upgraded via a license to support resilient Stackable Chassis configuration of up to eight Switches, the stack-enabled version of the ERS2500 Switches will not require a license kit or license file. The ERS 2550T supports 48 ports of 10/100 plus two Gigabit uplink ports that are a configuration of 1000BASE-T/SFP. The ERS 2550T-PWR supports PoE capabilities on half of the user ports, the ERS 2526T and ERS 2526T-PWR models offer 24 ports of 10/100 plus two Gigabit uplink ports that are a combo configuration of 1000BASE-T/SFP. The ERS 2526T-PWR model offers PoE support on half of the user ports, the system also has the ability to stack any combination of these Switches in a system. The ERS2500 Series of Switches can be stacked with Flexible Advanced Stacking Technology to allows eight switches to operate as single logical system with a 32 Gbit/s virtual backplane, the bi-directional paths allow the traffic to automatically redirect around any switch in the stack that is not operating properly. This stacking technology allows stackable switches to operate with the same performance, Avaya Releases Ethernet Routing Switch 3500. New Ethernet Switches from Avaya Simplify Operations for Small and Midsize Enterprises, Avaya targets small businesses with new network gear. Avaya Unveils Network Switches for Small Enterprises, research Triangle Park, NC, Nortel Press. Pp. 19–20,63,219, 221–223,296, 385–387, 399–400,467, ERS 5000/4500/2500 Advanced Configuration and Maintenance. Archived from the original on 1 March 2012, data Stackables Nortel Ethernet Routing Switch 2500 y 4500. Archived from the original on 28 February 2012, Avaya Official Ethernet Routing Switch Documentation List -Retrieved 22 July 2011 ERS2500 Fact Sheet ERS3500 Fact Sheet Stackable Chassis Architecture
9.
Small office/home office
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Small office/home office refers to the category of business or cottage industry that involves from 1 to 10 workers. Before the 19th century, and the spread of the industrial revolution around the globe, nearly all offices were small offices and/or home offices, most businesses were small, and the paperwork that accompanied them was limited. The industrial revolution aggregated workers in factories, to mass-produce goods, in most circumstances, the white collar counterpart—office work—was aggregated as well in large buildings, usually in cities or densely populated suburban areas. Beginning in the mid-1980s, the advent of the computer and fax machine, plus breakthroughs in telecommunications. Decentralization was also perceived as benefiting employers in terms of lower overheads, many consultants and the members of such professions as lawyers, real estate agents, and surveyors in small and medium-size towns operate from home offices. Several ranges of products, such as the desk and all-in-one printer, are designed specifically for the SOHO market. A number of books and magazines have published and marketed specifically at this type of office. These range from general advice texts to specific guidebooks on such challenges as setting up a small PBX for the office telephones, technology has also created a demand for larger businesses to employ individuals who work from home. Sometimes these people remain as independent businesspersons, and sometimes they become employees of a larger company, the small office home office has undergone a transformation since its advent as the internet has enabled anyone working from a home office to compete globally. Technology has made possible through email, the World-Wide Web, e-commerce, videoconferencing, remote desktop software, webinar systems. Bless This Home Office. With tax credits, An Adam Compilation, johnson, Karen K. ed. Orthos All About Home Offices. The Home Office, Setting Up, Furnishing and Decorating Your Own Work Space
10.
Fibre Channel
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Fibre Channel, or FC, is a high-speed network technology primarily used to connect computer data storage to servers. Fibre Channel is mainly used in storage area networks in commercial data centers, Fibre Channel networks form a switched fabric because they operate in unison as one big switch. Fibre Channel typically runs on optical fiber cables within and between data centers, most block storage runs over Fibre Channel Fabrics and supports many upper level protocols. Fibre Channel Protocol is a protocol that predominantly transports SCSI commands over Fibre Channel networks. Mainframe computers run the FICON command set over Fibre Channel because of its high reliability, Fibre Channel can be used for flash memory being transported over the NVMe interface protocol. To promote the fiber optic aspects of the technology and to make a unique name, Fibre Channel started in 1988, with ANSI standard approval in 1994, to merge the benefits of multiple physical layer implementations including SCSI, HIPPI and ESCON. Fibre Channel was designed as an interface to overcome limitations of the SCSI. FC was developed with leading edge multi-mode fiber technologies that overcame the limitations of the ESCON protocol. Initially, the standard also ratified lower speed Fibre Channel versions with 132.8125 Mbit/s,265.625 Mbit/s, Fibre Channel saw adoption at 1 Gigabit/s Fibre Channel and its success grew with each successive speed. Fibre Channel has doubled in speed every few years since 1996, Fibre channel has seen active development since its inception, with numerous speed improvements on a variety of underlying transport media. There are three major Fibre Channel topologies, describing how a number of ports are connected together, a port in Fibre Channel terminology is any entity that actively communicates over the network, not necessarily a hardware port. This port is usually implemented in a such as disk storage. Two devices are connected directly to each other and this is the simplest topology, with limited connectivity. In this design, all devices are in a loop or ring, adding or removing a device from the loop causes all activity on the loop to be interrupted. The failure of one device causes a break in the ring, Fibre Channel hubs exist to connect multiple devices together and may bypass failed ports. A loop may also be made by cabling each port to the next in a ring, a minimal loop containing only two ports, while appearing to be similar to point-to-point, differs considerably in terms of the protocol. Only one pair of ports can communicate concurrently on a loop, Arbitrated Loop has been rarely used after 2010. In this design, all devices are connected to Fibre Channel switches, advantages of this topology over point-to-point or Arbitrated Loop include, The Fabric can scale to tens of thousands of ports
11.
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
12.
Digital subscriber line
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Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line, DSL service can be delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data, on the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services. Bit rates of 1 Gbit/s have been reached in trials, in ADSL, the data throughput in the upstream direction is lower, hence the designation of asymmetric service. In symmetric digital subscriber line services, the downstream and upstream data rates are equal, researchers at Bell Labs have reached speeds of 10 Gbit/s, while delivering 1 Gbit/s symmetrical broadband access services using traditional copper telephone lines. These higher speeds are lab results, however, a 2012 survey found that DSL continues to be the dominant technology for broadband access with 364.1 million subscribers worldwide. For a long time it was thought that it was not possible to operate a conventional phone-line beyond low-speed limits, in the 1950s, ordinary twisted-pair telephone-cable often carried four megahertz television signals between studios, suggesting that such lines would allow transmitting many megabits per second. One such circuit in the UK ran some ten miles between the BBC studios in Newcastle-upon-Tyne and the Pontop Pike transmitting station and it was able to give the studios a low quality cue feed but not one suitable for transmission. However, these cables had other impairments besides Gaussian noise, preventing such rates from becoming practical in the field, the 1980s saw the development of techniques for broadband communications that allowed the limit to be greatly extended. A patent was filed in 1979 for the use of existing telephone wires for both telephones and data terminals that were connected to a computer via a digital data carrier system. Joseph W. Lechleiders contribution to DSL was his insight that an asymmetric arrangement offered more than double the capacity of symmetric DSL. ADSL supports two modes of transport—fast channel and interleaved channel, fast channel is preferred for streaming multimedia, where an occasional dropped bit is acceptable, but lags are less so. Interleaved channel works better for file transfers, where the data must be error-free. Older ADSL standards delivered 8 Mbit/s to the customer over about 2 km of unshielded twisted-pair copper wire, distances greater than 2 km significantly reduce the bandwidth usable on the wires, thus reducing the data rate. But ADSL loop extenders increase these distances by repeating the signal, until the late 1990s, the cost of digital signal processors for DSL was prohibitive. All types of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the twisted pair wires. Due to the advancements of very-large-scale integration technology, the cost of the equipment associated with a DSL deployment lowered significantly, the two main pieces of equipment are a digital subscriber line access multiplexer at one end and a DSL modem at the other end. A DSL connection can be deployed over existing cable, such deployment, even including equipment, is much cheaper than installing a new, high-bandwidth fiber-optic cable over the same route and distance
