1.
Intel
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Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California that was founded by Gordon Moore and Robert Noyce. It is the worlds largest and highest valued semiconductor chip makers based on revenue, and is the inventor of the x86 series of microprocessors, Intel supplies processors for computer system manufacturers such as Apple, Lenovo, HP, and Dell. Intel Corporation was founded on July 18,1968, by semiconductor pioneers Robert Noyce and Gordon Moore, the companys name was conceived as portmanteau of the words integrated and electronics. The fact that intel is the term for intelligence information made the name appropriate. Intel was a developer of SRAM and DRAM memory chips. Although Intel created the worlds first commercial microprocessor chip in 1971, during the 1990s, Intel invested heavily in new microprocessor designs fostering the rapid growth of the computer industry. The Open Source Technology Center at Intel hosts PowerTOP and LatencyTOP, and supports other projects such as Wayland, Intel Array Building Blocks, and Threading Building Blocks. Client Computing Group – 55% of 2016 revenues – produces hardware components used in desktop, data Center Group – 29% of 2016 revenues – produces hardware components used in server, network, and storage platforms. Internet of Things Group – 5% of 2016 revenues – offers platforms designed for retail, transportation, industrial, buildings, non-Volatile Memory Solutions Group – 4% of 2016 revenues – manufactures NAND flash memory products primarily used in solid-state drives. Intel Security Group – 4% of 2016 revenues – produces software, particularly security, programmable Solutions Group – 3% of 2016 revenues – manufactures programmable semiconductors. In 2016, Dell accounted for 15% of Intels total revenues, Lenovo accounted for 13% of total revenues, in the 1980s, Intel was among the top ten sellers of semiconductors in the world. In 1991, Intel became the biggest chip maker by revenue and has held the position ever since, other top semiconductor companies include TSMC, Advanced Micro Devices, Samsung, Texas Instruments, Toshiba and STMicroelectronics. Competitors in PC chip sets include Advanced Micro Devices, VIA Technologies, Silicon Integrated Systems, however, the cross-licensing agreement is canceled in the event of an AMD bankruptcy or takeover. Some smaller competitors such as VIA Technologies produce low-power x86 processors for small factor computers, however, the advent of such mobile computing devices, in particular, smartphones, has in recent years led to a decline in PC sales. Since over 95% of the worlds smartphones currently use processors designed by ARM Holdings, ARM is also planning to make inroads into the PC and server market. Intel has been involved in disputes regarding violation of antitrust laws. Intel was founded in Mountain View, California in 1968 by Gordon E. Moore, a chemist, and Robert Noyce, arthur Rock helped them find investors, while Max Palevsky was on the board from an early stage. Moore and Noyce had left Fairchild Semiconductor to found Intel, Rock was not an employee, but he was an investor and was chairman of the board
2.
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
3.
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
4.
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
5.
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
6.
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
7.
Line code
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In telecommunication, a line code is a code chosen for use within a communications system for transmitting a digital signal down a line. Line coding is used for digital data transport. Some line codes are digital baseband modulation or digital baseband transmission methods, Line coding consists of representing the digital signal to be transported, by a waveform that is appropriate for the specific properties of the physical channel. The pattern of voltage, current or photons used to represent the data on a transmission link is called line encoding. The common types of line encoding are unipolar, polar, bipolar, after line coding, the signal is put through a physical channel, either a transmission medium or data storage medium. Sometimes the characteristics of two very different-seeming channels are similar enough that the line code is used for them. The most common physical channels are, the signal can directly be put on a transmission line. The line-coded signal undergoes further pulse shaping and then modulated to create an RF signal that can be sent through free space, the line-coded signal can be used to turn on and off a light source in free-space optical communication, most commonly used in an infrared remote control. The line-coded signal can be printed on paper to create a bar code, the line-coded signal can be converted to magnetized spots on a hard drive or tape drive. The line-coded signal can be converted to pits on an optical disc, some of the more common or binary line codes include, Each line code has advantages and disadvantages. The running disparity is the total of the disparity of all previously transmitted words. Unfortunately, most long-distance communication channels cannot reliably transport a DC component, the DC component is also called the disparity, the bias, or the DC coefficient. The simplest possible line code, unipolar, gives too many errors on such systems, most line codes eliminate the DC component – such codes are called DC-balanced, zero-DC, or DC-free. There are three ways of eliminating the DC component, Use a constant-weight code, for example, Manchester code and Interleaved 2 of 5. In other words, the transmitter has to make sure that every word that averages to a negative level is paired with another code word that averages to a positive level. Therefore, it must keep track of the running DC buildup, the receiver is designed so that either code word of the pair decodes to the same data bits. For example, AMI, 8B10B, 4B3T, etc, for example, the scrambler specified in RFC2615 for 64b/66b encoding. This is important if the signal must pass through a transformer or a transmission line
8.
Twisted pair
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It was invented by Alexander Graham Bell. In balanced pair operation, the two wires carry equal and opposite signals, and the destination detects the difference between the two and this is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields, the noise thus produces a common-mode signal which is canceled at the receiver when the difference signal is taken. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles, one pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged, providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges, the twist rate makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the conductors of the different pairs may repeatedly lie next to each other. For this reason it is specified that, at least for cables containing small numbers of pairs. In contrast to shielded or foiled twisted pair, UTP cable is not surrounded by any shielding, UTP is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables. The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits, in the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, as electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles, in this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, such open-wire balanced lines with periodic transpositions still survive today in some rural areas. Twisted-pair cabling was invented by Alexander Graham Bell in 1881, by 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. UTP cables are found in many Ethernet networks and telephone systems, for indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T Corporation. A typical subset of these colors shows up in most UTP cables, for urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles. Each bundle consists of twisted pairs that have different twist rates, the bundles are in turn twisted together to make up the cable
9.
Optical fiber cable
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An optical fiber cable, also known as fiber optic cable, is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically coated with plastic layers. Different types of cable are used for different applications, for long distance telecommunication. Optical fiber consists of a core and a layer, selected for total internal reflection due to the difference in the refractive index between the two. In practical fibers, the cladding is coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties, individual coated fibers then have a tough resin buffer layer and/or core tube extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable, rigid fiber assemblies sometimes put light-absorbing glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications, for indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid, in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with an optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes and this protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be dry block or gel-filled, dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a tube, the fiber may be embedded in a heavy polymer jacket. Tight buffer cables are offered for a variety of applications, Breakout cables normally contain a ripcord, two non-conductive dielectric strengthening members, an aramid yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. The ripcord is a cord of strong yarn that is situated under the jacket of the cable for jacket removal. Distribution cables have an overall Kevlar wrapping, a ripcord, and these fiber units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching. A critical concern in outdoor cabling is to protect the fiber from contamination by water and this is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or water-absorbing powder surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, in September 2012, NTT Japan demonstrated a single fiber cable that was able to transfer 1 petabit per second over a distance of 50 kilometers
10.
Star topology
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Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one node, typically a switch or hub. In star topology, every node is connected to a central node, the switch is the server and the peripherals are the clients. A star network is an implementation of a spoke–hub distribution paradigm in computer networks, thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. Data on a star passes through the hub, switch. The hub, switch, or concentrator manages and controls all functions of the network and it also acts as a repeater for the data flow. This configuration is common with twisted pair cable and optical fibre cable, however, it can also be used with coaxial cable. The star topology reduces the impact of a failure by connecting all of the systems to a central node. All peripheral nodes may communicate with all others by transmitting to, and receiving from. Advantages If one node or its connection breaks it doesn’t affect the other computers and their connections
11.
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
12.
Duplex (telecommunications)
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A duplex communication system requires a pair of channels/frequencies hence the term duplex meaning two parts. The two channels are defined as uplink/downlink or reverse/forward, in a full-duplex system simultaneous transmission/reception is available, i. e. One can transmit and receive simultaneously, in a half-duplex system, each party can communicate with the other but not simultaneously, the communication is one direction at a time. Half duplex systems utilize separate channels for uplink and downlink, i. e. a transmit, in a half duplex communications system one user is allowed to transmit on the uplink channel at a time. The transmitted uplink signal is frequency translated via a radio/repeater to the downlink receive frequency which is received by all other radios tuned to the downlink/receive frequency. A half-duplex system is defined as system which operates two, hence duplex, dedicated uplink/downlink channels/frequencies. In a half duplex system a single path is provided for uplink, all uplink messages are broadcast via the downlink channel to all users simultaneously via a repeater which performs uplink to downlink channel/frequency translation. All cellular and land line PSTNs and PDSNs are full duplex systems, all full duplex systems require a channel/frequency translator via a radio/repeater. This is required in order to translate the uplink/transmit transmission from one to the downlink/receive channel/frequency of user two. Full duplex systems are one to one private systems unlike half duplex systems which broadcast to all users and this effectively makes the cable itself a collision-free environment and doubles the maximum total transmission capacity supported by each Ethernet connection. Time-division duplexing is commonly referred to as simplex communications, a single channel/frequency is employed for bidirectional communications. The term simplex communication as applied to TDM single channel systems predates the term TDD by at least 80 years, frequency-division duplexing as with any other duplex system is defined by two channel/frequency simultaneous communication. A channel/frequency pair are assigned to individual user on the system. An FDD system requires frequency translation from user 1 uplink/reverse frequency to user 2 downlink/forward frequency, full-duplex audio systems like telephones can create echo, which needs to be removed. Echo occurs when the coming out of the speaker, originating from the far end. The sound then reappears at the source end, but delayed. This feedback path may be acoustic, through the air, or it may be mechanically coupled, echo cancellation is a signal-processing operation that subtracts the far-end signal from the microphone signal before it is sent back over the network. Echo cancellation is important to the V.32, V.34, V.56, echo cancelers are available as both software and hardware implementations
13.
Ethernet switch
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A network switch is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, a network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer of the OSI model. Switches for Ethernet are the most common form and the first Ethernet switch was introduced by Kalpana in 1990, Switches also exist for other types of networks including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. A switch is a device in a network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices, Switches manage the flow of data across a network by transmitting a received network packet only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address and this maximizes the security and efficiency of the network. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain, an Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. In full duplex mode, each switch port can simultaneously transmit and receive, in the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would result in collisions, requiring retransmissions. The network switch plays an role in most modern Ethernet local area networks. Mid-to-large sized LANs contain a number of linked managed switches, in most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may include a telephone interface for Voice over IP protocol. Segmentation involves the use of a bridge or a switch to split a larger collision domain into smaller ones in order to reduce collision probability, in the extreme case, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports and this allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has one transmitter and one receiver per collision domain. Switches may operate at one or more layers of the OSI model, including the data link, a device that operates simultaneously at more than one of these layers is known as a multilayer switch. In switches intended for use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM. This connectivity can be at any of the layers mentioned, while the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing
14.
Media-independent interface
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The media-independent interface was originally defined as a standard interface to connect a Fast Ethernet media access control block to a PHY chip. The MII is standardized by IEEE802. 3u and connects different types of PHYs to MACs, being media independent means that different types of PHY devices for connecting to different media can be used without redesigning or replacing the MAC hardware. Thus any MAC may be used with any PHY, independent of the signal transmission media. The MII can be used to connect a MAC to an external PHY using a connector, or directly to a PHY chip which is on the same PCB. On a PC the CNR connector Type B carries MII bus interface signals, the Management Data Input/Output serial bus is a subset of the MII that is used to transfer management information between MAC and PHY. At powerup the PHY usually adapts to whatever it is connected to unless settings are altered via the MDIO interface, the original MII transfers data using 4-bit words in each direction. The data is clocked at 25 MHz to achieve 100 Mbit/s throughput, the original MII design has been extended to support reduced signals and increased speeds. The remaining transmit signals are driven by the MAC synchronously on the edge of TX_CLK. This arrangement allows the MAC to operate without having to be aware of the link speed, the transmit enable signal is held high during frame transmission and low when the transmitter is idle. This may be used to abort a frame when some problem is detected after transmission has already started, the MAC may omit the signal if it has no use for this functionality, in which case the signal should be tied low for the PHY. More recently, raising transmit error outside frame transmission is used to indicate the data lines are being used for special-purpose signalling. Specifically, the data value 0b0001 is used to request an EEE-capable PHY to enter low power mode, the first seven receiver signals are entirely analogous to the transmitter signals, except RX_ER is not optional and used to indicate the received signal could not be decoded to valid data. The receive clock is recovered from the signal during frame reception. When no clock can be recovered, the PHY must present a free-running clock as a substitute. The receive data valid signal is not required to go high immediately when the frame starts, some of the preamble nibbles may be lost. Similar to transmit, raising RX_ER outside a frame is used for special signalling, for receive, two data values are defined, 0b0001 to indicate the link partner is in EEE low power mode, and 0b1110 for a false carrier indication. The CRS and COL signals are asynchronous to the receive clock, carrier sense is high when transmitting, receiving, or the medium is otherwise sensed as being in use. If a collision is detected, COL also goes high while the collision persists, the interface requires 18 signals, out of which only two can be shared among multiple PHYs
15.
Ethernet hub
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It has multiple input/output ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the layer of the OSI model. Repeater hubs also participate in collision detection, forwarding a jam signal to all if it detects a collision. In addition to standard 8P8C ports, some hubs may also come with a BNC or Attachment Unit Interface connector to allow connection to legacy 10BASE2 or 10BASE5 network segments, hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE802.3, a network hub is an unsophisticated device in comparison with a switch. As a multiport repeater it works by repeating bits received from one of its ports to all other ports. It is aware of physical layer packets, that is it can detect their start, a hub cannot further examine or manage any of the traffic that comes through it, any packet entering any port is rebroadcast on all other ports. A hub/repeater has no memory to store any data in – a packet must be transmitted while it is received or is lost when a collision occurs, due to this, hubs can only run in half duplex mode. Consequently, due to a larger collision domain, packet collisions are frequent in networks connected using hubs than in networks connected using more sophisticated devices. The need for hosts to be able to detect collisions limits the number of hubs, for 10 Mbit/s networks built using repeater hubs, the 5-4-3 rule must be followed, up to five segments are allowed between any two end stations. For 10BASE-T networks, up to five segments and four repeaters are allowed between any two hosts, for 100 Mbit/s networks, the limit is reduced to 3 segments between any two end stations, and even that is only allowed if the hubs are of Class II. Most hubs detect typical problems, such as collisions and jabbering on individual ports. Thus, hub-based twisted-pair Ethernet is generally more robust than coaxial cable-based Ethernet, to pass data through the repeater in a usable fashion from one segment to the next, the framing and data rate must be the same on each segment. This means that a repeater cannot connect an 802.3 segment,100 Mbit/s hubs and repeaters come in two different speed grades, Class I delay the signal for a maximum of 140 bit times and Class II hubs delay the signal for a maximum of 92 bit times. In the early days of Fast Ethernet, Ethernet switches were relatively expensive devices, hubs suffered from the problem that if there were any 10BASE-T devices connected then the whole network needed to run at 10 Mbit/s. Therefore, a compromise between a hub and a switch was developed, known as a dual-speed hub and these devices make use of an internal two-port switch, bridging the 10 Mbit/s and 100 Mbit/s segments. When a network device becomes active on any of the physical ports and this obviated the need for an all-or-nothing migration to Fast Ethernet networks. These devices are considered hubs because the traffic between devices connected at the speed is not switched
16.
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
17.
Modular connector
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A modular connector is an electrical connector that was originally designed for use in telephone wiring, but has since been used for many other purposes. Many applications that used a bulkier, more expensive connector have converted to modular connectors. Probably the most well known applications of modular connectors are for telephone jacks and for Ethernet jacks, Modular connectors were originally used in the Registration Interface system, mandated by the Federal Communications Commission in 1976 in which they became known as registered jacks. The registered jack specifications define the wiring patterns of the jacks, instead, these latter aspects are covered by ISO standard 8877, first used in ISDN systems. TIA/EIA-568 is a standard for data circuits wired on modular connectors, other systems exist for assigning signals to modular connectors, physical interchangeability of plugs and jacks does not ensure interoperation, nor protection from electrical damage to circuits. For example, modular cables and connectors have used to supply low-voltage AC or DC power. Modular connectors also go by the names modular phone jack/plug, RJ connector, the term modular connector arose from its original use in a novel system of cabling designed to make telephone equipment more modular. This includes the 4P4C handset connector, a very popular use of 8P8C today is Ethernet over twisted pair, and that may be the most well known context in which the name RJ45 is known, even though it has nothing to do with the RJ45 standard. Likewise, the 4P4C connector is sometimes called RJ9 or RJ22, Modular connectors were originally developed and patented by General Cable Corp in 1974. They replaced the hard-wired connections on most Western Electric telephones around 1976, at the same time, they began to replace screw terminals and larger 3 and 4 pin telephone jacks in buildings. Modular connectors have gender, plugs are considered to be male, while jacks or sockets are considered to be female, plugs are used to terminate loose cables and cords, while jacks are used for fixed locations on surfaces such as walls and panels, and on equipment. Other than telephone extension cables, cables with a plug on one end. Instead, cables are connected using an adapter, which consists of two female jacks wired back-to-back. Modular connectors are designed to latch together, a spring-loaded tab on the plug snaps into a jack so that the plug cannot be pulled out. To remove the plug, the latching tab must be depressed, the standard and most common way to install a jack in a wall or panel is with the tab side down. This usually makes it easier to operate the tab when removing the plug, because the person grabs the plug with thumb on top, the modular connector suffers from a design flaw or weakness however, as the fragile latching tab easily snags on other cables and breaks off. When this happens, the connector is still functional, but the crucial latching feature is lost, some higher quality cables have a flexible sleeve called a boot over the plug, or a special tab design, to prevent this. These cables are marketed as snagless
18.
TIA/EIA-568
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ANSI/TIA-568 is a set of telecommunications standards from the Telecommunications Industry Association. The standards address commercial building cabling for telecommunications products and services, as of 2017, the standard is at revision D, replacing the 2009 revision C,2001 revision B, the 1995 revision A, and the initial issue of 1991, which are now obsolete. Perhaps the best known features of ANSI/TIA-568 are the pin/pair assignments for eight-conductor 100-ohm balanced twisted pair cabling and these assignments are named T568A and T568B. An IEC standard ISO/IEC11801 provides similar standards for network cables, ANSI/TIA-568 was developed through the efforts of more than 60 contributing organizations including manufacturers, end-users, and consultants. Work on the standard began with the EIA, to standards for telecommunications cabling systems. EIA agreed to develop a set of standards, and formed the TR-42 committee, the work continues to be maintained by TR-42 within the TIA, EIA is not longer in existence and hence EIA removed from the name. The first revision of the standard, TIA/EIA-568-A. 1-1991 was released in 1991, the standard was updated to revision B in 1995. The demands placed upon commercial wiring systems increased dramatically over this due to the adoption of personal computers and data communication networks. The development of twisted pair cabling and the popularization of fiber optic cables also drove significant change in the standards. These changes were first released in a revision C in 2009 which has subsequently replaced by the D series. ANSI/TIA-568 defines structured cabling system standards for buildings, and between buildings in campus environments. The main standard, ANSI/TIA-568. 0-D defines general requirements, while ANSI/TIA-568-C.2 focuses on components of balanced twisted-pair cable systems, ANSI/TIA-568. 3-D addresses components of fiber optic cable systems, and ANSI/TIA-568-C.4, addressed coaxial cabling components. The intent of these standards is to provide recommended practices for the design and installation of cabling systems that support a wide variety of existing. Developers hope the standards provide a lifespan for commercial cabling systems in excess of ten years. This effort has been successful, as evidenced by the definition of category 5 cabling in 1991. Thus, the process can reasonably be said to have provided at least a nine-year lifespan for premises cabling. All these documents accompany related standards that define commercial pathways and spaces, residential cabling, administration standards, grounding and bonding, the standard defines categories of unshielded twisted pair cable systems, with different levels of performance in signal bandwidth, insertion loss, and cross-talk. Generally increasing category numbers correspond with a cable system suitable for higher rates of data transmission, Category 3 cable was suitable for telephone circuits and data rates up to 16 million bits per second
19.
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
20.
Conventional PCI
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Conventional PCI, often shortened to PCI, is a local computer bus for attaching hardware devices in a computer. PCI is the initialism for Peripheral Component Interconnect and is part of the PCI Local Bus standard, the PCI bus supports the functions found on a processor bus but in a standardized format that is independent of any particular processors native bus. Devices connected to the PCI bus appear to a bus master to be connected directly to its own bus and are assigned addresses in the address space. It is a bus, synchronous to a single bus clock. Attached devices can take either the form of an integrated circuit fitted onto the motherboard itself or a card that fits into a slot. The PCI Local Bus was first implemented in IBM PC compatibles and it has subsequently been adopted for other computer types. Typical PCI cards used in PCs include, network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards, PCI video cards replaced ISA and VESA cards until growing bandwidth requirements outgrew the capabilities of PCI. The preferred interface for video cards then became AGP, itself a superset of conventional PCI and these have one locating notch in the card. Version 2.0 of the PCI standard introduced 3.3 V slots, universal cards, which can operate on either voltage, have two notches. Version 2.1 of the PCI standard introduced optional 66 MHz operation, a server-oriented variant of conventional PCI, called PCI-X operated at frequencies up to 133 MHz for PCI-X1.0 and up to 533 MHz for PCI-X2.0. An internal connector for laptop cards, called Mini PCI, was introduced in version 2.2 of the PCI specification, the PCI bus was also adopted for an external laptop connector standard – the CardBus. The first PCI specification was developed by Intel, but subsequent development of the standard became the responsibility of the PCI Special Interest Group, Conventional PCIs heyday in the desktop computer market was approximately 1995–2005. PCI and PCI-X have become obsolete for most purposes, however, they are common on modern desktops for the purposes of backwards compatibility. Many kinds of devices available on PCI expansion cards are now commonly integrated onto motherboards or available in USB. Work on PCI began at Intels Architecture Development Lab c. 1990, a team of Intel engineers defined the architecture and developed a proof of concept chipset and platform partnering with teams in the companys desktop PC systems and core logic product organizations. PCI was immediately put to use in servers, replacing MCA, in mainstream PCs, PCI was slower to replace VESA Local Bus, and did not gain significant market penetration until late 1994 in second-generation Pentium PCs. By 1996, VLB was all but extinct, and manufacturers had adopted PCI even for 486 computers, EISA continued to be used alongside PCI through 2000. Apple Computer adopted PCI for professional Power Macintosh computers in mid-1995, the 64-bit version of plain PCI remained rare in practice though, although it was used for example by all G3 and G4 Power Macintosh computers
21.
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
22.
Hub (network science)
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Hub is a concept in network science that refers to a node with a number of links that greatly exceeds the average. Emergence of hubs is a consequence of a property of networks. While hubs cannot be observed in a network, they are expected to emerge in scale-free networks. The uprise of hubs in networks is associated with power-law distribution. Hubs have a significant impact on the network topology, Hubs can be found in many real networks, such as Brain Network or Internet. A hub is a component of a network with a high-degree node, Hubs have a significantly larger number of links in comparison with other nodes in the network. The number of links for a hub in a network is much higher than for the biggest node in a random network, keeping the size N of the network. The existence of hubs is the biggest difference between networks and scale-free networks. In random networks, the k is comparable for every node. In scale-free networks, a few nodes have a high degree k while the nodes have a small number of links. Emergence of hubs can be explained by difference between networks and random networks. Scale-free networks are different from random networks in two aspects growth, preferential attachment, scale-free networks assume a continuous growth of the number of nodes N, compared to random networks which assume a fixed number of nodes. In scale-free networks the degree of the largest hub rises polynomially with the size of the network, therefore, the degree of a hub can be high in a scale-free network. In random networks the degree of the largest node rises logaritmically with N, a new node in a scale-free network has a tendency to link to a node with a higher degree, compared to a new node in a random network which links itself to a random node. This process is called preferential attachment, the tendency of a new node to link to a node with a high degree k is characterized by power-law distribution. This idea was introduced by Vilfredo Pareto and it explained why a small percentage of the population earns most of the money and this process is present in networks as well, for example 80 percent of web links point to 15 percent of webpages. The emergence of scale-free networks is not typical only of networks created by human action and this phenomenon may be explained by the example of hubs on the World Wide Web such as Facebook or Google. These webpages are very well known and therefore the tendency of other webpages pointing to them is higher than linking to random small webpages
23.
Network switch
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A network switch is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, a network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer of the OSI model. Switches for Ethernet are the most common form and the first Ethernet switch was introduced by Kalpana in 1990, Switches also exist for other types of networks including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. A switch is a device in a network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices, Switches manage the flow of data across a network by transmitting a received network packet only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address and this maximizes the security and efficiency of the network. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain, an Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. In full duplex mode, each switch port can simultaneously transmit and receive, in the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would result in collisions, requiring retransmissions. The network switch plays an role in most modern Ethernet local area networks. Mid-to-large sized LANs contain a number of linked managed switches, in most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may include a telephone interface for Voice over IP protocol. Segmentation involves the use of a bridge or a switch to split a larger collision domain into smaller ones in order to reduce collision probability, in the extreme case, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports and this allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has one transmitter and one receiver per collision domain. Switches may operate at one or more layers of the OSI model, including the data link, a device that operates simultaneously at more than one of these layers is known as a multilayer switch. In switches intended for use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM. This connectivity can be at any of the layers mentioned, while the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing
24.
Star network
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Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one node, typically a switch or hub. In star topology, every node is connected to a central node, the switch is the server and the peripherals are the clients. A star network is an implementation of a spoke–hub distribution paradigm in computer networks, thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. Data on a star passes through the hub, switch. The hub, switch, or concentrator manages and controls all functions of the network and it also acts as a repeater for the data flow. This configuration is common with twisted pair cable and optical fibre cable, however, it can also be used with coaxial cable. The star topology reduces the impact of a failure by connecting all of the systems to a central node. All peripheral nodes may communicate with all others by transmitting to, and receiving from. Advantages If one node or its connection breaks it doesn’t affect the other computers and their connections
25.
Ethernet crossover cable
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An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly. It is most often used to two devices of the same type, e. g. two computers or two switches to each other. By contrast, patch cables or straight through cables are used to connect devices of different types, the 10BASE-T and 100BASE-TX Ethernet standards use one wire pair for transmission in each direction. This requires that the pair of each device be connected to the receive pair of the device on the other end. When a terminal device is connected to a switch or hub, a standard straight through cable is used for this purpose where each pin of the connector on one end is connected to the corresponding pin on the other connector. One terminal may be connected directly to another without the use of a switch or hub, since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. A crossover cable may also be used to two hubs or two switches on their upstream ports. Such a cable will work for 10BASE-T or 100BASE-TX, the polarity of each pair is not swapped, but the pairs crossed as a unit, the two wires within each pair are not crossed. For this reason, there are no dedicated transmit and receive pairs, and consequently, crossover cables are never required for 1000BASE-T,2. 5GBASE-T, 5GBASE-T, 10GBASE-T, and 40GBASE-T communication. From 1000BASE-T onwards the physical medium attachment sublayer provides identification of each pair, however, when connecting an 100BASE-TX or 10BASE-T device to a faster port, a crossover may still be required in very rare situations. Since there are both transmitters and receivers present on a 1000BASE-T+ port on all pairs anyway, the Auto MDI-X function requires extremely little logic and is usually present. In practice, it does not matter if non-crossover Ethernet cables are wired as T568A or T568B, typical commercially available pre-wired cables can follow either format depending on the manufacturer. What this means is one manufacturers cables are wired one way and anothers the other way. In either case, T568A or T568B, a cable will have both ends wired identically according to the layout in either the Connection 1 column or the Connection 2 column. Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, for most optical fiber variants of Ethernet, fibers are used in pairs with one fiber for each direction. Obviously, the one needs to be connected to the other receiver. For this, fiber patch cables with duplex connectors are normally configured as crossover as well as the on-premises wiring. Thus, a connection with two patch cables at each end and a section of fixed cable in the middle has got three crossovers in total, resulting in a working connection
26.
4B5B
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In telecommunication, 4B5B is a form of data communications Block Coding. 4B5B maps groups of 4 bits onto groups of 5 bits, when NRZI-encoded, the 1 bits provide necessary clock transitions for the receiver. For example, a run of 4 bits such as 00002 contains no transitions, 4B5B solves this problem by assigning each block of 4 consecutive bits an equivalent word of 5 bits. These 5 bit words are pre-determined in a dictionary and they are chosen to ensure there will be at least two transitions per block of bits. A collateral effect of the code is that more bits are needed to send the information than with 4 bits. An alternate to using 4B5B coding is to use a scrambler, depending on the standard or specification of interest, there may be several 4B5B characters left unused. The presence of any of the characters in the data stream can be used as an indication that there is a fault somewhere in the link. Therefore, the characters can be used to detect errors in the data stream. The name 4B5B is generally taken to mean the FDDI version, other 4-to-5-bit codes have been used for magnetic recording and are known as group coded recording. On optical fiber, the 4B5B output is NRZI-encoded, FDDI over copper uses MLT-3 encoding instead, as does 100BASE-TX. The 4B5B encoding is used for USB Power Delivery communication on CC pin. The following character sets are referred to as command characters. Simulator - 4B/5B Encoder line written in Matlab
27.
Non-return-to-zero
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The pulses in NRZ have more energy than a return-to-zero code, which also has an additional rest state beside the conditions for ones and zeros. For a given data signaling rate, i. e. bit rate, when used to represent data in an asynchronous communication scheme, the absence of a neutral state requires other mechanisms for bit synchronization when a separate clock signal is not available. One is represented by a DC bias on the transmission line, for this reason it is also known as on-off keying. Among the disadvantages of unipolar NRZ is that it allows for long series without change, one solution is to not send bytes without transitions. More critically, and unique to unipolar NRZ, are related to the presence of a transmitted DC level - the power spectrum of the transmitted signal does not approach zero at zero frequency. One is represented by one level, while zero is represented by another level. In clock language, in bipolar NRZ-Level the voltage swings from positive to negative on the edge of the previous bit clock cycle. An example of this is RS-232, where one is −12 V to −5 V, one is represented by no change in physical level, while zero is represented by a change in physical level. In clock language, the transitions on the trailing clock edge of the previous bit to represent a zero. This change-on-zero is used by High-Level Data Link Control and USB and they both avoid long periods of no transitions by using zero-bit insertion. HDLC transmitters insert a 0 bit after five contiguous 1 bits, USB transmitters insert a 0 bit after six consecutive 1 bits. The receiver at the far end uses every transition — both from 0 bits in the data and these extra non-data 0 bits — to maintain clock synchronization, the receiver otherwise ignores these non-data 0 bits. Non return to zero, inverted is a method of mapping a binary signal to a signal for transmission over some transmission media. The two level NRZI signal has a transition at a clock if the bit being transmitted is a logical 1. One is represented by a transition of the level, while zero has no transition. Also, NRZI might take the convention, as in Universal Serial Bus signalling, when in Mode 1, in which a transition occurs when signaling zero. The transition occurs on the edge of the clock for the given bit. However, even NRZI can have long series of zeros, magnetic disk and tape storage devices generally use fixed-rate RLL codes, while USB uses bit stuffing, which inserts an additional 0 bit after 6 consecutive 1 bits, thus forcing a transition
28.
MLT-3 encoding
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MLT-3 encoding is a line code that uses three voltage levels. MLT-3 cycles sequentially through the voltage levels −1,0, +1,0 and it moves to the next state to transmit a 1 bit, and stays in the same state to transmit a 0 bit. Similar to simple NRZ encoding, MLT-3 has an efficiency of 1 bit/baud. Thus, the fundamental frequency is reduced to one fourth of the baud rate. This makes signal transmission more amenable to copper wires, MLT-3 was first introduced by Crescendo Communications as a coding scheme for FDDI copper interconnect. Later, the technology was used in the 100BASE-TX physical medium dependent sublayer. Signaling specified by 100BASE-T4 Ethernet, while it has three levels, is not compatible with MLT-3 and it uses selective base-2 to base-3 conversion with direct mapping of base-3 digits to line levels
29.
Fiber Distributed Data Interface
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Fiber Distributed Data Interface is a standard for data transmission in a local area network. FDDI provides a 100 Mbit/s optical standard for transmission in local area network that can extend in range up to 200 kilometers. In addition to covering large areas, FDDI local area networks can support thousands of users. FDDI offers both a Dual-Attached Station, counter-rotating token ring topology and a Single-Attached Station, token bus passing ring topology, FDDI, as a product of American National Standards Institute X3T9.5, conforms to the Open Systems Interconnection model of functional layering using other protocols. The standards process started in the mid 1980s, fDDI-II, a version of FDDI described in 1989, added circuit-switched service capability to the network so that it could also handle voice and video signals. Work started to connect FDDI networks to synchronous optical networking technology, a FDDI network contains two rings, one as a secondary backup in case the primary ring fails. The primary ring offers up to 100 Mbit/s capacity, when a network has no requirement for the secondary ring to do backup, it can also carry data, extending capacity to 200 Mbit/s. The single ring can extend the distance, a dual ring can extend 100 km. FDDI had a larger size than the standard Ethernet family. Designers normally constructed FDDI rings in a topology such as a dual ring of trees. A small number of devices, typically infrastructure devices such as routers and concentrators rather than host computers, were dual-attached to both rings, host computers then connect as single-attached devices to the routers or concentrators. The dual ring in its most degenerate form simply collapses into a single device, typically, a computer-room contained the whole dual ring, although some implementations deployed FDDI as a metropolitan area network. FDDI requires this network topology because the ring actually passes through each connected device. The standard actually allows for optical bypasses, but network engineers consider these unreliable, devices such as workstations and minicomputers that might not come under the control of the network managers are not suitable for connection to the dual ring. One of the connections becomes active while the one is automatically blocked. If the first connection fails, the backup link takes over with no perceptible delay, the Internet Engineering Task Force defined a standard for transmission of the Internet Protocol over FDDI. It was first proposed in June 1989 and revised in 1990, some aspects of the protocol were compatible with the IEEE802.2 standard for logical link control. For example, the 48-bit MAC addresses that became popular with the Ethernet family, thus other protocols such as the Address Resolution Protocol could be common as well
30.
Pulse-amplitude modulation
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Pulse-amplitude modulation, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulse. It is an analog pulse modulation scheme in which the amplitudes of a train of pulses are varied according to the sample value of the message signal. Demodulation is performed by detecting the level of the carrier at every single period. There are two types of pulse amplitude modulation, Single polarity PAM, In this a suitable fixed DC bias is added to the signal to ensure all the pulses are positive. Double polarity PAM, In this the pulses are positive and negative. In particular, all telephone modems faster than 300 bit/s use quadrature amplitude modulation, the number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some power of two, some versions of the Ethernet communication standard are an example of PAM usage. Pulse-amplitude modulation has also developed for the control of light-emitting diodes. Pulse-amplitude modulation LED drivers are able to synchronize pulses across multiple LED channels to enable perfect colour matching. Due to the inherent nature of PAM in conjunction with the switching speed of LEDs it is possible to use LED lighting as a means of wireless data transmission at high speed. The North American Advanced Television Systems Committee standards for digital television uses a form of PAM to broadcast the data that makes up the television signal. This system, known as 8VSB, is based on a three-level PAM like 100BASE-TX, using a single 6 MHz channel allocation, as defined in the previous NTSC analog standard, 8VSB is capable of transmitting 32 Mbit/s. After accounting for error correcting codes and other overhead, the rate in the signal is 19.39 Mbit/s
31.
Hewlett-Packard
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The Hewlett-Packard Company or shortened to Hewlett-Packard was an American multinational information technology company headquartered in Palo Alto, California. The company was founded in a garage in Palo Alto by William Bill Redington Hewlett and David Dave Packard. HP was the worlds leading PC manufacturer from 2007 to Q22013 and it specialized in developing and manufacturing computing, data storage, and networking hardware, designing software and delivering services. HP also had services and consulting business around its products and partner products.4 billion in 2008, in November 2009, HP announced the acquisition of 3Com, with the deal closing on April 12,2010. On April 28,2010, HP announced the buyout of Palm, on September 2,2010, HP won its bidding war for 3PAR with a $33 a share offer, which Dell declined to match. On October 6,2014, Hewlett-Packard announced plans to split the PC and printers business from its enterprise products, the split closed on November 1,2015, and resulted in two publicly traded companies, HP Inc. and Hewlett Packard Enterprise. William Redington Hewlett and David Packard graduated with degrees in engineering from Stanford University in 1935. The company originated in a garage in nearby Palo Alto during a fellowship they had with a past professor, Terman was considered a mentor to them in forming Hewlett-Packard. In 1939, Packard and Hewlett established Hewlett-Packard in Packards garage with a capital investment of US$538. Hewlett and Packard tossed a coin to decide whether the company they founded would be called Hewlett-Packard or Packard-Hewlett, HP incorporated on August 18,1947, and went public on November 6,1957. Of the many projects they worked on, their very first financially successful product was an audio oscillator. This allowed them to sell the Model 200A for $54.40 when competitors were selling less stable oscillators for over $200, the Model 200 series of generators continued until at least 1972 as the 200AB, still tube-based but improved in design through the years. They worked on technology and artillery shell fuses during World War II. Hewlett-Packards HP Associates division, established around 1960, developed semiconductor devices primarily for internal use, instruments and calculators were some of the products using these devices. HP partnered in the 1960s with Sony and the Yokogawa Electric companies in Japan to develop several high-quality products, the products were not a huge success, as there were high costs in building HP-looking products in Japan. HP and Yokogawa formed a joint venture in 1963 to market HP products in Japan, HP bought Yokogawa Electrics share of Hewlett-Packard Japan in 1999. HP spun off a company, Dynac, to specialize in digital equipment. The name was picked so that the HP logo hp could be turned upside down to be a reverse image of the logo dy of the new company
32.
Optical fiber
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An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors. Optical fibers typically include a transparent core surrounded by a transparent cladding material with an index of refraction. Light is kept in the core by the phenomenon of internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters, being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the cores. For applications that demand a permanent connection a fusion splice is common, in this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors, the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian physicist Narinder Singh Kapany who is acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon, John Tyndall included a demonstration of it in his public lectures in London,12 years later. When the ray passes from water to air it is bent from the perpendicular. If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, unpigmented human hairs have also been shown to act as an optical fiber. Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century, image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for medical examinations by Heinrich Lamm in the following decade
33.
Infrared
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It extends from the nominal red edge of the visible spectrum at 700 nanometers, to 1000000 nm. Most of the radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon, slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an effect on Earths climate. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements and it excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range, Infrared radiation is used in industrial, scientific, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected, Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatuses. Thermal-infrared imaging is used extensively for military and civilian purposes, military applications include target acquisition, surveillance, night vision, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm, Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm. This range of wavelengths corresponds to a range of approximately 430 THz down to 300 GHz. Below infrared is the portion of the electromagnetic spectrum. Sunlight, at a temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level, of this energy,527 watts is infrared radiation,445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight. Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wiens displacement law. Therefore, the band is often subdivided into smaller sections. Due to the nature of the blackbody radiation curves, typical hot objects, such as exhaust pipes, the three regions are used for observation of different temperature ranges, and hence different environments in space
34.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
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