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20,800 | Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, inc... | https://en.wikipedia.org/wiki?curid=9550 |
20,801 | The presence of an electric charge, which can be either positive or negative, produces an electric field. The movement of electric charges is an electric current and produces a magnetic field. | https://en.wikipedia.org/wiki?curid=9550 |
20,802 | When a charge is placed in a location with a non-zero electric field, a force will act on it. The magnitude of this force is given by Coulomb's law. If the charge moves, the electric field would be doing work on the electric charge. Thus we can speak of electric potential at a certain point in space, which is equal to ... | https://en.wikipedia.org/wiki?curid=9550 |
20,803 | Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the seventeenth and eighteenth centuries. The theory of electromagnetism was developed in the 19th century, and by the end of that century electricity was being put to industrial and residential use ... | https://en.wikipedia.org/wiki?curid=9550 |
20,804 | Long before any knowledge of electricity existed, people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish as the "Thunderer of the Nile", and described them as the "protectors" of all other fish. Electric fish were again reported millennia later by ancient Gree... | https://en.wikipedia.org/wiki?curid=9550 |
20,805 | Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, could be rubbed with cat's fur to attract light objects like feathers. Thales of Miletus made a series of observations on static electricity around 600 BCE, from which he believed that friction rendered amber magnetic, in contra... | https://en.wikipedia.org/wiki?curid=9550 |
20,806 | Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English scientist William Gilbert wrote "De Magnete", in which he made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber. He coined the... | https://en.wikipedia.org/wiki?curid=9550 |
20,807 | Further work was conducted in the 17th and early 18th centuries by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay. Later in the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key t... | https://en.wikipedia.org/wiki?curid=9550 |
20,808 | In 1775, Hugh Williamson reported a series of experiments to the Royal Society on the shocks delivered by the electric eel; that same year the surgeon and anatomist John Hunter described the structure of the fish's electric organs. In 1791, Luigi Galvani published his discovery of bioelectromagnetics, demonstrating tha... | https://en.wikipedia.org/wiki?curid=9550 |
20,809 | While the early 19th century had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering. Through such people as Alexander Graham Bell, Ottó Bláthy, Thomas Edison, Galileo Ferraris, Oliver Heaviside, Ányos Jedlik, William Thomson, 1st Baron Kelvin, Char... | https://en.wikipedia.org/wiki?curid=9550 |
20,810 | In 1887, Heinrich Hertz discovered that electrodes illuminated with ultraviolet light create electric sparks more easily. In 1905, Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets, energising ... | https://en.wikipedia.org/wiki?curid=9550 |
20,811 | The first solid-state device was the "cat's-whisker detector" first used in the 1900s in radio receivers. A whisker-like wire is placed lightly in contact with a solid crystal (such as a germanium crystal) to detect a radio signal by the contact junction effect. In a solid-state component, the current is confined to so... | https://en.wikipedia.org/wiki?curid=9550 |
20,812 | Solid-state electronics came into its own with the emergence of transistor technology. The first working transistor, a germanium-based point-contact transistor, was invented by John Bardeen and Walter Houser Brattain at Bell Labs in 1947, followed by the bipolar junction transistor in 1948. | https://en.wikipedia.org/wiki?curid=9550 |
20,813 | The presence of charge gives rise to an electrostatic force: charges exert a force on each other, an effect that was known, though not understood, in antiquity. A lightweight ball suspended by a fine thread can be charged by touching it with a glass rod that has itself been charged by rubbing with a cloth. If a similar... | https://en.wikipedia.org/wiki?curid=9550 |
20,814 | The force acts on the charged particles themselves, hence charge has a tendency to spread itself as evenly as possible over a conducting surface. The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb's law, which relates the force to the product of the charges and has an inver... | https://en.wikipedia.org/wiki?curid=9550 |
20,815 | Charge originates from certain types of subatomic particles, the most familiar carriers of which are the electron and proton. Electric charge gives rise to and interacts with the electromagnetic force, one of the four fundamental forces of nature. Experiment has shown charge to be a conserved quantity, that is, the net... | https://en.wikipedia.org/wiki?curid=9550 |
20,816 | The charge on electrons and protons is opposite in sign, hence an amount of charge may be expressed as being either negative or positive. By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of Benjamin Franklin. The amount of charge is ... | https://en.wikipedia.org/wiki?curid=9550 |
20,817 | Charge can be measured by a number of means, an early instrument being the gold-leaf electroscope, which although still in use for classroom demonstrations, has been superseded by the electronic electrometer. | https://en.wikipedia.org/wiki?curid=9550 |
20,818 | The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, electrical conduc... | https://en.wikipedia.org/wiki?curid=9550 |
20,819 | By historical convention, a positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called conventional current. The motion of negatively charged electrons around... | https://en.wikipedia.org/wiki?curid=9550 |
20,820 | The process by which electric current passes through a material is termed electrical conduction, and its nature varies with that of the charged particles and the material through which they are travelling. Examples of electric currents include metallic conduction, where electrons flow through a conductor such as metal,... | https://en.wikipedia.org/wiki?curid=9550 |
20,821 | Current causes several observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle in 1800, a process now known as electrolysis. Their work was greatly expanded upon by Michael Faraday in 18... | https://en.wikipedia.org/wiki?curid=9550 |
20,822 | In engineering or household applications, current is often described as being either direct current (DC) or alternating current (AC). These terms refer to how the current varies in time. Direct current, as produced by example from a battery and required by most electronic devices, is a unidirectional flow from the posi... | https://en.wikipedia.org/wiki?curid=9550 |
20,823 | The concept of the electric field was introduced by Michael Faraday. An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitation... | https://en.wikipedia.org/wiki?curid=9550 |
20,824 | An electric field generally varies in space, and its strength at any one point is defined as the force (per unit charge) that would be felt by a stationary, negligible charge if placed at that point. The conceptual charge, termed a 'test charge', must be vanishingly small to prevent its own electric field disturbing th... | https://en.wikipedia.org/wiki?curid=9550 |
20,825 | The study of electric fields created by stationary charges is called electrostatics. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday, whose term 'lines of force' still sometimes sees use. The field lines are th... | https://en.wikipedia.org/wiki?curid=9550 |
20,826 | A hollow conducting body carries all its charge on its outer surface. The field is therefore 0 at all places inside the body. This is the operating principal of the Faraday cage, a conducting metal shell which isolates its interior from outside electrical effects. | https://en.wikipedia.org/wiki?curid=9550 |
20,827 | The principles of electrostatics are important when designing items of high-voltage equipment. There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between the charged parts. Air, for example, tend... | https://en.wikipedia.org/wiki?curid=9550 |
20,828 | The field strength is greatly affected by nearby conducting objects, and it is particularly intense when it is forced to curve around sharply pointed objects. This principle is exploited in the lightning conductor, the sharp spike of which acts to encourage the lightning stroke to develop there, rather than to the buil... | https://en.wikipedia.org/wiki?curid=9550 |
20,829 | The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. The electric potential at any point is defined as the energy required to bring a unit test... | https://en.wikipedia.org/wiki?curid=9550 |
20,830 | For practical purposes, it is useful to define a common reference point to which potentials may be expressed and compared. While this could be at infinity, a much more useful reference is the Earth itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the name earth or gr... | https://en.wikipedia.org/wiki?curid=9550 |
20,831 | Electric potential is a scalar quantity, that is, it has only magnitude and not direction. It may be viewed as analogous to height: just as a released object will fall through a difference in heights caused by a gravitational field, so a charge will 'fall' across the voltage caused by an electric field. As relief maps ... | https://en.wikipedia.org/wiki?curid=9550 |
20,832 | The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre, the vector direction of the field is the line of greate... | https://en.wikipedia.org/wiki?curid=9550 |
20,833 | Ørsted's discovery in 1821 that a magnetic field existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces, the two forces of nature then known. ... | https://en.wikipedia.org/wiki?curid=9550 |
20,834 | Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: tw... | https://en.wikipedia.org/wiki?curid=9550 |
20,835 | This relationship between magnetic fields and currents is extremely important, for it led to Michael Faraday's invention of the electric motor in 1821. Faraday's homopolar motor consisted of a permanent magnet sitting in a pool of mercury. A current was allowed through a wire suspended from a pivot above the magnet and... | https://en.wikipedia.org/wiki?curid=9550 |
20,836 | Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as electromagnetic induction, enabled him to state the principle, now known as Faraday's law of induction, that the potential differ... | https://en.wikipedia.org/wiki?curid=9550 |
20,837 | The ability of chemical reactions to produce electricity, and conversely the ability of electricity to drive chemical reactions has a wide array of uses. | https://en.wikipedia.org/wiki?curid=9550 |
20,838 | Electrochemistry has always been an important part of electricity. From the initial invention of the Voltaic pile, electrochemical cells have evolved into the many different types of batteries, electroplating and electrolysis cells. Aluminium is produced in vast quantities this way, and many portable devices are electr... | https://en.wikipedia.org/wiki?curid=9550 |
20,839 | An electric circuit is an interconnection of electric components such that electric charge is made to flow along a closed path (a circuit), usually to perform some useful task. | https://en.wikipedia.org/wiki?curid=9550 |
20,840 | The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics. Electronic circuits contain active components, usually semiconductors, and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electri... | https://en.wikipedia.org/wiki?curid=9550 |
20,841 | The resistor is perhaps the simplest of passive circuit elements: as its name suggests, it resists the current through it, dissipating its energy as heat. The resistance is a consequence of the motion of charge through a conductor: in metals, for example, resistance is primarily due to collisions between electrons and ... | https://en.wikipedia.org/wiki?curid=9550 |
20,842 | The capacitor is a development of the Leyden jar and is a device that can store charge, and thereby storing electrical energy in the resulting field. It consists of two conducting plates separated by a thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the surface area per u... | https://en.wikipedia.org/wiki?curid=9550 |
20,843 | The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. T... | https://en.wikipedia.org/wiki?curid=9550 |
20,844 | Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. | https://en.wikipedia.org/wiki?curid=9550 |
20,845 | Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter "P". The term "wattage" is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current "I" consisting of a charge of "Q" coulombs every "t" seconds pass... | https://en.wikipedia.org/wiki?curid=9550 |
20,846 | Electricity generation is often done by a process of converting mechanical energy to electricity. Devices such as steam turbines or gas turbines are involved in the production of the mechanical energy, which is passed on to electric generators which produce the electricity. Electricity can also be supplied by chemical ... | https://en.wikipedia.org/wiki?curid=9550 |
20,847 | Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, optoelectronics, sensors and integrated circuits, and associated passive interconnection technologies. The nonlinear behaviour of active components and their ability to control electron flows ... | https://en.wikipedia.org/wiki?curid=9550 |
20,848 | Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. | https://en.wikipedia.org/wiki?curid=9550 |
20,849 | Faraday's and Ampère's work showed that a time-varying magnetic field acted as a source of an electric field, and a time-varying electric field was a source of a magnetic field. Thus, when either field is changing in time, then a field of the other is necessarily induced. Such a phenomenon has the properties of a wave,... | https://en.wikipedia.org/wiki?curid=9550 |
20,850 | Thus, the work of many researchers enabled the use of electronics to convert signals into high frequency oscillating currents, and via suitably shaped conductors, electricity permits the transmission and reception of these signals via radio waves over very long distances. | https://en.wikipedia.org/wiki?curid=9550 |
20,851 | In the 6th century BC, the Greek philosopher Thales of Miletus experimented with amber rods and these experiments were the first studies into the production of electrical energy. While this method, now known as the triboelectric effect, can lift light objects and generate sparks, it is extremely inefficient. It was not... | https://en.wikipedia.org/wiki?curid=9550 |
20,852 | Electrical power is usually generated by electro-mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. The modern steam turbine invented by Sir Charles Parsons in 1884 to... | https://en.wikipedia.org/wiki?curid=9550 |
20,853 | Since electrical energy cannot easily be stored in quantities large enough to meet demands on a national scale, at all times exactly as much must be produced as is required. This requires electricity utilities to make careful predictions of their electrical loads, and maintain constant co-ordination with their power st... | https://en.wikipedia.org/wiki?curid=9550 |
20,854 | Demand for electricity grows with great rapidity as a nation modernises and its economy develops. The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century, a rate of growth that is now being experienced by emerging economies such as those of India or China. ... | https://en.wikipedia.org/wiki?curid=9550 |
20,855 | Environmental concerns with electricity generation have led to an increased focus on generation from renewable sources, in particular from wind and solar. While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean. | https://en.wikipedia.org/wiki?curid=9550 |
20,856 | Electricity is a very convenient way to transfer energy, and it has been adapted to a huge, and growing, number of uses. The invention of a practical incandescent light bulb in the 1870s led to lighting becoming one of the first publicly available applications of electrical power. Although electrification brought with ... | https://en.wikipedia.org/wiki?curid=9550 |
20,857 | The resistive Joule heating effect employed in filament light bulbs also sees more direct use in electric heating. While this is versatile and controllable, it can be seen as wasteful, since most electrical generation has already required the production of heat at a power station. A number of countries, such as Denmark... | https://en.wikipedia.org/wiki?curid=9550 |
20,858 | Electricity is used within telecommunications, and indeed the electrical telegraph, demonstrated commercially in 1837 by Cooke and Wheatstone, was one of its earliest applications. With the construction of first transcontinental, and then transatlantic, telegraph systems in the 1860s, electricity had enabled communicat... | https://en.wikipedia.org/wiki?curid=9550 |
20,859 | The effects of electromagnetism are most visibly employed in the electric motor, which provides a clean and efficient means of motive power. A stationary motor such as a winch is easily provided with a supply of power, but a motor that moves with its application, such as an electric vehicle, is obliged to either carry ... | https://en.wikipedia.org/wiki?curid=9550 |
20,860 | Electronic devices make use of the transistor, perhaps one of the most important inventions of the twentieth century, and a fundamental building block of all modern circuitry. A modern integrated circuit may contain many billions of miniaturised transistors in a region only a few centimetres square. | https://en.wikipedia.org/wiki?curid=9550 |
20,861 | A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current. The threshold for perception varies with the supply frequency and with the path of the current, but is about 0.1 mA to 1 mA for mains-frequency... | https://en.wikipedia.org/wiki?curid=9550 |
20,862 | Electricity is not a human invention, and may be observed in several forms in nature, a prominent manifestation of which is lightning. Many interactions familiar at the macroscopic level, such as touch, friction or chemical bonding, are due to interactions between electric fields on the atomic scale. The Earth's magnet... | https://en.wikipedia.org/wiki?curid=9550 |
20,863 | §Bioelectrogenesis in microbial life is a prominent phenomenon in soils and sediment ecology resulting from anaerobic respiration. The microbial fuel cell mimics this ubiquitous natural phenomenon. | https://en.wikipedia.org/wiki?curid=9550 |
20,864 | Some organisms, such as sharks, are able to detect and respond to changes in electric fields, an ability known as electroreception, while others, termed electrogenic, are able to generate voltages themselves to serve as a predatory or defensive weapon; these are electric fish in different orders. The order Gymnotiforme... | https://en.wikipedia.org/wiki?curid=9550 |
20,865 | In 1850, William Gladstone asked the scientist Michael Faraday why electricity was valuable. Faraday answered, “One day sir, you may tax it.” | https://en.wikipedia.org/wiki?curid=9550 |
20,866 | In the 19th and early 20th century, electricity was not part of the everyday life of many people, even in the industrialised Western world. The popular culture of the time accordingly often depicted it as a mysterious, quasi-magical force that can slay the living, revive the dead or otherwise bend the laws of nature. T... | https://en.wikipedia.org/wiki?curid=9550 |
20,867 | As the public familiarity with electricity as the lifeblood of the Second Industrial Revolution grew, its wielders were more often cast in a positive light, such as the workers who "finger death at their gloves' end as they piece and repiece the living wires" in Rudyard Kipling's 1907 poem "Sons of Martha". Electricall... | https://en.wikipedia.org/wiki?curid=9550 |
20,868 | With electricity ceasing to be a novelty and becoming a necessity of everyday life in the later half of the 20th century, it required particular attention by popular culture only when it "stops" flowing, an event that usually signals disaster. The people who "keep" it flowing, such as the nameless hero of Jimmy Webb’s ... | https://en.wikipedia.org/wiki?curid=9550 |
20,869 | A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies, based on physically wired, opti... | https://en.wikipedia.org/wiki?curid=4122592 |
20,870 | The nodes of a computer network can include personal computers, servers, networking hardware, or other specialised or general-purpose hosts. They are identified by network addresses, and may have hostnames. Hostnames serve as memorable labels for the nodes, rarely changed after initial assignment. Network addresses ser... | https://en.wikipedia.org/wiki?curid=4122592 |
20,871 | Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth, communications protocols to organize network traffic, the network size, the topology, traffic control mechanism, and organizational intent. | https://en.wikipedia.org/wiki?curid=4122592 |
20,872 | Computer networks support many applications and services, such as access to the World Wide Web, digital video, digital audio, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications. | https://en.wikipedia.org/wiki?curid=4122592 |
20,873 | Computer networking may be considered a branch of computer science, computer engineering, and telecommunications, since it relies on the theoretical and practical application of the related disciplines. Computer networking was influenced by a wide array of technology developments and historical milestones. | https://en.wikipedia.org/wiki?curid=4122592 |
20,874 | A computer network extends interpersonal communications by electronic means with various technologies, such as email, instant messaging, online chat, voice and video telephone calls, and video conferencing. A network allows sharing of network and computing resources. Users may access and use resources provided by devic... | https://en.wikipedia.org/wiki?curid=4122592 |
20,875 | Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network. | https://en.wikipedia.org/wiki?curid=4122592 |
20,876 | Packets consist of two types of data: control information and user data (payload). The control information provides data the network needs to deliver the user data, for example, source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet... | https://en.wikipedia.org/wiki?curid=4122592 |
20,877 | With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched. When one user is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link isn't overu... | https://en.wikipedia.org/wiki?curid=4122592 |
20,878 | The physical link technologies of packet network typically limit the size of packets to a certain maximum transmission unit (MTU). A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message. | https://en.wikipedia.org/wiki?curid=4122592 |
20,879 | The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks, a single failure can cause the network to... | https://en.wikipedia.org/wiki?curid=4122592 |
20,880 | The physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDI, the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrele... | https://en.wikipedia.org/wiki?curid=4122592 |
20,881 | An overlay network is a virtual network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from t... | https://en.wikipedia.org/wiki?curid=4122592 |
20,882 | Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using modems before any data network existed. | https://en.wikipedia.org/wiki?curid=4122592 |
20,883 | The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network. Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Addr... | https://en.wikipedia.org/wiki?curid=4122592 |
20,884 | Another example of an overlay network is a distributed hash table, which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map) indexed by keys. | https://en.wikipedia.org/wiki?curid=4122592 |
20,885 | Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP multicast have not seen wide acceptance largely because they require modification of all routers in th... | https://en.wikipedia.org/wiki?curid=4122592 |
20,886 | For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes end system multicast, resilient routing and quality of service studies, among others. | https://en.wikipedia.org/wiki?curid=4122592 |
20,887 | The transmission media (often referred to in the literature as the "physical medium") used to link devices to form a computer network include electrical cable, optical fiber, and free space. In the OSI model, the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer. | https://en.wikipedia.org/wiki?curid=4122592 |
20,888 | A widely adopted "family" that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Wireless LAN standards use radio waves, others use infrared ... | https://en.wikipedia.org/wiki?curid=4122592 |
20,889 | Network connections can be established wirelessly using radio or other electromagnetic means of communication. | https://en.wikipedia.org/wiki?curid=4122592 |
20,890 | The last two cases have a large round-trip delay time, which gives slow two-way communication but doesn't prevent sending large amounts of information (they can have high throughput). | https://en.wikipedia.org/wiki?curid=4122592 |
20,891 | Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers (NICs), repeaters, hubs, bridges, switches, routers, modems, and firewalls. Any particular piece of equipment will frequently contain multiple building blocks and so may per... | https://en.wikipedia.org/wiki?curid=4122592 |
20,892 | A network interface controller (NIC) is computer hardware that connects the computer to the network media and has the ability to process low-level network information. For example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry. | https://en.wikipedia.org/wiki?curid=4122592 |
20,893 | In Ethernet networks, each network interface controller has a unique Media Access Control (MAC) address—usually stored in the controller's permanent memory. To avoid address conflicts between network devices, the Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. ... | https://en.wikipedia.org/wiki?curid=4122592 |
20,894 | A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of obstruction so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, ... | https://en.wikipedia.org/wiki?curid=4122592 |
20,895 | Repeaters work on the physical layer of the OSI model but still require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters used in a network, e.g., the ... | https://en.wikipedia.org/wiki?curid=4122592 |
20,896 | An Ethernet repeater with multiple ports is known as an Ethernet hub. In addition to reconditioning and distributing network signals, a repeater hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely obsoleted by modern network switches. | https://en.wikipedia.org/wiki?curid=4122592 |
20,897 | Network bridges and network switches are distinct from a hub in that they only forward frames to the ports involved in the communication whereas a hub forwards to all ports. Bridges only have two ports but a switch can be thought of as a multi-port bridge. Switches normally have numerous ports, facilitating a star topo... | https://en.wikipedia.org/wiki?curid=4122592 |
20,898 | Bridges and switches operate at the data link layer (layer 2) of the OSI model and bridge traffic between two or more network segments to form a single local network. Both are devices that forward frames of data between ports based on the destination MAC address in each frame. | https://en.wikipedia.org/wiki?curid=4122592 |
20,899 | They learn the association of physical ports to MAC addresses by examining the source addresses of received frames and only forward the frame when necessary. If an unknown destination MAC is targeted, the device broadcasts the request to all ports except the source, and discovers the location from the reply. | https://en.wikipedia.org/wiki?curid=4122592 |
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