Computer network - Wikipedia. A computer network or data network is a telecommunications network which allows computers to exchange data. In computer networks, networking devices exchange data with each 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. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other. Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the network's size, topology and organizational intent. Computer networks support an enormous number of 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 as well as many others. In most cases, application- specific communications protocols are layered (i.
Licklider developed a working group he called the . The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections. Throughout the 1. Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network. In 1. 96. 5, Thomas Marill and Lawrence G. Roberts created the first wide area network (WAN). This was an immediate precursor to the ARPANET, of which Roberts became program manager. Also in 1. 96. 5, Western Electric introduced the first widely used telephone switch that implemented true computer control. In 1. 96. 9 the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, and the University of Utah became connected as the beginning of the ARPANET network using 5. In July 1. 97. 6, Robert Metcalfe and David Boggs published their paper . CDNetworks is the highest performing global content delivery network (CDN), providing websites with the best performance, security and reliability. In machine learning and cognitive science, an artificial neural network (ANN) is a network inspired by biological neural networks (the central nervous systems of animals, in particular the brain) which are used to estimate or. In 1. 97. 9 Robert Metcalfe pursued making Ethernet an open standard. By 1. 99. 8, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 1. Gbit/s were added (as of 2. The ability of Ethernet to scale easily (such as quickly adapting to support new fiber optic cable speeds) 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. A network allows sharing of network and computing resources. Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer. Distributed computing uses computing resources across a network to accomplish tasks. A computer network may be used by computer crackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from accessing the network via a denial of service attack. Network packet. However, most information in computer networks is carried in packets. A network packet is a formatted unit of data (a list of bits or bytes, usually a few tens of bytes to a few kilobytes long) carried by a packet- switched network. In packet networks, the data is formatted into packets that are sent through the network to their destination. Once the packets arrive they are reassembled into their original message. 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 overused. Packets consist of two kinds 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 headers and trailers, with payload data in between. Often the route a packet needs to take through a network is not immediately available. In that case the packet is queued and waits until a link is free. Network topology. Most diagrams that describe a physical network are therefore topological, rather than geographic. The symbols on these diagrams usually denote network links and network nodes. Network links. In the OSI model, these are defined at layers 1 and 2 . The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 8. Ethernet transmits data over both copper and fiber cables. Wireless LAN standards (e. Power line communication uses a building's power cabling to transmit data. Wired technologies. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation helps minimize interference and distortion. Transmission speed ranges from 2. ITU- TG. hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high- speed (up to 1 Gigabit/s) local area network. Twisted pair wire is the most widely used medium for all telecommunication. Twisted- pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling (wired Ethernet as defined by IEEE 8. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 1. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted- pair (STP). Each form comes in several category ratings, designed for use in various scenarios. It carries pulses of light that represent data. Some advantages of optical fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea cables to interconnect continents. Price is a main factor distinguishing wired- and wireless- technology options in a business. Wireless options command a price premium that can make purchasing wired computers, printers and other devices a financial benefit. Before making the decision to purchase hard- wired technology products, a review of the restrictions and limitations of the selections is necessary. Business and employee needs may override any cost considerations. Terrestrial microwaves are in the low- gigahertz range, which limits all communications to line- of- sight. Relay stations are spaced approximately 4. Communications satellites . The satellites are stationed in space, typically in geosynchronous orbit 3. These Earth- orbiting systems are capable of receiving and relaying voice, data, and TV signals. Cellular and PCS systems use several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area has a low- power transmitter or radio relay antenna device to relay calls from one area to the next area. Radio and spread spectrum technologies . Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. IEEE 8. 02. 1. 1 defines a common flavor of open- standards wireless radio- wave technology known as Wifi. Free- space optical communication uses visible or invisible light for communications. In most cases, line- of- sight propagation is used, which limits the physical positioning of communicating devices. Exotic technologies. A lot of network interfaces are built- in. A network interface controller (NIC) is computer hardware that provides a computer with the ability to access the transmission 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. The NIC responds to traffic addressed to a network address for either the NIC or the computer as a whole. In Ethernet networks, each network interface controller has a unique Media Access Control (MAC) address. To avoid address conflicts between network devices, the Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets. The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least- significant octets of every Ethernet interface they produce. Repeaters and hubs. The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 1. With fiber optics, repeaters can be tens or even hundreds of kilometers apart. A repeater with multiple ports is known as a hub. Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance. As a result, many network architectures limit the number of repeaters that can be used in a row, e.
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