A computer network is a group of more computers connected to each electronically. Thismeans that the computers can "talk" to each other and that every computer in the network cansend information to the others. Usually, this means that the speed of the connection is fast - fasterthan a normal connection to the Internet. Some basic types of computer networks include: A local area network (often called a LAN) connects two or more computers, and may be called a corporate network in an office or business setting. An "internetwork", sometimes called a Wide Area Network (because of the wide distance between networks) connects two or more smaller networks together. The largest internetwork is called the Internet.A computer network is an interconnection between general purpose programmabledevices thatdeals with the handling of data. LAN - Local Area Network WLAN - Wireless Local Area Network WAN - Wide Area Network MAN - Metropolitan Area Network SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network PAN - Personal Area Network DAN - Desk Area NetworkLAN and WAN were the original categories of area networks, while the others have graduallyemerged over many years of technology evolution.Note that these network types are a separate concept from network topologies such as bus, ringand star. See also - Introduction to Network TopologiesLAN - Local Area NetworkA LAN connects network devices over a relatively short distance. A networked office building,school, or home usually contains a single LAN, though sometimes one building will contain afew small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby
buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IPsubnet.In addition to operating in a limited space, LANs are also typically owned, controlled, andmanaged by a single person or organization. They also tend to use certain connectivitytechnologies, primarily Ethernet and Token Ring.WAN - Wide Area NetworkAs the term implies, a WAN spans a large physical distance. The Internet is the largest WAN,spanning the Earth.A WAN is a geographically-dispersed collection of LANs. A network device called a routerconnects LANs to a WAN. In IP networking, the router maintains both a LAN address and aWAN address.A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are notowned by any one organization but rather exist under collective or distributed ownership andmanagement. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivityover the longer distances.LAN, WAN and Home NetworkingResidences typically employ one LAN and connect to the Internet WAN via an Internet ServiceProvider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem,and all of the computers on the home network use LAN (so-called private) IP addresses. Allcomputers on the home LAN can communicate directly with each other but must go through acentral gateway, typically a broadband router, to reach the ISP.Other Types of Area NetworksWhile LAN and WAN are by far the most popular network types mentioned, you may alsocommonly see references to these others: Wireless Local Area Network - a LAN based on WiFi wireless network technology Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation. Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus. Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel. System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network. ,,bus
ring star tree meshMore complex networks can be built as hybrids of two or more of the above basic topologies.Bus TopologyBus networks (not to be confused with the system bus of a computer) use a common backbone toconnect all devices. A single cable, the backbone functions as a shared communication mediumthat devices attach or tap into with an interface connector. A device wanting to communicatewith another device on the network sends a broadcast message onto the wire that all otherdevices see, but only the intended recipient actually accepts and processes the message.Ethernet bus topologies are relatively easy to install and dont require much cabling compared tothe alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernetcabling options many years ago for bus topologies. However, bus networks work best with alimited number of devices. If more than a few dozen computers are added to a network bus,performance problems will likely result. In addition, if the backbone cable fails, the entirenetwork effectively becomes unusable.Ring TopologyIn a ring network, every device has exactly two neighbors for communication purposes. Allmessages travel through a ring in the same direction (either "clockwise" or "counterclockwise").A failure in any cable or device breaks the loop and can take down the entire network.To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology.Ring topologies are found in some office buildings or school campuses.Star TopologyMany home networks use the star topology. A star network features a central connection pointcalled a "hub" that may be a hub, switch or router. Devices typically connect to the hub withUnshielded Twisted Pair (UTP) Ethernet.Compared to the bus topology, a star network generally requires more cable, but a failure in anystar network cable will only take down one computers network access and not the entire LAN.(If the hub fails, however, the entire network also fails.)Tree TopologyTree topologies integrate multiple star topologies together onto a bus. In its simplest form, onlyhub devices connect directly to the tree bus, and each hub functions as the "root" of a tree ofdevices. This bus/star hybrid approach supports future expandability of the network much better
than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star(limited by the number of hub connection points) alone.Mesh TopologyMesh topologies involve the concept of routes. Unlike each of the previous topologies, messagessent on a mesh network can take any of several possible paths from source to destination. (Recallthat even in a ring, although two cable paths exist, messages can only travel in one direction.)Some WANs, most notably the Internet, employ mesh routing.A mesh network in which every device connects to every other is called a full mesh. As shown inthe illustration below, partial mesh networks also exist in which some devices connect onlyindirectly to others.SummaryTopologies remain an important part of network design theory. You can probably build a homeor small business computer network without understanding the difference between a bus designand a star design, but becoming familiar with the standard topologies gives you a betterunderstanding of important networking concepts like hubs, broadcasts, and routes.Hub:Definition: In computer networking, a hub is a small, simple, inexpensive device that joins multiplecomputers together. Many network hubs available today support the Ethernet standard. Other typesincluding USB hubs also exist, but Ethernet is the type traditionally used in home networking.Route:Definition: Routers are physical devices that join multiple wired or wireless networks together.Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless routerconnects networks (as gateways do), and that the router operates at the network layer of the OSI model
…………………. Bus Network Topology Ring NetworkTopology Star Network Topology Mesh Network TopologyOperating system:An Operating System is a software program or set of programs that mediate access betweenphysical devices (such as a keyboard, mouse, monitor, disk drive or network connection) andapplication programs (such as a word processor, World-Wide Web browser or electronic mailclient).An Operating System is a computer program that manages the resources of a computer. It acceptskeyboard or mouse inputs from users and displays the results of the actions and allows the user to runapplications, or communicate with other computers via networked connections.Some characteristics of an Operating System are: Whether multiple programs can run on it simultaneously: multi-tasking Whether it can take advantage of multiple processors: multi-processing Whether multiple users can run programs on it simultaneously: multi-user Whether it can reliably prevent application programs from directly accessing hardware devices: protected Whether it has built-in support for graphics. Whether it has built-in support for networks.Some popular Operating Systems are: Unix: multi-tasking, multi-processing, multi-user, protected, with built-in support for networking but not graphics. Windows NT: multi-tasking, multi-processing, single-user, protected, with built-in support for networking and graphics. Windows 95/98: multi-tasking, multi-processing, single-user, unprotected, with built-in support for networking and graphics.
Windows 3.x: single-tasking, single-processing, single-userss, unprotected, with built-insupport for graphics but not networking.DOS: single-tasking, single-processing, single-user, unprotected with no built-in supportfor graphics or networking.NetWare: multi-tasking, multi-processing, single-user, unprotected, with built-in supportfor networking but not graphics