UNIT -III Computer Network Overview Computer Networking Or Data
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UNIT -III Computer Network Overview Computer networking or data communication is a most important part of the information technology. Today every business in the world needs a computer network for smooth operations, flexibly, instant communication and data access. Just imagine if there is no network communication in the university campuses, hospitals, multinational organizations and educational institutes then how difficult are to communicate with each other. In this article you will learn the basic overview of a computer network. The targeted audience of this article is the people who want to know about the network communication system, network standards and types. A computer network is comprised of connectivity devices and components. To share data and resources between two or more computers is known as networking. There are different types of a computer network such as LAN, MAN, WAN and wireless network. The key devices involved that make the infrastructure of a computer network are Hub, Switch, Router, Modem, Access point, LAN card and network cables. LAN stands for local area network and a network in a room, in a building or a network over small distance is known as a LAN. MAN stands for Metropolitan area network and it covers the networking between two offices within the city. WAN stands for wide area network and it cover the networking between two or more computers between two cities, two countries or two continents. There are different topologies of a computer network. A topology defines the physical layout or a design of a network. These topologies are star topology, bus topology, mesh topology, star bus topology etc. In a star topology each computer in a network is directly connected with a centralized device known as hub or switch. If any computer gets problematic in star topology then it does not affect the other computers in a network. There are different standards and devices in computer network. The most commonly used standard for a local area network is Ethernet. Key devices in a computer network are hub, switch, router, modem and access point etc. A router is used to connect two logically and physical different networks. All the communication on the internet is based on the router. Hub/Switch is used to connect the computers in local area network. Hopefully, in this article you may have learnt that what a computer network is, how important it is in our lives, what are different network devices, standards, topologies and communication types. Types of Computer Network One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are: •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 Network LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution. Note that these network types are a separate concept from network topologies such as bus, ring and star. LAN - Local Area Network A 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 a few 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 IP subnet. In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring. WAN - Wide Area Network As 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 router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances. LAN, WAN and Home Networking Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (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. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP. Other Types of Area Networks While LAN and WAN are by far the most popular network types mentioned, you may also commonly 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. Computer network A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics. A computer network allows sharing of resources and information among interconnected devices. History Early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE) and its relative the commercial airline reservation system Semi-Automatic Business Research Environment (SABRE), starting in the late 1950s.[1][2] In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. Development of the network began in 1969, based on designs developed during the 1960s.[3] The ARPANET evolved into the modern Internet. Purpose Computer networks can be used for a variety of purposes: • Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing. • Sharing hardware. In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer. • Sharing files, data, and information. In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks. • Sharing software. Users connected to a network may run application programs on remote computers. • Information preservation. • Security. • Speed up. Network classification The following list presents categories used for classifying networks. Connection method Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet, wireless LAN, HomePNA, power line communication or G.hn. Ethernet as it is defined by IEEE 802 utilizes various standards and mediums that enable communication between devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.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. Wired technologies • Twisted pair wire is the most widely used medium for 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 networking cabling consist of 4 pairs of copper cabling that can be utilized for both voice and data transmission. 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 100 million bits per second. Twisted pair cabling comes in two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are rated in categories which are manufactured in different increments for various scenarios. • Coaxial cable is widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second. • Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second.