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=COMPUTER NETWORK=

INTRODUCTION


A computer network is a collection of computers or digital devices ("nodes") connected by telecommunication links or other networks. The network allows the computers to share resources, workloads, or data. The communications on the network follow protocol that determines how data is encoded, how access to the network is handled, and how errors are reported and corrected. These rules of communication are understood by all participants. A computer network may also be defined as the coordination or interconnection of a number of individual computers.

More specific, a computer network is an infrastructure which provides connectivity to multiple autonomous computer systems in order to communicate (e.g., e-mail) and share resources. These resources include hardware, such as storage media and peripherals (e.g : hard disks, printers, etc.), software (i.e : computer programs), and information/data (i.e : computer files - for example, a database).

Computer network is also has two or more computers that are connected together to share resources such as hardware, data, and software. Most common are the local area network (LAN) and the wide area network (WAN). A LAN can range from a few computers in a small office to several thousand computers spread throughout dozens of buildings on a school campus or in an industrial park. Expand this latter scenario to encompass multiple geographic locations, possibly on different continents, and you have a WAN.

BACKGROUND
Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behaviors seen in today's Internet were demonstrably present in the nineteenth century and arguably in even earlier networks using visual signals.

In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network"Bold text, a precursor to the ARPANet.

In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at MIT, a research group supported by General Electric and Bell Labs used a computer DEC's to route and manage telephone connections.

Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used datagrams or packets that could be used in a network between computer systems.

1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network (WAN).The first widely used PSTN switch that used true computer control was the Western Electric introduced in 1965.

In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANET network using 50 kbit/s circuits. Commercial services using X.25 were deployed in 1972, and later used as an underlying infrastructure for expanding TCP/IP networks. Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user. Today, computer networks are the core of modern communication. All modern aspects of the Public Switched Telephone Network (PSTN) are computer-controlled, and telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade, and this boom in communications would not have been possible without the progressively advancing computer network.

BENEFIT
Following are some of the advantages of computer networks.


 * File Sharing: The major advantage of a computer network is that is allows file sharing and remote file access. A person sitting at one workstation of a network can easily see the files present on the other workstation, provided he is authorized to do so. It saves the time which is wasted in copying a file from one system to another, by using a storange devices. In addition to that, many people can access or update the information stored in a database, making it up-to-date and accurate.
 * Resource Sharing: Resource sharing is also an important benefit of a computer network. For example, if there are four people in a family, each having their own computer, they will require four modems (for the Internet connection) and four printers, if they want to use the resources at the same time. A computer network, on the other hand, provides a cheaper alternative by the provision of resource sharing. In this way, all the four computers can be interconnected, using a network, and just one modem and printer can efficiently provide the services to all four members. The facility of shared folders can also be availed by family members.
 * Increased Storage Capacity: As there is more than one computer on a network which can easily share files, the issue of storage capacity gets resolved to a great extent. A standalone computer might fall short of storage memory, but when many computers are on a network, memory of different computers can be used in such case. One can also design a storage server on the network in order to have a huge storage capacity.
 * Increased Cost Efficiency: There are many softwares available in the market which are costly and take time for installation. Computer networks resolve this issue as the software can be stored or installed on a system or a server and can be used by the different workstations.

There are some of benefits for the computer networks:


 * Computers which are connected through a network can share resources as hard drives, printers, scanners etc with each other.
 * Can send filefrom one computer to another quite easily.
 * Can connect all the computers which are connected through a network to the internetby using a single line.
 * If you want to access data from the other computer which is the part of network then you can access data from that computer.
 * Users can run those programs which are not installed on their computers but are installed on any other user's computer.

WHAT IS THE NETWORK CLASSIFICATION
A computer network is a system for communication among two or more computers. Computer networks can be categorized by range, functional relationship, network topology and specialized function.

By range


 * personal area network (PAN)
 * wireless PAN
 * local area network (LAN)
 * wireless LAN
 * metropolitan area network (MAN)
 * wide area network (WAN)

By functional relationship


 * client-server
 * multitier architecture
 * Peer-to-peer

By network topology

Classification of computer network by range is:

Personal Area Network (PAN)

A personal area network (PAN) is a computer network used for communication amon computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the internet. Personal area networks may be wired with computer busses such a USB and Firewire.

Local Area Network (LAN)

These connect over a relatively small geographical are, typically connecting computers within a single office or building. In most cases they connect to a common electronic connection- commonly known as a network backbone. LAN's can connect to other networks either directly or through a WAN or MAN. A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. Most LANs connect workstations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data.

Metropolitan Area Network (MAN)

Short for Metropolitan Area Network, a data network designed for a town or city. In terms of geographic breadth, MANs are larger than local-area networks (LANs), but smaller than wide-area networks (WANs). MANs are usually characterized by very high-speed connections using fiber optical cable or other digital media.

Wide Area Networks (WAN)

These connect networks over a large geographical area, such as between different buildings, towns or even countries. A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network. A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks.

Classification of computer network by functional relationship is:

Client server

The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area network (LANs). Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and DNS.

Client/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients.

A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Multitier Architecture

N-Tier architecture refers to the architecture of an application that has at least 3 "logical" layers -- or parts -- that are separate. Each layer interacts with only the layer directly below, and has specific function that it is responsible for. Each layer can be located on physically different servers with only minor code changes, hence they scale out and handle more server load. Also, what each layer does internally is completely hidden to other layers and this makes it possible to change or update one layer without recompiling or modifying other layers.This is a very powerful feature of n-Tier architecture, as additional features or change to a layer can be done without redeploying the whole application. For example, by separating data access code from the business logic code, when the database servers change you only needs to change the data access code. Because business logic code stays the same, the business logic code does not need to be modified or recompiled.

Peer to Peer (P2P)

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or work loads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes. Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts. Peers are both suppliers and consumers of resources, in contrast to the traditional client-server model where only servers supply, and clients consume.

BASIC HARDWARE COMPONENTS
Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use MAC Addresses

Repeater 

A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmit it 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 100 meters. Repeaters work on the Physical Layer of the OSI model.

Hubs

A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address. It works on the Physical Layer of the OSI model.

Bridges

A network bridge connects multiple network segment at the data link layer (layer 2) of the OSI Model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC Addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only.

Bridges come in three basic types:
 * Local bridges: Directly connect local area networks (LANs)
 * Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
 * Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Switches

A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches.Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content.

Router

A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from (Layer of 3 OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data).

TWO TYPES OF NETWORK BASED ON PHYSICAL SCOPE
Local Area Network

A Local Area Network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU.TG.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines). Typical library network, in a branching tree topology and controlled access to resourcesAll interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.

Personal Area Network

A Personal Area Network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

Home Network

A Home Area Network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line (DSL) provider. It can also be referred as an office area network (OAN).

CONCLUSION
The computer network have more benefit for the people for example if their business has more than one computer, chances are they could benefit from networking them. A local area network (LAN) connects their company's computers, allowing them to shareand exchange a variety of information. While one computer can be useful on its own, several networked computers can be much more useful. Of course, this isn't a complete list; once they have a network, ythey will probably find many other uses for it. And once they get used to the benefits of a network, they will never look at their computer the same way again. When they are ready to network they computers, one of the first choices they will encounter is the speed of connection. They might also wonder whether to spring for a wireless LAN.

How fast is fast enough? Given the speed and power of today's computers, as well as the fact that even routine desktop applications handle large files, most businesses should avoid networking systems that deliver much less than 10Mbps. Wireless 802.11b LANs have a number of advantages, and they deliver enough speed to satisfy most business users. But other networking technologies, including those using phone and power lines to transmit data, are too slow and unreliable for business users. So that, with using the computer network we can get more benefits of networking computers and other devices include lower costs and increased productivity. With networks, resources can be shared, which results in less duplication and corruption of data.

REFERENCE
http://www.developerfusion.com/article/3058/boosting-your-net-application-performance/2/

http://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htm

http://wiki.answers.com/Q/What_is_a_computer_network

http://wiki.answers.com/Q/What_are_the_classification_of_computer_network

http://www.blurtit.com/q605597.html

http://www.spamlaws.com/network-advantage.html