Computer Network Assignment A131110 & A131148 & A131254

INRTODUCTION
A computer network or network is a computer network is a system in which computer are connected to share information and resources. The connection can be done as peer-to-peer or client/server. A computer network allows sharing of resources and information among interconnected devices. 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. It was the first computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s.==

Purpose
Computer networks can be used for several 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.

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.

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Benefits Of Computer Networking== Technically speaking networking can be defined as a bunch of computers that have with wires running in between them. If proper implementation of a network is done it acts as a system that provides unique capabilities, to its users. These are much beyond the abilities of individual machines and software applications associated with them.

 The benefits networking offers to its users can be separated into two main groups i.e. sharing and connectivity. Networks make computers and their users capable of being connected together. This facilitates sharing of resources and information between the users. The modern businesses are expanded all over the world. So, uses and significance of networking has gained momentum during the last years. The many benefits that networking offers to us are:

1.Helps to enhance connectivity

Networks connect and link unlimited number of computers. This in turn connects the people using those computers. Individuals within a work group are connected through local area networks. Many LANs in far off locations are interconnected through larger wide area networks (WANs). These connections ease out communication between people using technologies like e-mail. Today e-mail has become the easiest, and cheapest mode of transformation of information between the users.

2.Networking helps in sharing of hardware

Networks help in sharing of different kinds of hardware devices. For example, sharing of a single printer in an office of twenty people is done through networking of wires. This saves lot of cost that could otherwise have incurred if twenty different printers were provided for each computer in use.

3.Eases out management of data.

Networking provides the advantage of centralization of data from all the user systems to one system where it can be managed in an easy and better way. Administrators can thus manage all this data efficiently and in the best interest of the company. Even the access of this data becomes easy for the users.

4.Internet

The most beautiful gift of networking is internet that is massively used by people all over the world. Whenever you are accessing Internet, you are making use of a network. The benefits of internet need no mentioning. Thanks to the wonderful world of networking.

5.Data Sharing Sharing of data through the use of networks helps save a lot of time and energy.

It also facilitates the use of applications like databases that are based on ability of many individuals to access and to share exactly the same data.

6.Networking has promoted gaming. Many internet games like WOW accounts are being played by players all over the world using common servers. These give fun and enjoyment to people and also improve their skills.

NETWORK CLASSIFICATION
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Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets in certain contexts, sent by any machine are received by all the other. An address field with the packet specifies for whom it is intended. Upon receiving a packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignore.
 * broadcast,
 * point-to-point (peer-to-peer).

As an analogy, consider someone standing at the end of a corridor with many rooms off it and shouting.
Although the packet may actually be received (heard) by many people, only Watson responds. The other just ignore it. Another example is an airport announcement asking all flight 444 passengers to report to gate 10.

Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with his code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Some broadcast system also support transmission to a subset of the machines, something known as multicasting. one possible scheme is to reserve on e bit to indicate multicasting. the remaining n-1 address bits hold a group number. Each machine can "subscribe" to any or all the the groups. When a packet is sent to a certain group, it is delivered to all machines subscribing to that group.

On the other hand, point-to-point (peer-to-peer) networks consist of many connections between individual pairs of machines. To go fro the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often multiple routes, of different lengths are possible, so routing algorithms play an important role in point-to-point networks. As a general rule (although there are many exception), smaller, geographically localized networks tend to use broadcasting, whereas larger networks usually are point-to-point

===Local Area Networks (LAN) === a) Local Are Networks (LANs) : 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.

b) 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. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.  

===Metropolitan Area Networks (MAN) === a) Metropolitan Area Networks (MAN's): These connect networks around a town or city. it is smaller than a WAN, but larger4 than a LAN. An example of a Man is the EaStMAN (Edinburgh and Stirling MAN) network that connects universities and colleges in Edinburgh and Stirling, UK.

b) 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) === a) Wide Area Networks( WANs) : These connect networks over a large geographical area, such as between different buildings, towns or even countries.

b) 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.

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OF NETWORKS BASED ON PHYSICAL SCOPE == 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 and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.
 * 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

Note that these network types are a separate concept from network topologies such as bus, ring and star.

See also - Introduction to Network Topologies

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:  BASIC HARDWARE COMPONENTS
 * 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.

Headline text
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 of MAC addresses. [edit]Repeaters A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits 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. [edit]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.[7] It works on the Physical Layer of the OSI model.. [edit]Bridges 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.

[edit]Switches A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.[8] 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.[9] 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 (e.g., a Web URL identifier). [edit]Routers 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 3 of the 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).