Computer Network Assignment A134567 & A134576

INTRODUCTION
- A computer network is a system in which computers are connected to share information and resources. The connection can be done as peer-to-peer or client/server. This web site reviews the techniques you can use to set up and possibly manage a network for home or a small business.

- A computer network, often simply referred to as a network, is a group 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. 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.

BACKGROUND
Computer networks have existed for more than thirty years ago, but only relatively recently have they become popular in homes. In 1999, only a few hundred thousand households in the United States possessed a home network, although many more "expressed interest" in having one.

Today, many millions of households in the U.S. and worldwide have adopted home computer networking. Millions more have yet to build their first home network. Even those who've previously taken the plunge are now beginning to revamp their networks for wireless - the current wave of useful technology for home networking.

BENEFITS

 * file sharing - Network file sharing between computers gives you more flexibity than using floppy drives or Zip drives. Not only can you share photos, music files, and documents, you can also use a home network to save copies of all of your important data on a different computer. Backups are one of the most critical yet overlooked tasks in home networking.
 * printer / peripheral sharing - Once a home network is in place, it's easy to then set up all of the computers to share a single printer. No longer will you need to bounce from one system or another just to print out an email message. Other computer peripherals can be shared similarly such as network scanners, Web cams, and CD burners.
 * Internet connection sharing - Using a home network, multiple family members can access the Internet simultaneously without having to pay an ISP for multiple accounts. You will notice the Internet connection slows down when several people share it, but broadband Internet can handle the extra load with little trouble. Sharing dial-up Internet connections works, too. Painfully slow sometimes, you will still appreciate having shared dial-up on those occasions you really need it.
 * multi-player games - Many popular home computer games support LAN mode where friends and family can play together, if they have their computers networked.
 * Internet telephone service - So-called Voice over IP (VoIP) services allow you to make and receive phone calls through your home network across the Internet, saving you money.
 * home entertainment - Newer home entertainment products such as digital video recorders (DVRs) and video game consoles now support either wired or wireless home networking. Having these products integrated into your network enables online Internet gaming, video sharing and other advanced features.

WHAT IS NETWORK CLASSIFICATION
Definition: The word "cluster" is used broadly in computer networking to refer to a number of different implementations of shared computing resources. Typically, a cluster integrates the resources of two or more computing devices (that could otherwise function separately) together for some common purpose.

A Web server farm (a collection of networked Web servers, each with access to content on the same site) function as a cluster conceptually. However, purists may debate the classification of a server farm as a cluster, depending on the details of the hardware and software configuration. It is important to recognize that network clustering involves a long past history of research and development with many offshoots and variations.

Also Known As: Farm, Network of Workstations (NOW), distributed system, parallel system.

Computer networks can be classified by means of a lot of types like the network size, structure, mode of connectivity, topology and others. Some of them are,

Network Size Considering the size of the implemented network, Computer networks are classified into 3 main divisions namely Local Area Network (LAN), Wide Area Network (WAN) and Metropolitan Area Network (MAN). In certain fields, they are also further classified into Personal Area Network (PAN), Campus Area Network (CAN) and Global Area Network (GAN). Structure Of The Network Considering the structure and relationship between the elements of a computer network, the network may be classified into 3 divisions namely Client-Server model, Peer to Peer model and Active Networking model. Each of the classifications has a separate and unique structure which differentiates them in connectivity and working mode.
 * LAN: - A network of computers which cover only a small area like an office or a building can be referred to as a Local Area Network. All the individual computers must have a common protocol layer for their connectivity with the basic functionality taking place at the network layer. In general, LANs are based on Ethernet technology.
 * WAN: - Wide Area Network is basically an extension of the Local Area Network except for the fact that the size of the network extends to a very large area. The major functionality of the WAN networks take place at the 3 lower layers of the OSI model namely network layer, data link layer and the physical layer.
 * MAN: - Metropolitan Area network is a combination of two or more individual Local Area Networks but with a small criterion of the boundary of the network not exceeding the city limits, thus integrating the network as a single unit within a city.
 * PAN: - Personal network is the smallest of all networks with most of the networks not exceeding a total size of 25 feet.
 * CAN: - This is similar to a wide area network but the size of the network is limited to a certain social limit, for example the network in an university where the total network is formed by the collaboration of more than one Local Area Network.
 * GAN: - Global Area Networks are large scale WANs and are implemented globally. The total network consists of a large number of sub-networks with most of the connectivity between the networks is done using wireless networks.

Mode of Connectivity By means of the connection mechanisms, computer networks are divided into wired networks and wireless networks. The wired networks are further divided into some sub-divisions like Optical Fiber and Ethernet networks.

Topology In general, a computer network is technically classified based on the topology of the total network which includes the structure of the networks too. They are divided into Bus networks, Ring network, Star network, Mesh network, Star-bus network, Tree network.

Hardware Requirements for a Network Set-Up Other than the computers required for a network establishment, the requirement arises for other hardware components too. Some of them are,

Routers Routers simply function as an intermediary device which forwards the data packets that it receives, to the next available or neighboring router or a terminal.

Switches Switches are the virtual controllers of routers and bridges. These are operated from each of the individual layers of the OSI layer. Certain cases where the devices operate on multiple layers are called multilayer switch.

Bridges Technically, a bridge acts a connector between the data link layer and the network layer. The three types of bridges are Local Bridges, Remote Bridges and Wireless bridges.

Network Cards Network cards are the most important hardware component of a computer network. The most important functionality of the layer is to enable communication between the computers in a network.

TWO TYPES 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.
 * LAN - Local Area Network
 * WAN - Wide Area Network

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 and Relay and X.25 for connectivity over the longer distances.

BASIC HARDWARE COMPONENTS
All networks are made up of basic hardware building blocks to interconnect network nodes such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cabel). Less common are microwave links or optical cable ("optical fiber").

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.

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.

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 segments 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 learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

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 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.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 (e.g., a Web URL identifier).

Routers
A routers 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).

CONCLUSION
We've all become much smarter about computer networking as the past few years of Internet time have passed. Expect the next five years to also bring their share of surprises and advances. Besides that, the new breed of NAS networking products has succeeded in providing a reasonable alternative to traditional file servers in client/server networks. Entry-level NAS products containing 20-50 gigabytes of storage can be purchased for $500 (USD) or less, whereas mid-range and high-end NAS systems can run in the tens of thousands of dollars. Besides cost, a NAS promises reliable operation and easy management. Look for the Network Attached Storage technology to keep evolving as the field matures over the next several years.

REFRENCES
1.About.com:wireless/networking

2.About.com:search results

3. http://en.wikipedia.org/wiki/Computer_network

4. http://en.wikipedia.org/wiki/Computer_appliance