Computer Network Assignment A134258 & A134624

INTRODUCTION


A computer network maybe defined as the coordination or interconnection of a number of in individual computers. A computer network is basically established by the network layer in the Open System Infrastructure model, known as the OSI model.

A computer network is an ideal way to share computer resources with multiple computers. There are many types of computer resources that can be shared through a computer network. Here, are a few popular ones: == BACKGROUND==
 * Broadband Internet Access
 * Online gaming
 * Files such as documents, pictures and music
 * printers
 * Security.

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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.=====

Computer Network is a scientific journal of computer and telecommunications networking published by Elsevier. Computer Network is an international, archival journal providing a publication vehicle for complete coverage of all topics of interest to those involved in the computer communications networking area. The audience includes researches, managers and operators of networks as well as designers and implementers.

BENEFITS
Some benefits of computer networks are given below :
 * 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.

The following list presents categories used for classifying networks.
&nbsp Connection method

Computer networks can be classified according to the hardware and software technology that is used ti interconnect the individual devices inthe network, such as optical fiber, Ethernet, wireless LAN, HomePNA, power line communication or G. hn.

Ethernet uses physical wiring to connect 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 aas a transmission medium. ITU-T G.hn technology uses existing home writing (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 wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used 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.


 * 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. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire.


 * Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.


 * Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.


 * Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.


 * Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.


 * Infrared communication ,which can transmit signals between devices within small distances not more than 10 meters peer to peer or ( face to face ) without any body in the line of transmitting.

Network are often classified as local area network (LAN), wide area network (WAN), metropolitan area network (MAN), personal area network(PAN), virtual private network(VPN), campus area network(CAN), storage are network(SAN), and other depending of their scale, scope, purpose, e.g., controller area network( CAN) usage, trust level, and access right often differ between these types of networks. LANs tend to be designed for internal use by an organization's while WANs may connect physically separate parts of an organization and may include connections to third parties.

Computer network may be classified according to the functional relationship which exist among the elements of the network, e.g. active networking, client server and peer to peer (workgroup) architecture.

Main article: Network topology

Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

TWO TYPS OF NETWORKS BASED ON PHYSICAL SCOPE
Two main types of networking:

• LAN (Local Area Network)

• WAN (Wide Area Network)

Local Area Network (LAN):


A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link. Typically, connected devices share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network).

Wide Area Network (WAN):


A wide area network (WAN)is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN').

A set of switches and routers are interconnected to form a Wide Area Network. The switches can be connected in different topologies such as full mesh and half mesh. A wide area network may be privately owned or rented from a service provider, but the term usually connotes the inclusion of public (shared user) networks.

Both packet switching and circuit switching technologies are used in the WAN. Packet switching allows users to share common carrier resources so that the carrier can make more efficient use of its infrastructure. In a packet switching setup, networks have connections into the carrier's network, and many customers share the carrier's network. The carrier can then create virtual circuits between customers' sites by which packets of data are delivered from one to the other through the network.

Circuit Switching allows data connections to be established when needed and then terminated when communication is complete. This works like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network.

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 cable). Less common are microwave links (as in IEEE 802.12) or optical cable (" 'optical fiber ' ").

== Network Interface Cards



A network card, network adapter, or NIC (network interface card) is a piece of computer hardwaredesigned 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.

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Repeaters



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 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.

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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 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).

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CONCLUSION
In conclusion,computer network is so important to us especially in today's generation.It had makes our life easier and lighten up our future.Computer networks are collections of computers which are connected together in order to communicate and transfer information.The Native Computer Communications Network Project was a good example of how a focus on creating a network of computers does not necessarily ensure the interpersonal networking of the potential users of that technology. If the people were not communicating with each other before, developing another method of communication doesn't mean they'll start.

REFERENCES

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

http://www.webopedia.com/TERM/N/network_computer.html

http://en.wikipedia.org/wiki/Computer_Networks_(journal)

http://www.blurtit.com/q349357.html

http://www.nvtechusa.com/computernetwork.html