Computer Network Assignment A134634 & A134371

INTRODCUTION
A computer network is an interconnected group of computer. Networks maybe classified by the network layer at which they operate according to basic reference models considered as standard in in the industry such as the five-layer Internet Protocol Suite model. While the others is the seven-layer Open Systems Interconnection (OSI) model which commonly known as academia. Majority of the networks use the Internet Protocol Suite(IP).

BACKGROUND
The Internet has had a relatively brief, but explosive history. It grew out of an experiment begun in the 1960s by the U.S. Department of Defense. The DoD wanted to create a computer network that would continue to function in the event of a disaster, such as a nuclear war. If part of the network was damaged or destroyed, the rest of the system still had to function. That network was called ARPANET(Advanced Research Projects Agency Network) which linked U.S. scientific and academic researchers, the forerunner of today's Internet. Before the advent of computer networks that were based upon some type of telecommunication 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 Avanced 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 Weatern Electric introduced in 1965. In 1969 the University of Califirnia 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 or 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.

BENEFITS
Many of the benefits we can obtained by using the computer networks. As a facilitating communication by using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.Besides 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. User also use the networking to 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. Users connected to a network may run application programon remote computers.

WHAT IS NETWORK CLASSIFICATION
*By scale

Computer networks are classified according to the scale: Personal area network (PAN), Local Area Network (LAN), Campus Area Network (CAN), Metropolitan Area Network (MAN) and Wide Area Network (WAN).

*By connection method

Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as Optical fibra, Wireless LAN, Ethernet, HomePNA and Power Line communication. Ethernets use physical wiring to connect devices. Often they employ hubs, switches, bridges, and/or routers. Wireless LAN technology is built to connect devices without wiring. These devices use a radio frequency to connect.

*By functional relationship (Network Architectures)

Computer networks may be classified according to the functional relationships which exist between the elements of the network like Active Networking, Client-server, and per-to-peer architecture.

* By Network Topology

Computer networks may be classified according to the Network Topology upon which the network is based, such as Bus Network, Star Network, Mesh Network, Bus-Star Network, Tree or Hierarchical topology network and etc. Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the word "logical" is significant. Thus the network Topology independent the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via 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; the logical network topology is not necessarily the same as the physical layout.

*By Protocol

Computer network may be classified as communication protocol that is being used on the network. Communication protocol is the information exchange on a device via a network or other communication mediumis governed by rules set out in a technical specification. The nature of the communication, the actual data exchanged and any state-dependent behaviors are defined by the specification.

TWO TYPS OF NETWORKS BASED ON PHYSICAL SCOPE
The two types of networks based on physical scope:

*Personal Area Network (PAN)

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs or scanners. The reach of a PAN is typically within about 6-9 metres. Personal area networks may be wired with computer buses such as USB and FireWire. . A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.

*Local Area Network (LAN)

A local area network covering a small geographic area, like a home, office, or building. Each computer or device on the network is a node. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a wired or wireless LAN for users to interconnect local devices like printers or servers and to connect to the internet. Besides there are also have a way to create a wired LAN using existing home wires like coaxial cables, phone lines and power lines. All interconnected devices must understand the network layer(layer 3) because they are handling multiple subnets(the different colours). Those inside the library which 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 lack of a need for leased telecommunication lines. Current Ethernet or other IEEE802.3 LAN technologies operate at speeds up to 10 Gbit/s.

BASIC HARDWARE COMPONENT
All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NIC), 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 IEEE802.11) or optical cable ("optical fibre").

*Network Interface Cards

&nbsp A network card, network adapter or NIC (network interface card) is a piece of computer haedware 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 address. It allows users to connect to each other either by using cables or wirelessly.

*Repeaters

A repeater is an eletronic device that receives a signal and retransmit it at a higher level or higher power, or onto 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 runs longer than 100 meters.

*Hubs

A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hab.

*Bridges

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


 * 1)  Local bridges: Directly connect local area networks (LANs)


 * 1) 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 by routers.


 * 1)   Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

*Switches

A switch is a device that performs switching. Specifically, it forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the Mac-Addresses in the packets. This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports with the intention that most or all of the network be connected directly to a switch, or another switch that is in turn connected to a switch. Switches is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, datalink, network, or transport. A device that operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

*Routers

Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP or IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media. This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent. They use preconfigured static routes, status of their hardware interfaces, and routing protocol to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home and even office use, have been integrated with routers to allow multiple home/office computers to access the Internet through the same connection. Many of these new devices also consist of wireless access points (waps) or wireless routers to allow for IEEE 802b/g wireless enabled devices to connect to the network without the need for a cabled connection.

CONCLUSION
As the nowadays technology improvement network will be a part from today's relatively ones that simply carry packets from one end to the other. With the explosion of Peer-To-Peer high definition video streaming and ubiquitous computing projects like Internet are looking at a scenario where even light bulbs and toasters will have an Internet Protocol (IP) address in affect making household compliances capable of accessing as well as being controlled by the internet. This said networks of the future will look different and will most probably work on different protocols. Such networks will not need full time chaperoning which is the job of many a systems administrator. Thus, user must use wisely the network in their daily life because many advantages can obtained from here.