Computer Network Assignment A134139 & A134392

INTRODUCTION
A computer network is a system in which computers are connected to share information and resources. The connection can be done peer-to-peer or client/server. A computer network also may be defined as the coordination or interconnection of a number of a individual computers. Since the computers are connected electronically, it can facilitate communications among users besides sharing the information.

BACKGROUND
A computer network is basically established by the network layer in the Open Systems Infrastructure model, popularly known as the OSI model.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.

BENEFITS
First of all, computers which are connected through a network can share resources as hard drives, printers, scanners with each other. Not only that, they also can send file from one computer to another quite easily. We can connect the all the computers which are connected through a network to the internet by using a single line. With this, we can save the connection cost for each computer but the internet connection must be fast. We also can easily access data from the computer which is the part of the network. Last but not least, users can run those programs which are not installed on their computers but are installed on any other user's computer.

NETWORK CLASSIFICATIONS
Computer networks can be classified by means of a lot of types like the network size, structure, mode of connectivity, topology and others. 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). 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.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. 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.

TWO TYPES OF NETWORK CLASSIFICATION BASED ON PHYSICAL SCOPE
Common types of computer networks may be identified by their scale:

1.Local area network

Alocal 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 likeITU-T G.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. [3]

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. [4] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

3. 1. 2. Home area 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).

3. 2. Wide area network
A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OS reference model:: the physic layer, the data link layer, and the network layer.

3. 2. 1. Campus network
A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).

In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls.

3. 3. Metropolitan area network
A Metropolitan area network is a large computer network that usually spans a city or a large campus. Sample EPN made of frame delay WAN connections and dialup remote access. Sample VPN used to interconnect 3 offices and remote users ==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 IEEE 8002.12) or optical cable ("optical fibre").

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 ADRESS.

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 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 ADRESSES 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 datagram (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 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
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.

While the age-old concept of the network is foundational in virtually all areas of society, Computer Networks and Protocols have forever changed the way humans will work, play, and communicate. Forging powerfully into areas of our lives that no one had expected, digital networking is further empowering us for the future. New protocols and standards will emerge, new applications will be conceived, and our lives will be further changed and enhanced. While the new will only be better, the majority of digital networking's current technologies are not cutting-edge, but rather are protocols and standards conceived at the dawn of the digital networking age that have stood solid for over thirty years.

REFERENCE

 * Wikipedia//computer network.com
 * ,New global network for fully networked home, ITU-T Press Release