Computer Network Assignment A134087 & A134570

INTRODUCTION
A computer network is a group of computers and devices interconnected by communications channels that facilitate communications among users. The connection can be done as peer-to-peer or client or server. A computer network allows sharing of resources and information among interconnected devices. It is also two or more computers connected so that they can communicate with each other and share information, software, peripheral devices, and/or processing power.

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, SRL (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.

1.Enhance networks connectivity
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.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.

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

2. Scale
Networks 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 area network (SAN), and others, depending on their scale, scope and purpose.

3. Functional relationship (network architecture)
Computer networks may be classified according to the functional relationships which exist among the elements of the network such as active networking, client-server and peer-to-peer (workgroup) architecture.

4. Network topology
Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. 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.

1. Local area network
A local 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 like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (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 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.

2. 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 personal area network(PAN) may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

BASIC HARDWARE COMPONENTS
All networks are made up of basic hardware building blocks to interconnect network nodes.

1. Network interface cards
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.

2. Repeaters
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.

3. Hubs
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.

4. Bridges
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.

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.

5.Switches
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 such as a Web URL identifier).

6.Routers
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.

CONCLUSION
Computer networks makes our life more easier to communicate with each other and the world using the computer. It also allows sharing of resources and information among interconnected devices.