Computer Network Assignment A135529 & A135421 & A135601

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 grown dramatically in complexity, geographical range and ubiquity over the last few years. This introductory chapter looks at the current state of networking and provides a brief conceptual context for the mass of technical information contained in the remainder of this book.

The Nature of the Network
- Data traversing the modern global network must run the gauntlet of a wide range of modern communications technology. Each packet is transmitted, bounced, copied, and mangled so often during its brief life that, at times, it seems remarkable that it is delivered at all. Yet, despite its complexity, the modern network is robust and reliable. This is testimony to the rapid pace of developments in communications hardware but perhaps equally as much to the adoption of a consensus approach to design issues by developers.

BENEFITS
The many benefits that networking offers to us are:

1.Helps to enhance connectivity
Networks connect and link unlimited number of computers. 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.Networking helps in 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.

WHAT IS NETWORK CLASSIFICATION
- There are two type of transmission technology: - Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets in certain contexts, sent by any machine are received by all the other. An address field with the packet specifies for whom it is intended. Upon receiving a packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignore. As an analogy, consider someone standing at the end of a corridor with many rooms off it and shouting.
 * broadcast,
 * point-to-point (peer-to-peer).

- Although the packet may actually be received (heard) by many people, only Watson responds. The other just ignore it. Another example is an airport announcement asking all flight 444 passengers to report to gate 10.

- Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with his code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Some broadcast system also support transmission to a subset of the machines, something known as multicasting. one possible scheme is to reserve on e bit to indicate multicasting. the remaining n-1 address bits hold a group number. Each machine can "subscribe" to any or all the the groups. When a packet is sent to a certain group, it is delivered to all machines subscribing to that group.

- On the other hand, point-to-point (peer-to-peer) networks consist of many connections between individual pairs of machines. To go fro the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often multiple routes, of different lengths are possible, so routing algorithms play an important role in point-to-point networks. As a general rule (although there are many exception), smaller, geographically localized networks tend to use broadcasting, whereas larger networks usually are point-to-point.

==  TWO TYPES OF NETWORKS BASED ON PHYSICAL SCOPE ==

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. 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.

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 OSI reference model: the physical layer, the data link layer, and the network layer.

- WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private.

- Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are often built using leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Leased lines can be very expensive. Instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods.

1. 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.

2. 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.

3. 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.

4. Bridges
- A network bridge connects multiple network segments at the data link layer 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.

5. Switches
- A network switch is a device that forwards and filters OSI layer 2 datagrams between ports 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.

6. Routers
- A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet. In many situations, this information is processed in conjunction with the routing table. Routers use routing tables to determine what interface to forward packets.

CONCLUSION
- While the age-old concept of the network is foundational in virtually all areas of society, Computer Networks 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.