Computer Networks PDF

Computer Networks Topic Contents Why there is a need to create network? Devices used to connect a network. What is computer network? What are types of computer network? Point of differentiation between LAN and WAN. Computer topologies.  Need of Computer Network: File shar...

Computer Networks Topic Contents Why there is a need to create network? Devices used to connect a network. What is computer network? What are types of computer network? Point of differentiation between LAN and WAN. Computer topologies.  Need of Computer Network: File sharing Resource sharing Communication and collaboration Remote access Data protection  Devices Use To Connect Network: Routers Gateways Repeaters Bridges Hub Modem Advantages of a network Resources (Hardware and Software) can be shared. Allows more effective communication between users e.g. via e-mail. Networks are cheaper than “stand-alone PCs.” Information held on the network can be accessed by all users with authorised access. Disadvantages of a network The set-up and maintenance costs can be expensive. A fault with the network server can cause difficulties with the organisation. Networks need security measures to restrict access to users. WANs are vulnerable to hackers and viruses. What is a computer network? A network consists of two or more computers that are linked in order to share resources, exchange files, or allow electronic communications. Network can be as simple as two computers connected by a single cable or as complex as hundreds of computers connected to devices that control the flow of information. A computer network is a group of computers connected to each other electronically by which they can talk to each other and exchange data. Types of networks LAN (Local Area Network) MAN (Metropolitan Area Network) WAN (Wide Area Network) LAN What is a local area network (LAN)? LAN covers a small region of space typically a single building, school or at home. In LAN, group of computers and other devices dispersed over a relatively limited area say within a building and connected by a communication link that enables each device to interact with any other device on the network. Advantages of LAN Sharing of expensive resources High speed exchange of essential Information One can store all critical data at a central place Back-up of all important files Metropolitan area network(MAN) MAN is a data network intended to serve an area approximately that of a large city. Such networks are being implemented by techniques like running fibre cables through subway tunnels and satellites. MAN Cont… A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network but smaller than the area covered by a wide area network (WAN). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines wide area network (WAN)? Network that covers large geographic area using many types of media Internet is world’s largest WAN Can be a collection of LANs or WANs or the mix of two with a very large geographical area for instant a country or even beyond the border Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network.  Comparison between the three types of computer Networks CRITERIA LAN MAN WAN Cost Low High Higher Network Size Small Larger Largest Speed Fastest Slower Slowest Transmission media type Twisted-pair Twisted-pair and fiber- Fiber optic, radio wave optic cables and satellite Number of computers Smallest Large Largest Transmission media (Wired Networking Media ) – Twisted-Pair Cable Pairs of insulated wires twisted together Used for telephone and network connections (LANs) – Coaxial Cable Thick center wire surrounded by insulation Used for computer networks and cable television delivery – Fiber-Optic Cable Utilizes hundreds of thin transparent clear glass or plastic fibers over which lasers transmit data as light Used for high-speed communications Transmission media (Wired Networking Media ) Network Topologies Ring Bus Star Mash The Ring Topology: Computers are connected together to form a ring shape so that none of them is more important than any of the others. Advantages: They are cheap to expand. The data flows around the network in one direction so it is fast. There is no reliance on a central computer. Disadvantages: If there are a lot of users on the network, it could slow down as all the data is sent along a single line. If one computer in the ring stops working, the whole network stops. The Bus (or line) Topology Computers are connected like bus stops on a main road. None of them is more important than any of the others. Advantages: It is cheap as it uses the least amount of cable. More computers can be added without disruption. Disadvantages: With a lot of users, the network will be slow as data has to travel through the same central cable. Failure of the central cable will stop the network from working. The Star Network Computers are connected like a star to a central computer such as a mainframe. This is also called the “host” computer. Advantages: If a cable fails, it will only affect one workstation. More computers can be added without disruption. Disadvantages: It is more expensive as it uses the most cabling. Failure of the central computer will stop the network from working.