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Note for Computer Network - CN By Sangu Mallikharjuna reddy

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UNIT-1 Introduction: Network Topologies WAN, LAN , MAN ,Reference model- The OSI Reference model –the TCP/IP Reference Model-A Comparison of the OSI and TCP/IP Reference Model. Computer network: A computer network is a system in which multiple computers are connected to each other to share information and resources. The physical connection between networked computing device is established using either cable media or wireless media. The best-known computer network is the Internet. Components of Data Communication 1. Message: It is the information to be delivered. 2. Sender: Sender is the person who is sending the message. 3. Receiver: Receiver is the person to whom the message is being sent to. 4. Medium: It is the medium through which the message is sent. For example: A Modem. 5. Protocol: These are some set of rules which govern data communication. Network topologies: • A Network Topology is the arrangement with which computer systems or network devices are connected to each other. • Topologies may define both physical and logical aspect of the network. Both logical and physical topologies could be same or different in a same network.

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Point-to-Point • Point-to-point networks contains exactly two hosts such as computer, switches or routers, servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa. • • If the hosts are connected point-to-point logically, then may have multiple intermediate devices. • But the end hosts are unaware of underlying network and see each other as if they are connected directly. BUS Topology • Bus topology is a network type in which every computer and network device is connected to single cable. • When it has exactly two endpoints, then it is called Linear Bus topology. • Features of Bus Topology 1. It transmits data only in one direction. 2. Every device is connected to a single cable Advantages of Bus Topology 1. It is cost effective. 2. Cable required is least compared to other network topology. 3. Used in small networks.

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4. It is easy to understand. 5. Easy to expand joining two cables together. Disadvantages of Bus Topology 1. Cables fails then whole network fails. 2. If network traffic is heavy or nodes are more the performance of the network decreases. 3. Cable has a limited length. 4. It is slower than the ring topology. RING Topology • It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. • Exactly two neighbours for each device. • Features of Ring Topology • The transmission is unidirectional, but it can be made bidirectional by having 2 connections between each Network Node, it is called Dual Ring Topology. Advantages of Ring Topology 1. Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data. 2. Cheap to install and expand

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Disadvantages of Ring Topology 1. Troubleshooting is difficult in ring topology. 2. Adding or deleting the computers disturbs the network activity. 3. Failure of one computer disturbs the whole network. STAR Topology • In this type of topology all the computers are connected to a single hub through a cable. • This hub is the central node and all others nodes are connected to the central node. • Features of Star Topology 1. Every node has its own dedicated connection to the hub. 2. Hub acts as a repeater for data flow. 3. Can be used with twisted pair, Optical Fibre or coaxial cable. Advantages of Star Topology 1. Fast performance with few nodes and low network traffic. 2. Hub can be upgraded easily. 3. Easy to troubleshoot. 4. Easy to setup and modify. 5. Only that node is affected which has failed, rest of the nodes can work smoothly.

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