Network Topology In order to build a simple network, the first and foremost requirement is to define the ‘structure of the network’. It must satisfy the two questions • How are the computers going to be connected in the network? • How will the computers communicate with each other? In technical terms, the structure of the network is called as the network topology. Network Topology has two parts namely physical and logical topology. Physical Topology tells us how to connect the computers whereas Logical Topology tells us how the computers can communicate in the network. PHYSICAL TOPOLOGY: To begin with, one can think of physical topology as a network's "shape" and so let’s take a look at the commonly used “shapes” for designing a network... BUS: • A bus network has a common cable which connects all the devices in the network • This common cable functions as the backbone of the network and all the devices share this cable. • This cable is the lifeline of communication between the devices • Now, in a bus network let us assume that computer A wants to communicate with one another computer B. In such a case, the computer A sends a message to B which all the computers in the network can ‘see’ but only commuter B can respond. RING: • As the name implies, the computers are connected to form a ‘ring’. • In this network, one computer has exactly two neighbors for communication purposes. • All messages in this network travel through this ring in the same direction • But a failure at one terminal will cause the whole network to breakdown. This is the major disadvantage of a ring network. STAR: • Here all the computers are connected to a central connection point called as a hub. • While comparing with a bus network, the star network uses more cable but it is more reliable as the failure in any of the star network cable will result in the failure of only one terminal and not the entire network. • Many home networks use star topology. More complex networks can be built as hybrids of two or more of the above basic topologies. TREE: • Tree topologies are formed by integrating many star topologies. • This is done by attaching the hub of each star network to a ‘tree’ bus. The tree bus acts as the common bus for the several hubs connected. • Now each hub functions as the "root" to its star network. • This bus/star hybrid approach helps us to expand the network in the future easily. MESH: • Each computer is connected to every other computer in the network. • So, the messages sent on a mesh network can take any of several possible paths from one terminal to the other • This network provides the best possible protection • One excellent example to cite is the use of mesh networks in the networked control systems of a nuclear power plant. LOGICAL TOPOLOGY: The two types are • Broadcast • Token passing Broadcast topology simply means that each computer sends its data to all other computers. One good example is the Ethernet Token passing controls network access by passing an electronic token to a computer. When a computer receives the token, it can send data. If the computer has no data to send, it passes the token to the next computer and the process repeats itself. Additional Resources on the Internet :
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