Users or nodes can be interconnected in different ways to form a network. However, there are some popular configurations which are used again and again. These network configurations or arrangements are known as 'Network Topologies'. A network's topology refers not only to the physical layout of its computers, cables and other resources, but also to how these components communicate with each other.
Types of network topologies : 1. Star, 2. Bus, 3. Ring, 4.Hybrid.
• Star Topology : In this type the computers are connected by cable segments to a central controller which is called hub. When the signal is sent from a computer, it is received by the hub and retransmitted down every other cable segment to all other computers. There are two types of hubs : active and passive. Active hubs regenerate the signals as they receive them and send them along. In a passive hubs, the signal is passed through the hub without any amplification or regeneration. It is simply a central connection point. A mainframe or minicomputer servers as the central controller for many video terminals with keyboard or PCs. Private branch exchange (PBX) is also a type of star network. PBX is a small telephone system within an office or building which can be used for voice applications or digital data.
• Bus Topology : In this type all nodes are attached to a common cable, called as bus. This type is widely used. Communication is bidirectional on the bus by allowing anyone station to communicate with any other station. The sending station broadcasts its message on the hub which all stations can receive. In the bus topology, two stations desiring to communicate, do so directly without interferences from any other stations. The common cable is called as trunk and it acts as backbone of the network.
• Ring Topology : In this type a computer is connected directly to the next computer in line, forming a circle of cable. When a computer receives a signal, it either acts on it, or regenerates it and passes it along signals travel in only one direction. There is no central controller stations. In token passing method of sending data in ring, the message is passed from one station to the next until the destination is reached. All stations can send and receive the message. They have the ability to recognize their assigned code or address and capability of retransmitting a received signal. In this type, if one station fails, the whole system fails.
• Hybrid Topology : To maximize the network's efficiency and utilize the benefits of different topologies, hybrid topologies are used.
Types of hybrid topologies are : 1. Tree Topology, 2. Star-Ring Topology, 3. Star-Bus Topology
1. Tree Topology : This is a variation of the bus system. The bus is extended into several branches so that more stations can be interconnected. A controller node is present, in some large tree systems. It can be easily extended and faults can be isolated.
2. Star-Ring Topology : In this type a network is wired as a star, but the network traffic is handled as in a ring. A single computer failure can be allowed without affecting network traffic. The inner ring can be extended by connecting several outer hubs to the inner hub.
3. Star-Bus Topology : This is a combination of the star and the bus. Many star hubs can be connected along a bus backbone (trunk). As star configuration is used, a single computer's failure-effect on the network is minimized. If a hub fails, the computers attached to it will not be able to communicate, but other hub-computer connections remain in good condition and communication continues.