Basic Structure of Star Topology

Basic Structure of Star Topology

Each device is connected point-to-point to a central device which is either a hub or switch Hub manages and controls all the functions of the network. It also acts as a multi port repeater for the data flow. Hub is used to connect segments of LAN and contains multiple ports. Hubs can be passive or active. Passive hubs are used as a connection point which routes all the traffic towards the devices. It does not amplify or regenerate the signals. They simply take all of the packets they receive on a single port and broadcast them across all ports. Active hub contains electronic circuits that regenerate and retransmit the information. Active have all of the features of passive hubs, with the added feature of actually watching the data before being sent out. Active hubs take a larger role in Ethernet communications by implementing a technology called store and forward where the hubs actually look at the data they are transmitting before sending it. Also it repairs certain "damaged" packets. The basic structure of star topology is shown in Figure

Data is passed through the hub before reaching the destination. For example, device A wants to transmit data to device B. Device A first sends data to the hub. If the hub is passive, it broadcasts the data to all the devices in star network, except device A. Each device has to read the address specified in data to determine if the data is intended for that device. If the address is different, then that data is discarded. If the address matches then the data is received. If the hub is active, it regenerates the data before it is broadcasted.

A physical star network that uses a central hub operates as per logical bus topology. The hub broadcasts data to all segments and thus uses a bus topology for transmission of data. On the other hand, a physical star network using a switch functions as per logical star topology. This is because the switch has a capacity to read the address mentioned in data and to direct the data to the intended receiver.

Advantages and Disadvantages of Star Topology

A star network requires more cable wires, but in any cable will affect only that particular device and not the entire LAN. Star network is easy to install and configure. Advantages of star topology are

• Easy to install
• configure and manage
• Easy to detect faulty device
• Easier to expand
• Connecting or removing device does not affect the network
• Switch provides a centralized management


Disadvantages of star topology are:
• Increased devices causes traffic which makes the network slow
• Requires more cable length than a linear topology
• Hub failure leads to network failure
• More expensive
Basic Structure of Bus Topology

Introduction of Topology