Network topology describes the arrangement of a network. The topology sums up all nodes, intersecting points & network connections of the network. The genuine geometric distribution of the cables, nodes & workstations are described with the help of physical network topology. Star topology is one popular & extensively used network topology. The article discusses about star topology in brief.
Star Topology Definition
The topology where branching nodes are connected with one central device is termed as star topology. A switch or hub acts as the central networking device. The central switch or hub is considered as the server & the outlying devices on the nodes acts like clients. The client server network exists between the central & peripheral devices.
The central switch or hub generates all traffic. The central device controls all the peripheral networks & devices. The central switch or hub is usually a fast device. The peripheral computers communicate through the central device.
Star topology diagram
Figure: Star topology
The above diagram illustrates a basic star topology. The center device can be a switch or hub/ router and peripheral computers are connected with it through connecting cables.
Characteristics of Star Network Topology
Some characteristics features of the topology are mentioned below
- All cables present in the network are directed towards the central node
- This topology gives outstanding scalability
- Establishes point to point network connection.
- On failure of a single cable, only the computer connected with the cable gets disconnected from the total network.
- To modify the network, a new computer is added to the central connection point of the hub. In similar way, to remove a device connection needs to be disconnected from the central connection point.
Star topology examples
Ethernet is a good example of star topology. The Ethernet network is modeled following the star topology. Star topology uses Ethernet Star 802.3 [10Base-T or 10Base-Tx] protocol in data transmission.
Tree Topology
Bus Topology
Star Topology
Ring Topology
Mechanism of star topology
The central switch in this topology follows a Content Addressable Memory[CAM] table. The memory inside the switch preserves the hardware addresses of all connected computers. The sender computer sends message to the switch. The switch checks the destination address from the memory & relays the message towards the destination computer.
There is no memory in the hub. So when the hub is the central device, during transmission of a message the hub announces the destination address & asks to the leaf nodes that has the address. This is termed as Address Resolution Protocol [ARP]. Hub finds the destination address through the ARP & drops the message at the destination address.
Advantages of Star Network Topology
The reason behind such popularity of this topology is its wide range of advantages. Some advantages are
- Sets up a central management for the network activities
- Adding a new computer to the network is quite easy. Only the central device needs to be updated on adding a new node.
- Failing of one peripheral computer doesnt interrupt the function of other peripheral computers.
- A very secure topology due to isolation of individual computers.
- Trouble shooting of this network is comparatively easy.
Disadvantages of Star Topology
Apart from goodness, star topology has downsides too. Some of its disadvantages are
- The central switch/hub will choose how many node the network would handle. In fact, performance of this central device demonstrates the performance of the branch network.
- Direct communication between two computers at periphery is not allowed. All communications are routed through the central hub or switch.
- At the central server, the network is prone to bottleneck / single point failure. The total network shuts down when the central hub / switch fails. The peripheral computers then get disconnected from the central one.
Establishment & maintenance of this topology is expensive due to the presence of switch or hub as the central device. In fact, expense also increase due to the increase in number of cable.
Like other network topology star topology has limitation too. Cable length, available ports on the network are some considerable limitation of the topology. In consideration of such physical problem, the star topology extends to multiple stars & ends up having only one central switch or hub in the middle. The central device can be termed as backbone of the total network in network terminology. In such design, the message generated for one system travels to its stars centre then into the backbone [core hub/switch]. The backbone transmits the message to the destination stars central hub & the central one transmits it to the ultimate destination computer.
Figure: Star topology with backbone.
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Where Star Topology is used
Star topology is thoroughly used in Local Area Network [LAN]. Almost all the network installation like small home & offices prefer to use some sort of star topology. In a home network, the users wirelessly connect their cell phone, laptop, tablet, smart TV etc to the router so that they can access the internet.
Bank is an excellent example of star topology. All branches of the bank should configure star topology. The purpose of such configuration is lock down of one branch will not affect the transaction of other branches. In fact to attack on the data of one branch, the intruder needs to work on the central hub first.
The topology works well on smaller networks. Number of cable is high in this topology. Twisted pair cable, optical fiber, RJ-45 & coaxial cable are genuinely used in cabling of the network. Each single computer at the leaf node uses separate twisted pair to connect to the hub or switch. The type of network card chooses the cable connection i.e. coaxial cable or an RJ-45 network cable to join the computers. On using a RJ-45 connector, joining up to 1024 nodes are possible.
Star Network Topology works best in a smaller network. It preserves data on the emergency of network failure. The security issues of switch or hub should be handled with much care & attention. Star topology is really a very comfortable topology to design the network.