Introduction to Star Topology
Star Topology plays a pivotal role in connecting various devices to share information in real time and to execute transactions online. The choice of the topology depends on the physical environment of the organization, end-user requirements, and the level of IT investments. It is needless to say that right network topology will have to be selected before installation and it will be too costly to change it later.
Any computer networks can be broadly classified under 3 major categories, namely:
- Ring Topology
- Star Topology
- Bus Topology
Out of these three topologies, Star network is used extensively in most Industries, Institutions and Home applications as well.
In this article let us analyze the unique features, pros, and cons of Star Topology.
What is Star Topology?
In this Topology, a set of computer devices are connected individually to central network equipment called Hub or Switch. These Hub/switches are in turn connected to the Datacenter and other service provider networks either directly or through other switches/routers. This physical shape of the network does not look like a star but all the nodes are connected to and controlled centrally by Hub/Switch and hence the name.
This is one of the most traditional topologies, used mostly in Local area networks and it was developed over telecommunication technology where the calls are routed through switching stations centrally and the switch manages the calls.
How does it work?
If a computer in an office wants to send a communication to another computer in a remote office, it sends the data along with the recipient address to the Hub/Switch it is connected to. The Hub/Switch transfer the data to the end destination through routers and other network resources and network management software keeps track of the data delivery.
The role of Switches and Hub in data communication is explained below.
Whenever Hub gets a data packet to be transferred to a node, it just sends the packet to all the nodes connected to the Hub and the recipient node only consumes the data. This broadcasting model increases the load in the network as the data is transmitted to all nodes and it results in a collision.
Bandwidth is limited in the nodes served by Hub. There are no management modules and other intelligence functionalities in Hub and the network traffic is heavy due to the broadcasting model it adopts.
Switches get a request from its node for the transfer of data to another node in the network. This request contains a data frame along with the recipient address. The data is transferred through routers/other network resources to that switch where the recipient node is connected.
Each switch maintains a Content Addressable Memory (CAM) table containing the MAC address of the nodes connected to it and the port numbers. Whenever the data frame reaches a switch, the recipient’s address is matched with the Mac addresses in the CAM table and if the match is found the data is transmitted to that node using the port number. Otherwise, the data is broadcasted once to all its node and the recipient node consumes the data and its MAC address is updated in the table for further use.
There is no limit on the bandwidth at its node and it can reach 1Gbps level. Since the data is sent only to the intended node, the load in the network is low when compared to Hub and there is no possibility of collision.
Co-axial Cables, Twisted Pair, and Optical fiber are the common media in this network. Shielded or unshielded twist pair copper cabling is used in the star network. One side of this cable is connected to the network card of the devices and the other end is connected to a port in Hub/ Switch.
Ethernet is the protocol used in the Star network. It uses Carrier sense multiplier access (CSMA) and Carrier detection (CD) access methods. In order to avoid a collision, traffic in the line is checked before sending any data pocket and in case the link is busy the node will wait and resend the data pocket.
Physical layer (L1) protocol of Open System interconnection (OSI) model is used in Hubs in local communication and Data link layer (L2) and Network layer (L3) protocols are used in switches to communicate across LAN and WAN.
Why do we use Star Topology?
Star topologies are preferred over others due to its following unique features.
Hub/Switches acts as a central monitoring agency on the performance of the individual nodes and glitches in the performance can be easily tracked and rectified. If the Switch/Hub are the bottlenecks, the capacity of the Hub/switch can be enhanced.
New nodes can be easily added in the network without affecting the network performance. Centralized control of the network helps easy manageability and quick scalability of the star network.
Each node is connected by a separate link to central Hub in this network and in case of any issues in any of the nodes in the network, the problematic node can be isolated and the rest of the network can function unaffected. This topology is simple to understand and troubleshoot and hence the downtime of these networks is significantly lower.
4. High-performance level
This topology avoids unwanted traffic in the network by sending the data pockets to the target node directly and hence performance of this network is superior to any other topologies. Data packets are delivered to the recipient in the shortest possible time, unlike the other networks.
Disadvantages of Star Topology
The disadvantages of the following are given below:
1. Higher Cost
This network is expensive when compared to other topologies for two reasons: 1. It Consumes more cable length due to its nature of architecture, 2. Hub/Switch is a very costly network equipment.
2. Central Hub/Switch is everything
The whole network revolves around the functioning of central equipment and any failure in this will bring the network to halt and it is a single point of failure. The performance of the network solely depends on the ability of the central Hub to manage the existing communication load effectively and accommodate the addition of new nodes.
Star Topology is widely used in local area networks and it is also used in conjunction with bus topology as a hybrid network.
This is a guide to Star Topology. Here we discuss the introduction, Why we use Star topology? along with disadvantages. You can also go through our other related articles to learn more –