What is topology? Explain start and ring topology and mention their merits and demerits.

Subject Introduction to Computer System
NU Year Set: 5.(c) Marks: 1+5=6 Year: 2009

Network topology is the interconnected pattern of network elements. A network topology may be physical, mapping hardware configuration, or logical, mapping the path that the data must take in order to travel around the network.

There are many identified topologies but they are not strict, which means that any of them can be combined. However, each topology has a different standard and may use different hardware methods so they are not interchangeable.


Star Topology

 In Star topology, all the components of network are connected to the central device called “hub” which may be a hub, a router or a switch. Unlike Bus topology (discussed earlier), where nodes were connected to central cable, here all the workstations are connected to central device with a point-to-point connection. So it can be said that every computer is indirectly connected to every other node by the help of “hub”.

Merits of Star Topology:

1)  As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.
2)  Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily.
3)  Centralized management. It helps in monitoring the network.
4)  Failure of one node or link doesn’t affect the rest of network. At the same time its easy to detect the failure and troubleshoot it.

Dismerit of Star Topology

1)  Too much dependency on central device has its own drawbacks. If it fails whole network goes down.
2)  The use of hub, a router or a switch as central device increases the overall cost of the network.
3)   Performance and as well number of nodes which can be added in such topology is depended on capacity of central device.


Ring Topology:

In Ring Topology, all the nodes are connected to each-other in such a way that they make a closed loop. Each workstation is connected to two other components on either side, and it communicates with these two adjacent neighbors. Data travels around the network, in one direction. Sending and receiving of data takes place by the help of TOKEN.


Merit of Ring Topology
1)   This type of network topology is very organized. Each node gets to send the data when it receives an   empty token. This helps to reduces chances of collision. Also in ring topology all the traffic flows in only one  direction at very high speed.
2)   Even when the load on the network increases, its performance is better than that of Bus topology.
3)   There is no need for network server to control the connectivity between workstations.
4)   Additional components do not affect the performance of network.
5)   Each computer has equal access to resources.

Dismerits of Ring Topology

1)   Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.
2)   If one workstation or port goes down, the entire network gets affected.
3)   Network is highly dependent on the wire which connects different components. 
4)   MAU’s and network cards are expensive as compared to Ethernet cards and hubs. 

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