Network topology is the structural layout of a network, which consists of various elements of a computer network. Network topology is two types physical and logical. Physical topology is the physical design of the network including various device,cable installation and their location. Logical topology show how data is actually transferred in a network. Topology show only the virtual shape or structure of a network. It doesnot actual physical design of the devices on the network.
Factors to be considered while selecting a network topology.
• Cost : For a network to be cost effective, one would try to minimize installation cost. This may be achieved by using well understood media and also, to a lesser extent, by minimizing the distances involved.
• Flexibility : Because the arrangement of furniture, internal walls etc. in office is often subject to change, the topology should allow for easy recognition of the network . This involves moving existing nodes and adding new ones.
• Reliability : Failure in a network can take two forms. Firstly, an individual node can malfunction. This is not nearly as serious as the second type of fault where the network itself fails to operate. The topology chosen for the network can help by allowing the location of the fault to be detected and to provide some means of isolating it.
There are different types of topologies.
In bus topology all nodes are connected to the central cable or called backbone cable.Each computer or server is connected to the single bus cable through some kind of connector. A terminator is required at each end of the bus cable to prevent the signal from bouncing back and forth on the bus cable. In this topology if any node goes faulty then all nodes may be stop work.
Advantages of bus topology
1:- It is easy to install.
2:- It is cheap when compare to other network.
3:- It is easy to use and maintaince.
4:- Required less cable.
Disadvantages of bus topology
1:- It can used only small network.
2:- It is difficult to find fault.
3:- If backbone cable became faulty then whole network stop working.
In ring topology all nodes are connected to one another in the shape of a closed loop,so that each node is connected directly to two other nodes, one on either side of it. Data is transmitted around the ring in one direction only;each node passing on the data to the next station till it reaches its destination.
Information travels around the ring from one node to the next. Each packet of data sent on the ring is prefixed by the address of the station to which it is being sent. When a packet of data arrives, the node checks to see if the packet address is the same as its own, if it is, it graps the data. If the packet does not belong to it, it sends the packet to the next node int the ring. Example is token ring.
Advantages of ring topology
1:- Easy to install and modify.
2:- Fault isolation is simplified.
3:- There is not loss of signal other than bus topology.
Disadvantages of ring topology
1:- It is difficult to adding or removing nodes in the network.
2:- If any fault is occured in the node then whole network goes down.
3:- Difficult to find fault.
4:- Expensive when compares to other topologies.
In start topology all nodes are connected to a central device it may be hub or switch. A star topology take more cable since Every node has its own dedicated connection to the central device.
Advantages of Star Topology
- Better performance with few nodes.
- Troubleshooting is easy.
- Easy to setup and modify.
Disadvantages of Star Topology
- Cost of installation is high. since take more cable compare to bus topology.
- If the central device fails then the whole network is stopped because all the nodes depend on the Central device.
- Performance is depends on capacity of central device.
Tree topology combine features of Star and Bus Topology. It has a central node(Hub/Switch) and all other nodes are connected with this central node to form a hierarchy. It is also called hierarchical topology. Star Topology ensures that if one node goes down, all the rest are operational because it is direct linking with central node. A cable TV network has such a topology, with the main feed cable getting divided into smaller branches, which ultimately reach homes.
Advantages of Tree Topology
- It is extension of bus and star topologies.
- It is easy to managed and maintained.
- We can easy expansion our network.
- Troubleshooting is vey easy.
Disadvantages of Tree Topology
- It required huge cable. that why it is costly
- If when more nodes added then its maintenance became difficult.
- If main link or node fail then whole network became stop.
In mesh topology each computer and network device is interconnected with one another, allowing for most transmissions to be distributed, even if one of the connections go down. The number of connections in this network can be calculated using the following formula (n is the number of computers in the network): n(n-1)/2. It is not widely used in computer network.
Types of Mesh Topology
- Partial Mesh Topology : In Partial Mesh topology some of the systems are connected in mesh topology but some devices are only connected to two or three devices.
- Full Mesh Topology : Every nodes or devices are connected to each other.
It is fully connected topology that why it very robustness and fault tolerance
Advantages of Mesh Topology
- Every device can transmit it own data simultaneously and it handle huge traffic.
- It is robust.
- Easy to fault tolerance.
Disadvantages of Mesh Topology
- Installation and configuration is very difficult.
- Cost of this topology is vey high as compared with other topology.
- Bulk wiring is required.
If two or more network topology combine to one topology then it's called Hybrid topology. In this topology good feature of one topology is combine with good feature of other topology. This combination of topologies is done according to the requirements of the organization.
For example if one department ring topology is used and in another department star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology).
Advantages of Hybrid Topology
- Reliable as Error detecting and trouble shooting is easy.
- Scalable it is easy to increase of network by adding more node without disturbing old network.
- Effective. Since it is combination of two topology with their strengths more used and while their weaknesses are neutralized.
Disadvantages of Hybrid Topology
- Complex in design.
- It is costly.
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