What are the various types of network topology? What are the implications of having different topology?


36.What are the various types of network topology? What are the implications of having different topology?

Network topologies:

Network topology defined as the logical connection of various computers in the network. The six basic network topologies are: bus, ring, star, tree, mesh and hybrid.

1. Bus Topology:

In bus topology all the computers are connected to a long cable called a bus. A node that wants to send data puts the data on the bus which carries it to the destination node. In this topology any computer can data over the bus at any time. Since, the bus is shared among all the computers. When two or more computers to send data at the same time, an arbitration mechanism is needed to prevent simultaneous access to the bus.

Bus Topology
Bus Topology

A bus topology is easy to install but is not flexible i.e., it is difficult to add a new node to bus. In addition to this the bus stops functioning even if a portion of the bus breaks down. It is also very difficult to isolate fault.

2. Ring Topology:

In ring topology, the computers are connected in the form of a ring. Each node has exactly two adjacent neighbors. To send data to a distant node on a ring it passes through many intermediate nodes to reach to its ultimate destination.

Ring Topology
Ring Topology

A ring topology is as to install and reconfigure. In this topology, fault isolation is easy because a signal that circulates all the time in a ring helps in identifying a faulty node.

The data transmission takes place in only one direction. When a node fails in ring, it breaks down the whole ring. To overcome this drawback some ring topologies use dual rings. The topology is not useful to connect large number of computers.

3. Star Topology:

In star topology all the nodes are connected to a central node called a hub. A node that wants to send some six data to some other node on the network, send data to a hub which in turn sends it the destination node. A hub plays a major role in such networks.

Star Topology
Star Topology

Star topology is easy to install and reconfigure. If a link fails then it separates the node
connected to link from the network and the network continues to function. However, if the hub goes down, the entire network collapses.

4. Tree Topology:

Tree topology is a hierarchy of various hubs. The entire nodes are connected to one hub or the other. There is a central hub to which only a few nodes are connected directly.

Tree topology
Tree topology

The central hub, also called active hub, looks at the incoming bits and regenerates them so that they can traverse over longer distances. The secondary hubs in tree topology may be active hubs or passive hubs. The failure of a transmission line separates a node from the network.

5. Mesh Topology:

A mesh topology is also called complete topology. In this topology, each node is connected directly to every oilier node in the network. That is if there are n nodes then there would be n(n — 1)/2 physical links in the network.

Tree topology
Tree topology

As there are dedicated links, the topology does not have congestion problems. Further it does not need a special Media Access Control (MAC) protocol to prevent simultaneous access to the transmission media since links are dedicated, not shared. The topology also provides data security.

The network can continue to function even in the failure of one of the links. Fault identification is also easy.

The main disadvantage of mesh topology is the complexity of the network and the cost associated with the cable length. The mesh topology is not useful for medium to large networks.

6. Hybrid Topology:

Hybrid topology is formed by connecting two or more topologies together. For example, hybrid topology can be created by using the bus, star and ring topologies, as shown in figure 22.6.

Hybrid Topology
Hybrid Topology

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