NAVODAYA VIDYALAYA SAMITI, NOIDA�

E-Content for Class XII (Informatics Practices)�Topic: Network Topologies

�BY

Jitendra Kumar, PGT IT

JNV, Medak

Learning Objectives

• Learning about different physical or logical arrangement of a network
• Advantages of different topologies
• Disadvantages of topologies over one another

Definition

Network topology is the way a network is arranged, including the physical or logical description of how links and nodes are set up to relate to each other. There are numerous ways a network can be arranged, all with different pros and cons, and some are more useful in certain circumstances than others.

Bus Topology

A bus topology is a network setup where each computer and network device is connected to a single cable or backbone.

There is a device called tap that connects the drop line to the main cable.

Advantages

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• It is best-suited for small networks.
• It is easy to set up, handle, and implement.
• It costs very less.

Disadvantages

• It is not easy to isolate faults in the network nodes.
• It is suitable for networks with low traffic. High traffic increases load on the bus, and the network efficiency drops.
• The cable length is limited. This limits the number of network nodes that can be connected.
• This network topology can perform well only for a limited number of nodes. When the number of devices connected to the bus increases, the efficiency decreases.
• It is heavily dependent on the central bus. A fault in the bus leads to network failure.
• Each device on the network "sees" all the data being transmitted, thus posing a security risk.

Star Topology

A star topology is a topology for a Local Area Network (LAN) in which all nodes are individually connected to a central connection point, like a hub or a switch.

Hub/Switch

A star takes more cable than e.g. a bus, but the benefit is that if a cable fails, only one node will be brought down.

Advantages

• As the analysis of traffic is easy, the topology poses lesser security risk.
• Adding or removing network nodes is easy, and can be done without affecting the entire network.
• Due to its centralized nature, the topology offers simplicity of operation.
• It also achieves isolation of each device in the network.
• Due to the centralized nature, it is easy to detect faults in the network devices.
• Data packets do not have to pass through many nodes, like in the case of a ring network. Thus, with the use of a high-capacity central hub, traffic load can be handled at fairly decent speeds.

Disadvantages

• The number of nodes that can be added, depends on the capacity of the central device.
• Network operation depends on the functioning of the central device. Hence,the failure of central device leads to failure of the entire network.
• The setup cost is high.

Ring Topology

A ring topology is a network configuration in which device connections create a circular data path. Each networked device is connected to two others, like points on a circle. Together, devices in a ring topology are referred to as a ring network.

Unidirectional ring network:allow packets to travel only in one direction, called a unidirectional ring network.

Bidirectional ring network: permits data to move in either direction, called bidirectional ring network.

Advantages

• In this topology, each node has the opportunity to transmit data. Thus, it is a very organized network topology.
• The adding or removing of network nodes is easy, as the process requires changing only two connections.
• The traffic is unidirectional and the data transmission is high-speed.
• The data being transmitted between two nodes passes through all the intermediate nodes. A central server is not required for the management of this topology.
• In comparison to a bus, a ring is better at handling load.
• The configuration makes it easy to identify faults in network nodes.
• It is less costly than a star topology.

Disadvantages

• Data sent from one node to another has to pass through all the intermediate nodes. This makes the transmission slower in comparison to that in a star topology. The transmission speed drops with an increase in the number of nodes.
• The failure of a single node in the network can cause the entire network to fail.
• The movement or changes made to network nodes affect the entire network's performance.
• There is heavy dependency on the wire connecting the network nodes in the ring

Mesh Topology

In mesh topology each device is connected to every other device on the network through a dedicated point-to-point link.

Lets say we have n devices in the network then each device must be connected with (n-1) devices of the network. Number of links in a mesh topology of n devices would be n(n-1)/2.

Advantages

• It can handle heavy traffic, as there are dedicated paths between any two network nodes.
• The arrangement of the network nodes is such that it is possible to transmit data from one node to many other nodes at the same time.
• The failure of a single node does not cause the entire network to fail as there are alternate paths for data transmission.
• Point-to-point contact between every pair of nodes, makes it easy to identify faults.

Disadvantages

• A lot of cabling is required. Thus, the costs incurred in setup and maintenance are high.
• The arrangement wherein every network node is connected to every other node of the network, many connections serve no major purpose. This leads to redundancy of many network connections.
• Owing to its complexity, the administration of a mesh network is difficult.

Tree Topology

Tree topologies have a root node, and all other nodes are connected which form a hierarchy. So it is also known as hierarchical topology.

Tree topology based networks are not suitable for small networks because of the requirement for additional devices and cables.

Advantages

• Fault identification is easy.
• The advantages of centralization that are achieved in a star topology are inherited by the individual star segments in a tree network.
• The tree topology is useful in cases where a star or bus cannot be implemented individually. It is most-suited in networking multiple departments of a university or corporation, where each unit (star segment) functions separately, and is also connected with the main node (root node).
• Each star segment gets a dedicated link from the central bus. Thus, failing of one segment does not affect the rest of the network.
• The network can be expanded by the addition of secondary nodes. Thus, scalability is achieved.

Disadvantages

• Owing to its size and complexity, maintenance is not easy and costs are high. Also, configuration is difficult in comparison to that in other topologies.
• As multiple segments are connected to a central bus, the network depends heavily on the bus. Its failure affects the entire network.
• Though it is scalable, the number of nodes that can be added depends on the capacity of the central bus and on the cable type.

Hybrid Topology

A hybrid topology combines two or more topologies and is meant to reap their advantages. Obviously, the advantages and disadvantages of a hybrid topology are a combination of the merits and demerits of the topologies used to structure it.