Network Topology

A network topology is the way in which devices are connected in a network both physically and logically. By understanding the network topology one can determine how the network functions i.e.e whether the network has a central controller device, how the signals are travelling between the connected device and if the network is flexible to accommodate new devices in the network.

These are two ways of defining network topology: the physical topology and the logical (or signal) topology.

Physical Topology

The devices in a network can be connected in following ways:

1. Mesh Topology

– A topology where each device has a direct connection to every other device in a network is called the mesh topology.

– The mesh topology can be either full mesh or partial mesh

– In full mesh topology, each device is a connected directly to other device in the network.

– In partial mesh topology, some of the devices are connected to all the others, and some are connected only to those other devices with which they communicate the most.

network topology
Mesh Designs Partial-Mesh Topology Full-Mesh Topology

Partial mesh and full mesh

In mesh topology even if one device fails there will always be an alternative route present (as every device has a connection to almost all the other devices) so the transmission is not affected.

Mesh topology is very expensive to implement.

Adding a new device in mesh topology is time consuming.

2. Star Topology

– In star topology every device is connected to central controller called hub or switch. The hub is common point of contact for all the devices.
– All the data passes through hub before reaching the destination.
– The hub is a signal repeater i.e it repeats or retransmits a signal at a higher power so that the signal can cover longer distances.

network topology

Star topology

– An advantage of star topology is that, new devices can b easily added or removed from the network.

– The primary disadvantage is that the hub represents a single point of failure. If the hub stops working the entire network stops working.

– If the topology has a switch instead of hub then the functionality will be different. With a hub the traffic is broadcasted to all the devices, the intented recipient keeps the data, and others discard. With a switch only the intented recipient gets the data.

3. Bus topology

– In a bus topology, every device is connected to a common cable called the bus. The communication takes place via the bus.
– Since the bus topology consists of only one wire (bus), it is expensive to implement when compared to other topologies.

network topology diagram

Bus topology

– Cable length and number of stations are limited.

– A terminator is added at end of the cable, to prevent signal travelling back from cable. Basically the role of terminators is to dump the signals.

– Since only one cable is utilized (Shared), it can be the single point of failure.

4. Ring Topology

– In a ring topology th devices are connected to each other in circular form.

– Every device can communicate with its adjacent device.

– The data travels in one direction in the topology.

Network topology

Ring topology

– A token is continuosly travelling in the network stopping at each device, A device can send data when it receives an empty token.
– The token travels in the network till destination machine is found, which takes the data off the token.

– In a ring topology there is no central controller.

– The disadvantage of the topology is that if one device stops working, the entire network stops working.

5. Hybrid Topology

– Hybrid networks use a combination of any two or more of the above mentioned topologies.

– The resulting topologies shows the characteristics of both.

– The combination of topologies is chosen based on the requirement of the organization.

Example:
– A star bus network consists of two or more star topologies connected using a common wire as in bus topology.

– Extended star is a widely used in hybrid topology.

network topology

Hybrid Topology

Logical Topology

Unlike the physical topology, logical topology describes how the data flows within the physical topology and how the devices communicate. Generally there are two ways:



Shared Media

– In shared media topology, all the devices have the ability to access the physical media in the topology whenever they need it.

– The man disadvantage of this topology is collisions. If two systems send informationon the wire at the same time, the packets collide and are discarded.

– Shared media is used in bus and star topology.

Read: What is networking

Token Based

In a token basednetwork, there is a token that travels around the network.

When a system needs to send data to device, it grabs the token, attach data to italong with the destination address, and release the token on the network.

When the token arrives at destination device it copies the information off the token and the token continuesto travel until it gets back to the sender.

When the sender receives the token back, it takes the token off the network and sends out a new empty token to be used by the next machine.

The ring topology uses token based approach.




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