NETWORK TOPOLOGY


In networking, the term “topology” refers to the layout of connected devices on a network.

Network Topology refers to layout of a network and how different nodes in a network are connected to each other and how they communicate.

Topologies are either physical or logical

Network topologies are categorized into the following basic types:

§  Bus Topology

§  Star Topology

§  Ring Topology

§  Tree Topology

§  Mesh Topology

§  Hybrid Topology

Bus Topology:

Bus topology is a network type in where every computer and network device is connected to single cable.

Bus Topology is the simplest of network topologies.




Features:

§  It transmits data only in one direction.

§  Every device is connected to a single cable

§  The central cable is the backbone of the network and is known as Bus.

§  A device, who wants to communicate with another device on the network, sends a broadcast message onto the wire that all other devices see.

§  But only the actual receiver who can receive the message actually accepts and processes the message. Other devices can only see the messages but cannot process it.

§  Because all devices have its own IP addresses.

§  When the sender sends the message with receiver’s IP address. The message is broadcast to all the devices but the relevant device whose IP address matches can accept.

§  If IP address of machine does not match with the relevant receiver then machine discards the signal.

§  A terminator is added at ends of the central cable, to prevent bouncing of signals.

§  A barrel connector can be used to extend it.

Advantages:

§  It is cost effective.

§  It is easy to understand.

§  It is used in small networks.

§  Cable length required for this topology is the least compared to other networks.

§  Linear Bus network is mostly used in small networks.

§  This topology is good for LAN (Local Area Network).

Disadvantages:

§  If central cable fails whole network fails

§  If the number of devices connected to it increases then the efficiency of Bus network reduces.

§  Maintenance costs can get higher when the devices are increased.

§  Cable has a limited length

§  It is slower than the ring topology

§  Security is very low because broadcasting is available in this topology. Whole devices can see the information. So there is no privacy in this topology.

Star Topology:

In this type of topology all the computers are connected to a single hub which may be a hub, a router or a switch through a cable

This hub is the central node and all others nodes are connected to the central node.

Unlike Bus topology, where nodes were connected to central cable, here all the workstations are connected to central device with a point-to-point connection.

Therefore it can say that every computer is indirectly connected to every other node by the help of hub.

Features:

§  Every node has its own dedicated connection to the hub.

§  Hub acts as a repeater for data flow.

§  All the data on the star topology passes through the central device (hub) before reaching its destination.

§  It also manages and controls whole of the network.

Advantages:

§  As compared to Bus topology it gives far much better performance, signals do not need to get transmitted to all the workstations.

§  Performance of the network is dependent on the capacity of central hub.

§  In star topology new nodes can be added easily without affecting rest of the network. Similarly nodes can also be removed easily.

§  Failure of one node or link does not affect the rest of network.

§  Easy to troubleshoot.

Disadvantages:

§  Cost of installation is high.

§  If Hub fails whole network goes down.

§  Expensive to use.

§  Performance is based on the hub that is it depends on its capacity

Ring Topology:

It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first.

This topology has exactly two neighbours for each device.

It communicates with these two adjacent neighbours.

Sending and receiving of data takes place by the help of Token.

Token Passing

§  Token contains a piece of information which along with data is sent by the source computer.

§  This token then passes to next node, which checks this data is for this computer or not.

§  If yes then the computer accepts it for processing otherwise passes token along with data to the next node.

§  This process continues until the signal reaches its right destination.

Features:

§  A number of repeaters are used and the transmission is unidirectional.

§  The ring topology was most commonly used in schools, offices, and smaller buildings where networks are smaller.

Advantages:

§  Cheap to install and expand.

§  Even when the load on the network increases, its performance is better than that of Bus topology.

§  It reduces the chances of collision due to token passing.

§  There is no need for network server to control the connectivity between workstations.

§  Each computer has equal access to resources.

§  Additional nodes do not affect the performance of network.

Disadvantages:

§  Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.

§  If one computer fails, the entire network can fail.

§  Performance is based on the hub that is it depends on its capacity

§  Adding or deleting the computers disturbs the network activity.

§  Troubleshooting is difficult in ring topology.

Tree Topology:

A tree topology is a combination of bus topology and star topology.

In Tree Topology, the number of Star networks is connected using Bus.

This main cable seems like a main stem of a tree, and other star networks as the branches.

It is also called Expanded Star Topology.

Features:

§  This Topology is ideal if workstations are located in groups.

§  This Topology is used in Wide Area Network.

Advantages:

§  This Topology is the extension of bus and star topologies.

§  The expansion of nodes is possible and easy.

§  This Topology can easily manage and maintained.

§  If error occurs then the error detection is easy to be done.

Disadvantages:

§  Heavily cabled.

§  This Topology is costly.

§  If more nodes are added maintenance is difficult.

§  Central hub fails, network fails.

Mesh Topology:

In a mesh network topology, each of the network node, computer and other devices, are interconnected with one another.

In a mesh topology, if any cable or node fails, there are many other ways for two nodes to communicate.

There are two types of Mesh Topologies:

§  Full Mesh Topology

§  Partial Mesh Topology

Full Mesh Topology

§  Full Mesh topology occurs when every node has a circuit connecting it to every other node in a network.

§  Full Mesh is very expensive to implement.

§  Full Mesh is usually reserved for backbone networks.

Partial Mesh Topology

§  With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network.

§  Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone.

§  It is less expensive to implement.

Features:

§  Fully connected.

§  Robust.

§  Not flexible.

Advantages:

§  Each connection can carry its own data load.

§  This topology provides security and privacy.

§  It is robust.

§  Expansion and modification in topology can be done without interrupting other nodes.

Disadvantages:

§  Installation and configuration is difficult.

§  There are high chances of redundancy in many of the network connections.

§  The cost of this topology is much higher than other network topologies.

§  Central hub fails, network fails.

Hybrid Topology:

Network Topology is a connection of various links and nodes, communicating with each other for transfer of data.

Network topologies like Star, Bus, Mesh, Tree, Ring Topology have their own advantages and disadvantages.

Hybrid Topology uses a combination of any two or more topologies.

A hybrid topology is produced when two different basic network topologies are connected.

Two common Examples for Hybrid Topology are: Star Ring Topology and Star Bus Topology.

A Star Ring Topology consists of two or more star topologies connected using a centralized hub.

A Star Bus Topology consists of two or more star topologies connected using a bus. 

Features:

§  It is a combination of two or more topologies

§  It inherits the advantages and disadvantages of the topologies included.

Advantages:

§  Reliable as Error detecting.

§  Trouble shooting is easy.

§  Its easy to increase the size of network by adding new components, without disturbing existing architecture.

§  Hybrid Topology can be designed according to the requirements. So, it is Flexible in nature.

§  Hybrid Topology is the combination of two or more topologies, so we can design it in such a way that strengths of particular topologies are maximized while their weaknesses are minimized.

Disadvantages:

§  One of the biggest drawbacks of this topology is its design. It is very tough task to install and configure of topology for the designers.

§  This Topology is costlier than other topologies.

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