4.2 Network Topologies

Network Topologies: -

• A Network Topology is the arrangement with which computer systems or network devices are connected to each other.

• Topologies may define both physical and logical aspect of the network. Both logical and physical topologies could be same or different in a same network.

• The arrangement of a network which comprises of nodes and connecting lines via sender and receiver is referred as network topology.

• The major topologies of LAN are:

1) Point-to-Point: -

• Point-to-point networks contain exactly two hosts such as computer, switches or routers, servers connected back to back using a single piece of cable.

• Often, the receiving end of one host is connected to sending end of the other and vice-versa.

• If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly.

 

2) Bus Topology: -

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

• When it has exactly two endpoints, then it is called Linear Bus topology.

• It transmits the data from one end to another in single direction.

• No bi-directional feature is in bus topology.

• Bus topology may have problem while multiple hosts sending data at the same time. Therefore, Bus topology either uses CSMA/CD technology or recognizes one host as Bus Master to solve the issue.

• Carrier Sense Multiple Access with Collision Detection

• It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning.

• Both ends of the shared channel have line terminator.

• The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from the line.      

 Features of Bus Topology

• It transmits data only in one direction.

• Every device is connected to a single cable

 

Advantages of Bus Topology

• It is cost effective.

• Cable required is least compared to other network topology.

• Used in small networks.

• It is easy to understand.

• Easy to expand joining two cables together.

 

Disadvantages of Bus Topology

• Cables fails then whole network fails.

• If network traffic is heavy or nodes are more the performance of the network decreases.

• Cable has a limited length.

• It is slower than the ring topology.

 

 3) Star Topology: -

• ​ In star topology, all the devices are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node.

• The hub can be passive in nature i.e. not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active hubs. Active hubs have repeaters in them.

• All hosts in Star topology are connected to a central device, known as hub device, using a point-to-point connection. That is, there exists a point to point connection between hosts and hub. The hub device can be any of the following:

                    Layer-1 device such as hub or repeater.

                    Layer-2 device such as switch or bridge.

                    Layer-3 device such as router or gateway.

 

 Features of Star Topology

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

• Hub acts as a repeater for data flow.

• Can be used with twisted pair, Optical Fibre or coaxial cable.

 

Advantages of Star Topology

• Fast performance with few nodes and low network traffic.

• Hub can be upgraded easily.

• Easy to troubleshoot.

• Easy to setup and modify.

• Only that node is affected which has failed, rest of the nodes can work smoothly.

 

Disadvantages of Star Topology

• Cost of installation is high.

• Expensive to use.

• If the hub fails then the whole network is stopped because all the nodes depend on the hub.

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

 

4) Ring Topology :

• In this topology, it forms a ring connecting devices with its exactly two neighbouring devices.

• In ring topology, each host machine connects to exactly two other machines, creating a circular network structure.

• When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts.

• To connect one more host in the existing structure, the administrator may need only one more extra cable.

• Failure of any host results in failure of the whole ring. Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring.

 

 

Features of Ring Topology

• A number of repeaters are used for Ring topology with large number of nodes, because if someone wants to send some data to the last node in the ring topology with 100 nodes, then the data will have to pass through 99 nodes to reach the 100th node. Hence to prevent data loss repeaters are used in the network.

• The transmission is unidirectional, but it can be made bidirectional by having 2 connections between each Network Node, it is called Dual Ring Topology.

 

Advantages of Ring Topology

• Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.

• Cheap to install and expand

 

Disadvantages of Ring Topology

• Troubleshooting is difficult in ring topology.

• Adding or deleting the computers disturbs the network activity.

• Failure of one computer disturbs the whole network.

 

5) Mesh Topology: -

• In this type of topology, a host is connected to one or multiple hosts.

• This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection to few hosts only.

• Every device is connected to another device via particular channel.

• Every device is connected with another via dedicated channels. These channels are known as links.

• If suppose, N number of devices are connected with each other in mesh topology, then total number of ports that is required by each device is ​ N-1. In the Figure 1, there are 5 devices connected to each other, hence total number of ports required is 4.

• If suppose, N number of devices are connected with each other in mesh topology, then total number of dedicated links required to connect them is NC2 i.e. N(N-1)/2. In the Figure 1, there are 5 devices connected to each other, hence total number of links required is 5*4/2 = 10.

• Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to-point links.

• Mesh technology comes into two types:

            a) Full Mesh: All hosts have a point-to-point connection to every other host in the network.                                     Thus for every new host n(n-1)/2 connections are required. It provides the                                             most reliable network structure among all network topologies.

        b) Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts                                                  connect to each other in some arbitrarily fashion. This topology exists where                                             we need to provide reliability to some hosts out of all.

 

Features of Mesh Topology

• Fully connected.

• Robust.

• Not flexible.

 

Advantages of Mesh Topology

• Each connection can carry its own data load.

• It is robust.

• Fault is diagnosed easily.

• Provides security and privacy.

 

Disadvantages of Mesh Topology

• Installation and configuration is difficult.

• Cabling cost is more.

• Bulk wiring is required.