Network Topologies | Computer Networks - Computer Science Engineering (CSE) PDF Download

Network Topology

The configuration, or topology, of a network, is key to determining its performance. 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. Admins have a range of options when it comes to choosing a network topology, and this decision must account for the size and scale of their business, its goals, and budget. Several tasks go into effective network topology management, including configuration management, visual mapping, and general performance monitoring. The key is to understand your objectives and requirements to create and manage the network topology in the right way for your business.

Mesh Topology

In a mesh topology, every device is connected to another device via a 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 a mesh topology, the total number of ports that are required by each device is N-1. In the above figure, there are 5 devices connected to each other, hence a total number of ports required is 4.
• If suppose, N number of devices are connected with each other in a mesh topology, the total number of dedicated links required to connect them is ^NC₂ i.e. N(N-1)/2. In the above figure, there are 5 devices connected to each other, hence a total number of links required is 5*4/2 = 10.

Advantages of Mesh Topology

• It is robust.
• A fault is diagnosed easily. Data is reliable because data is transferred among the devices through dedicated channels or links.
• Provides security and privacy.

Problems with Mesh Topology

• Installation and configuration is difficult.
• The cost of cables is high as bulk wiring is required, hence suitable for less number of devices.
• The cost of maintenance is high.

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.

A star topology having five systems connected to a single point of connection i.e. hub.Advantages of Star Topology 

• If N devices are connected to each other in star topology, then the number of cables required to connect them is N. So, it is easy to set up.
• Each device requires only 1 port i.e. to connect to the hub.

Problems with Star Topology

• If the concentrator (hub) on which the whole topology relies fails, the whole system will crash down.
• The cost of installation is high.
• Performance is based on the single concentrator i.e. hub.

Bus Topology

Bus topology is a network type in which every computer and network device is connected to a single cable. It transmits the data from one end to another in a single direction. No bi-directional feature is in bus topology.

A bus topology with a shared backbone cable. The nodes are connected to the channel via drop lines.

Advantages of Bus Topology

• If N devices are connected to each other in a bus topology, then the number of cables required to connect them is 1 which is known as backbone cable and N drop lines are required.
• The cost of the cable is less as compared to other topologies, but it is used to build small networks.

Problems with Bus Topology

• If the common cable fails, then the whole system will crash down.
• If the network traffic is heavy, it increases collisions in the network. To avoid this, various protocols are used in the MAC layer known as Pure Aloha, Slotted Aloha, CSMA/CD etc.

Ring Topology

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

A ring topology comprises 4 stations connected with each forming a ring.

The following operations take place in ring topology are:

1. One station is known as a monitor station which takes all the responsibility to perform the operations.
2. To transmit the data, the station has to hold the token. After the transmission is done, the token is to be released for other stations to use.
3. When no station is transmitting the data, then the token will circulate in the ring.
4. There are two types of token release techniques : Early token release releases the token just after the transmitting the data and Delay token release releases the token after the acknowledgement is received from the receiver.

Advantages of Ring Topology

• The possibility of collision is minimum in this type of topology.
• Cheap to install and expand.

Problems with Ring Topology

• Troubleshooting is difficult in this topology.
• The addition of stations in between or removal of stations can disturb the whole topology.

Hybrid Topology

This topology is a collection of two or more topologies which are described above. This is a scalable topology that can be expanded easily. It is a reliable one but at the same, it is a costly topology.