## What is network topology and types of network topology?

Topology is derived from two Greek words topo and logy, where topo means 'place' and logy means 'study'. In computer networks, a topology is used to explain how a network is physically connected and the logical flow of information in the network. A topology mainly describes how devices are connected and interact with each other using communication links.

In computer networks, there are mainly two types of topologies, they are:
1. Physical Topology: A physical topology describes the way in which the computers or nodes are connected with each other in a computer network. It is the arrangement of various elements(link, nodes, etc.), including the device location and code installation of a computer network. In other words, we can say that it is the physical layout of nodes, workstations, and cables in the network.
2. Logical Topology: A logical topology describes the way, data flow from one computer to another. It is bound to a network protocol and defines how data is moved throughout the network and which path it takes. In other words, it is the way in which the devices communicate internally.

Network topology defines the layout, virtual shape, or structure of the network, not only physically but also logically. A network can have one physical topology and multiple logical topologies at the same time.

In this blog, we will mainly concentrate on physical topologies. We'll learn about different types of physical topologies, their advantages, and disadvantages.

In a computer network, there are mainly six types of physical topology, they are:
1. Bus Topology
2. Ring Topology
3. Star Topology
4. Mesh Topology
5. Tree Topology
6. Hybrid Topology

Now let us learn these topologies one by one:

#### Bus Topology

Bus topology is the simplest kind of topology in which a common bus or channel is used for communication in the network. The bus is connected to various taps and droplines. Taps are the connectors, while droplines are the cables connecting the bus with the computer. In other words, there is only a single transmission line for all nodes.

When a sender sends a message, all other computers can hear it, but only the receiver accepts it(verifying the mac address attached with the data frame) and others reject it. Bus technology is mainly suited for small networks like LAN, etc.

In this topology, the bus acts as the backbone of the network, which joins every computer and peripherals in the network. Both ends of the shared channel have line terminators. The data is sent only in one direction and as soon as it reaches the end, the terminator removes the data from the communication line(to prevent signal bounce and data flow disruption).

In a bus topology, each computer communicates to another computer on the network independently. Every computer can share the network's total bus capabilities. The devices share the responsibility for the flow of data from one point to the other in the network.

For Example Ethernet cable, etc.

Following are the advantages of Bus topology:
1. Simple to use and install.
2. If a node fails, it will not affect other nodes.
3. Less cabling is required.
4. Cost-efficient to implement.
Following are the disadvantages of Bus topology:
1. Efficiency is less when nodes are more(strength of signal decreases).
2. If the bus fails, the network will fail.
3. A limited number of nodes can connect to the bus due to limited bus length.
4. Security issues and risks are more as messages are broadcasted to all nodes.
5. Congestion and traffic on the bus as it is the only source of communication.

#### Ring Topology

Ring topology is a topology in which each computer is connected to exactly two other computers to form the ring. The message passing is unidirectional and circular in nature.

This network topology is deterministic in nature, i.e., each computer is given access for transmission at a fixed time interval. All the nodes are connected in a closed-loop. This topology mainly works on a token-based system and the token travels in a loop in one specific direction.

In a ring topology, if a token is free then the node can capture the token and attach the data and destination address to the token, and then leaves the token for communication. When this token reaches the destination node, the data is removed by the receiver and the token is made free to carry the next data.

For Example, Token Ring, etc.

Following are the advantages of Ring topology:
1. Easy Installation.
2. Less Cabling Required.
3. Reduces chances of data collision(unidirectional).
4. Easy to troubleshoot(the faulty node does not pass the token).
5. Each node gets the same access time.
Following are the disadvantages of Ring topology:
1. If a node fails, the whole network will fail.
2. Slow data transmission speed(each message has to go through the ring path).
3. Difficult to reconfigure(we have to break the ring).

#### Star Topology

Star topology is a computer network topology in which all the nodes are connected to a centralized hub. The hub or switch acts as a middleware between the nodes. Any node requesting for service or providing service, first contact the hub for communication.

The central device(hub or switch) has point to point communication link(the dedicated link between the devices which can not be accessed by some other computer) with the devices. The central device then broadcast or unicast the message based on the central device used. The hub broadcasts the message, while the switch unicasts the messages by maintaining a switch table. Broadcasting increases unnecessary data traffic in the network.

In a star topology, hub and switch act as a server, and the other connected devices act as clients. Only one input-output port and one cable are required to connect a node to the central device. This topology is better in terms of security because the data does not pass through every node.

For Example High-Speed LAN, etc.

Following are the advantages of Star topology:
1. Centralized control.
2. Less Expensive.
3. Easy to troubleshoot(the faulty node does not give response).
4. Good fault tolerance due to centralized control on nodes.
5. Easy to scale(nodes can be added or removed to the network easily).
6. If a node fails, it will not affect other nodes.
7. Easy to reconfigure and upgrade(configured using a central device).
Following are the disadvantages of Star topology:
1. If the central device fails, the network will fail.
2. The number of devices in the network is limited(due to limited input-output port in a central device).

#### Mesh Topology

Mesh topology is a computer network topology in which nodes are interconnected with each other. In other words, direct communication takes place between the nodes in the network.

There are mainly two types of Mesh:

1. Full Mesh: In which each node is connected to every other node in the network.
2. Partial Mesh: In which, some nodes are not connected to every node in the network.

In a fully connected mesh topology, each device has a point to point link with every other device in the network. If there are 'n' devices in the network, then each device has exactly '(n-1)' input-output ports and communication links. These links are simplex links, i.e., the data moves only in one direction. A duplex link(in which data can travel in both the directions simultaneously) can replace two simplex links.

If we are using simplex links, then the number of communication links will be 'n(n-1)' for 'n' devices, while it is 'n(n-1)/2' if we are using duplex links in the mesh topology.

For Example, the Internet(WAN), etc.

Following are the advantages of Mesh topology:
1. Dedicated links facilitate direct communication.
2. No congestion or traffic problems on the channels.
3. Good Fault tolerance due to the dedicated path for each node.
4. Very fast communication.
5. Maintains privacy and security due to a separate channel for communication.
6. If a node fails, other alternatives are present in the network.
Following are the disadvantages of Mesh topology:
1. Very high cabling required.
2. Cost inefficient to implement.
3. Complex to implement and takes large space to install the network.
4. Installation and maintenance are very difficult.

#### 5. Tree Topology:

Tree topology is a computer network topology in which all the nodes are directly or indirectly connected to the main bus cable. Tree topology is a combination of Bus and Star topology.

In a tree topology, the whole network is divided into segments, which can be easily managed and maintained. There is a main hub and all the other sub-hubs are connected to each other in this topology.

Following are the advantages of Tree topology:
1. Large distance network coverage.
2. Fault finding is easy by checking each hierarchy.
3. Least or no data loss.
4. A Large number of nodes can be connected directly or indirectly.
5. Other hierarchical networks are not affected if one of them fails.
Following are the disadvantages of Tree topology:
1. Cabling and hardware cost is high.
2. Complex to implement.
3. Hub cabling is also required.
4. A large network using tree topology is hard to manage.
5. It requires very high maintenance.
6. If the main bus fails, the network will fail.

#### Hybrid Topology:

A Hybrid topology is a computer topology which is a combination of two or more topologies. In practical use, they are the most widely used.

In this topology, all topologies are interconnected according to the needs to form a hybrid. All the good features of each topology can be used to make an efficient hybrid topology.

Following are the advantages of Hybrid topology:
1. It can handle a large volume of nodes.
2. It provides flexibility to modify the network according to our needs.
3. Very Reliable(if one node fails it will not affect the whole network).
Following are the disadvantages of Hybrid topology:
1. Complex design.
2. Expensive to implement.
3. Multi-Station Access Unit(MSAL) required.
Hence, after learning the various computer network topologies, we can conclude that some points need to be considered when selecting a physical topology:
• Ease of Installation.
• Fault Tolerance.
• Implementation Cost.
• Cabling Required.
• Maintenance Required.
• Reliable Nature.
• Ease of Reconfiguration and upgradation.

This is all about the topology and its types in a computer network. Hope you learned something new today. That's it for this blog.