In networking, the term topology is the way of connecting computers or nodes on a network. There are many ways in which computers can be connected to a computer network. How computers or other devices are connected in a network is called network topology. Shortly the term network topology refers to the physical layout or shape of the network. The commonly used network topologies are as follows.
Bus topology Star topology
Ring topology Mesh topology
Tree topology Hybrid topology
In a Bus topology, all nodes are connected to a common communication medium. Usually, a central cable is used as a communication medium. This cable is called Bus. The nodes are connected to the Bus through interface connector. Both ends of the bus (central cable) are closed with terminators. A terminator is a special device that absorbs data signals (or prevents data signals from reflecting onto the bus). It is also known as terminating resistance. Bus topology is suitable for small networks. The shape of the bus network is shown in the following figure.
Working of Bus Topology
In the Bus network, each computer or device is assigned a unique address. The computers in the network communicate with each other through the bus. When a computer wants to transmit a message, it has to determine whether the media is in use or free. If no other device is transmitting the data, it sends a message to another computer. The computer also attaches the address of the destination computer with the message. This message moves from one computer to another through the bus. Each computer connected to the network receives the message, checks the address attached to the message, and then sends the message toward the next computer. When a message reaches the destination computer, it accepts the message. In this way, the message is received by the destination computer.
The main advantages of Bus topology are as follows:
- It is a very simple network.
- It is less expensive.
- It is easy to install and to maintain.
- It does not require much cabling to connect nodes as compared to other networks.
- When nodes are added and removed in the network, the network is not affected.
- If one node fails in the network, other nodes are not affected.
The main disadvantages of Bus topology are as follows:
- The entire network fails if there is any problem with the bus (central cable).
- It supports only a small number of nodes. So it is not suitable for a large network.
In a star network, all nodes are directly connected to a central device, called Hub or Switch. This form of network shape looks like a Star. Usually, the nodes are connected to the Hub with unshielded twisted pair (UTP). A larger network may consist of many hubs/switches. All the hubs or switches in the network are connected. Star topology is most commonly used in LAN. The shape of the star network with five nodes connected to a single hub is shown in the figure.
Working of Star Topology
Instar network, the computers communicate with each other through a central device i.e. hub. The sending computer sends data to the central device. The central device sends data to the receiving computer. In this way, data is transferred from one computer to another in the Star network.
The main advantages of star topology are as follows:
- It is easy to install and to maintain.
- The nodes can easily be added or removed without affecting the network.
- If any node or cable fails then the rest of the network is not affected.
- It is easy to detect and remove faults in the network.
- It is suitable for small and large networks.
The main disadvantages of star topology are as follows:
- This type of network depends upon the central device. If this device fails, the whole network breaks down.
- It requires more cables than any other network. So it becomes more costly.
In a ring topology, each node is connected to the next node and the last node is connected to the first. Thus, the shape of the network is formed just like a ring. Data on the network flows in one direction around the ring until it reaches to destination. The shape of the ring network is shown in the figure.
Working of Ring Topology
In-ring topology, a token is passed around the network. The computer that has control of the token can transmit data/messages. When ‘a computer sends a message to ‘another computer on the network, the message flows from one computer to the next computer. Every computer receives a message from the previous computer and retransmits it to the next computer until the destination computer receives the message. The destination computer sends an acknowledgment of receiving a message to the sender computer. The sender computer then releases the token back to the network. This method of controlling access to the shared network cable is called token passing.
The main advantages of ring topology are as follows:
- It is less expensive to implement.
- It is easy to install and to maintain.
- All computers have equal access to the network.
- Every computer regenerates/refreshes the data signal that’s why it can travel over a longer distance.
The main disadvantages of ring topology are as follows:
- If one node fails (or ring is broken at any point), the entire network stops functioning.
- Adding or removing a computer in the network affects the whole network.
In a mesh topology, each node is directly connected to every other node on the network. This type of network involves the concept of routes. Mesh topology is rarely used • LAN. It is mostly used in \VANS like the Internet use mesh topology. The shape of the mesh network is shown in the figure.
Working of Mesh Topology
In a mesh topology, each node can send a message to the destination through multiple paths. It means that each node of the mesh network has several possible paths to send or to receive a message, but in Bus, Star, and Ring topologies each node has only one path. The data always travels through the best-suited path.
Mesh topology has the following advantages:
- It provides multiple routes. If one route is blocked, then another suitable route can be used for data communication.
- Its performance is not affected by a heavy load of data transmission.
- It ensures data privacy or security.
- Troubleshooting of this topology is easy as compared with other networks.
Mesh topology has the following disadvantages:
- It becomes very expensive because a large number of cabling and 1/0 ports are required.
- It is difficult to install and configure. Its maintenance is also difficult.
Tree topology has combined features of both bus and star topologies. The whole network is divided into segments. Typically, to form a tree network, multiple star topologies are combined through central cable or bus. The tree network looks like a tree structure. In the following figure, three-star networks are combined through a bus.
In the tree topology network, usually, multiple hubs are used. Each hub controls the nodes directly connected to it and exchanges data among them. It also exchanges data to other devices connected to the other hubs.
The cable TV network is an example of tree topology. In this network, the main cable is divided into branches and each branch is further divided into smaller branches, and so on. The hub is used when a new branch is created.
Following are the main advantages of tree topology:
- Its existing network: can be expanded very easily (i.e. easily scalable).
- Each segment of the network can be easily managed and maintained.
- If one segment fails, other segments are not affected.
- Errors detection and correction is easy.
Following are the main disadvantages of tree topology: or
- It is more expensive because more hubs are required to be installed in the network.
- It relies on the central cable or bus. If it breaks, the whole network is affected.
- Scalability of the network depends on the type,
A hybrid network is the combination of different topologies such as a star, ring, mesh, bus, etc. For example, a department uses a Star network, the second department uses the ring network, and the third department uses the Bus network. All the networks of different types (of three departments) can be connected through a hub (in the form of a star network) as shown in the figure.