Explain network topology .Explain tis types with its advantages and disadvantges.

Network topology

Network topology refers to how the nodes and links in a network are arranged. A network node is a device that can send, receive, store, or forward data. A network link connects nodes and may be either cabled or wireless links.
Understanding topology types provides the basis for building a successful network. There are a number of topologies but the most common are bus, ring, star, and mesh:

• A bus network topology is when every network node is directly connected to a main cable.
• In a ring topology, nodes are connected in a loop, so each device has exactly two neighbors. Adjacent pairs are connected directly; non-adjacent pairs are connected indirectly through multiple nodes.
• In a star network topology, all nodes are connected to a single, central hub and each node is indirectly connected through that hub. 
• A mesh topology is defined by overlapping connections between nodes. You can create a full mesh topology, where every node in the network is connected to every other node. You can also create partial mesh topology in which only some nodes are connected to each other and some are connected to the nodes with which they exchange the most data. Full mesh topology can be expensive and time-consuming to execute, which is why it's often reserved for networks that require high redundancy. Partial mesh provides less redundancy but is more cost effective and simpler to execute.

OR,

Network Topology

1. Bus Topology:

 Every computer and network device is connected to a single cable in a bus topology network. Linear Bus topology is defined as having exactly two terminals.

Advantage

• Installation is simple.
• Compared to mesh, star, and tree topologies, the bus utilizes less cabling.

Disadvantages

• Difficulty in reconfiguring and isolating faults.
• A bus cable malfunction or break interrupts all communication.

2. Ring Topology: 

The topology is named ring topology because one computer is connected to another, with the final one being connected to the first. Exactly two neighbors for each device. A signal is passed along the ring in one direction. Each ring incorporates a repeater. 

Advantages

• Data transmission is relatively straightforward because packets only move in one direction.
• There is no requirement for a central controller to manage communication between nodes.
• Easy installation & Reconfiguration
• Simplified Faulty connections

Disadvantages

• In a Unidirectional Ring, a data packet must traverse through all nodes.
• All computers must be turned on in order for them to connect with one another.

3. Star Topology: 

Each device in a star topology has a dedicated point-to-point link to a central controller, which is commonly referred to as the HUB. There is no direct connection between the devices. Traffic between the devices is not allowed in this topology. As an exchange, the controller is used.

Advantages

• When attaching or disconnecting devices, there are no network interruptions.
• It’s simple to set up and configure.
• Identifying and isolating faults is simple.
• Less Expensive than mesh 
• Easy to install & configure

Disadvantages

• Nodes attached to the hub, switch, or concentrator is failed if they fail.
• Because of the expense of the hubs, it is more expensive than linear bus topologies.
• More cable is required compared to a bus or ring 
• Too much dependency on Hub

Example: Used in high-speed LANs

4. Mesh Topology: 

Every device in a mesh topology has dedicated point-to-point connectivity to every other device. The term “dedicated” refers to the fact that the link exclusively transports data between the two devices it links. To connect n devices, a fully connected mesh network contains n *(n-1)/2 physical channels.

Advantages

• Data can be sent from multiple devices at the same time. This topology can handle a lot of traffic.
• Even if one of the connections fails, a backup is always available. As a result, data transit is unaffected.
• Physical boundaries prevent other users from gaining access to messages
• Point to Point links make fault transmission & fault isolation easy 

Disadvantages

• The amount of cabling and the number of I/O ports that are necessary.
• The sheer bulk of wiring can be greater than the available space can accommodate.
• It is difficult to install and reconfigure.

Example:  connection of telephone regional office in which each regional office needs to be connected to every other regional office. 

5. Tree Topology: 

The topology of a tree is similar to that of a star. Nodes in a tree, like those in a star, are connected to a central hub that manages network traffic. It has a root node, which is connected to all other nodes, producing a hierarchy. Hierarchical topology is another name for it. The number of Star networks is connected via Bus in Tree Topology

Advantages

• Network expansion is both possible and simple.
• We partition the entire network into pieces (star networks) that are easier to manage and maintain.
• Other segments are unaffected if one segment is damaged.

Disadvantages

• Tree topology relies largely on the main bus cable because of its basic structure, and if it fails, the entire network is handicapped.
• Maintenance becomes more challenging when more nodes and segments are added.

OR,

Topology 

Topology defines the structure of the network of how all the components are interconnected to each other. There are two types of topology: physical and logical topology.

Types of Network Topology

Physical topology is the geometric representation of all the nodes in a network. There are six types of network topology which are Bus Topology, Ring Topology, Tree Topology, Star Topology, Mesh Topology, and Hybrid Topology.

1)Bus 

• The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable.
• Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.
• When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not.
• The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks.
• The configuration of a bus topology is quite simpler as compared to other topologies.
• The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations.

The most common access method of the bus topologies is CSMA (Carrier Sense Multiple Access).

CSMA: 

It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost. There are two alternative ways of handling the problems that occur when two nodes send the messages simultaneously.

CSMA CD: 

CSMA CD (Collision detection) is an access method used to detect the collision. Once the collision is detected, the sender will stop transmitting the data. Therefore, it works on "recovery after the collision".

CSMA CA: 

CSMA CA (Collision Avoidance) is an access method used to avoid the collision by checking whether the transmission media is busy or not. If busy, then the sender waits until the media becomes idle. This technique effectively reduces the possibility of the collision. It does not work on "recovery after the collision".

Advantages of Bus topology:

• Low-cost cable: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.
• Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps.
• Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.
• Limited failure: A failure in one node will not have any effect on other nodes.

Disadvantages of Bus topology:

• Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.
• Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.
• Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other.
• Reconfiguration difficult: Adding new devices to the network would slow down the network.
• Attenuation: Attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal.

2) Ring Topology

• Ring topology is like a bus topology, but with connected ends.
• The node that receives the message from the previous computer will retransmit to the next node.
• The data flows in one direction, i.e., it is unidirectional.
• The data flows in a single loop continuously known as an endless loop.
• It has no terminated ends, i.e., each node is connected to other node and having no termination point.
• The data in a ring topology flow in a clockwise direction.

The most common access method of the ring topology is token passing.

Token passing: It is a network access method in which token is passed from one node to another node.

Token: It is a frame that circulates around the network.

Working of Token passing

A token moves around the network, and it is passed from computer to computer until it reaches the destination.

The sender modifies the token by putting the address along with the data.

The data is passed from one device to another device until the destination address matches. Once the token is received by the destination device, then it sends the acknowledgment to the sender.

In a ring topology, a token is used as a carrier.

Advantages of Ring topology:

Network Management: Faulty devices can be removed from the network without bringing the network down.

Product availability: Many hardware and software tools for network operation and monitoring are available.

Cost: Twisted pair cabling is inexpensive and easily available. Therefore, the installation cost is very low.

Reliable: It is a more reliable network because the communication system is not dependent on the single host computer.

Disadvantages of Ring topology:

Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.

Failure: The breakdown in one station leads to the failure of the overall network.

Reconfiguration difficult: Adding new devices to the network would slow down the network.

Delay: Communication delay is directly proportional to the number of nodes. Adding new devices increases the communication delay.

3) Star Topology

• Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer.
• The central computer is known as a server, and the peripheral devices attached to the server are known as clients.
• Coaxial cable or RJ-45 cables are used to connect the computers.
• Hubs or Switches are mainly used as connection devices in a physical star topology.
• Star topology is the most popular topology in network implementation.
• Star topology follows primary secondary relationship between devices.

Advantages of Star topology

Efficient troubleshooting: Troubleshooting is quite efficient in a star topology as compared to bus topology. In a bus topology, the manager has to inspect the kilometers of cable. In a star topology, all the stations are connected to the centralized network. Therefore, the network administrator has to go to the single station to troubleshoot the problem.

Network control: Complex network control features can be easily implemented in the star topology. Any changes made in the star topology are automatically accommodated.

Limited failure: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network.

Familiar technology: Star topology is a familiar technology as its tools are cost-effective.

Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub.

Cost effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable.

High data speeds: It supports a bandwidth of approx 100Mbps. Ethernet 100BaseT is one of the most popular Star topology networks.

Disadvantages of Star topology

A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.

Cable: Sometimes cable routing becomes difficult when a significant amount of routing is required.

4) Tree topology

• Tree topology combines the characteristics of bus topology and star topology.
• A tree topology is a type of structure in which all the computers are hierarchically connected with each other.
• The topmost node in tree topology is known as a root node, and all other nodes are the descendants of the root node.
• There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy.

Advantages of Tree topology

Support for broadband transmission: Tree topology is mainly used to provide broadband transmission, i.e., signals are sent over long distances without being attenuated.

Easily expandable: We can add the new device to the existing network. Therefore, we can say that tree topology is easily expandable.

Easily manageable: In tree topology, the whole network is divided into segments known as star networks which can be easily managed and maintained.

Error detection: Error detection and error correction are very easy in a tree topology.

Limited failure: The breakdown in one station does not affect the entire network.

Point-to-point wiring: It has point-to-point wiring for individual segments.

Disadvantages of Tree topology

Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem.

High cost: Devices required for broadband transmission are very costly.

Failure: A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network.

Reconfiguration difficult: If new devices are added, then it becomes difficult to reconfigure.

5) Mesh topology

• Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections.
• There are multiple paths from one computer to another computer.
• It does not contain the switch, hub or any central computer which acts as a central point of communication.
• The Internet is an example of the mesh topology.
• Mesh topology is mainly used for WAN implementations where communication failures are a critical concern.
• Mesh topology is mainly used for wireless networks.
• Mesh topology has highest reliability.
• Mesh topology can be formed by using the formula:
• Number of cables = (n*(n-1))/2;
• Where n is the number of nodes that represents the network.
• In mesh topology if there are n devices in a network each devies has n-1 ports of cable.

Mesh topology is divided into two categories:

1. Fully connected mesh topology
2. Partially connected mesh topology

Full Mesh Topology: 

In a full mesh topology, each computer is connected to all the computers available in the network.

Partial Mesh Topology: 

In a partial mesh topology, not all but certain computers are connected to those computers with which they communicate frequently.

Advantages of Mesh topology:

Reliable: The mesh topology networks are very reliable as if any link breakdown will not affect the communication between connected computers.

Fast Communication: Communication is very fast between the nodes.

Easier Reconfiguration: Adding new devices would not disrupt the communication between other devices.

Disadvantages of Mesh topology

Cost: A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies.

Management: Mesh topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected.

Efficiency: In this topology, redundant connections are high which reduces the efficiency of the network.

6) Hybrid Topology

• The combination of various different topologies is known as Hybrid topology.
• A Hybrid topology is a connection between different links and nodes to transfer the data.
• When two or more different topologies are combined together is termed Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology.
•  For example, if there exists a ring topology in one branch of ICICI bank and a bus topology in another branch of ICICI Bank, connecting these two topologies will result in a Hybrid topology.

Advantages of Hybrid Topology

Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the network.

Scalable: The size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network.

Flexible: This topology is very flexible as it can be designed according to the requirements of the organization.

Effective: Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and the weakness of the network is minimized.

Disadvantages of Hybrid Topology

Complex design: The major drawback of the Hybrid topology is the design of the Hybrid network. It is very difficult to design the architecture of the Hybrid network.

Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from the usual Hubs used in other topologies.

Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc.