Part A : Understanding of 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.
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.
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".
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.
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.
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.
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 received by the destination device, then it sends the acknowledgment to the sender.
In a ring topology, a token is used as a carrier.
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.
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.
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.
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.
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.
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 connected with each other in hierarchical fashion.
The top-most 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.
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.
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.
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 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.
Mesh topology is divided into two categories:
Fully connected mesh topology
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.
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.
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 that reduces the efficiency of the network.
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 as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in 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: 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 weakness of the network is minimized.
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 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.
The way in which data is transmitted from one device to another device is known as transmission mode.
The transmission mode is also known as the communication mode.
Each communication channel has a direction associated with it, and transmission media provide the direction. Therefore, the transmission mode is also known as a directional mode.
The transmission mode is defined in the physical layer.
The Transmission mode is divided into three categories:
Simplex mode
Half-duplex mode
Full-duplex mode
In Simplex mode, the communication is unidirectional, i.e., the data flow in one direction.
A device can only send the data but cannot receive it or it can receive the data but cannot send the data.
This transmission mode is not very popular as mainly communications require the two-way exchange of data. The simplex mode is used in the business field as in sales that do not require any corresponding reply.
The radio station is a simplex channel as it transmits the signal to the listeners but never allows them to transmit back.
Keyboard and Monitor are the examples of the simplex mode as a keyboard can only accept the data from the user and monitor can only be used to display the data on the screen.
The main advantage of the simplex mode is that the full capacity of the communication channel can be utilized during transmission.
In simplex mode, the station can utilize the entire bandwidth of the communication channel, so that more data can be transmitted at a time.
Communication is unidirectional, so it has no inter-communication between devices.
In a Half-duplex channel, direction can be reversed, i.e., the station can transmit and receive the data as well.
Messages flow in both the directions, but not at the same time.
The entire bandwidth of the communication channel is utilized in one direction at a time.
In half-duplex mode, it is possible to perform the error detection, and if any error occurs, then the receiver requests the sender to retransmit the data.
A Walkie-talkie is an example of the Half-duplex mode. In Walkie-talkie, one party speaks, and another party listens. After a pause, the other speaks and first party listens. Speaking simultaneously will create the distorted sound which cannot be understood.
In half-duplex mode, both the devices can send and receive the data and also can utilize the entire bandwidth of the communication channel during the transmission of data.
In half-duplex mode, when one device is sending the data, then another has to wait, this causes the delay in sending the data at the right time.
In Full duplex mode, the communication is bi-directional, i.e., the data flow in both the directions.
Both the stations can send and receive the message simultaneously.
Full-duplex mode has two simplex channels. One channel has traffic moving in one direction, and another channel has traffic flowing in the opposite direction.
The Full-duplex mode is the fastest mode of communication between devices.
The most common example of the full-duplex mode is a telephone network. When two people are communicating with each other by a telephone line, both can talk and listen at the same time.
Both the stations can send and receive the data at the same time.
If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into two parts.
Basis for comparison
Simplex mode
Half-duplex mode
Full-duplex mode
Direction of communication
In simplex mode, the communication is unidirectional.
In half-duplex mode, the communication is bidirectional, but one at a time.
In full-duplex mode, the communication is bidirectional.
Send/Receive
A device can only send the data but cannot receive it or it can only receive the data but cannot send it.
Both the devices can send and receive the data, but one at a time.
Both the devices can send and receive the data simultaneously.
Performance
The performance of half-duplex mode is better than the simplex mode.
The performance of full-duplex mode is better than the half-duplex mode.
The Full-duplex mode has better performance among simplex and half-duplex mode as it doubles the utilization of the capacity of the communication channel.
Example
Examples of Simplex mode are radio, keyboard, and monitor.
Example of half-duplex is Walkie-Talkies.
Example of the Full-duplex mode is a telephone network.
A communication subsystem is a complex piece of Hardware and software. Early attempts for implementing the software for such subsystems were based on a single, complex, unstructured program with many interacting components. The resultant software was very difficult to test and modify. To overcome such problem, the ISO has developed a layered approach. In a layered approach, networking concept is divided into several layers, and each layer is assigned a particular task. Therefore, we can say that networking tasks depend upon the layers.
The main aim of the layered architecture is to divide the design into small pieces.
Each lower layer adds its services to the higher layer to provide a full set of services to manage communications and run the applications.
It provides modularity and clear interfaces, i.e., provides interaction between subsystems.
It ensures the independence between layers by providing the services from lower to higher layer without defining how the services are implemented. Therefore, any modification in a layer will not affect the other layers.
The number of layers, functions, contents of each layer will vary from network to network. However, the purpose of each layer is to provide the service from lower to a higher layer and hiding the details from the layers of how the services are implemented.
The basic elements of layered architecture are services, protocols, and interfaces.
Service: It is a set of actions that a layer provides to the higher layer.
Protocol: It defines a set of rules that a layer uses to exchange the information with peer entity. These rules mainly concern about both the contents and order of the messages used.
Interface: It is a way through which the message is transferred from one layer to another layer.
In a layer n architecture, layer n on one machine will have a communication with the layer n on another machine and the rules used in a conversation are known as a layer-n protocol.
Let's take an example of the five-layered architecture.
In case of layered architecture, no data is transferred from layer n of one machine to layer n of another machine. Instead, each layer passes the data to the layer immediately just below it, until the lowest layer is reached.
Below layer 1 is the physical medium through which the actual communication takes place.
In a layered architecture, unmanageable tasks are divided into several small and manageable tasks.
The data is passed from the upper layer to lower layer through an interface. A Layered architecture provides a clean-cut interface so that minimum information is shared among different layers. It also ensures that the implementation of one layer can be easily replaced by another implementation.
A set of layers and protocols is known as network architecture.
Divide-and-conquer approach: Divide-and-conquer approach makes a design process in such a way that the unmanageable tasks are divided into small and manageable tasks. In short, we can say that this approach reduces the complexity of the design.
Modularity: Layered architecture is more modular. Modularity provides the independence of layers, which is easier to understand and implement.
Easy to modify: It ensures the independence of layers so that implementation in one layer can be changed without affecting other layers.
Easy to test: Each layer of the layered architecture can be analyzed and tested individually.
Part B : Q N A >Topology
1. What is the primary purpose of network topology?
A) To define the IP address
B) To determine the layout of the network
C) To improve software quality
D) To monitor user activities
Answer: B) To determine the layout of the network
2. Which topology connects all nodes to a central hub?
A) Star
B) Ring
C) Bus
D) Mesh
Answer: A) Star
3. In which topology is data transmitted in a unidirectional circular path?
A) Star
B) Ring
C) Bus
D) Tree
Answer: B) Ring
4. Which topology is known for its high redundancy and fault tolerance?
A) Mesh
B) Star
C) Tree
D) Bus
Answer: A) Mesh
5. Which network topology is most vulnerable to a central node failure?
A) Mesh
B) Ring
C) Star
D) Bus
Answer: C) Star
6. Which of these is a disadvantage of bus topology?
A) High cost
B) Difficult to install
C) Poor performance with heavy traffic
D) Requires more cables
Answer: C) Poor performance with heavy traffic
7. Which topology is primarily used in large organizations for hierarchal structure?
A) Star
B) Tree
C) Ring
D) Bus
Answer: B) Tree
8. In a mesh topology with 5 nodes, how many cables are needed?
A) 10
B) 20
C) 15
D) 5
Answer: C) 15
9. Which topology uses a backbone cable to connect all devices?
A) Bus
B) Ring
C) Mesh
D) Tree
Answer: A) Bus
10. Which of the following is a benefit of ring topology?
A) High redundancy
B) Cost-effectiveness
C) Easy to install
D) Fast data transfer in one direction
Answer: D) Fast data transfer in one direction
11. In star topology, what happens if the central hub fails?
A) The entire network fails
B) Only that node is affected
C) Data is rerouted
D) None of the nodes are affected
Answer: A) The entire network fails
12. What type of topology is the internet mostly structured in?
A) Mesh
B) Tree
C) Hybrid
D) Ring
Answer: C) Hybrid
13. Which of these is a characteristic of hybrid topology?
A) Only a ring design
B) Combination of multiple topologies
C) Single failure point
D) Limited scalability
Answer: B) Combination of multiple topologies
14. What is a disadvantage of mesh topology?
A) Low security
B) High cabling costs
C) Slow data transfer
D) Limited connectivity
Answer: B) High cabling costs
15. Which topology allows direct connection between each pair of nodes?
A) Star
B) Mesh
C) Tree
D) Bus
Answer: B) Mesh
16. In which topology is a token used to control data transfer?
A) Star
B) Tree
C) Ring
D) Bus
Answer: C) Ring
17. In a tree topology, what are end devices often referred to as?
A) Nodes
B) Leaves
C) Hubs
D) Roots
Answer: B) Leaves
18. Which topology is easiest to expand?
A) Bus
B) Ring
C) Star
D) Mesh
Answer: C) Star
19. In bus topology, what happens if the main cable fails?
A) Only a few nodes are affected
B) The entire network goes down
C) It reroutes data
D) Performance slows
Answer: B) The entire network goes down
20. Which topology combines features of both star and bus topologies?
A) Tree
B) Mesh
C) Ring
D) Hybrid
Answer: A) Tree
A) Mesh
B) Star
C) Ring
D) Tree
Answer: A) Mesh
A) Bus
B) Star
C) Mesh
D) Hybrid
Answer: A) Bus
A) Cost-effectiveness
B) Simple cable layout
C) Easy to troubleshoot
D) High speed
Answer: C) Easy to troubleshoot
A) The network performance is unaffected
B) The entire network fails
C) Data is rerouted
D) Only that node is affected
Answer: B) The entire network fails
A) Ring
B) Bus
C) Mesh
D) Star
Answer: C) Mesh
A) Switch
B) Router
C) Modem
D) Repeater
Answer: A) Switch
A) Star
B) Bus
C) Mesh
D) Hybrid
Answer: B) Bus
A) Star
B) Mesh
C) Bus
D) Ring
Answer: A) Star
A) Ring
B) Bus
C) Tree
D) Mesh
Answer: C) Tree
A) Cost
B) Data loss
C) Maintenance difficulty
D) High redundancy
Answer: C) Maintenance difficulty
A) Mesh
B) Star
C) Tree
D) Bus
Answer: B) Star
A) Ring
B) Bus
C) Mesh
D) Star
Answer: C) Mesh
A) Mesh
B) Star
C) Tree
D) Bus
Answer: A) Mesh
A) Bus
B) Star
C) Mesh
D) Tree
Answer: C) Mesh
A) Ring
B) Mesh
C) Star
D) Bus
Answer: B) Mesh
A) Star
B) Mesh
C) Logical
D) Ring
Answer: C) Logical
A) Mesh
B) Bus
C) Star
D) Ring
Answer: A) Mesh
A) Mesh
B) Ring
C) Bus
D) Tree
Answer: A) Mesh
A) Bus
B) Star
C) Ring
D) Tree
Answer: A) Bus
A) Root
B) Hub
C) Branch
D) Leaf
Answer: A) Root