Network

Computer Network

An interconnection of multiple devices, also known as hosts, that are connected using multiple paths for the purpose of sending/receiving data or media. Computer networks can also include multiple devices/mediums which help in the communication between two different devices; these are known as Network devices and include things such as routers, switches, hubs, and bridges.

A computer network is a set of devices connected through links. A node can be computer, printer, or any other device capable of sending or receiving the data. The links connecting the nodes are known as communication channels.

Computer Network is a group of computers connected with each other through wires, optical fibres or optical links so that various devices can interact with each other through a network. The aim of the computer network is the sharing of resources among various devices. In the case of computer network technology, there are several types of networks that vary from simple to complex level.

Computer Network uses distributed processing in which task is divided among several computers. Instead, a single computer handles an entire task, each separate computer handles a subset

Advantages of Distributed processing

Security
Faster problem solving
Security through redundancy

Components Of Computer Network

NIC(National interface card)

A network interface card (NIC) is a hardware component without which a computer cannot be connected over a network. It is a circuit board installed in a computer that provides a dedicated network connection to the computer. It is also called network interface controller, network adapter or LAN adapter.

NIC is a device that helps the computer to communicate with another device. The network interface card contains the hardware addresses, the data-link layer protocol use this address to identify the system on the network so that it transfers the data to the correct destination.

NIC allows both wired and wireless communications.

NIC allows communications between computers connected via local area network (LAN) as well as communications over large-scale network through Internet Protocol (IP).

NIC is both a physical layer and a data link layer device, i.e. it provides the necessary hardware circuitry so that the physical layer processes and some data link layer processes can run on it.

NIC cards are of two types − Internal & External

Every computer on a network, both clients and servers, requires a network interface card (or NIC) in order to access the network. A NIC is usually a separate adapter card that slides into one of the server’s motherboard expansion slots. However, most newer computers have the NIC built into the motherboard, so a separate card isn’t needed

Internal Network Cards

In internal networks cards, motherboard has a slot for the network card where it can be inserted. It requires network cables to provide network access. Internal network cards are of two types. The first type uses Peripheral Component Interconnect (PCI) connection, while the second type uses Industry Standard Architecture (ISA).
PCI NICs fit into a PCI slot on a motherboard. ISA NICs fit into an ISA slot.

ISA and PCI Compared

For many years, ISA and PCI were equivalents. Because PCI was introduced as a complement to, rather than a direct competitor to ISA, it is not uncommon for motherboards to have both ISA and PCI ports. ISA, at least for a time, was concurrent with the PCI standard. ISA would give better performance in some areas, while PCI yielded better performance in other areas.

In physical appearance the ISA and PCI ports are vastly different. The ISA is longer (by about two inches), and thus the I/O cards that connect via ISA tend to be bulkier as well. Their differences do not stop there. PCI is a significantly faster (in theory) bus. PCI has double (or in rare instances, quadruple) the bit-width, resulting in faster data transfer.

When placed head-to-head, PCI is definitely the better and faster option. Which is to be expected, considering PCI is a full ten years newer. While, in 2010, ISA is practically obsolete and PCI is well on its way to extinction as PCI-E and Mini-PCI-E gain steam, they are still in use by many consumers and industries. ISA and PCI made a significant impact on the computer industry.

External Network Cards

In desktops and laptops that do not have an internal NIC, external NICs are used. External network cards are of two types: Wireless and USB based. Wireless network card needs to be inserted into the motherboard, however no network cable is required to connect to the network. They are useful while traveling or accessing a wireless signal.

Hub

Hub is a central device that splits the network connection into multiple devices. When computer requests for information from a computer, it sends the request to the Hub. Hub distributes this request to all the interconnected computers

A hub is a physical layer networking device which is used to connect multiple devices in a network. They are generally used to connect computers in a LAN.

A hub has many ports in it. A computer which intends to be connected to the network is plugged in to one of these ports. When a data frame arrives at a port, it is broadcast to every other port, without considering whether it is destined for a particular destination or not.

They operate in the physical layer of the OSI model.
It is a non-intelligent network device that sends message to all ports.
It primarily broadcasts messages.
Transmission mode is half duplex.
Collisions may occurs during setup of transmission when more than one computers place data simultaneously in the corresponding ports.
They are passive devices, they don’t have any software associated with it.
They generally have fewer ports of 4/12.

switches

Switch is a networking device that groups all the devices over the network to transfer the data to another device. A switch is better than Hub as it does not broadcast the message over the network, i.e., it sends the message to the device for which it belongs to. Therefore, we can say that switch sends the message directly from source to the destination.

A switch is a data link layer networking device which connects devices in a network and uses packet switching to send and receive data over the network.

Like a hub, a switch also has many ports, to which computers are plugged in. However, when a data frame arrives at any port of a network switch, it examines the destination address and sends the frame to the corresponding device(s). Thus, it supports both unicast and multicast communications.

They operate in the data link layer of the OSI model.
It is an intelligent network device that sends message to selected destination ports.
Transmission mode is full duplex.
Collisions do not occur since the communication is full duplex.
They are active devices, equipped with network software.
The number of ports is higher – 24/48.

Cables and connectors

Cable is a transmission media that transmits the communication signals. There are three types of cables:

Twisted pair cable:

It is a high-speed cable that transmits the data over 1Gbps or more. One of the earliest guided transmission media is twisted pair cables. A twisted pair cable comprises of two separate insulated copper wires, which are twisted together and run in parallel. The copper wires are typically 1mm in diameter. One of the wires is used to transmit data and the other is the ground reference.

Reason for Twisting - All transmissions are prone to noise, interferences, and crosstalks. When the wires are twisted, some part of the noise signals is in the direction of data signals while the other parts are in the opposite directions. Thus the external waves cancel out due to the different twists. The receiver calculates the difference in the voltages of the two wires for retrieving data. Thus a much better immunity against noise is obtained.

Applications of Twisted-Pair Cables - In telephone lines, In DSL lines, In LANs.

There are two types of twisted pair cables −
Unshielded Twisted Pair ( UTP ): These generally comprise of wires and insulators.
Shielded Twisted Pair ( STP ): They have a braided wired mesh that encases each pair of insulated wires.

EIA has classified twisted pair cables into seven categories

Coaxial cable:

Coaxial cable resembles like a TV installation cable. Coaxial cable is more expensive than twisted pair cable, but it provides the high data transmission speed.

Coaxial cables, commonly called coax, are copper cables with metal shielding designed to provide immunity against noise and greater bandwidth. Coax can transmit signals over larger distances at a higher speed as compared to twisted pair cables.

Coax has a central core of stiff copper conductor for transmitting signals. This is covered by an insulating material. The insulator is encased by a closely woven braided metal outer conductor that acts as a shield against noise. The outer conductor is again enclosed by a plastic insulating cover.

Coaxial cables are categorized into three types as per radio government (RG) ratings - RG – 59, RG – 58, RG – 11

Applications of Coaxial Cables -
In analog telephone networks: A single coaxial network can carry about 10,000 voice signals.
In digital telephone networks: A coax has a data rate of 600 Mbps.
In cable TV networks
In traditional Ethernet LANs
In MANs

Fibre optic cable:

Fibre optic cable is a high-speed cable that transmits the data using light beams. It provides high data transmission speed as compared to other cables. It is more expensive as compared to other cables, so it is installed at the government level.

Optical fiber cables are transparent, flexible fibers made up of glass or plastic through which light waves can pass

Structure of a Fiber – Optic Cable

A cross section of a fiber optic cable reveals three parts −

Core − It is the innermost portion of an optical fiber through which light propagates. It is cylindrical in shape and it made up of a flexible glass of high refractive index. The diameter of the core of a single mode fiber is 8 – 10 μm while multimode fibers are 50 μm in diameter. It is also called the optical waveguide since it is the main channel through which light signals are transmitted.

Cladding − The core is surrounded by a glass cladding. The glass of cladding has a lower refractive index than the core. This enables total internal reflection of light waves in the core, and eventually propagation of light waves within the core.

Outer Coating or Jacket − The outer jacket is a thin plastic sheath or coating that is opaque to light. It prevents light rays from outside to enter the optical fiber. Fibers are typically bundles together, where each bundle is covered by a protective outer sheath that prevents the fibers from physical damage.

There are two types of fibers −

Step-index fiber : In these, the refractive index of the core is constant and undergoes an abrupt change at the interface with the cladding.

Graded-index fiber: The refractive index of the core varies in a radial manner from the center. The fiber is densest at the core and becomes rarer towards the edge of the core.

Both of these are further divided into two categories depending upon propagation modes of the fibers −

Single-mode fiber
Multi-mode fiber

Router

Router is a device that connects the LAN to the internet. The router is mainly used to connect the distinct networks or connect the internet to multiple computers.

Routers are networking devices operating at layer 3 or a network layer of the OSI model. They are responsible for receiving, analysing, and forwarding data packets among the connected computer networks. When a data packet arrives, the router inspects the destination address, consults its routing tables to decide the optimal route and then transfers the packet along this route.

Features of Routers

A router is a layer 3 or network layer device.
It connects different networks together and sends data packets from one network to another.
A router can be used both in LANs (Local Area Networks) and WANs (Wide Area Networks).
It transfers data in the form of IP packets. In order to transmit data, it uses IP address mentioned in the destination field of the IP packet.
Routers have a routing table in it that is refreshed periodically according to the changes in the network. In order to transmit data packets, it consults the table and uses a routing protocol.
In order to prepare or refresh the routing table, routers share information among each other.
Routers provide protection against broadcast storms.
Routers are more expensive than other networking devices like hubs,bridges and switches.

Routers are manufactured by some popular companies like −
Cisco
D-Link
HP
3Com
Juniper
Nortel

Routing Table

The functioning of a router depends largely upon the routing table stored in it. The routing table stores the available routes for all destinations. The router consults the routing table to determine the optimal route through which the data packets can be sent.

A routing table typically contains the following entities −

IP addresses and subnet mask of the nodes in the network
IP addresses of the routers in the network
Interface information among the network devices and channels

Routing tables are of two types −

Static Routing Table − Here, the routes are fed manually and are not refreshed automatically. It is suitable for small networks containing 2-3 routers.

Dynamic Routing Table − Here, the router communicates with other routers using routing protocols to determine the available routes. It is suited for larger networks having large number of routers.

Types of Routers
A variety of routers are available depending upon their usages. The main types of routers are −

Wireless Router − They provide WiFi connection WiFi devices like laptops, smartphones etc. They can also provide standard Ethernet routing. For indoor connections, the range is 150 feet while its 300 feet for outdoor connections.

Broadband Routers − They are used to connect to the Internet through telephone and to use voice over Internet Protocol (VoIP) technology for providing high-speed Internet access. They are configured and provided by the Internet Service Provider (ISP).

Core Routers − They can route data packets within a given network, but cannot route the packets between the networks. They helps to link all devices within a network thus forming the backbone of network. It is used by ISP and communication interfaces.

Edge Routers − They are low-capacity routers placed at the periphery of the networks. They connect the internal network to the external networks, and are suitable for transferring data packets across networks. They use Border Gateway Protocol (BGP) for connectivity. There are two types of edge routers, subscriber edge routers and label edge routers.

Brouters − Brouters are specialised routers that can provide the functionalities of bridges as well. Like a bridge, brouters help to transfer data between networks. And like a router, they route the data within the devices of a network.

Modem

Modem connects the computer to the internet over the existing telephone line. A modem is not integrated with the computer motherboard. A modem is a separate part on the PC slot found on the motherboard.
The data stored on the computer is digital whereas a telephone line or cable wire can transmit only analog data.

The main function of the modem is to convert digital signal into analog and vice versa. Modem is a combination of two devices − modulator and demodulator. The modulator converts digital data into analog data when the data is being sent by the computer. The demodulator converts analog data signals into digital data when it is being received by the computer.

Depending on direction of data transmission, modem can be of these types −

Simplex − A simplex modem can transfer data in only one direction, from digital device to network (modulator) or network to digital device (demodulator).

Half duplex − A half-duplex modem has the capacity to transfer data in both the directions but only one at a time.

Full duplex − A full duplex modem can transmit data in both the directions simultaneously.

Modem is abbreviation for Modulator – De-modulator. Modems are used for data transfer from one computer network to another computer network through telephone lines. The computer network works in digital mode, while analog technology is used for carrying massages across phone lines.

Modulator converts information from digital mode to analog mode at the transmitting end and de-modulator converts the same from analog to digital at receiving end. The process of converting analog signals of one computer network into digital signals of another computer network so they can be processed by a receiving computer is referred to as digitizing.

When an analog facility is used for data communication between two digital devices called Data Terminal Equipment (DTE), modems are used at each end. DTE can be a terminal or a computer.

The modem at the transmitting end converts the digital signal generated by DTE into an analog signal by modulating a carrier. This modem at the receiving end demodulates the carrier and hand over the demodulated digital signal to the DTE.

The transmission medium between the two modems can be dedicated circuit or a switched telephone circuit. If a switched telephone circuit is used, then the modems are connected to the local telephone exchanges. Whenever data transmission is required connection between the modems is established through telephone exchanges.

Computer Network Architecture

Computer Network Architecture is defined as the physical and logical design of the software, hardware, protocols, and media of the transmission of data. Simply we can say that how computers are organized and how tasks are allocated to the computer.

The two types of network architectures are used:
Peer-To-Peer network
Client/Server Network

Peer-To-Peer network

Peer-To-Peer network is a network in which all the computers are linked together with equal privilege and responsibilities for processing the data.
Peer-To-Peer network is useful for small environments, usually up to 10 computers.
Peer-To-Peer network has no dedicated server.
Special permissions are assigned to each computer for sharing the resources, but this can lead to a problem if the computer with the resource is down.

Advantages Of Peer-To-Peer Network:

It is less costly as it does not contain any dedicated server.
If one computer stops working but, other computers will not stop working.
It is easy to set up and maintain as each computer manages itself.

Disadvantages Of Peer-To-Peer Network:

In the case of Peer-To-Peer network, it does not contain the centralized system . Therefore, it cannot
back up the data as the data is different in different locations.
It has a security issue as the device is managed itself.

Client/Server Network

Client/Server network is a network model designed for the end users called clients, to access the resources such as songs, video, etc. from a central computer known as Server.
The central controller is known as a server while all other computers in the network are called clients.
A server performs all the major operations such as security and network management.
A server is responsible for managing all the resources such as files, directories, printer, etc.
All the clients communicate with each other through a server. For example, if client1 wants to send some data to client 2, then it first sends the request to the server for the permission. The server sends the response to the client 1 to initiate its communication with the client 2.

Advantages Of Client/Server network:

A Client/Server network contains the centralized system. Therefore we can back up the data easily.
A Client/Server network has a dedicated server that improves the overall performance of the whole system.
Security is better in Client/Server network as a single server administers the shared resources.
It also increases the speed of the sharing resources.

Disadvantages Of Client/Server network:

Client/Server network is expensive as it requires the server with large memory.
A server has a Network Operating System(NOS) to provide the resources to the clients, but the cost of NOS is very high.
It requires a dedicated network administrator to manage all the resources.

Topology

• Bus
• Ring
• Tree
• Star
• Mesh
• Hybrid

Bus 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".

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.

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 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.

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.

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.

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 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.

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.

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 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.

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 that reduces the efficiency of the network.

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 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.

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: 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.

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 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.

Transmission modes

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

Simplex 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.

Half-Duplex mode

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.

Full-duplex mode

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.