Computer Network

AMPICS

Ganpat Univeresity

What is computer Network

• 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.

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Uses of computer network

• Resource sharing: Resource sharing is the sharing of resources such as programs, printers, and data among the users on the network without the requirement of the physical location of the resource and user.
• Server-Client model: Computer networking is used in the server-client model. A server is a central computer used to store the information and maintained by the system administrator. Clients are the machines used to access the information stored in the server remotely.
• Communication medium: Computer network behaves as a communication medium among the users. For example, a company contains more than one computer has an email system which the employees use for daily communication.
• E-commerce: Computer network is also important in businesses. We can do the business over the internet. For example, amazon.com is doing their business over the internet, i.e., they are doing their business over the internet

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Features Of Computer network�

• Communication speed
• File sharing
• Back up and Roll back is easy
• Software and Hardware sharing
• Security
• Scalability
• Reliability

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Goals of Computer Networks: 

• Resource Sharing – Many organization has a substantial number of computers in operations, which are located apart. Ex. A group of office workers can share a common printer, fax, modem, scanner, etc. � 
• High Reliability – If there are alternate sources of supply, all files could be replicated on two or more machines. If one of them is not available, due to hardware failure, the other copies could be used. � 
• Inter-process Communication – Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications. � 
• Flexible access – Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another. 

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• Security– Computer networks must be secure to protect against unauthorized access, data breaches, and other security threats. This includes implementing measures such as firewalls, antivirus software, and encryption to ensure the confidentiality, integrity, and availability of data.
• Performance– Computer networks must provide high performance and low latency to ensure that applications and services are responsive and available when needed. This requires optimizing network infrastructure, bandwidth utilization, and traffic management.
• Scalability- Computer networks must be designed to scale up or down as needed to accommodate changes in the number of users, devices, and data traffic. This requires careful planning and management to ensure the network can meet current and future needs

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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

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.

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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.

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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.

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Client/Server Network

• 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

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

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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.

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• Without this device, networking cannot be done. This is also known as network adapter card, Ethernet Card and LAN card. NIC allows our PC to communicate with other PCs. Basically it converts data transmission technology.

• In simple language modem is a device that is used to connect with internet. Technically it is a device which enables digital data transmission to be transmitted over the telecommunication lines.

• To understand the functionality of hub let’s take an example from real life.
• There are four friends who share everything. One of them finds a photo of Amitabh Bachchan. To share this with friends, he will make three photo copies from Xerox machine and give one copy to each friend. He doesn’t need a copy of photo for himself as he has the original one.
• Now change the characters in this example. Replace friends with HUB’s port, photo with data signal and Xerox machine with HUB.
• There is a HUB which has four ports. Ports share everything. One port received data signal from its connected device. It will make three copies of data signal from HUB and give one copy to each port. Receiver port doesn’t need a copy of data signal for itself as it has it the original version.
• This is what exactly a HUB do. When a hub receives signal on its port, it repeats the signal and forwards that signal from all ports except the port on which the signal arrived.

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Basically routers are used :-

• To connect different network segments.
• To connect different network protocols such as IP and IPX.
• To connect several smaller networks into a large network (known as internetwork)
• To break a large network in smaller networks (Known as subnet usually created to improve the performance or manageability)
• To connect two different media types such as UTP and fiber optical.
• To connect two different network architectures such as token ring and Ethernet.
• To connect LAN network with Telco company’s office (Known as DTE device).
• To access DSL services (known as DSL Router).

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Gateway

• A gateway is a hardware device that acts as a "gate" between two networks. It may be a router, firewall, server, or other device that enables traffic to flow in and out of the network.
• While a gateway protects the nodes within network, it also a node itself. The gateway node is considered to be on the "edge" of the network as all data must flow through it before coming in or going out of the network.

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Examples of Gateway

• A router is a common type of gateway used in home networks. It allows computers within the local network to send and receive data over the Internet.
• A firewall is a more advanced type of gateway, which filters inbound and outbound traffic, disallowing incoming data from suspicious or unauthorized sources.
• A proxy server is another type of gateway that uses a combination of hardware and software to filter traffic between two networks. For example, a proxy server may only allow local computers to access a list of authorized websites.

What is the Internet?

• Internet is a global network that connects billions of computers across the world with each other and to the World Wide Web. It uses standard internet protocol suite (TCP/IP) to connect billions of computer users worldwide. It is set up by using cables such as optical fibers and other wireless and networking technologies. At present, internet is the fastest mean of sending or exchanging information and data between computers across the world.
• It is believed that the internet was developed by "Defence Advanced Projects Agency" (DARPA) department of the United States. And, it was first connected in 1969.

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Difference between Internet & Intranet

• Internet�1. Internet is wide network of computers and is

open for all.� 2. Internet itself contains a large number of

intranets.� 3. The number of users who use internet is

Unlimited.� 4. The Visitors traffic is unlimited.� 5. Internet contains different source of

information and is available for all.

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• Intranet�1. Intranet is also a network of computers

designed for a specific group of users.� 2. Intranet can be accessed from Internet but

with restrictions.� 3. The number of users is limited.� 4. The traffic allowed is also limited.� 5. Intranet contains only specific group

information.

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Baseband & Broadband Transmission

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BROADCAST

• Broadcast is the communication that occurs when a communication channel is shared not just between two devices or nodes but also between numerous devices or nodes participating in the conversation.
• A multipoint connection is one that connects more than two devices together. Multidrop line configuration is another name for the multipoint connection. Numerous devices share a single link in a multipoint connection. As a result, it is possible to say that all devices connected to the link temporarily share the channel capacity. The devices use a turn-by-turn link, which is called a time-shared line configuration.
• In a broadcast network, the packet transmitted by the sender is received and processed by each device on the link. However, the receiver evaluates whether the packet belongs to it or not based on the address field in the packet; if it does not, the packet is discarded. If the packet belongs to the recipient, store it and respond appropriately to the sender

Point-to-Point Communication

• A point-to-point communication is also known as P2P. In the context of telecommunication, it is an established connection between two nodes that may be used to communicate back and forth. A basic telephone call, in which one phone is connected to another, and both nodes can send and receive audio, is the most common example of point-to-point communication.
• These P2P connections were first established utilizing circuit-switched landlines in the early days of telephony. However, point-to-point communication in modern networks nowadays is made possible by complex fibre-optic networks. P2P connections of various forms can transmit many types of data, including digital and analog signals.
• The point-to-point connection is one of the line configuration methods that explains how two communication devices are connected in a link. It is a unicast connection. A dedicated link exists between each pair of sender and receiver. The entire channel's capacity is reserved solely for packet transmission between the sender and receiver.

Differences between Broadcast and Multicast

• Broadcasting is a method of sending a message to all recipients simultaneously. In contrast, multicasting is a group communication method in which data is sent simultaneously to a group of target computers.
• Broadcasting consumes bandwidth since packets are given to sites that are not interested in receiving them. In contrast, multicasting successfully utilizes bandwidth because the packet is transmitted only to hosts that are interested in receiving it.
• The transmission of a packet in broadcast is one-to-all, whereas the transmission of a packet in multicast is one-to-many.
• Broadcasting creates a large amount of network traffic by delivering each packet to every site on the network. In contrast, multicasting controls traffic by delivering packets only to interested hosts, lowering network load.
• In broadcasting, no group administration is necessary. In contrast, group management is needed in multicasting to establish the network in which at least one host is interested in receiving the packet.
• Broadcast creates a large amount of traffic that can slow down the computer system. However, when compared to broadcasting, multicast generates less traffic, which speeds up the system.
• Broadcasting is slower. In contrast, multicast is faster.

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What is Network 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.

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 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).

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• 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.

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Ring Topology

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• 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.

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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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Synchronous Communication

Synchronous transmission is an effective and dependable method of sending huge amounts of data. The data travels in a full-duplex method in the type of frames or blocks in Synchronous Transmission. The transmitter and receiver must be synced so that the sender knows where to start the new byte. As a result, every data block is marked with synchronization characters, and the receiving device obtains the data until a certain ending character is found.

It also allows connected devices to interact in real time. Synchronous transmission can be seen in chat rooms, video conferencing, telephonic talks, and face-to-face interactions. It utilizes the broad-band and voice band channels because they enable quicker speeds of up to 1200 bps and meet the objective of high data transfer speed.

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• Advantages
• It aids the user in transferring a huge amount of data.
• Every byte is sent without a pause before the next.
• It also helps to reduce timing errors.
• It allows connected devices to communicate in real-time.
• Disadvantages
• The sender and receiver must operate at the same clock frequency simultaneously.
• The accuracy of the received data is determined by the receiver's capacity to count the received bits precisely.

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Asynchronous Communication

• Asynchronous transmission is also referred to as start and stop transmission. It sends data from the transmitter to the receiver using the flow control approach and synchronizes data between the source and destination without utilizing a clock.
• This transmission technique sends 8 bits or one letter at a time. In this system, each character transmits the start bit before the transmission process begins, and it also transmits the stop bit when the character is sent. The total number of bits is 10, including the character, start, and stop bits.
• It employs character-based synchronization for the receiving terminal to synchronize with receiving data on a character. It is easy, quick, and inexpensive and doesn't need two-way communication. Asynchronous transmission is demonstrated via letters, televisions, emails, forums, and radios.
• Asynchronous transmission makes use of voice-band channels that are narrow and operate at a slower speed. In this case, the transmitting device operates manually or intermittently.

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• Advantages
• It doesn't require synchronizing the receiver and transmitter.
• It is a very flexible technique of data transmission.
• This kind of transmission is simple to implement.
• It allows users to send signals from sources with varying bit rates.
• When the data byte transmission is complete, the data transmission may be resumed.
• Disadvantages
• The timing errors may occur because synchronization is difficult to determine.
• These bits could be mistakenly recognized due to the noise on the channel.
• The start and stop bits are extra bits that must be utilized in asynchronous transmission.
• It transmits information at a slower rate.

LAN, WAN & MAN

CATEGORIES OF NETWORKS

� II.1. Common Types of Computer Network �

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• Personal Area Network (PAN)

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• Local Area Network (LAN).

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• Wide Area Network (WAN).

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• Metropolitan Area Network ( MAN).

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Advantages of WAN are :

• It covers large geographical area therefore networks can be made between long distances.
• Different peripherals can be shared with all the computers in the network.
• Shares software and resources with connecting workstations.

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Disadvantage of WAN are :

• Setting up the network could be expensive.
• Maintaining a network is a full-time job which requires network supervisors and technicians to be employed.
• Security is a real issue when many different people have the ability to use information from other computers.
• Protection against hackers and viruses adds more complexity and expense.
• Need a good firewall to restrict outsiders from entering and disrupting the network .

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Differences between LAN, WAN, & MAN

Simplex

• In the simplex method, the data transmission can be performed only in one direction.
• At a time, only one client (either sender or receiver) can be active.
• That means among the two devices, one device can only transmit a link while the other device can only receive it.
• A sender can only transmit the data, and the receiver can only accept that data.
• The receiver cannot reply back to the sender. In another case, if the receiver sends the data, the sender will only accept it.
• The sender cannot reply back to the receiver.�

• Example 1: Keyboard and CPU are the best examples of a simplex. The keyboard always transmits characters to the CPU (Central processing unit), but the CPU does not require transmitting characters or data to the keyboard.

Half Duplex

• In the half-duplex, the sender and receiver can communicate in both directions, but not at the same time. If a sender sends some data, the receiver is able to accept it, but at that time, the receiver cannot send anything to the receiver. Same as if the receiver sends data to the sender, the sender cannot send. If there is a case where we don't need to communicate at a time in both the direction, we can use the half-duplex. 

For example, the internet is a good example of half-duplex. With the help of internet, if a user sends a web page request to the web server, the server processes the application and sends the requested page to the user�

Full Duplex

• In the full-duplex, the sender and the receiver are able to send and receive at the same time. The communication mode of full-duplex is widely used in the world. In this mode, signals travelling in one direction are able to share the capacity of links with signals travelling in the opposite directions. There are two ways in which sharing can occur, which is described as follow:
• Either capacity of the link is divided into the signals going in both directions.
• Or the links have two physically separated transmission parts. Where one part can be used for sending, and another part can be used for receiving

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Examples: Telephone Network is a good example of full-duplex mode. While using the telephone or phone, the two persons are able to talk and hear both things at the same time. �Audio calling or Video calling is also an example of full-duplex. In audio or video calling, two persons are able to communicate at the same time. In audio calling, they are able to speak and listen at the same time, and in video calling, they are able to communicate by seeing each other at the same time. 

There are two types of login:

• Local Login
• Remote login
• The commands in NVT forms are transmitted to the TCP/IP at the remote machine.
• Here, the characters are delivered to the operating system and then pass to the TELNET server.
• The TELNET server transforms the characters which can be understandable by a remote computer. However, the characters cannot be directly passed to the operating system as a remote operating system does not receive the characters from the TELNET server.
• Therefore it requires some piece of software that can accept the characters from the TELNET server.
• The operating system then passes these characters to the appropriate application program.
• Network Virtual Terminal (NVT)

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Telnet

• The main task of the internet is to provide services to users. For example, users want to run different application programs at the remote site and transfers a result to the local site. This requires a client-server program such as FTP, SMTP. But this would not allow us to create a specific program for each demand.
• The better solution is to provide a general client-server program that lets the user access any application program on a remote computer. Therefore, a program that allows a user to log on to a remote computer. A popular client-server program Telnet is used to meet such demands. Telnet is an abbreviation for Terminal Network.
• Telnet provides a connection to the remote computer in such a way that a local terminal appears to be at the remote side

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FTP

• FTP stands for File transfer protocol.
• FTP is a standard internet protocol provided by TCP/IP used for transmitting the files from one host to another.
• It is mainly used for transferring the web page files from their creator to the computer that acts as a server for other computers on the internet.
• It is also used for downloading the files to computer from other servers.

Objectives of FTP

• It provides the sharing of files.
• It is used to encourage the use of remote computers.
• It transfers the data more reliably and efficiently.

Why FTP?

• Although transferring files from one system to another is very simple and straightforward, but sometimes it can cause problems. For example, two systems may have different file conventions. Two systems may have different ways to represent text and data. Two systems may have different directory structures. FTP protocol overcomes these problems by establishing two connections between hosts. One connection is used for data transfer, and another connection is used for the control connection.

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There are two types of connections in FTP

• Control Connection: The control connection uses very simple rules for communication. Through control connection, we can transfer a line of command or line of response at a time. The control connection is made between the control processes. The control connection remains connected during the entire interactive FTP session.

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• Data Connection: The Data Connection uses very complex rules as data types may vary. The data connection is made between data transfer processes. The data connection opens when a command comes for transferring the files and closes when the file is transferred

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Advantages and Disadvantages of FTP

Advantages

• It is simple to use and implement.
• There is no need to worry about losing a connection while uploading data because you may resume it later. The data transfer can be stopped and then resumed at any time.
• All users of the operating systems (Linux, Windows, and Mac) can successfully connect to the server using the FTP or Secure FTP protocol.
• It sends info to control commands over a separate TCP connection. It allows for faster data transport.
• It is a connection-oriented protocol with powerful control commands.

Disadvantages

• It needs large memory and programming.
• It doesn't enable server-to-server copy and recursive directory removal tasks.
• It is difficult to script jobs utilizing the FTP protocol.
• When sending files via FTP, compliance may be an issue.
• Filtering active FTP connections on your local system is a difficult task.

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What is TFTP?

• TFTP is an abbreviation for "Trivial File Transfer Protocol". It is a sample protocol that is commonly used for file transmission.
• TFTP employs the User Datagram Protocol (UDP) to transport data from one end to the other.
• In comparison to the FTP, it is very simple in design and has limited functionalities (FTP).
• TFTP doesn't provide authentication or security while transferring data.
• As a result, boot data or configuration files are typically shared between computer systems in a local setup.
• It aids in booting devices and systems that lack storage devices or hard disk drives because utilizing a small amount of memory may be easily installed.
• It is primarily used for booting systems that store configuration on a remote TFTP server. It operates on Port number 69, and its service is given by UDP.

Advantages and Disadvantages of TFTP

Advantages

• It utilizes the User Datagram Protocol (UDP) protocol.
• It is very easy to use and implement.
• It needs minimum coding.
• It needs minimum memory utilization.
• It is a faster file transfer protocol.

Disadvantages

• It doesn't offer file security as compared to FTP.
• It doesn't list the directory's contents.
• It is an unsecured FTP.
• There is no encryption or authentication mechanism.

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Main Differences between FTP and TFTP

SNMP

• SNMP stands for Simple Network Management Protocol.
• SNMP is a framework used for managing devices on the internet.
• It provides a set of operations for monitoring and managing the internet.
• If an organization has 1000 devices then to check all devices, one by one every day, are working properly or not is a hectic task. To ease these up, Simple Network Management Protocol (SNMP) is used. 
• Simple Network Management Protocol (SNMP) – �SNMP is an application layer protocol that uses UDP port number 161/162.SNMP is used to monitor the network, detect network faults, and sometimes even used to configure remote devices. 
• SNMP components – �There are 3 components of SNMP: 
• SNMP Manager – �It is a centralized system used to monitor network. It is also known as Network Management Station (NMS) 
• SNMP agent – �It is a software management software module installed on a managed device. Managed devices can be network devices like PC, routers, switches, servers, etc.  
• Management Information Base – �MIB consists of information on resources that are to be managed. This information is organized hierarchically. It consists of objects instances which are essentially variables. 

SNMP Concept

• SNMP has two components Manager and agent.
• The manager is a host that controls and monitors a set of agents such as routers.
• It is an application layer protocol in which a few manager stations can handle a set of agents.
• The protocol designed at the application level can monitor the devices made by different manufacturers and installed on different physical networks.
• It is used in a heterogeneous network made of different LANs and WANs connected by routers or gateways.

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• SNMP defines five types of messages: GetRequest, GetNextRequest, SetRequest, GetResponse,

Trap.

• GetRequest: The GetRequest message is sent from a manager (client) to the agent (server) to retrieve the value of a variable.

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• GetNextRequest: The GetNextRequest message is sent from the manager to agent to retrieve the value of a variable. This type of message is used to retrieve the values of the entries in a table. If the manager does not know the indexes of the entries, then it will not be able to retrieve the values. In such situations, GetNextRequest message is used to define an object.

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• GetResponse: The GetResponse message is sent from an agent to the manager in response to the GetRequest and GetNextRequest message. This message contains the value of a variable requested by the manager.

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• SetRequest: The SetRequest message is sent from a manager to the agent to set a value in a variable.

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• Trap: The Trap message is sent from an agent to the manager to report an event. For example, if the agent is rebooted, then it informs the manager as well as sends the time of rebooting.

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SMTP

• SMTP is an application layer protocol. The client who wants to send the mail opens a TCP connection to the SMTP server and then sends the mail across the connection. The SMTP server is an always-on listening mode. As soon as it listens for a TCP connection from any client, the SMTP process initiates a connection through port 25. After successfully establishing a TCP connection the client process sends the mail instantly. 

• The SMTP model is of two types:
• End-to-end method
• Store-and-forward method
• The end-to-end model is used to communicate between different organizations whereas the store and forward method is used within an organization. An SMTP client who wants to send the mail will contact the destination’s host SMTP directly, in order to send the mail to the destination. The SMTP server will keep the mail to itself until it is successfully copied to the receiver’s SMTP. 
• The client SMTP is the one that initiates the session so let us call it the client-SMTP and the server SMTP is the one that responds to the session request so let us call it receiver-SMTP. The client-SMTP will start the session and the receiver SMTP will respond to the request. 

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Model of SMTP System� �In the SMTP model user deals with the user agent (UA), for example, Microsoft Outlook, Netscape, Mozilla, etc. In order to exchange the mail using TCP, MTA is used. The user sending the mail doesn’t have to deal with MTA as it is the responsibility of the system admin to set up a local MTA. The MTA maintains a small queue of mail so that it can schedule repeat delivery of mail in case the receiver is not available. The MTA delivers the mail to the mailboxes and the information can later be downloaded by the user agents.�

• Advantages of SMTP
• If necessary, the users can have a dedicated server.
• It allows for bulk mailing.
• Low cost and wide coverage area.
• Offer choices for email tracking.
• Reliable and prompt email delivery.
• Disadvantages of SMTP
• SMTP’s common port can be blocked by several firewalls.
• SMTP security is a bigger problem.
• Its simplicity restricts how useful it can be.
• Just 7-bit ASCII characters can be used.
• If a message is longer than a certain length, SMTP servers may reject the entire message.

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POP Protocol

• The POP protocol stands for Post Office Protocol. As we know that SMTP is used as a message transfer agent. When the message is sent, then SMPT is used to deliver the message from the client to the server and then to the recipient server. But the message is sent from the recipient server to the actual server with the help of the Message Access Agent. The Message Access Agent contains two types of protocols, i.e., POP3 and IMAP.

What is POP 3?

• The POP3 is a simple protocol and having very limited functionalities. In the case of the POP3 protocol, the POP3 client is installed on the recipient system while the POP3 server is installed on the recipient's mail server.

History of POP3 protocol

• The first version of post office protocol was first introduced in 1984 by the internet engineering task force. The developers developed a simple and effective email protocol known as the POP3 protocol, which is used for retrieving the emails from the server. 
• In 1985, the post office protocol version 2 was introduced.
• it was replaced with the post office protocol version 3 in 1988. Although the POP3 protocol has undergone various enhancements, the developers maintained a basic principle that it follows a three-stage process at the time of mail retrieval between the client and the server. They tried to make this protocol very simple, and this simplicity makes this protocol very popular today.

Let's understand the working of the POP3 protocol.

The following are the advantages of a POP3 protocol:

• It allows the users to read the email offline. It requires an internet connection only at the time of downloading emails from the server.
• It provides easy and fast access to the emails as they are already stored on our PC.
• There is no limit on the size of the email which we receive or send.
• It requires less server storage space as all the mails are stored on the local machine.
• There is maximum size on the mailbox, but it is limited by the size of the hard disk.
• It is a simple protocol so it is one of the most popular protocols used today.
• It is easy to configure and use.

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The following are the advantages of a POP3 protocol:

• If the emails are downloaded from the server, then all the mails are deleted from the server by default.
• Transferring the mail folder from the local machine to another machine can be difficult.
• Since all the attachments are stored on your local machine, there is a high risk of a virus attack if the virus scanner does not scan them. The virus attack can harm the computer.
• The email folder which is downloaded from the mail server can also become corrupted.
• The mails are stored on the local machine, so anyone who sits on your machine can access the email folder.

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