UNIT1:INTRODUCTION

 

Unit1:Introduction Introduction To Computer Networks: What is a Computer Network? 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. Components Of Computer Network: Major components of a computer network are: NIC(National interface card) 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. There are two types of NIC: wireless NIC and wired NIC. Wireless NIC: All the modern laptops use the wireless NIC. In Wireless NIC, a connection is made using the antenna that employs the radio wave technology. Wired NIC: Cables use the wired NIC to transfer the data over the medium. 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. 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. 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. 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. 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. 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. 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. 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.   Features Of Computer network Communication speed File sharing Back up and Roll back is easy Software and Hardware sharing Security Scalability Reliability Communication speed Network provides us to communicate over the network in a fast and efficient manner. For example, we can do video conferencing, email messaging, etc. over the internet. Therefore, the computer network is a great way to share our knowledge and ideas. File sharing File sharing is one of the major advantage of the computer network. Computer network provides us to share the files with each other. Back up and Roll back is easy Since the files are stored in the main server which is centrally located. Therefore, it is easy to take the back up from the main server. Software and Hardware sharing We can install the applications on the main server, therefore, the user can access the applications centrally. So, we do not need to install the software on every machine. Similarly, hardware can also be shared. Security Network allows the security by ensuring that the user has the right to access the certain files and applications. Scalability Scalability means that we can add the new components on the network. Network must be scalable so that we can extend the network by adding new devices. But, it decreases the speed of the connection and data of the transmission speed also decreases, this increases the chances of error occurring. This problem can be overcome by using the routing or switching devices. Reliability Computer network can use the alternative source for the data communication in case of any hardware failure. Service Computer Network Components Computer network components are the major parts which are needed to install the software. Some important network components are NIC, switch, cable, hub, router, and modem. Depending on the type of network that we need to install, some network components can also be removed. For example, the wireless network does not require a cable. Following are the major components required to install a network: NIC NIC stands for network interface card. NIC is a hardware component used to connect a computer with another computer onto a network It can support a transfer rate of 10,100 to 1000 Mb/s. The MAC address or physical address is encoded on the network card chip which is assigned by the IEEE to identify a network card uniquely. The MAC address is stored in the PROM (Programmable read-only memory). There are two types of NIC:

1.                  Wired NIC 2.                  Wireless NIC Wired NIC: The Wired NIC is present inside the motherboard. Cables and connectors are used with wired NIC to transfer data. Wireless NIC: The wireless NIC contains the antenna to obtain the connection over the wireless network. For example, laptop computer contains the wireless NIC. A Hub is a hardware device that divides the network connection among multiple devices. When computer requests for some information from a network, it first sends the request to the Hub through cable. Hub will broadcast this request to the entire network. All the devices will check whether the request belongs to them or not. If not, the request will be dropped. The process used by the Hub consumes more bandwidth and limits the amount of communication. Nowadays, the use of hub is obsolete, and it is replaced by more advanced computer network components such as Switches, Routers. Switch A switch is a hardware device that connects multiple devices on a computer network. A Switch contains more advanced features than Hub. The Switch contains the updated table that decides where the data is transmitted or not. Switch delivers the message to the correct destination based on the physical address present in the incoming message. A Switch does not broadcast the message to the entire network like the Hub. It determines the device to whom the message is to be transmitted. Therefore, we can say that switch provides a direct connection between the source and destination. It increases the speed of the network. Router A router is a hardware device which is used to connect a LAN with an internet connection. It is used to receive, analyze and forward the incoming packets to another network. A router works in a Layer 3 (Network layer) of the OSI Reference model. A router forwards the packet based on the information available in the routing table. It determines the best path from the available paths for the transmission of the packet. Advantages Of Router: Security: The information which is transmitted to the network will traverse the entire cable, but the only specified device which has been addressed can read the data. Reliability: If the server has stopped functioning, the network goes down, but no other networks are affected that are served by the router. Performance: Router enhances the overall performance of the network. Suppose there are 24 workstations in a network generates a same amount of traffic. This increases the traffic load on the network. Router splits the single network into two networks of 12 workstations each, reduces the traffic load by half. Network range Modem A modem is a hardware device that allows the computer to connect to the internet over the existing telephone line. A modem is not integrated with the motherboard rather than it is installed on the PCI slot found on the motherboard. It stands for Modulator/Demodulator. It converts the digital data into an analog signal over the telephone lines. Based on the differences in speed and transmission rate, a modem can be classified in the following categories: Standard PC modem or Dial-up modem Cellular Modem Cable modem  Cables and Connectors Cable is a transmission media used for transmitting a signal. There are three types of cables used in transmission: Twisted pair cable Coaxial cable Fibre-optic cable    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. Advantage of Simplex mode:   In simplex mode, the station can utilize the entire bandwidth of the communication channel, so that more data can be transmitted at a time. Disadvantage of Simplex mode: 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. Advantage of Half-duplex mode: 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. Disadvantage of Half-Duplex mode: 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. Advantage of Full-duplex mode: Both the stations can send and receive the data at the same time. Disadvantage of Full-duplex mode: If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into two parts. Differences b/w Simplex, Half-duplex and Full-duplex mode 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.   Computer networks and its applications:  Some  of the network applications in different field are the following : · Marketing and sales: – Computer networks are widely used in both marketing sales firms. These are used by marketing professionals to collect, exchange, and analyzes data relating to customer requirements and product development cycles. Teleshopping is also important part of sales applications that use order-entry computers or telephones connected to an order-processing network, and on-line reservation services for hotels airline and so on. · Manufacturing: – Now days, computer networks are used in a several aspects of manufacturing, including the manufacturing process itself. Two applications which use a network to provide necessary services are computer-assisted manufacturing (CAM) and computer –assisted designing (CAD) both of which permit multiple users to work on a project simultaneously. · Financial Services: – In Present, Financial services are completely dependent on computer networks. Main applications are credit history searches, foreign exchange and investment services, and Electronic Funds Transfer (EFT) that permits a user to transfer money without going into bank. · Teleconferencing: – With The help of teleconferencing conferences are possible to occur without the participants being in the same place. Applications include simple text conferencing, voice conferencing, and video conferencing. · Cable Television:-Future Services provided by cable television network can include video on request, as well as the same information, financial and communications services currently provided by the telephone companies and computer networks. · Information Services:- Network information services include bulletin boards and data banks. A World Wide Web site offering the technical specifications for a new product is an information service. · Electronic Messaging:– Electronic mail (e-mail) is the most widely used network application. · Electronic Data Interchange (EDI):– EDI permits business information to be transferred without using paper. · Directory services: – By using directory services, it is possible to store the last of files in a central location to speed worldwide search operations. · Cellular Telephone: – In the past, two parties desiring to use the services of the telephone company had to be linked by a fixed physical connection. But, in present cellular network make it possible to maintain wireless phone connections even while travelling over large distance Network architecture: 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.

Topologies: Types of Network Topology

Network Topology is the schematic description of a network arrangement, connecting various nodes(sender and receiver) through lines of connection.

BUS Topology

Bus topology is a network type in where every computer and network device is connected to single cable.

 

Features of Bus Topology

1.     It transmits data only in one direction.

2.     Every device is connected to a single cable

Advantages of Bus Topology

1.     It is cost effective.

2.     Cable required is least compared to other network topology.

3.     Used in small networks.

4.     It is easy to understand.

5.     Easy to expand joining two cables together.

Disadvantages of Bus Topology

1.     Cables fails then whole network fails.

2.     If network traffic is heavy or nodes are more the performance of the network decreases.

3.     Cable has a limited length.

4.     It is slower than the ring topology.

RING Topology

It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbours for each device.

 

Features of Ring Topology

1.     A number of repeaters are used and the transmission is unidirectional.

2.     Date is transferred in a sequential manner that is bit by bit.

Advantages of Ring Topology

1.     Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.

2.     Cheap to install and expand

Disadvantages of Ring Topology

1.     Troubleshooting is difficult in ring topology.

2.     Adding or deleting the computers disturbs the network activity.

3.     Failure of one computer disturbs the whole network.

 STAR Topology

In this type of topology all the computers are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node.

 

Features of Star Topology

1.     Every node has its own dedicated connection to the hub.

2.     Acts as a repeater for data flow.

3.     Can be used with twisted pair, Optical Fibre or coaxial cable.

Advantages of Star Topology

1.     Fast performance with few nodes and low network traffic.

2.     Hub can be upgraded easily.

3.     Easy to troubleshoot.

4.     Easy to setup and modify.

5.     Only that node is affected which has failed rest of the nodes can work smoothly.

Disadvantages of Star Topology

1.     Cost of installation is high.

2.     Expensive to use.

3.     If the hub is affected then the whole network is stopped because all the nodes depend on the hub.

4.     Performance is based on the hub that is it depends on its capacity

MESH Topology

It is a point-to-point connection to other nodes or devices. Traffic is carried only between two devices or nodes to which it is connected. Mesh has n (n-2)/2 physical channels to link h_n devices.

 

Types of Mesh Topology

1.     Partial Mesh Topology : In this topology some of the systems are connected in the same fashion as mesh topology but some devices are only connected to two or three devices.

2.     Full Mesh Topology : Each and every nodes or devices are connected to each other.

Features of Mesh Topology

1.     Fully connected.

2.     Robust.

3.     Not flexible.

Advantages of Mesh Topology

1.     Each connection can carry its own data load.

2.     It is robust.

3.     Fault is diagnosed easily.

4.     Provides security and privacy.

Disadvantages of Mesh Topology

1.     Installation and configuration is difficult.

2.     Cabling cost is more.

3.     Bulk wiring is required.

 TREE Topology

It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy.

 

Features of Tree Topology

1.     Ideal if workstations are located in groups.

2.     Used in Wide Area Network.

Advantages of Tree Topology

1.     Extension of bus and star topologies.

2.     Expansion of nodes is possible and easy.

3.     Easily managed and maintained.

4.     Error detection is easily done.

Disadvantages of Tree Topology

1.     Heavily cabled.

2.     Costly.

3.     If more nodes are added maintenance is difficult.

4.     Central hub fails, network fails.

HYBRID Topology

It is two different types of topologies which is a mixture of two or more topologies. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology).

 

Features of Hybrid Topology

1.     It is a combination of two or topologies

2.     Inherits the advantages and disadvantages of the topologies included

Advantages of Hybrid Topology

1.     Reliable as Error detecting and trouble shooting is easy.

2.     Effective.

3.     Scalable as size can be increased easily.

4.     Flexible.

Disadvantages of Hybrid Topology

1.     Complex in design.

2.     Costly.

Computer Network Types

A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications.

A computer network can be categorized by their size. A computer network is mainly of four types:

 

• • LAN(Local Area Network)
  • PAN(Personal Area Network)
  • MAN(Metropolitan Area Network)
  • WAN(Wide Area Network)

   LAN(Local Area Network)

  • Local Area Network is a group of computers connected to each other in a small area such as building, office.
  • LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc.
  • It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and ethernet cables.
  • The data is transferred at an extremely faster rate in Local Area Network.
  • Local Area Network provides higher security.

   

PAN(Personal Area Network)

• Personal Area Network is a network arranged within an individual person, typically within a range of 10 meters.
• Personal Area Network is used for connecting the computer devices of personal use is known as Personal Area Network.
• Thomas Zimmerman was the first research scientist to bring the idea of the Personal Area Network.
• Personal Area Network covers an area of 30 feet.
• Personal computer devices that are used to develop the personal area network are the laptop, mobile phones, media player and play stations.

 

There are two types of Personal Area Network:

• • Wired Personal Area Network
  • Wireless Personal Area Network

  Wireless Personal Area Network: Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network.

  Wired Personal Area Network: Wired Personal Area Network is created by using the USB.

    Examples Of Personal Area Network:

  • Body Area Network: Body Area Network is a network that moves with a person. For example, a mobile network moves with a person. Suppose a person establishes a network connection and then creates a connection with another device to share the information.
  • Offline Network: An offline network can be created inside the home, so it is also known as a home network. A home network is designed to integrate the devices such as printers, computer, television but they are not connected to the internet.
  • Small Home Office: It is used to connect a variety of devices to the internet and to a corporate network using a VPN

  MAN(Metropolitan Area Network)

  • A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network.
  • Government agencies use MAN to connect to the citizens and private industries.
  • In MAN, various LANs are connected to each other through a telephone exchange line.
  • The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL, etc.
  • It has a higher range than Local Area Network(LAN).

   

Uses Of Metropolitan Area Network:

• MAN is used in communication between the banks in a city.
• It can be used in an Airline Reservation.
• It can be used in a college within a city.
• It can also be used for communication in the military.

WAN(Wide Area Network)

• A Wide Area Network is a network that extends over a large geographical area such as states or countries.
• A Wide Area Network is quite bigger network than the LAN.
• A Wide Area Network is not limited to a single location, but it spans over a large geographical area through a telephone line, fibre optic cable or satellite links.
• The internet is one of the biggest WAN in the world.
• A Wide Area Network is widely used in the field of Business, government, and education.

Examples Of Wide Area Network:

• Mobile Broadband: A 4G network is widely used across a region or country.
• Last mile: A telecom company is used to provide the internet services to the customers in hundreds of cities by connecting their home with fiber.
• Private network: A bank provides a private network that connects the 44 offices. This network is made by using the telephone leased line provided by the telecom company.

Advantages Of Wide Area Network:

Following are the advantages of the Wide Area Network:

• Geographical area: A Wide Area Network provides a large geographical area. Suppose if the branch of our office is in a different city then we can connect with them through WAN. The internet provides a leased line through which we can connect with another branch.
• Centralized data: In case of WAN network, data is centralized. Therefore, we do not need to buy the emails, files or back up servers.
• Get updated files: Software companies work on the live server. Therefore, the programmers get the updated files within seconds.
• Exchange messages: In a WAN network, messages are transmitted fast. The web application like Facebook, Whatsapp, Skype allows you to communicate with friends.
• Sharing of software and resources: In WAN network, we can share the software and other resources like a hard drive, RAM.
• Global business: We can do the business over the internet globally.
• High bandwidth: If we use the leased lines for our company then this gives the high bandwidth. The high bandwidth increases the data transfer rate which in turn increases the productivity of our company.

Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

• Security issue: A WAN network has more security issues as compared to LAN and MAN network as all the technologies are combined together that creates the security problem.
• Needs Firewall & antivirus software: The data is transferred on the internet which can be changed or hacked by the hackers, so the firewall needs to be used. Some people can inject the virus in our system so antivirus is needed to protect from such a virus.
• High Setup cost: An installation cost of the WAN network is high as it involves the purchasing of routers, switches.
• Troubleshooting problems: It covers a large area so fixing the problem is difficult.

 

OSI Model OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI consists of seven layers, and each layer performs a particular network function. OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications. OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. Each layer is self-contained, so that task assigned to each layer can be performed independently. Characteristics of OSI Model:

 

The OSI model is divided into two layers: upper layers and lower layers. The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications. An upper layer refers to the layer just above another layer. The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium. 7 Layers of OSI Model There are the seven OSI layers. Each layer has different functions. A list of seven layers are given below: 1.                  Physical Layer 2.                  Data-Link Layer 3.                  Network Layer 4.                  Transport Layer 5.                  Session Layer 6.                  Presentation Layer 7.                  Application Layer   1) Physical layer   The main functionality of the physical layer is to transmit the individual bits from one node to another node. It is the lowest layer of the OSI model. It establishes, maintains and deactivates the physical connection. It specifies the mechanical, electrical and procedural network interface specifications. Functions of a Physical layer: Line Configuration: It defines the way how two or more devices can be connected physically. Data Transmission: It defines the transmission mode whether it is simplex, half-duplex or full-duplex mode between the two devices on the network. Topology: It defines the way how network devices are arranged. Signals: It determines the type of the signal used for transmitting the information. 2) Data-Link Layer   This layer is responsible for the error-free transfer of data frames. It defines the format of the data on the network. It provides a reliable and efficient communication between two or more devices. It is mainly responsible for the unique identification of each device that resides on a local network. It contains two sub-layers: Logical Link Control Layer It is responsible for transferring the packets to the Network layer of the receiver that is receiving. It identifies the address of the network layer protocol from the header. It also provides flow control. Media Access Control Layer A Media access control layer is a link between the Logical Link Control layer and the network's physical layer. It is used for transferring the packets over the network. Functions of the Data-link layer Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address.   Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header. Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed. Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occurr, then the receiver sends the acknowledgment for the retransmission of the corrupted frames. Access Control: When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time. 3) Network Layer   It is a layer 3 that manages device addressing, tracks the location of devices on the network. It determines the best path to move data from source to the destination based on the network conditions, the priority of service, and other factors. The Data link layer is responsible for routing and forwarding the packets. Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an internetwork. The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6. Functions of Network Layer: Internetworking: An internetworking is the main responsibility of the network layer. It provides a logical connection between different devices. Addressing: A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet. Routing: Routing is the major component of the network layer, and it determines the best optimal path out of the multiple paths from source to the destination. Packetizing: A Network Layer receives the packets from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP). 4) Transport Layer   The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no duplication of data. The main responsibility of the transport layer is to transfer the data completely. It receives the data from the upper layer and converts them into smaller units known as segments. This layer can be termed as an end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably. The two protocols used in this layer are: Transmission Control Protocol It is a standard protocol that allows the systems to communicate over the internet. It establishes and maintains a connection between hosts. When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end. User Datagram Protocol User Datagram Protocol is a transport layer protocol. It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable. Functions of Transport Layer: Service-point addressing: Computers run several programs simultaneously due to this reason, the transmission of data from source to the destination not only from one computer to another computer but also from one process to another process. The transport layer adds the header that contains the address known as a service-point address or port address. The responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of the transport layer is to transmit the message to the correct process. Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers. Connection control: Transport layer provides two services Connection-oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route. Flow control: The transport layer also responsible for flow control but it is performed end-to-end rather than across a single link. Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error. 5) Session Layer   It is a layer 3 in the OSI model. The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices. Functions of Session layer: Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either half-duplex or full-duplex. Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery. 6) Presentation Layer   A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems. It acts as a data translator for a network. This layer is a part of the operating system that converts the data from one presentation format to another format. The Presentation layer is also known as the syntax layer. Functions of Presentation layer: Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end. Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network. Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video. 7) Application Layer An application layer serves as a window for users and application processes to access network service. It handles issues such as network transparency, resource allocation, etc. An application layer is not an application, but it performs the application layer functions. This layer provides the network services to the end-users. Functions of Application layer: File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. Mail services: An application layer provides the facility for email forwarding and storage. Directory services: An application provides the distributed database sources and is used to provide that global information about various objects.  The TCP/IP reference model: TCP/IP Model The OSI Model we just looked at is just a reference/logical model. It was designed to describe the functions of the communication system by dividing the communication procedure into smaller and simpler components. But when we talk about the TCP/IP model, it was designed and developed by Department of Defense (DoD) in 1960s and is based on standard protocols. It stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a concise version of the OSI model.  It contains four layers, unlike seven layers in the OSI model. The layers are: ·       Process/Application Layer ·       Host-to-Host/Transport Layer ·       Internet Layer ·       Network Access/Link Layer The diagrammatic comparison of the TCP/IP and OSI model is as follows :

Difference between TCP/IP and OSI Model:

TCP/IP	OSI
TCP refers to Transmission Control Protocol.	OSI refers to Open Systems Interconnection.
TCP/IP has 4 layers.	OSI has 7 layers.
TCP/IP is more reliable	OSI is less reliable
TCP/IP does not have very strict boundaries.	OSI has strict boundaries
TCP/IP follow a horizontal approach.	OSI follows a vertical approach.
TCP/IP uses both session and presentation layer in the application layer itself.	OSI uses different session and presentation layers.
TCP/IP developed protocols then model.	OSI developed model then protocol.
Transport layer in TCP/IP does not provide assurance delivery of packets.	In OSI model, transport layer provides assurance delivery of packets.
TCP/IP model network layer only provides connection less services.	Connection less and connection oriented both services are provided by network layer in OSI model.
Protocols cannot be replaced easily in TCP/IP model.	While in OSI model, Protocols are better covered and is easy to replace with the change in technology.

The first layer is the Process layer on the behalf of the sender and Network Access layer on the behalf of the receiver. During this article, we will be talking on the behalf of the receiver.

1. Network Access Layer –

This layer corresponds to the combination of Data Link Layer and Physical Layer of the OSI model. It looks out for hardware addressing and the protocols present in this layer allows for the physical transmission of data.
We just talked about ARP being a protocol of Internet layer, but there is a conflict about declaring it as a protocol of Internet Layer or Network access layer. It is described as residing in layer 3, being encapsulated by layer 2 protocols.

2. Internet Layer –

This layer parallels the functions of OSI’s Network layer. It defines the protocols which are responsible for logical transmission of data over the entire network. The main protocols residing at this layer are :

IP – stands for Internet Protocol and it is responsible for delivering packets from the source host to the destination host by looking at the IP addresses in the packet headers. IP has 2 versions:
IPv4 and IPv6. IPv4 is the one that most of the websites are using currently. But IPv6 is growing as the number of IPv4 addresses are limited in number when compared to the number of users.

ICMP – stands for Internet Control Message Protocol. It is encapsulated within IP datagrams and is responsible for providing hosts with information about network problems.

ARP – stands for Address Resolution Protocol. Its job is to find the hardware address of a host from a known IP address. ARP has several types: Reverse ARP, Proxy ARP, Gratuitous ARP and Inverse ARP.

3. Host-to-Host Layer –

This layer is analogous to the transport layer of the OSI model. It is responsible for end-to-end communication and error-free delivery of data. It shields the upper-layer applications from the complexities of data. The two main protocols present in this layer are :

Transmission Control Protocol (TCP) – It is known to provide reliable and error-free communication between end systems. It performs sequencing and segmentation of data. It also has acknowledgment feature and controls the flow of the data through flow control mechanism. It is a very effective protocol but has a lot of overhead due to such features. Increased overhead leads to increased cost.

User Datagram Protocol (UDP) – On the other hand does not provide any such features. It is the go-to protocol if your application does not require reliable transport as it is very cost-effective. Unlike TCP, which is connection-oriented protocol, UDP is connectionless.

4. Application Layer –

This layer performs the functions of top three layers of the OSI model:

Application, Presentation and Session Layer. It is responsible for node-to-node communication and controls user-interface specifications. Some of the protocols present in this layer are: HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X Window, LPD.

 

 Protocols other than those present in the linked article are :

HTTP and HTTPS – HTTP stands for Hypertext transfer protocol. It is used by the World Wide Web to manage communications between web browsers and servers. HTTPS stands for HTTP-Secure. It is a combination of HTTP with SSL(Secure Socket Layer). It is efficient in cases where the browser need to fill out forms, sign in, authenticate and carry out bank transactions.

SSH – SSH stands for Secure Shell. It is a terminal emulations software similar to Telnet. The reason SSH is more preferred is because of its ability to maintain the encrypted connection. It sets up a secure session over a TCP/IP connection.

 

NTP – NTP stands for Network Time Protocol. It is used to synchronize the clocks on our computer to one standard time source. It is very useful in situations like bank transactions. Assume the following situation without the presence of NTP. Suppose you carry out a transaction, where your computer reads the time at 2:30 PM while the server records it at 2:28 PM. The server can crash very badly if it’s out of sync.

 

TCP/IP Reference Model is a four-layered suite of communication protocols. It was developed by the DoD (Department of Defence) in the 1960s. It is named after the two main protocols that are used in the model, namely, TCP and IP. TCP stands for Transmission Control Protocol and IP stands for Internet Protocol.

The four layers in the TCP/IP protocol suite are −

Host-to- Network Layer −It is the lowest layer that is concerned with the physical transmission of data. TCP/IP does not specifically define any protocol here but supports all the standard protocols.

Internet Layer −It defines the protocols for logical transmission of data over the network. The main protocol in this layer is Internet Protocol (IP) and it is supported by the protocols ICMP, IGMP, RARP, and ARP.

Transport Layer − It is responsible for error-free end-to-end delivery of data. The protocols defined here are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Application Layer − This is the topmost layer and defines the interface of host programs with the transport layer services. This layer includes all high-level protocols like Telnet, DNS, HTTP, FTP, SMTP, etc.

 

The following diagram shows the layers and the protocols in each of the layers –

 

  

 

Advantages of TCP/IP Model

The main advantages of TCP/IP are as follows −

It is a broadly accepted model which can deploy effectively in all the practical networking issues.

TCP / IP can also enable cross-platform communications among the heterogeneous networks.

It supports connection-oriented reliable service. It defines that it maintains the transfer of data packets. If the data packet is missing across the web, thus the TCP will retransmit the lost packets.

It removes the congestion by using a network congestion avoidance algorithm that contains multiple procedures, including additive increase/multiplicative decrease (AIMD), slow start, and congestion window.

It supports error disclosure by using checksum and error control by using Go Back or ARP protocol.

Disadvantages of TCP/IP Model

The main disadvantages of TCP/IP are as follows −

The model does not characterise the terms of service, interface, and protocol.

The TCP/IP model is not shared and is appropriated to represent any protocol stack other than TCP/IP.

The host-to-network layer is not a layer at all in the ordinary sense that the method is used in the framework of layered protocols.

The TCP/IP model does not determine the physical and data link layers.

TCP / IP is complex to set up and maintain as compared to the Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) or NetBIOS Extended User Interface (NetBEUI).

It can improve a considerable overhead as every structure obtains its TCP header. Therefore, fragmentation through the router improves the overhead.