 Hello, everyone. Myself, Mr. Chopa. I am Madhugar. I am working as an assistant professor in computer science and engineering department at Walsh and Institute of Technology, Solapur. In the last video, we have discussed about the network software, network hardware. This video, we will going to discuss about VESA reference model. Let us see the learning outcome. At the end of this session, students will be able to describe the concept of VESA reference model and functions of each layer, ok. Zenda, physical layer, data link layer, network layer, transport layer, system layer, presentation layer and application layer. These are the layers I am going to cover in this video. Let us see one by one in detail. First one is physical layer, about VESA reference model. The principle for the seven layers are, there is a seven layers can be prepared for different purpose in a communication that are seven layers created for different abstractions or each layer performs well defined functions in a communication, functions for each layer chosen with the definition of international standard protocols in mind, ok. Each layer can contain the different protocol for different purpose and then each layer can be used and then it can perform the different functions and then in a communication, ok. The model is called OSI that is Open System Interconnection. ISO reference model because it deals with connecting open systems, we just call it as an OSI reference model. This is an OSI reference model. It can contain the total seven layers, whatever the layers we have listed in a agenda, ok. First in the layer, the center side layers and the resource side layers here, the layer one is an application layer, then while transmitting any data, the present layer can communicate with the next layer that is application layer can interface with the presentation layer, then if it is free, then it can send the data and if it is not free, then the current layer how to wait, then parallely these layers are virtually can communicate with each other, it means dotted line indicates a virtual communication and the dark line indicates the actual communication, then same way they have to send the data from current layer that application layer to the presentation layer and the presentation layer to the session layer, same thing they have to. This one is network layer host router protocol or it can just while transmitting how to use for different purpose, then internal subnet protocol is there, communication subnet boundaries there and then these layers directly they can communicate with each other that is application layer to the application layer, presentation layer to presentation layer, session to session and transport to transport, these layers they can send the communicate through subnet that is sender side subnet and receiver side. Here these three layers can contain the they have to send the data and receive the data from host A to host B, it is an OSI reference model. First one is physical layer, in the physical layer the user can transmit a raw bits from one computer to another computer in the form of bit streams. In the form of zeros while transmitting the data if the user is using in the form of points it means he can get the acknowledgement in the form of zeros and then in the receiver side if they are sending the data in the form of ones he can get the data reply in the form of one and then it can defines how the cable is attached to the network layer, network adapter it means how the user can use the connection between transmit and receiver, in this layer only the user can use the physical path between the transmitter and receiver, it deals with the issues like definition of zeros and ones, design issues it deals with the mechanism, electrical line, mechanical electrical line, procedural interfaces it means how we have what are the different issues they have to face in a physical layer. Next one is data link layer, in the data link layer packages raw bits from physical layer into frames, it means in the data link layer the user can send the data in the form of frames, it can contains the source information, destination information and as well as some other information related to the sender and receiver, they can send the data in the form of frames, provides a reliable transmission of frames, it waits for an acknowledgement from the receiving computer after sending the data, the user should have to in the data link layer the user can wait until to get the acknowledgement from the receiver side. retransmits, transmits frames for which acknowledgement is not received it means, if the user how to mention the mention time is reached and then they have not get the acknowledgement from the receiver side it means, again they have to retransmit the frames, the network layer manages addressing or routing of data within the subnet, determines how the packets are route from source to the destination computer or manage traffic problem such as switching, routing, controlling the congestion of data packets, determine at start of each session and individually determine for each packets reflecting the current network load it means, the network layer the user how to check out the how the availability of the network while transmitting the data in this network layer, transport layer. The transport layer manages the transmission of packets or packages long messages when necessary into small packets for transmission, reassembles packets in correct order to get the original messages, handles, error, recognition and recovery it means, in the transport layer the user can use some protocol that is TCP and UDP that protocol can be used one is a connection oriented TCP is in connection oriented UDP is in connection list by using that the user can reassemble the packets in correct order how they can based on what they can reassemble the packet it means here we have to use some path for that before transmitting the data they can use some sequence number based on that or sequence number they can transfer the data to the receiver side if the sequence is then after issuing all the data to the receiver side they how to check out the sequence number if any number is missing based on that only they can check out this data is or this packet is not received to the receiver side if the data is not reached then again they can resend the packet that is reassembles packets in correct order to get their original machine based on the sequence number they have to get the original sequences, handles, error, recognition and recovery it means based on that protocol only they can recognize the error and then they can recover the detected error transport layer transport layer at receiving acknowledgement packet delivery it means in this one the user should have to get the acknowledgement otherwise if they are not get the acknowledgement once again they have to resend the same packet to the receiver ok resend missing packets ok it is true end to end layer it provides a flow control to the user ok next one is question and answer section think and write it can contain two questions what are the different service of OSI reference model list some difference between network layer and transport layer now pause the video and answer the above question answer for the above question is services and OSI model each layer provides services to layer above and consumes services provided by layer below it ok active elements in each layer called an entities ok entities in different layers different layers or layers and different machines called peer entities it is a difference between network layer and transport layer network layer the function for this layer is to deliver the packets from source to the destination across multimedia or multiple networks here the transport layer is in responsible for source to destination delivery of the entire message it provides the connection connection services including network layer flow control error control and packet sequence number transport layer can be either connection or connection oriented or connection less it translates logical network address into physical machine address it divides each message into packets at the source and reassembles then at the destination session layer session layer allows two applications on different computers to establish use and end assessment that is file file transfer remote logging establish the dialogue control regulates which side transmits plus when and how long it transmits how much time it will takes to transfer the data we have to study in this establish the dialogue control perform token management and synchronization presentation related to the representation of transmitted data translates different data representation from application layer into uniform standard format ok provide services for secure efficient data transmission that is example encryption and decryption and data compression before transmitting the data in the presentation layer the user can encrypt data it means they have to modify the original data into the another form after modifying they can send that modify data to the receiver side the receiver if the somebody how use that or hack that then it is not possible to get the original data for that we have to use the encryption technique before transmitting the data application layer an application level at which application access network services contain a variety of protocol that are commonly needed represent services that directly support software applications for transfer database access and electronic mail in the application layer the different protocols we have to use and then are there in a application that application layer that protocols can be used for different purposes that is it's a variety of protocol that commonly needed these are the references I have used for preparing the above ppt thank you