Hello friends, today in this video tutorial we are going to learn about open system interconnection model or OSI model. We will discuss what is OSI model, the use or purpose of OSI model, what is OSI model layers and we'll discuss SAML layer architecture of OSI model where each layer having specific functionality. To understand the network communication it's very important to clear your concept and understand how OSI model works, especially if you are working or studying in networking field. OSI is a reference model for how applications communicate over a network.
It used to understand how data transfer from one computer to another in computer network or across the globe. For example, there are two computers connected to each other via Ethernet cable and RJ45 connector sharing data with the help of network. card between both computers. But if one computer running on Macintosh operating system and other one having Windows 10, then how these two computers with different operating system are going to communicate to each other.
To solve this issue and for successful communication between two computers or networks, Open System Interconnection Model or OSI model was introduced in 1976. The OSI model developed by International Organization for Standardization or simply called ISO. The purpose of OSI reference model is to guide technology vendors and developers so their hardware and software can inter-operate and define the common framework. There are seven layers in OSI model. From top there is application layer, then presentation layer, session layer, transport layer, Network layer, Data link layer and Physical layer. If you feel difficult to remember OSI model layers name and their sequence then try to remember this phrase.
All people seems to need data processing. Start from top to bottom. A from all means Application layer.
P from people means Presentation layer. S to Session layer. T to Transport layer. N to network layer, D to data link layer and P for physical layer.
So, to remember this single phrase, you will always remember OSI model layer's name and their sequence. It's very famous face and I hope so many of you already know it. OSI model is a 7 layer architecture where every layer having his own specific functionality.
Very commonly asked question regarding OSI model is, which layer is first layer of OSI model? On top of all application layer or bottom one physical layer. To answer this question always remember it's depend on your position. Means you are on sender side or on receiver side. See if you are on sender side then top layer of OSI model or application layer is your layer 1. Because as a sender you will interact or come in touch with application layer first.
Because as a sender when you work on any application like Google Chrome, Facebook or Yahoo, they will use application layer protocols like HTTP, HTTPS or SNMP to send the data. But if you are on receiver side then the first OSA layer is physical layer. Because as a receiver you receive data and first layer who interact with data is physical layer. So your layer 1 is depend on your location.
You are on sender side or on receiver side. All the 7 layers work together in collaboratively to transfer data from one computer to another computer in the network or across the globe. Also note each layer having his own protocols to perform his job.
That will be explained and discussed into another video with details. The top three layers, Application Layer, Presentation Layer and Session Layer are also called Software Layer because application software like Google Chrome, Firefox, Facebook, Gmail and file sharing application like Dropbox protocols are exist and work in Application Layer. The bottom three layers, Network Layer, Data Link Layer and Physical Layer are called Hardware Layer.
Because network hardware like router, switches, hub, UTP cable and RJ45 connectors are used in these layers. The middle one or transport layer is called Backbone of OSI model or Heart of OSI model because it make a connection between top layers or software layers and Hardware or bottom layers. Now I am trying to explain you OSI model layers basic functionality step by step.
in form of story. So to understand how OSI model work, listen and try to remember this story. After that story, we will unwrap this story and I will explain you OSI model in very simple words. So let's start it. Just assume there is one company in Qatar and they have seven employees, each employee having his own specific task.
On the top There is CEO of the company and his name is Abdul. Abdul belong to Qatar and can speak and understand Arabic language only. There are another 6 employees who working in Abdul company.
Their names are Pintu, Saqib, Tuba, Noor, Danish and Peter. The CEO of the company Abdul told Pintu to send these 400 very important pages to another company named ABC. and make sure it delivered. Pintu say, okay boss and take 400 pages from Abdul. And what he found all pages are in Arabic language.
But the ABC company in Canada, they don't know Arabic. So what Pintu did, he convert these 400 pages into English first. So Pintu task is translate the data or input information in a way that receiver end understand it.
So after converting Pintu hand over this 400 pages data to Saqib and inform Saqib these 400 pages are very important and will be sent now to company name ABC. When Saqib receive and check it will go to company name ABC in Canada. So Saqib contact to ABC company first on his equivalent position person and ask is your company open now? They replied yes. Then Saqib inform there is one document coming to your company from us.
And when you receive it, please confirm us or send acknowledgement that you received our document. They say ok and they both agreed to establish a connection between sender and receiver until they not receive the data. So, Sakib create end to end connection between sender and receiver and then hand over these 400 pages to Tuba.
Tuba found there is big data file with very important and confidential 400 pages. So, what Tuba did? She divided these 400 pages into 4 sets of 100 pages or segments and marked these segments as segment 1, segment 2, segment 3 and segment 4. Because big file take more time to send from one place to another. Also if they lose that file, they lost all data at once. But in other hand, Tuba divided them into small bundle or segment and if one segment lost other data will be safe.
in other segments. After data segmentation, Tuba sent this four bundle to Noor. Noor received four bundles from Tuba and write to and from address on each bundle or packet.
On to, Noor mentioned receiver or ABC company address in Canada and on from side, she mentioned his company address in Qatar. Also, Noor informed delivery man, these are very important papers and CO1 urgent to deliver. So don't send via normal post. Noor instruct to take a flight from Qatar to Canada and deliver by yourself. So what basically Noor did, she write to and from address on each packet and decide the route.
And after that Noor sent these packets to Danish. Danish check each envelope and found okay. Documents are also inside on each envelope. And sender and receiver address also mention on each envelope.
But all envelopes are open anyone can see and read these documents. Then what Danish did he closed all envelopes and put seal on it to protect the envelopes. So if anyone try to open those envelopes receiver know that someone tried to tamper the documents. After this Danish handover this envelope to Peter and told Peter to send this envelope to ABC company in Canada.
Peter go to ABC company in Canada and handover this envelope to receptionist. in ABC company. Receptionist received the delivery and sent to next department.
That department checked all four envelopes are closed and sealed so no temper original documents then he open the envelopes and send document to next department next department check the to and from addresses and confirm this is his company address and receive the document and send to next department when next department received that all four envelopes and they check there are envelope 1 envelope 2 envelope 3 and envelope 4 basically these are one document but in four different envelopes What he did, he opened all four envelopes and put 100 pages from envelope 2 to under envelope 1 pages and envelope 3 pages under envelope 2 pages and envelope 4 pages under envelope 3 and make them as a one bundle again of 400 pages and send to next department. Next department already in touch with sender and after getting 400 pages from lower level he confirmed to sender that they received their documents and after confirmation they disconnect the connection and send this 400 pages to upper level after acknowledgement or confirmation the sender responsibility finished and after that receiver hire management take a look on that document or no this is not his problem so what sender did they all did their job that is deliver data from sender to receiver this is full osi model in story. If you understand and still remember the story, you will easily understand that how OSI model work. So let's start to unwrap the story.
So first there is Abdul in the story. As per story Abdul gave 400 pages to Pintu to send other company. Abdul means application layer as per OSI model and that 400 pages mean any data that user generate or create on Application Layer.
And Application Layer task is to provide interface to user. All applications and software we use in daily life like Google Chrome, Firefox, Gmail, Yahoo or any file sharing application like Dropbox that all work with the help of Application Layer protocols. User basically work on applications but it include Application Layer protocols that need to make this application to work correctly in the network or on internet.
Different types of applications use different protocol. Like if you browse something on Google Chrome or Firefox, they use HTTP or HTTPS protocol for web browsing. For email like Gmail or Yahoo application they use SNMP protocol. Or if you transfer any file by using any file sharing website like Dropbox, That time application layer use FTP protocol to make this application to work correctly.
So as per story, Abdul give 400 pages to Pintu and what Pintu did? Pintu translate that pages from Arabic to English because Pintu know other company don't know Arabic. Pintu means presentation layer as per OSI model.
Basic function of presentation layer is convert application layer data into machine understandable binary format. 1 and 0s. Also note presentation layer performing 3 functions.
First data translation, number 2 encryption and number 3 decryption of data. So actually presentation layer function is data translation, data encryption on sender side and data decryption on receiver end. I explain you in simple words what presentation layer actually doing. You saw many time there is audio file in your PC.
For example, name song.mp3 or some document like file.docx or file.pdf If you double click on song.mp3 file where it will be open. You will see it will open in mp3 player or if you double click on file.docx you will see it will open on different application like Microsoft word. Or same if you double click on file.pdf it will open in pdf application.
Who telling this? Where to open this file? That.mp3 or.tocx or.pdf extension telling to computer. So that extension tell PC which application open this file. These extensions basically is the translation of application layer input.
So presentation layer work is how to present data in form of.mp3,.tocx or.pdf. That's why in story Pintu translate 400 pages from Arabic to English because presentation layer task is present the data After in story Pintu send 400 pages data to Saqib and Saqib contact to receiver end and check their availability and establish connection After establish connection Saqib inform them we are going to sending data and when you receive let us know So Saqib mean session layer in OSI model And session layer task is establish an end to end connection between sender and receiver. Both session layer keep connected until all data not received to other party.
And if some data lost, sender get message from receiver end that data lost or unsuccessful. And if receiver end receive all data, then session layer get reply that data sent successfully. That's why session layer also called end to end layer.
So session layer main task is to ensure that all data received to other party without loss. Back to story, Sakib sent this data to Tuba. What Tuba did?
Tuba divide 400 pages into 100 pages in small units. Tuba stands for transport layer as per OSI model and the basic function of transport layer is divide the data into small units called segments. Also, it controls the data flow and error control. In data flow control, transport layer controls the amount of data being transmitted.
For example, a laptop connected to a YouTube server and suppose YouTube server can send data at 100 Mbps speed but my laptop can process data maximum at 10 Mbps speed. In that case, when I am downloading file from YouTube server, and server starts sending data at 75 Mbps speed which is greater than the data rate that my laptop can process so by using transport layer my laptop send request to server to slow down data transmission rate up to 10 Mbps that can maximum handle by my laptop and no data get lost same in reverse case if server is sending data at 5 Mbps my laptop tell server to increase the data transmission rate at 10 Mbps to maintain system performance. Also there is two type of protocol in transport layer transmission control protocol or TCP and user datagram protocol or UDP. To get acknowledgement from receiver after receiving data or need to send any data segment again if data loss between transmission we use TCP protocol.
It's also called connection oriented transmission. TCP send data at low speed and retransmit it again also if some data lost. But if you want to send data on fast speed without established session and don't care it it received on other side or no, in that case we use UDP protocol. Normally voice and video streaming using UDP protocol to transmit data. So after that transport layer send data segment to network layer as per story.
tuba sends segment to nur and nur put the to and from address on each segment and decide the route. So the nur means network layer as per the same model and the function of network layer is logical addressing, routing and path determination of each data unit. Data unit in the network layer is called packet and this is the osi layer where router exists.
IPv4 and IPv6 addressing done on network layer. and it's called logical addressing. The network layer sends data in form of packet to data link layer. So in the story, Noor sent packet to Danish. So Danish means data link layer as per OC model and in reality what data link layer do, he add sender and receiver MAC address on each packet.
There are two type of addressing in network. Logical Addressing and Physical Addressing. Logical Addressing done on Network Layer where Sender and Receiver IP Address are assigned to each segment to form a data packet. It also called Layer 3 Addressing.
Physical Addressing are done on Data Link Layer where Sender and Receiver MAC Address are assigned to each data packet to form a frame and then send this frame on Physical Media. like copper wire or optical fiber. Basically, data link layer allow upper layer of OSI model to access media using technique called framing.
After that there is physical layer or peter as per story. What peter did in story, he just send data frame to receiver end on available media. So in OSI model, physical layer convert this binary sequence into signals and transmitted it on local available media. It can be electrical signal in case of Ethernet LAN cable or light signal in case of optical fiber cable.
So the generated signal on physical layer depends on the type of media used to connect two devices. So that's it on sender side as per OSI model and when signal reach on receiver and physical layer same process what happened on sender side repeat on receiver side but in reverse direction. Like when signal reach physical layer on receiver side in form of electrical or light signal physical layer convert them into binary bits 0 and 1 and send to data link layer.
Data link layer convert them into a frame and forward that frame to network layer. Network layer check to and from IP address and confirm this is his logical IP address and send these packets to transport layer. Transport layer receive 4 packet.
and convert them into one segment and send that segment to session layer. After receiving on session layer, session layer send message to sender that they received the data or 400 pages as per story and session or connection between sender and receiver disconnected and session layer send this data to presentation layer. Presentation layer convert data into same format as it send like.mp3 or.docx or.pdf format.
So application can understand the data at application layer. And application layer open that data on that specific application. So this is very simple and basic intro of OSI model in form of story.
Soon I will make video for each layer of OSI model and will discuss more technically. I hope so you understand OSI model functionality and importance in network. Thanks for watching my video and please don't forget to like and subscribe my channel.