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“For us to get a visual representation of how the osi model works on each each layer. I will be using this simulation from the net sales net. This is great simulation where you can see how information goes through each layer. And what data is added to the packets on each layer.
Okay. The osi model has seven different layers on each node. There s seven different layers on the sending node. And there s seven different nodes on the receiving node three three notes over here these are the nodes that are going to be corresponding to these two routers.
Okay. When you send an information each layer talk to the corresponding layer on the destination node. We will see how this work on go throughout our simulation. Okay okay let s look at how different layers works on the osi protocol.
Stack. What we re doing here is we are sending an email using an email application can be outlook can be a web browser using email applications you re sending an email from this laptop to the receiving node this server over here. It has to go through a physical medium internet land. And it has to go through those two routers so the first layer.
We are gonna look at is the application layer application layer is the layer the closest to the user and application layer is responsible of providing support and service to application that require network resources for an example in this example. The application that we are using is let s say outlook or a web browser that you can send an email okay this is the layer this is the top layer that is the user actually interacting with so we you open different type of application and that application can be a web browser outlook and this is the actual application that you are actually working on to open a web page or to send files all to ensign email..
Ok. The next layer is the presentation layer presentation layer is responsible to transform data between the format that required for the network and format that required by the application layer for an example. I outlook might be using different type of data so the presentation layer is responsible for transferring this transforming this information that can be read by the specific application and this slayer. This lays lay that actually is the operating system is working on operating system is taking care of transferring the data received by the session layer and then then using the presentation layer it will convert the data that received to a data that can be read by a specific application ok next layer.
We are looking at is the session layer the session layer allows application running on different computers to communicate using a connection that is called a dialog ok. The session layer is responsible for creating a session between you this laptop and receiving nor the server so as you can see for our email packet. We have forehead three headed added so far ok. The next layer.
We ll look at here is the transport layer transport layer also known as the end to end layer is responsible for ensuring reliable reliable data delivery so that the packets arrive at the destination without any errors also this layer will decide how much information sent. You should send for an example distillate on this example. This layer will decide how much information of this email will send to the email server and how much information you will receive back from the server ok the next layer. We ll look at here is the network layer network.
Layer is actually responsible for adding. The destination ip address and the source ip address for this example. The source ip address will added to the packet is 133 point. Eight eight point six point.
Four and the destination ip. Address will added is 152 point eight..
Point. 711. Also remember network. Lays delay.
Actually your routers operate ad. For an example. You might have a router at home. A wireless router.
There are the routers on this section. Well. This is a router here. This is router here so this is the lay actually the routers actually work on okay the next layer we ll look at here is the data link layer data link layer is responsible for transferring data between devices for incoming data.
It organized ones and zeros from the physical layer into a structured unit call frames data link layer that actually your switches work on so you can communicate with each other back and forth. And this is the layer is responsible for those type of communications. Okay let s look at the next layer this is the bottom layer this is the physical layer the physical layer is responsible for connecting different devices on a network for example your computer might be connected to a router using a wireless medium or might be connected to through a cat5 cable. It might be connected to a cross over cable.
So this is the physical medium that connect different computers or different nodes on a network. So this layer is responsible for transmission and receiving of bits from one computer to another computer for an example some of the devices..
I found at the physical layer is the transceiver media access unit. The part of a network. Adapter that sense and receive signals over the network media. Media.
Converter. Converts. Man media signal to a another type of a media. A repeater repeatable amplifies.
The signal to extend the maximum allowable distance for a media type a hub hub works on a physical way a hub is a multi point repeater. This is deployed as a central point of a connecting for network segments through wires in using the star topology. A modem. If you remember the modems that we used to use a modem a device that converts the converts between digital and analog signals for transmission so now you can see on this packet there are seven headed added to the packet from all these different layers.
We looked at through application layer presentation layer session layer transport layer network layer data link layer finally the physical layer okay now let s see what happens the packet next the packet is sent from the laptop to the first router. Okay on the there are few different layers on the router. We mentioned okay data link layer and the network layer so the physical layer the router removes the data link information and send it to the network layer the network layer uses the destination ip address and data mind they are to send the packet next. If this is only happens if we have routers in between your network to the receiving end and then the route ends can capsulate the data with the proper datalink information and send it back to the physical layer through to the next router on this router.
You will see the packet was dropped lost. Because of the sender transport layer had a acknowledgement issue and it did it was dropped this would not happen..
All the time that could be sent back to the router. Okay and same process. We looked before go through the data link layer network layer send it back and now. It sends to the server on this sec session.
It was dropped 16 dissection poly to ethernet data link layer does when the sending layer does not receive an acknowledgment from the receivers layer it resents the frame. So what happened here was the sending lady did not receive acknowledgement saying okay the packet was delivered to the email server. So that didn t happen so it will resend the frame back from the lab from the router back to the server. Okay now you will see what happened to each layer of the receiving node physical layer will receive the packet okay and the data link layer removes the data link layer network layer removes the ip header receive destination ip and the receiving ip address transport layer will reassemble the data back into the original data and used to the port number on this case.
The port number 25 to determine which application to send the data. So it s the application the session will determine which communication stream is this data is belong to okay and here s the presentation layer presentation layer use the information and convert the data that can be read by the application use this information for an example. Let s say we are using outlook. So it use the outlook to decide what application the application that can be read this data application receives smtp data and here where you can see actually see your email in clear text.
Okay hopefully hopefully this helped you to better ” ..
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