we went over our layers in death. We talked about Roos. I model as a general overview and we talked about our new Monica to remember it.
But let's backtrack a little bit in. Let's revisit our shipping model Now that we know a little bit more about the details of our laywer ones through layer seven,
layer where we have our object that we ordered online and we put in the box. We put our box on the truck. We sent the truck over to our house and we received the device. And we have our manager here overseeing the whole process. And we have our guy on the truck driving the truck to our house. So
we talked about how we can break this up in the different layers and how we can sort of generally compare this to Roos. I model for our network. Well,
let's take a look now and let's move over to our network. Before we had the object ship to our house, we went online and we we ordered it and then the factory. They have their internal computers, and here's their network in here, where they're sending files
from their sales computer over to their shipping and receiving department. Let's take a look at their shipping and receiving department. And let's see if we can break down the transfer of our order as a single file that's encrypted and over to their shipping and receiving department. We have our
computer here, and this computer is on a 1 92.1 68.1 dot five address. That's its I P address. So right there, we recognize layer of this computer has layer three capabilities at our network layer.
But we have our file and we need to We created it and we made it down into electrical bits and we are electrical signals, and we're sending it out over our cable. So our electrical signals and our transfer over our cable is all going to be layer one, so
electrical signals are going through this entire diagram.
So we have our cables, we have electrical, we have our devices, we have our network interface cards, and these are all going to be layer one objects. These are all going to be everything's gonna be happening at a layer one level, because through the entire process We're transmitting electrical signals.
So that's our layer one.
Next, we have our laywer too.
We're sending electrical signals out of our layer one network interface card. And our network interface card has a Mac address. This Mac address is unique to that particular card and that network interface That one network interface card is going to try and send a data packet to our switch here.
Now, this is going to send it to its port, which also has a Mac address.
Now, just because our switch doesn't have an I P address our switch, they can't perform routing functions and it doesn't have an I. P address doesn't mean it doesn't have a Mac address. Our switch here still has a Mac address on its ports because it's still need. We still need to have away from our computer
in order to recognize. Okay, this is where I need to send it to.
There may be several other cables that the branch off that connect in before we get to our switch. So we need to have a way that our switch can recognize this packet is being sent to it in a way that our switch can know what port is coming in and know what port to send out back to us.
So our switch also has a Mac address here.
this connection going between us and our switch here we have layers. We have Ah, Layer two. We have data link because we're utilizing our Mac addresses, realizing that point to point connective ity. So our data link
also going on at the same time we have our network layer. Our packets have been formatted. They have i p addresses stamped on them. They have i p addresses of where they're trying to go to. And ultimately, this packet that we're sending from 1 92.1 68.1 dot five needs to go over to 10.0 dot 0.5
Now, we can't reach this computer just on a layer to data link level. We need to actually send this packet over a layer three. We need to send this through a network layer. We need to actually route this packet. We need to send it through a couple different routers that we have set up. So we're going to do that.
we have going on right here
and right there as well. A cz when we're sending our packet through an I P address. So we're sending the packet to the router, the routers a layer three device because that can actually route our packets to a different a different network, a different i p address.
So our incoming port on our router that's connected towards us
is going to be 1 92.1 68.1 dot one. That's also what will have set on our computer here as the default gateway. Eso we're connecting from our computer to that router
and that router is receiving that I p address. Are that that particular packet? And it's saying, Okay, I need to take this packet and I need to route it to a different different network. It's gonna route it over to our 1 92.1 68.5 dot three network.
We'll talk about I P addresses and specifics later and a separate module,
But just know for now that I P addresses again are logical addresses that we map to physical that we met to physical addresses, a map to physical ports.
So it's going to change that over to a different. A different I p address the network,
and that packet is going to go to us another switch. We have a second switch,
and then that switch is also going to be connected to a second router.
And that second router is going to be on our correct network. That's connected to our shipping and receiving computer here
so we can see how, this entire time.
Not only are we sending over layer to because we're hitting all of our Mac addresses here, there's a Mac address on our switch. There's a Mac address on our computer. There's a Mac address on both of our routers. There's a Mac address on our intermediate switch. There's a Mac address on our in computer. There's Mac addresses at every point where we have our data going to,
so there's a layer to there's data link.
There's a data link layer functionality occurring everywhere,
then our layer three functionality. Our network layer is also occurring everywhere. Were our we're sending the data were routing it through routers throughout the entire time. We're trying to point to a particular I p address, so there's layer three networking going on everywhere. Layer three layer is in play.
That brings us to our laywer for our transport layer.
Now, we talked about our layer four is going to allow us to manage how we are cutting up this packet on how we're transferring this file. We're gonna manage a TCP or UDP. So this file that we're sending is going to be sent over TCP because we need to make sure that we receive a
that our computer that's managing this sending process over TCP
receives a Okay, It's good receipt back. Every time it breaks up, the file will say that our entire file is
this big. But our computer can't send that whole packet at one time. So it's going to break that into chunks,
and it's gonna send those one at a time making sure. Okay. Did I receive a receipt for this one yet? This one got there. This one got there. This one got there. This one got there. This one that got there. Now my whole file's been transferred. So the whole time are they our entire transfer process here we're using on our layer four our transport layer.
in order to transfer that packet and then are in point Computer is also using TCP in order to ensure and in order to send the receipt back to us that we did receive. We did receive each separate package and we got it in order. And it's all good.
So we have our layer one, our physical layer going on throughout our whole process. Here we have our laywer too. Or data link Lee or Mac addresses going on throughout this whole process. Here,
our layer three network layer R p R I P addresses and our routers are layer for our transport layer. Are TCP
And next we have our layer five. Our session layer now are layer five. Our session later, before computer can start sending packets to this address, it needs to make sure that it can establish and maintain a connection. We can't just
say Okay, I know what this I p addresses. Send a packet and then wait,
wait, wait, wait. I haven't received anything. 10.0 dot 0.5. Doesn't seem to be talking back. What's going on?
We're not gonna do that. We're not just gonna
willingly send the packet out into, uh, into the abyss and then hope that we get a response back. That's that's the job of our session layer. Our session layer is going to before it starts sending this packet, it's going to establish and maintain that connection to our other computer, and it's gonna maintain Okay,
our computers are computer A in our computer be here. We have established a connection. We've had our handshake, so we know that we have a good we know. We have a good connection. We've established how big the packets you are. You're allowed to send our we've established who's gonna talk, Win
A. You're gonna talk first
and then be when you received the packet, you're gonna receipts ended an acknowledgement and a if you don't hear from be within such an amount of time, then you're going to try and rescind the packet and see if you can get another acknowledgment and we're going to keep doing that until the package is fully sent.
And then our session layer is going to provide us with a termination.
It's going to provide us with a We had our first handshake that said, Okay, we're good to start sending packages. We can see each other. We've established communications, our session layers. Also going to say, OK,
you don't have anything left for me. Okay, bye.
We're no longer. I'm no longer connected to you. So that a step that session has been terminated. So that's gonna be all at our layer five level. It's gonna be at our session later. Then we have a presentation layer. So we sent this packet and this packet. We need to encrypt it before we send it over our network.
Because our this network that are shipping and receiving department is on
or somewhere in between our computer and our shipping and receiving computer. There may be someone potentially listening in, so we don't want to just send this over standard FTP. We want to send this over possibly f t. P. S. Because we don't want to just send this in a way that anyone on the same network can be sniffing our packets on. Then just say, Oh, look, here's a packet.
That's f D P s are just standard FTP.
Let me take this packet and then reassemble it myself or make a copy of it and just listen in on this so that I can see what they're sending back and forth. So
are my session on layer six before its sins is going to be what encrypts the data computer A is going to use layer six, our presentation layer. It's gonna encrypt this data before start sending it over our network.
And then when it gets to our computer, be computer B is going to be able to decrypt this data is going to say, OK, I know. How did I know how to do grip this before I pass this on to the application layer? So I'm just gonna go ahead and start decrypting this Some of our some computers and some ways that we encrypt and decrypt files
require specialized applications, specialized programs.
Those wouldn't really be working at a layer six layer present a presentation layer in our network model. That may be a different idea entirely say, if we put a single file and then we used a program like True Crypt and we encrypted that file and then we just moved it to a different computer and we
took that file off and then decrypted it.
That's not roos I model going on there. That's that's just transferring our file through a USB connector. But if we're transferring our file through a protocol, so we have T c p.
But T C P is sort of our base protocol either UDP or TCP. And then we also have us. It's a F T. P s that we are securely sending this file rather than just a standard ftp just a standard file transfer protocol. Then we're sending that over a encrypted protocol. So we send it,
We get to site B and we decrypt it. That's gonna be our layer six. That'll be our presentation later.
And then, lastly, our layer seven, our application layer we're going to take when our computer A gets ready to send that we have our application that wants to send this file problem. Possibly our operating system wants to send this file because we've selected this particular computer or were
we've initiated a session to send this particular fire file.
Our application layer is going to say, OK, do you have network access? Can I confirm who you're sending this to? You. Can I get this? Can I get this ready And can I create? Make this package in a way and get it ready to send and give you permit and give this application permission to send. That's all gonna be in our application layer
and then at our site B when we're receiving this package, our application, which is receiving our operating system, may be communicating with our computer and saying, OK, uh, do I have permission to access the network to receive this file? Am I able to take this file?
And now, now that it's decrypted, can I present this and I can I Can I get it ready to show to the user?
So that's all gonna be going on in a layer seven that's gonna be going on in our application layer.
with those in mind, we can really, with our entire diagram in mind, we can see all of our layers and play. It's when we're throwing everything all in together rather than breaking down our individual layers. One by one,
we see how it gets a lot more complicated. It can may maybe even a lot more confusing, to understand the distinction between the layers,
you may want to go back,
maybe want to review those layers one by one. And then once you get a good, solid understanding of the difference between layer one our physical layer layer 23 et cetera. Once you get a good, solid understanding of individual layers, you can see how on our wide scale on our wide scale network here,
how those apply and how those can change.
We can see how we can use those for troubleshooting. So if someone on our technician on a layer B side says,
Hey, we got we got, ah, Layer six issue where Seo got a issue with the presentation layer with formatting, possibly the encryption or the decryption of the files going, there's some issue going on there or we've got a Layer three issue. Maybe this router here isn't properly routing data. It's not properly taking the data,
and it's not routing it over to the other network
properly. We've got a layer one. We've got a physical issue. Maybe, uh, we have our cables going through the ceiling there, and there's ah, small visitor in our ceiling, which is chewed up, chewed up someone of our cables inside of the ceiling and now we have a layer one. We have the physical layer issue. So
take a take a look at our OS I model. Learn the OS I model, learn what each of the layer means, and then use this when you are analyzing a network when you are analyzing connective ity issues in order to help narrow down problems and individual layers, and helped to better understand how networking works and how we send and receive data.