OK, so now we're going to get into one of my favorite topics always on.
It all the way is because we understand how these players work, everything else they play.
So in order to understand the application first, you first need to take a step back and get a grip
on the policy.
A lot of the generals.
Right.
What is the oversight?
Well, we've all heard of it.
You know, we hear about it in theory, but what exactly is it and why was it needed all those things?
Right.
So, Olesya.
Right.
So this is the open systems interconnection model.
All right, so I think one of the best ways to understand this is to give you an example, right?
So let's say.
You are at a computer right here, that's you and what's up, and you want to connect to a Web server
over here.
You want to connect to that Web server.
There's a couple of things that happen, right?
Doesn't just happen automatically.
There's a couple of things that need to take place before this connection can actually be established.
So we open a browser and you enter and you need to connect a Web server on the Internet.
Even if you need to connect to an internal file server, a false server on your local area network,
what happens versus the application layer gets to work.
This is where the.
Network where application was.
OK, application network aware application lives at this later.
All right, and so from there, the data is going to move down to another layer, right?
And the second layer may have already guessed, but it's going to actually move down to the presentation
layer.
Yeah.
Then Tatian.
And we get to the presentation later, you know, this is where, you know, there's encryption or formatting
or any translation, all that stuff gets done at this layer and then the data will continue to move
down even further, right.
Until it gets to the next layer, which you then have the session layer and essentially handles the
discussions, I think, about being logged into a Web page.
Now, there's a session in a website, right, so that, you know, when you click through multiple
pages, the computer can tie together all those connections to a single user.
Right.
That's pretty much what a session is.
Now, all of these things, all of them, all these things happen on one physical system.
Write the application, the presentation, the session.
This is on your computer does not leave your computer.
That doesn't hit the network yet.
OK, but after you get here, this is when things get kind of interesting.
Let me go ahead and clear this out.
Let's talk about what happens to the other layers, so then we have what's known as the transport layer
transport and you can guess what happens at the transport layer, right?
This is basically the layer that is responsible for the reliable or unreliable delivery of protocol
data units known as segments at this layer.
And it can track those messages up into segments.
You can label them and reassemble them.
That all takes place at this transport layer there.
The data is continually sent.
It's continues to traverse the network and ends up at the next there, which is the network layer.
OK, this is the layer that most of us, I think are familiar with network.
Because, you know, this is when we start to talk about IP addresses or source and destination IP addresses,
all those things live at this layer.
The next layer in our journey down the TCP IP protocol stack or even Ossi model, next layer is the
datalink layer data link.
And this is layer two and this is where everything is put into a nice, tidy envelope and it's sent
over the network as a stream of ones and zeros, OK, because that's all data is right.
It's just ones and zeros.
And the transmission medium can be either the air.
If it's Wi-Fi, it can be glass.
If it's fiber optics, it could be copper if using Ethernet cable.
Right.
But, you know, that's pretty much how this works conceptually, that it goes down the stack.
It flows all the way down.
Right.
And then on the other side in the server, it passes up.
So to move up from the physical layer into the destinations data layer and then into the destination's
network layer transport layer all the way up to the application layers.
Right.
The session, the presentation of the application until it finally gets to the application.
Right.
And then the same happens in reverse at the data sent back to the client.
So that's pretty much how that works.
The main thing you need to really know here is that this is just a model.
And really what we're using in today's networks isn't the same model.
We're using the.
So, you know, just to kind of break this down a little bit more at the transport layer transport,
what you have is a segment, the data is referred to as a segment that when you get to the network layer.
Data is technically referred to as a packet.
Another term package gets moved around a lot and people use it in their vernacular interchangeably with
just data anywhere, but specifically you look at the RFID, if you look at how the TCP IP networks
functioned, how they were designed, and that work layer is home to packets, just trying to be syntactically
correct here.
And then finally, we have a data link layer.
You actually have a frame.
OK, so the date actually changed its name as it moves down through the TCP IP stack.
OK.
And of course, when it hits the physical layer, it's just bits and bytes and zeros and ones that ons
it.
Right.
But that's pretty much one thing I want you to know right there.
Another thing that's really important, but I want you to know is that routers live.
At the network, layer and routers move packets at layer three.
That's where the writers live.
And later to.
You've got switches.
OK, and switches move frames at layer two.
So they make forward decisions based on the Destination Mac address and the frame compares the incoming
Mac address to what's in its content addressable memory, S.A.M. content addressable.
Memory and it can make a forwarding decision based on the destination Mac address and the data that's
in the camp table at that given moment in time.
Right.
That's really all you need to know.
The main thing that's really important is the application layer deals with network aware applications.
Right.
So Chrom, they'll be an application layer application.
Microsoft Paint.
That's not an application layer application because that layer, that application, isn't that where.
Right.
So that's the key point there.
If you get that, you've got it.
All right.
You got what you need for this particular section.
So the next one, we're actually going to dig into the transport protocol and dig a little bit deeper
into segments and how these rates will rise in the next.