It takes an amazing amount of software and hardware working together to make a network function.
So the challenge to all of this is that if you have different pieces of software and hardware they don't
have to be able to talk to each other and interact and able to make your network go.
You might have a network card from 3Com and you might be running a Windows 8 operating system and all
of these devices have to work together to help make interconnectivity work.
Then came up with something a long time ago called the OS 7 layer model the OS 7 layer model is seven
distinct functions that a network must do.
Now the LSI is being supplanted with something called the TCAP model.
So let's do a quick overview and take a look at OS I and TZP now for OS I we're going to start basically
there's no real bottom or top but I tend to look at it at the bottom which is your most basic part which
is what we call the physical layer the physical layer is.
That's like the easiest part of the OS 7 layer model.
It's just what type of cables do I use and things like that.
Now coming up from that is the data Linkletter.
Now the data like layers a little bit more important.
Basically anything that works with a MAC address works at the data Linkletter.
So when we're talking about data link we start talking about things like the network cards themselves
start talking about switches things like that.
The third layer is the network layer.
Now the network layer is important because the network layer has to do with logical addresses.
So when you see the network layer you're talking about IP addresses.
So things like routers in particular work at Layer 3 the next layer up is the transport layer the transport
layer is kind of interesting.
Data is big.
And the actual chunks of data that go through a network are relatively small.
So there has to be a assembly disassembly area for data as it gets broken down into individual packets
and that's what the transport layer is all about the transport layer.
Not only disassembles packets but make sure the packets get to the other system in good order.
Next one is the session.
Now the session is kind of interesting when we work at a session layer here we're talking about the
actual connection between two systems.
Are we making a TZP connection between a web server and a web client or are we just sending e-mail.
Are we sharing a folder between two computers on a local network.
And it's the session layer that defines what's taking place in terms of how that connectivity really
works.
Next is the presentation layer the presentation layer is old and weird but since it is on the OS I would
need to at least make a quick mention of it just because a big chunk o data comes into your computer
does that necessarily mean that this data is in a form that your computer can read it.
Now let's use Microsoft Office as an example.
If I open up my Microsoft Office I can open up almost any kind of document you can dream of.
Office has the smarts built into it to automatically read it.
But that wasn't always the case.
So the presentation layer used to be used to convert data into a format that your applications can read
or at the top is applications applications is important because it's the applications themselves and
it's not really the applications you have to be careful here.
What we're talking about is the smarts in the applications that make the network aware little simple
things that you and I never think of.
For example if we were to open up Microsoft Word and we could literally go to the network to go find
a particular file.
And that's because Microsoft Office itself is network aware.
We often use the term API or application programmers interface as the definition of the smarts that
are built into an application that allows us to make the application network aware.
So this is the most high.
All right.
The TCAP IP model is more simplistic than the OS simply because if you're using only TCAP IP there's
a lot of parts don't really come into play as much.
Let me show you what I'm talking about.
First of all we have what they call the network interface layer so the network interface layer covers
all the physical cabling MAC addresses network cards pretty much everything in terms of hardware with
a couple of small exceptions routers are all covered here under network interface so that ties similarly
to the data link and physical for the OS side.
Now your next one is your internet link.
Your indirect leads for IP addresses.
So things like routers or anything it has to do with an IP address works at the Internet layer.
The next one is transport.
Now transport does all the assembly and disassembly but it also has to do with whatever it takes to
connect to the other system to make sure the data gets there.
So in this case we're talking about things like for example TZP or UDP whatever it takes to get those
chunks of data from one application to the next.
Now the last one is called application.
So application actually takes into consideration the old OS application presentation and session layer.
So everything that has to do with the application itself works at this layer.
Keep in mind that the IP model looks at this a little bit differently the no S-I TCAP model looks at
applications as applications for example email or FGP or telnet.
All of these very distinct things that each have their unique port numbers all play into this one particular
area.
So if it were up to me and it's not but to me I would change just a little bit.
First of all I would go ahead and take the transport layer and put the old OS I.S. layer into that as
well as the transport layer.
But that's really not the way we look at it for the example we put that back.
And that's pretty much your TZP IP model.
Now what I want to do is let's take a look at both of these guys.
First we have the OS I model older more detailed and then we have the TCAP IP model more modern.
Not as much detail but not as complicated.
Make sure for the network plus exam that you know both of these models that don't worry about it we've
got a lot more to talk about.
We've got lots of episodes that are going to break down all the different layers in these models and
a lot more detail.
But for right now the important thing you need to appreciate is that each one of these layers has a
distinct function.
Each one of these layers has a name.
But not only that it's also got a number.
So let's use as an example.
If I'm talking about OS I am looking at the network layer now understand its network layer but there's
also numbers associated with it and they go from one up to seven.
So if I'm talking about OS I and I say Layer 3 you need to know that I'm talking about the network level.
That's also very true with TCAP IP.