Original subtitles

We live in an incredible world today where we could use our smartphones and get all kinds of information

are we considered our desktops and play incredible games with other people in real time.

It is a great great time to be a tech.

However they come to you a plus really wants you to understand networking in a deep and profound way.

So if you really want to understand networking well enough to be able to pass the A plus and to succeed

as a technician out there we've got to bring it down a little bit forget the smartphones.

Forget the fancy tablets.

Forget Google.

Let's take it down to a simpler world a time before the internet a time when networking was really just

for a few computers maybe five computers maybe 15 maybe 20 computers that work together in the same

office that we're all hooked together and the only thing they shared back in the old days was they probably

share a printer and they probably share each other's folders so that we could access each other's Microsoft

Word documents.

So we're going back to a very very simple time very basic networking and what we call a local area network

or LAN.

So let's talk about that for a minute.

So imagine I've got a nice little office here and I've got some people with some computers and they're

working away and maybe there's somebody with a laptop over here and here's a printer and what we would

do back in the old days and still do today is we would run wires not between the computers but to a

central little box that at least for the moment I'm going to call a hub.

So everybody is physically connected from this central point called again.

Momentarily we're going to call it a hub.

Now in today's society it still works that way in a wireless world for example we would have something

called a wireless access point and everybody's talking on the same frequency to that particular wireless

access point.

Well that sounds OK but right off the top I see two big problems.

Problem number one how do we keep any one person from hogging up the network and problem number two.

How do we know how to send data to this computer and not that computer.

Let's take a look.

So imagine a situation where I've got Shannon data who are all plugged together on this one local area

network.

Now Dana wants to access Shannon's Microsoft Word document.

Now if she were to simply start grabbing that anybody else who wanted to talk would say it's a huge

document.

He kind of hogs up everything and that could be a real problem.

So to keep anybody from hogging up the entire network a bunch of folks got together back really in the

late 1970s and developed a type of networking called Ethernet.

Now it may be old but it is still the most popular type of networking that we use today Ethernet defines

what kind of cabling we use what kind of these little hubs.

It defines speeds and defines all kinds of stuff but it also to find something really important and

it says you can only make your data in discrete chunks of fifteen hundred bytes.

So if you want to send data.

For example if you want to send a Microsoft Word document and it's 100 megabytes big there'd be a big

word document.

It has to be broken up into zillions of these little fifteen hundred by chunks called a frame.

Now don't worry we'll see that the operating systems have the smarts to take the word document apart

and then put it back together on the other end.

But for right now a frame is only going to be fifteen hundred bytes tops.

Well that takes care of one problem but it doesn't take care of another.

So here's poor data over here and she wants to go talk to the Shannon computer because she wants to

get a hold of this Microsoft Word document.

But there's lots of other computers on this network.

We have to come up with some way to uniquely identify each computer on the network so that we know how

to talk to these guys and not to the others.

So what I've got set up in front of me is a very very simple network.

So here's one computer now it used to be we had network cards you snap in but they're all pretty much

built into the motherboards today.

So on this motherboard right here is a Ethernet connection.

And as we go over to this other one he's got an ethernet connection as well and they all come together

in this central box which I'm going to temporarily call a hub.

In fact there's even another computer I don't care about.

He's somewhere else.

So in this particular situation I've got three computers we uniquely identify every system on the local

area network through something called a media access control or MAC address a MAC address is a 48 bit

address which is always manifested as 12 hexadecimal characters.

So let's put up a MAC address right here.

So this is example of what a MAC address might look like.

So every network card in the universe gets a unique MAC address.

So if it's got 12 hexadecimal characters the first six characters are what we call the OEM I.D..

So if I'm going to start making network cards I am issued those first six characters from the issuing

body of the Internet and then I could spin up all the other ones as much as I want.

So these two computers in front of me have Mac on them.

So what I'm gonna do is his mac address is this.

And this one's MAC address looks like that.

Would you like to see the MAC addresses on your computers.

It's easy.

If you go on a Windows system just open up a command prompt and type in the command I.P. config space

slash all hll if you type it you're going to see something that looks like this.

There's a lot in there but there's one particular line I want you to concentrate on.

You see it says physical address.

That's the actual MAC address for the network card and your computer.

This also works with Mac as well as Linux systems except you use the command I f config or you could

just use i f and you can get basically similar results.

All right.

So we now have mac addresses that are assigned to every network card out there.

So what I'm going to do now is I'm going to add to this frame and what we're going to do every time

we send out a frame

instead of just the data at the beginning we're going to put the destination MAC address and then the

source back address.

So actually I've got some mac addresses in here already.

So this will get it to the correct computer.

And as a courtesy we always put the source MAC address in case they want to talk back to us.

They know our mac address already.

Now as you take a look at this there's only one other thing I want to add and that is what we call a

frame check sequence or FCX the frame check sequence is nothing more than a checker so that when this

data gets over to its destination they can compare this value to the data and it gives them a pretty

good idea as to whether the data came in in good order.

So what you're looking at here is the basics of what we call an Ethernet frame.

These frames were invented almost 40 years ago and we still use them on the highest speed networks out

there today.

What you may not be noticing is a term that people love to use a lot called IP address.

IP addresses are important but in a small local area network like this they don't really do much in

order to appreciate IP addresses.

We need to start making our networks bigger through something called a wide area network.