WEBVTT

0:00:02.920000 --> 0:00:07.960000
 So welcome to this video that I've
 titled, What is a Computer Network?

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 In this video, we're going
 to cover several things.

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 We're going to cover the parts
 of a common computer network.

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 We're going to talk about what is a
 computer network in case you don't

0:00:17.120000 --> 0:00:20.880000
 know, and why would you use one
 and some common vocabulary?

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 Like I said, why do we need computer
 networks in the first place?

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 So let's start with the basic high
 level fundamental question that you

0:00:28.340000 --> 0:00:32.180000
 need to answer, which is what
 is a computer network?

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 Now chances are you've probably been
 working on computer networks of some

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 size or shape for years, maybe decades
 if you're as old and ancient as

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 I am. But you may have never used that
 term before and don't really know

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 what a network is.

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 Well, a network is really simple.

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 At its basic core, a network is two
 or more devices that need to share

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 information. And those two devices,
 nor to share that information, well,

0:00:57.600000 --> 0:01:01.980000
 they need to be connected to some common
 media like a cable in which they

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 will share that information most likely,
 electrically using electrical

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 signals or pulses.

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 Same type of electricity that comes
 out of your wall jack when you plug

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 something in. Now of course, networks
 these days can also be wireless.

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 And I'm going to talk about
 that in just a moment.

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 So in the old days, let's go back
 to the 19, I don't know, 19.

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 I'm not sure how far we'd
 have to go back here.

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 1950, 1940, 1950, 1960.

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 If two people were working on their
 own individual computers and they

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 wanted to share information,
 how did they do that?

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 Well, if you weren't born back
 then, you probably don't know.

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 What you did was you had something called
 a floppy disk, which depending

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 on the size could be like this big or
 maybe about this big, but you plug

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 the floppy disk into your computer,
 you copy your information onto it,

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 and then you walked it over to the other
 person's desk, handed them the

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 floppy disk. Hopefully they
 paid you a handsome tip.

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 They put the floppy disk into their computer
 and voila, you had just networked

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 with them. There was actually a term
 for this, which was called sneaker

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 net, because you had to use your sneakers
 to walk over the person and

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 give them your data.

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 Clearly, not a very scalable
 way of networking.

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 So networks came out with this idea
 of, hey, let's connect everything

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 initially with a cable.

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 Have all the devices connected to a
 cable, and then by using electrical

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 signals and impulses, we can just digitally
 send our information back

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 and forth between the devices.

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 So that's like what
 we have right here.

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 Here we have two departments, department
 A and department B, they're both

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 on their own separate networks, and
 they can talk to each other because

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 they're connected
 to the same wire.

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 Now, what if it turns out that we say,
 hey, I actually want department

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 A and department B to be able to exchange
 information between the departments?

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 Well, certainly I could take this wire
 and connect it, and now everybody's

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 connected to one big wire, and in original
 networks, that was the way

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 it worked. But here was
 the downside to this.

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 When original networks first came out,
 this wire was a shared medium,

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 which meant that only one person
 could talk at a time.

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 It's kind of like you're in a room
 with a bunch of people, right?

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 If everybody's talking at the same
 time, kind of hard to make out any

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 conversations going on.

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 So everybody has to be polite, only
 one person can talk at a time while

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 everybody else has to be quiet.

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 Well, that's fine if let's say you're
 in a room with four, five, or six

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 people, everybody can
 sort of take turns.

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 But what happens when you get in a room
 of like 100 people or 1000 people?

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 Good luck getting your turn to talk,
 because everybody's going to have

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 something they want to say, and everybody's
 going to want to jump into

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 that quiet space in order
 to say something.

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 Same thing here.

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 In the original networks, as the wire
 got longer and longer and longer,

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 there were more devices that were wanting
 to talk, and so there ended

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 up being problems.

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 Where devices would say,
 hey, let me tell.

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 And then all of a sudden somebody else
 is talking at the same time as

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 you, which was called a collision.


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 So they had to stop
 and retry again.

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 So connecting everything to the same
 wire was okay as long as there were

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 only a few devices on that wire, but
 it was not a scalable situation.

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 So networks evolved, and somebody came
 up with a bright idea of, hey,

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 let's connect a networking device to
 these two wires that will keep the

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 wires separate. All right, so
 let's take a look at this.

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 So for example, why
 don't we do this?

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 Instead of having everybody connected
 to the same general cable, let's

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 give each person their own unique cable,
 their own independent cable into

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 this networking device
 called a bridge.

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 Nowadays, we call it a switch.

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 So those dashed red lines here represent
 individual cables that each person's

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 computer or laptop is connecting
 up to the switch.

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 Now, the idea with this is much better,
 because each one of these people

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 could talk whenever
 they wanted to.

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 They could send data on their own individual
 wire whenever they wanted

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 to, and the switch would collect
 all this information.

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 Now, if all the information came in
 at the same time, like, let's say

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 two or three people talk simultaneously,
 the switch was okay with that.

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 It had the intelligence to take in all
 this information, and then it had

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 even more intelligence to say, oh,
 this message here came from Bob is

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 going to Sally. Sally lives on this
 wire over here, so I'll convey Bob's

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 message to Sally over here.

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 So we didn't have to worry about, hey,
 when I'm talking like in a room,

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 everybody has to be quiet because
 everybody's going to hear me.

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 Now, maybe I'm just talking to Sally
 who's in the room with me, but in

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 that environment, everybody in the
 room's going to hear you, right?

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 You can't really have a private conversation
 between you and Sally, because

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 John and Pablo are also in
 the same room with you.

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 That was like the original way,
 where everybody was on one wire.

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 When one person talked,
 everybody heard it.

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 Even if John was just trying
 to communicate to Sally.

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 Here, with a network switch or bridge
 introduced, everybody has their

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 own wire, and so now the switch or
 bridge in the middle is collecting

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 all the information and playing it out
 on the individual wires where it

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 needs to go. So this is a way of expanding
 our network and connecting

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 multiple departments together without
 worrying about that whole thing

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 of only one person
 can talk at a time.

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 Now, this is your basic
 wired networking here.

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 Then a few years later, wireless
 networking was introduced.

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 So now we have the idea of, hey, what
 I'm transmitting into is the air.

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 I'm using radio frequencies, like the
 exact same radio frequencies that

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 come to your car radio when you're
 driving around, right?

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 And so using radio frequencies, I can
 transmit my data into the air, and

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 that data is received by a special
 device called an access point.

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 We'll look at that
 in a little bit.

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 Okay, it also has a radio,
 it also has antennas on it.

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 So your data is going to him, and then
 that device can put your data onto

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 the wire. So these two people here
 could talk to each other wirelessly

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 by sending their information
 through the access point.

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 Maybe they're connected to the
 same access point, maybe not.

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 But now if I have these people down
 here in this department, and they

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 want to talk to any of the people up
 here in the wire department, clearly

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 I have to have a connection
 between them.

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 Okay, so once again,
 I could do this.

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 I could connect one switch to the other
 switch, just to connect a wire

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 between them. I could
 certainly do that.

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 But then some people said, hey, we
 should have some way of segmenting

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 or dividing our networks
 logically.

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 And so, you know, Sally, when you're connected
 to the network, your device,

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 your laptop per PC, will not only know
 that it's connected to a wire,

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 or connected to the wireless network,
 it will also know what part of the

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 network you're on.

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 So Sally's device will know, hey, I'm on
 the payroll network, or the engineering

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 network. It's a little bit more complicated
 than that, but that's the

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 essence of it. And so the idea was,
 if we can do that, if we can group

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 users into certain sections of the network,
 like payrolls over here and

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 all the devices in that section know
 what group they're in, now we can

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 introduce some sort of security.

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 We could say, all right, it's okay for
 payroll to talk to human resources

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 and exchange data, but we don't want
 payroll and marketing talking to

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 each other. Now, if everybody was just in
 one big network with an interconnection

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 of wires and access points and stuff, they
 would be kind of hard to implement

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 that kind of security.

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 But people said, hey, let's divide networks
 into groups, and then we'll

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 have another device that knows where
 all those groups are, and when data

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 comes in from payroll going to marketing,
 it will have the intelligence

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 to know, oh, marketing is over here,
 or engineering is over here, and

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 that device could also implement
 some security if we want to.

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 So that device is what we call a router,
 and we see that right here.

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 So now the router is connecting up those
 two switches, but now the router

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 has the intelligence to know that, okay,
 department A and B are on this

0:08:44.740000 --> 0:08:48.900000
 side of me, and the wireless users
 are over here, and I can send their

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 data back and forth because I
 know where everybody lives.

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 Okay, so this was all great.

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 Okay, now back once again in the early
 days of networking, the information

0:08:58.160000 --> 0:09:03.540000
 that you had was locally stored on your
 laptop or PC, and the information

0:09:03.540000 --> 0:09:07.900000
 you were trying to get from Sally was
 locally stored on her laptop or

0:09:07.900000 --> 0:09:11.560000
 PC. Well, people started realizing,
 hey, you know, I've got a thousand

0:09:11.560000 --> 0:09:16.960000
 employees in my company, and it's getting
 kind of complicated to know,

0:09:16.960000 --> 0:09:19.080000
 where is the data that I want?

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 Where, you know, where's
 that file?

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 Where's that image or picture
 on trying to get digitally?

0:09:24.080000 --> 0:09:26.980000
 Is it on Sally's or is it on John's
 or is it on Paco's laptop?

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 Where is it? So people said, hey, let's
 take all our data and store it

0:09:31.740000 --> 0:09:33.220000
 in a central place.

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 We'll take a certain section
 of our network.

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 We'll make it very secure.

0:09:36.340000 --> 0:09:39.160000
 You can only get in there with a badge
 just behind a locked door, you

0:09:39.160000 --> 0:09:42.080000
 know, with a policeman with a machine
 gun and a couple machetes standing

0:09:42.080000 --> 0:09:44.860000
 right there to protect it from getting
 in there, and that's where all

0:09:44.860000 --> 0:09:46.340000
 data is going to be stored.

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 So the users will have to get to
 that place over the network.

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 They'll have to send the request over
 the network to that place to retrieve

0:09:53.660000 --> 0:09:59.420000
 whatever data they want, and that was
 called, funny enough, our data center,

0:09:59.420000 --> 0:10:00.820000
 the center of our data.

0:10:00.820000 --> 0:10:02.420000
 That's where we're
 going to store it.

0:10:02.420000 --> 0:10:07.660000
 So you can see here we these pictures
 that we see are just stacks of what

0:10:07.660000 --> 0:10:11.020000
 we call servers, which is basically
 a computer like the computer you're

0:10:11.020000 --> 0:10:15.120000
 working on is just a very high powered
 computer with a lot more brain

0:10:15.120000 --> 0:10:19.320000
 power than your computer has, and a
 lot more information to store a lot

0:10:19.320000 --> 0:10:24.340000
 more stuff. So we have a data center
 here, we connect it to the network,

0:10:24.340000 --> 0:10:28.120000
 and so this is your common network here,
 and then people said, hey, this

0:10:28.120000 --> 0:10:33.120000
 is all well and good if the only data
 I want to push somewhere or retrieve

0:10:33.120000 --> 0:10:35.800000
 somewhere is within my company.

0:10:35.800000 --> 0:10:39.260000
 But now this great thing called the
 internet came up, and I want to get

0:10:39.260000 --> 0:10:44.120000
 data from John's data center who's in
 another state or Sally's data center

0:10:44.120000 --> 0:10:46.480000
 who's in another country
 or continent.

0:10:46.480000 --> 0:10:50.400000
 So we needed the internet
 to do that.

0:10:50.400000 --> 0:10:52.140000
 So we need a connection
 to the internet.

0:10:52.140000 --> 0:10:53.400000
 And what is the internet?

0:10:53.400000 --> 0:10:58.040000
 The internet is just an interconnection
 of networks.

0:10:58.040000 --> 0:11:03.320000
 So the internet is just billions of
 networks all connected together.

0:11:03.320000 --> 0:11:06.760000
 The network at your house
 is part of the internet.

0:11:06.760000 --> 0:11:10.520000
 The network at your company is another
 network connected to the internet.

0:11:10.520000 --> 0:11:15.180000
 So originally the network, a lot of
 people called it the world wide web,

0:11:15.180000 --> 0:11:18.340000
 you might remember that www the world
 wide web because they thought of

0:11:18.340000 --> 0:11:22.720000
 it as like the spider web of interconnected
 networks all connected together

0:11:22.720000 --> 0:11:25.280000
 like in a spider's web, they
 called the world wide web.

0:11:25.280000 --> 0:11:27.160000
 Now we don't really call
 it that anymore.

0:11:27.160000 --> 0:11:28.840000
 Now it's just called the internet.


0:11:28.840000 --> 0:11:32.420000
 But our network also needed
 a connection to that.

0:11:32.420000 --> 0:11:36.460000
 And so we would have some sort of cable
 or wire leading out to a company

0:11:36.460000 --> 0:11:40.080000
 that would provide service called
 an internet service provider.

0:11:40.080000 --> 0:11:46.720000
 You probably know them as time one or
 cable or AT&T or Sprint or Comcast.

0:11:46.720000 --> 0:11:50.400000
 Those are companies that you pay a monthly
 bill to you connect over cable

0:11:50.400000 --> 0:11:54.220000
 to them. And then they connect you to
 all these other those of billions

0:11:54.220000 --> 0:11:55.660000
 of networks around the world.

0:11:55.660000 --> 0:11:59.500000
 They are your internet
 service provider.

0:11:59.500000 --> 0:12:03.460000
 All right. So just some common vocabulary
 here in the terms of networking

0:12:03.460000 --> 0:12:07.300000
 first of all lands and wands you'll find
 as you start going down the road

0:12:07.300000 --> 0:12:11.780000
 of networking that there's about five gazillion
 acronyms you have to memorize

0:12:11.780000 --> 0:12:14.680000
 and they never seem to
 stop creating new ones.

0:12:14.680000 --> 0:12:17.500000
 So land stands for
 local area network.

0:12:17.500000 --> 0:12:19.740000
 WAN is wide area network.

0:12:19.740000 --> 0:12:21.280000
 What's the difference?

0:12:21.280000 --> 0:12:27.040000
 So a local area network is a network
 that's locally in your surroundings.

0:12:27.040000 --> 0:12:30.860000
 Okay, it's for example, in the building
 you're in like that picture.

0:12:30.860000 --> 0:12:33.180000
 I just shoot. Let's just go
 back to this for a second.

0:12:33.180000 --> 0:12:41.720000
 All right. So everything inside this
 green sort of oblong shape here is

0:12:41.720000 --> 0:12:46.040000
 a land. So all of this is
 our local area network.

0:12:46.040000 --> 0:12:49.700000
 It's fairly confined
 in geographic scope.

0:12:49.700000 --> 0:12:53.760000
 So one end of a land going to the other
 end of a land typically is not

0:12:53.760000 --> 0:12:55.200000
 very far in distance.

0:12:55.200000 --> 0:13:01.000000
 You know, maybe a few hundred feet,
 maybe, you know, certainly less than

0:13:01.000000 --> 0:13:03.980000
 a mile, like a quarter
 of a mile at the most.

0:13:03.980000 --> 0:13:05.680000
 So that's a local area network.

0:13:05.680000 --> 0:13:08.980000
 And some of the characteristics of
 a local area network are if you're

0:13:08.980000 --> 0:13:12.500000
 the network administrator who's in
 charge of that local area network,

0:13:12.500000 --> 0:13:14.000000
 you're in charge of all of it.

0:13:14.000000 --> 0:13:16.740000
 You're in charge of figuring out what
 cables need to be there and laying

0:13:16.740000 --> 0:13:17.960000
 those cables down.

0:13:17.960000 --> 0:13:20.560000
 You're in charge of figuring out what
 networking equipment like routers

0:13:20.560000 --> 0:13:24.540000
 and bridges and switches we just talked
 about what you need and installing

0:13:24.540000 --> 0:13:25.980000
 those and placing them.

0:13:25.980000 --> 0:13:28.740000
 So that entire network
 is your baby.

0:13:28.740000 --> 0:13:30.920000
 It's completely under
 your control.

0:13:30.920000 --> 0:13:33.380000
 That's a characteristic of a land.


0:13:33.380000 --> 0:13:37.960000
 Now, as a when though, a when is when
 you want to connect two networks

0:13:37.960000 --> 0:13:43.460000
 together that are far apart and you don't
 have the resources or the money

0:13:43.460000 --> 0:13:46.640000
 to actually string a cable
 between those two networks.

0:13:46.640000 --> 0:13:50.680000
 For example, maybe you're you have
 a network in your office in Boise,

0:13:50.680000 --> 0:13:54.420000
 Idaho and another network
 in Miami, Florida.

0:13:54.420000 --> 0:13:58.900000
 Well, between Boise and Miami, you
 can't string a cable between those.

0:13:58.900000 --> 0:14:01.300000
 Now, maybe if you were Donald Trump
 and you had billions of dollars, you

0:14:01.300000 --> 0:14:04.000000
 actually really could
 afford that cable.

0:14:04.000000 --> 0:14:06.940000
 But if you could buy the cable, you're
 not going to be able to get the

0:14:06.940000 --> 0:14:12.900000
 government permits to dig a trench
 3000 miles from Boise to Miami.

0:14:12.900000 --> 0:14:14.220000
 It's just not going to happen.

0:14:14.220000 --> 0:14:19.400000
 Fortunately, for us, there are companies
 out there like AT&T, like Time

0:14:19.400000 --> 0:14:24.860000
 Warner Cable that have already dug those
 cables or laid the cables across

0:14:24.860000 --> 0:14:27.680000
 in conjunction with
 telephone lines.

0:14:27.680000 --> 0:14:31.940000
 So the connections, the physical cables
 do exist, interspersing the country

0:14:31.940000 --> 0:14:34.600000
 and the continents, but
 they're not yours.

0:14:34.600000 --> 0:14:36.560000
 They're owned by these
 other companies.

0:14:36.560000 --> 0:14:40.820000
 So in order to connect to those companies
 and use those cables, we use

0:14:40.820000 --> 0:14:42.540000
 a wide area network.

0:14:42.540000 --> 0:14:44.660000
 And that is what a when is.

0:14:44.660000 --> 0:14:55.280000
 So wide area network is a network that's
 there when they're in charge

0:14:55.280000 --> 0:14:58.400000
 of setting it up, they're in charge
 of maintaining it, and you're just

0:14:58.400000 --> 0:15:02.760000
 paying for the right to transport
 your data across that when.

0:15:02.760000 --> 0:15:05.960000
 And there's lots of different
 kinds of whens as well.

0:15:05.960000 --> 0:15:08.580000
 A node or a host.

0:15:08.580000 --> 0:15:12.660000
 So node and host is basically
 the same type of thing.

0:15:12.660000 --> 0:15:18.760000
 It's basically any device that's connected
 to the network is called a

0:15:18.760000 --> 0:15:23.460000
 node. So for example, a node could be
 your laptop, your PC, it could be

0:15:23.460000 --> 0:15:25.380000
 your smartphone, your tablet.

0:15:25.380000 --> 0:15:29.880000
 A node is also the router, the switch,
 the bridge, the access point.

0:15:29.880000 --> 0:15:32.560000
 We call all of those things nodes.


0:15:32.560000 --> 0:15:36.560000
 Now, sort of what makes a distinction
 between a node and a host is that

0:15:36.560000 --> 0:15:38.900000
 a host is a node.

0:15:38.900000 --> 0:15:43.320000
 It's one of the many types of nodes,
 but a host is a specific node that's

0:15:43.320000 --> 0:15:47.940000
 responsible for creating data
 and putting it on the network.

0:15:47.940000 --> 0:15:49.360000
 Or it's the endpoint of data.

0:15:49.360000 --> 0:15:54.960000
 In other words, data goes through the
 network and terminates at a host.

0:15:54.960000 --> 0:15:59.640000
 So for example, we would call your laptop
 per PC a host, because a laptop

0:15:59.640000 --> 0:16:04.320000
 per PC is what's creating the request
 for data, or it's pushing the data

0:16:04.320000 --> 0:16:05.740000
 onto the network.

0:16:05.740000 --> 0:16:09.800000
 And maybe at the other end of the network,
 another laptop per PC or a

0:16:09.800000 --> 0:16:11.760000
 server is receiving that data.

0:16:11.760000 --> 0:16:13.660000
 So those would be hosts.

0:16:13.660000 --> 0:16:18.120000
 We wouldn't typically call a router or
 a switch or a bridge, what we typically

0:16:18.120000 --> 0:16:22.280000
 call network infrastructure devices
 infrastructure, meaning these are

0:16:22.280000 --> 0:16:25.840000
 the components that build the network
 and present the network to us.

0:16:25.840000 --> 0:16:29.860000
 We wouldn't typically call those hosts,
 because they're just transporting

0:16:29.860000 --> 0:16:31.960000
 data back and forth.

0:16:31.960000 --> 0:16:36.020000
 We don't normally think of them as originating
 and creating data or data

0:16:36.020000 --> 0:16:40.060000
 terminating on a router, a
 switch, or an access point.

0:16:40.060000 --> 0:16:45.680000
 Now, but in this terminology here, that's
 sort of the distinction between

0:16:45.680000 --> 0:16:51.160000
 node and host. We also have local
 versus remote resources.

0:16:51.160000 --> 0:16:55.980000
 This is basically a distinction of
 the data that you're trying to get.

0:16:55.980000 --> 0:16:59.920000
 Is it locally stored on
 your own laptop per PC?

0:16:59.920000 --> 0:17:04.220000
 So if you completely disconnected from
 any network at all, would you still

0:17:04.220000 --> 0:17:06.200000
 have access to that data?

0:17:06.200000 --> 0:17:09.160000
 If the answer is yes, that's
 a local resource.

0:17:09.160000 --> 0:17:12.780000
 If the answer is no, the only way I can
 get to that data is if I'm connected

0:17:12.780000 --> 0:17:14.260000
 to a network somehow.

0:17:14.260000 --> 0:17:18.580000
 For example, Facebook, you can't get
 to the resources on Facebook unless

0:17:18.580000 --> 0:17:20.140000
 you're connected to a network.

0:17:20.140000 --> 0:17:23.780000
 So the resources on Facebook, all the
 images it can give you, the text

0:17:23.780000 --> 0:17:28.240000
 it can give you, those would be
 considered remote resources.

0:17:28.240000 --> 0:17:30.740000
 And we've already talked about
 what the internet is.

0:17:30.740000 --> 0:17:32.580000
 I don't think we need
 to go into that.

0:17:32.580000 --> 0:17:38.980000
 So hopefully this points becoming a
 little bit more of a way to avoid

0:17:38.980000 --> 0:17:42.320000
 sneaker net. Of course, sneaker
 net is good for exercise.

0:17:42.320000 --> 0:17:45.060000
 If I have to change data with somebody
 in Idaho, what better exercise

0:17:45.060000 --> 0:17:49.320000
 than to walk 3000 miles over their
 PC and hand them a floppy disk, but

0:17:49.320000 --> 0:17:51.800000
 not really all that scalable.

0:17:51.800000 --> 0:17:55.920000
 So it helps us to exchange data between
 devices, and we don't have to

0:17:55.920000 --> 0:17:56.800000
 get out of our chair.

0:17:56.800000 --> 0:17:59.820000
 We can get nice and lazy and fat
 and not even worry about it.

0:17:59.820000 --> 0:18:03.360000
 So networks basically allow us to
 share things between devices.

0:18:03.360000 --> 0:18:07.200000
 We can share files, we can
 share programs, right?

0:18:07.200000 --> 0:18:11.420000
 Maybe I've got a program that's used
 to draw graphics, or I have a program

0:18:11.420000 --> 0:18:13.260000
 that's used to create music.

0:18:13.260000 --> 0:18:16.340000
 And over the network, I can send you
 that program so you can install it

0:18:16.340000 --> 0:18:19.540000
 on your device. Or we
 can share resources.

0:18:19.540000 --> 0:18:22.720000
 For example, a network-based
 printer would be a resource.

0:18:22.720000 --> 0:18:26.220000
 Okay, I could say, hey, you know, I don't
 need to send every single employee

0:18:26.220000 --> 0:18:30.080000
 in my office their own unique printer
 as much as they probably like that.

0:18:30.080000 --> 0:18:32.980000
 I can say, hey, there's a printer
 over here in the corner.

0:18:32.980000 --> 0:18:37.420000
 Let me give you the access instruction
 so you can reach it over the network.

0:18:37.420000 --> 0:18:41.540000
 That would be considered a resource
 that you can reach over the network.

0:18:41.540000 --> 0:18:43.880000
 So that concludes this
 particular video.

0:18:43.880000 --> 0:18:45.340000
 I hope you learned a lot.

0:18:45.340000 --> 0:18:46.540000
 And thank you so much
 for watching.