Cisco Certified Network Associate

Day One. Welcome back everybody.

I am Imran Rafai, your trainer for this entire series.

Today we would be starting with network fundamentals

and when I say fundamentals we would deal with the

very very basic of the networking

industry. So this video ideally is not

only for the people who are going for the CCNA certification but

anybody who's interested to, OR looking to start a career

in networking feel free to watch this because you

are going to learn as lot. But CCNA as a certification, is a very valuable

certification and I urge everybody to go ahead and

take that certification because it is gonna add a lot of value.

Before I go any further I would ask

everybody to concentrate on the first three days

of our video because we will be covering

the very basic concepts

which, if I can dare, I would say

is going to be the base

of your entire networking career, maybe even twenty years from now.

So please concentrate and

be clear with every concept we cover here.

And in case you still have doubts please feel free to email me

at imran.rafai@NWKING.ORG

imran.rafai@NWKING.ORG

imran.rafai@NWKING.ORG

imran.rafai@NWKING.ORG

Alright, without further ado, let

us get into the video. Let's start with the

very basic question, "What is a network"

well when I asked this question to my students

more often than not I get answers like Facebook

Twitter Picasa whatever whatever you see on the screen but

well that is social network, that's not the network we are here to learn

and that definitely is not the network I am going to talk about

what I am intrested in is it

this network the network between computers

well this network is also the foundation or the base on which

applications like Twitter Facebook picassa

is built on. So we learn about

this network and maybe if we have time over the course of this

this series, we will talk a little bit about those

applications here and there. While preparing for this

video lecture

I was preparing this a image that you see on the screen and I was thinking

okay let me see how to explain this concept

to students who are starting

on at the networking industry so

how do I explain this concept without actually using a lot of technical terms

Or saying - 'okay this thing communicates with that

thing over this thing' - I mean it was difficult

and then I thought okay I need a better way to explain this and I i remember the

story that a teacher of mine told me when she taught me

networking. It is about

the olden days of how Kings exchanged messages with

the ally, they would pass the message

to a messenger who used to ride on horse backs

and they used to go through all these paved paths

along the road and then they used to go through the city gate and then

this go to other King and deliver the message.

So if you compare that to computer network

the the messenger sending the message

so the 'message' is like the data that you send and the data could be anything

it could be a

doc file - a Word document or it could be an excel file it could be an image

could be a Video.... it could be anythng... the DATA.

And the road on which the the messenger travelled

that basically is the network. Of course

computer network is much more interesting than just paving

roads, but

if you see that is the very reason why computer network is

invented..... to communicate between computers!

If you see this image you would see.... let me just take a

highlighter..... you will see that we have the Windows PC,

we have Linux systems, an iMac

and we have laptop, mobile phone, palm top

you have web servers, maybe it's running on CentOS, you have database server

file servers but

in spite of them all running on different operating systems,

they all can communicate absolutely perfectly with each other!!!

This is the magic of computer networks

the computer network runs on

a global standard called the OSI Models

and things like that which defines clearly what

when any manufacturer manufactures a networking device

what and how they should communicate with each other!

So they all know the language of networking

and that enables them to communicate with each other.

Let's try to break this a little more further and see

how Internet works!

So if you look at the picture on your screens

this is the very basic network!

TWO computers connected with a wire... in this case we will use

a cat5 cable, a cat 5 cable looks something like this!

And they come in different colors, you have

blue colour ones, red color ones and this is obviously another color.

And this outer cover is just a protective layer.

Inside you have eight tiny cables

these cables go into a connector called RJ45

that looks something like this that you see on the screen. And on the back of your

computer

and most the computer that you have today

you have a port a port like this

that is your interface, your network interface card.

So your network interface card is where this RJ45 connects

and using this you can communicate

these two computers can communicate with each other.

This is the very basic form of networking and this is called as

ETHERNET!

Let me just

write it down. Its E sorry about my handwriting.

It's very difficult to write on screen

especially with my mouse but lemme

just......ETHERNET!

Maybe for my next video I will buy a stylus so that I can just

write it with a more legible

handwriting. Alright but for now...

Yeah.... this cable connects between these two computers

and you can have a very basic network.

But what happens if you have more than two computers so

lets say you have five computers. You obviously .... I mean there is one way

obviously you can go on adding more

network interface cards on your computer then you can have

but a better of connecting is by making use of a networking device

maybe a switch or hub - of course switch and hub are two different devices

they have totally different functions...we will obviously learn about them in

future video episodes

but for now you know we have a networking device.... in this case it is a

switch

and these computers can communicate with each other.

So for instance this guy has got a word document that he wants to send across

the network to this guy, all he has to do is send it across

to his IP address! 'What is an IP address?'

you would ask. IP addresses is how

computers recognize each other on the network!

We will learn about IP addresses in the next

video series but for now just know they are identifiers

for computers!

Another critical reason why people use networking is

because of devices like this. Maybe, let's assume, that this was a very

expensive

printer or scanner that the company invested in.

If networking was not available the way this device would be connected is

to this .... let me just change the colour to show that it is....

okay lets use BLACK. This is how

it would have had to be connected directly to the computer.

Now let's assume that this user maybe prints one

page a day and maybe all the

users in this company has similar requirement that they have

to print one or two pages

every day! So the company will have to invest on more

printer, so you will have one more print here. This guy will have one more printer

so company will have to unnecessarily

invest on a lot of printers when the usage on them...

in all the printers are gonna be very very minimal!

Better way for companies to invest money on IT infrastructures is to

have one printer

very expensive good quality printer. Plug it onto the network and everybody can

print to it!

That's a lot of money saved and that's very efficient way of using

IT Budget!

So that is the very basic

requirement and the reason why we have computer network!

So a computer network in a local office you know maybe one

home office, in a room...in a single company.... that's called as a LAN or

Local Area Network and 'local' signify that is very local

to a geographical area!

If this same local LANs, now these are

LANs and you have another LAN here

and let's assume that your company has two offices, one in New York and then you

have another office in Boston!

One way you could communicate or create a network between the

the two offices of your company is.... ofcourse if you had

the kind of money that is required to cable from New York to Boston

and of course if you can get the permissions you could run your own

private cable from your Boston office to New York office.... no problem at all!

But not too many companies have that kind of money

and not many companies would like to waste that kind of money.

We have a better way of doing it!

You could connect your office to a local ISP

ISP is nothing but Internet Service Provider.

and the similar thing happens on the other end...Boston connects

their office to an ISP ...Internet Service Provider

and ISP's already have their backbone, very massive, high bandwidth connections

between their offices!

So your data that you sent from here goes through the network to the ISP

from ISP to the ISP in Boston and then through that

they go back to the Boston office and a computer. So this computer

can communicate with this computer absolutely fine

using the ISP. Now this

forms the Wide Area Network where

LANs are inter-connected with each other to form a

Wide Area Network and 'wide' here signifies

a wide geographical area! It could be across the country

it could be in different cities in the the same country or

maybe in different countries.... basically it's a WAN.

So that is how it works...now how do you connect from ISP

to your Local Area Network... how do you connect?

Well.... in normal situation... what happens is

you get a a jack on the wall

you might have a small jack on the wall and your LAN

....you just connect it to the jack! So from the switch... or from the router

of your company

you connect it to the jack! On the backend this ISP, they would

lay cable.... maybe they would lay it under the

ground .....they lay a cable to their office

and from their office they go here from From their office again maybe underground

they lay a cable to

the Boston office. Again there will be a wall socket

that is provided and you just plug a cable from the wall to your

Router.... and that is how

your WAN link works. Well this is also

INTERNET because we are using the ISP.

Internet is nothing but a very massive

WAN which covers the entire world,

where you have a lot of public resources! So

if you google this is the definition of what an

internet is! "A global computer network providing

a variety of information and communication facilities

consisting of interconnected networks using standardized communication

protocols!". WOW... that is big definition...

Well that's exactly what it is ...you know.... Internet

is nothing but you have a lot of WANs. So you have a WAN here you have a WAN here

you have a WAN here

you have a WAN here and then just WANs are connected with each other.

So you have another WAN here and you have another WAN here

another one here another one here maybe few

more here....I know in India there are quite a lot...

you have all these things and they are connected .....let's say for instance you are connected

from here its

connected here, from here connected here and this is connected..... this is connected

this is connected....this is connected ....this is connected......

so this is nothing but how an internet works! So for instance if from

India somebody has to communicate

to New York this is how the data will transfer.... they will go..

if this thing disconnects you will have

the data going through a longer path! So this is what

internet is .....it is just nothing but interconnections of a lot of WANs!

Let's find out more about the applications we were talking about earlier.

There are lot of usage of the Internet or

networking as a whole.... we have YouTube, CNN

EBay, Skype.... this is just very,

very very few examples that use the Internet!

But they're lots of sites and applications which use the internet as

you already know!

Now how it works is YouTube for instance is owned by Google ...So Google

has put a

public server somewhere on the Internet that is accessible

to anybody on internet!

So if I want to watch a video on youtube

I go to my web browser and type 'www.youtube.com'

The process that takes place in the background

is much more complicated ....I'm simplifying this whole process.... we will look into

exactly how it works

in future video.....but for now when somebody times

'youtube.com' and hit enter

my computer sends an HTTP request

to YouTube's public server!

When the server gets that information it says 'Ah fine that is an HTTP request ...so I

will send an HTMLfile back'

and it creates and sends that HTML file back to me.

My web browser takes that and says..'Ah that's an HTML file and I know how to

process it'.

So it processes that and your YouTube website come to life and you see that

it shows a lot of videos and you click on one of those videos this process

repeats...

they send you back the Video and that's how that works.

Similarly it happens to eBay.... you go to CNN, Skype

that's how it works! So this is how internet

works.... basically they have a public server... they put all the files there

your computer request that....they send the file back to you and this

is how internet helps you

run this globalized world!

When we talk about internet, very critically we need to talk about the

speed of Internet!

Before we get to the speed of internet lets get to

'What is the difference between bit and byte?'

Bit is the smallest

information computer can understand.... it's either 0 or 1

Whereas byte is nothing but.... its formed by 8

bits.... so 8 bits together form one byte!

It could be some thing like

11011101.... whatever ....something!

So that is a BYTE. So eight BITs form one BYTE.

Now a lot of people get confused - DATA is

always denoted by 'bytes'... so when I say I have 1gb of

RAM it is one gigaBYTE of

RAM but when I tell I have a 10 Mbps connection

it is 10 mbps... connection 'bits' per second mega'BITS' per second

connection.

If you confuse these two.... it's going to be very very difficult

at one mBps.... 'byte' per second connection

is 8 mbps connection ....eight times

the speed of what it is supposed to be! So

speed is always denoted by the small 'b' data size is always

in big 'B'.

In computer world kilo is always '1024' so....

one kilo bit is 1024 bits.... similarly

one kilobyte is 1024 bytes!

Right so for instance let me see I have 1 Mbps connection

and I have a file of 128 KBytes.

So lets say for instance you have WORD and in word you type

the alphabet 'A'.... now with one

.... to produce that one alphabet ....that

takes about one BYTE.... capital

'B' of space.... so one

BYTE is how much it needs to store this

alphabet A..... one BYTE is

is 8 BITs.... right?.....

according the convertion.... so to type A... it takes eight bits or one

BYTE of data. Alright having known that let's look at this example.... so

you have 128 KB.... that is BYTE

a file of 128 KB

now it needs to go across a network with speeds of

1 Mbps.... one megabits per second!

How much time will it take? It is a very simple question .... let's try to convert

128 kilobyte if we convert it to

bits it is...... 128 into 8 bits... this conversion if you know!

bit to byte..... its 8 right?

So 128 BYTE

is..... if you convert it into

bits .....it is 1024

kilobits of data

right? so 1024 kilobits

where is that .... its 1024 kilobits is nothing but

1 megabit..... right? One Megabit!

What is the speed .....it is 1 megabit per second is

the speed of our connection..... so on a connection of 1mbps

a 1mb file will take

exactly one second!!!

So that's what speed is..... so understand this...... the difference between speed

and data....... the difference between bit and byte.

So if you can understand different between bit and byte..... the whole process

of understanding further videos can be very very easy!!!

When we talk about speed we need to want to talk about three other critical

factors that is..... Speed

Delay and Availability....the three of them always go hand in hand!

Like for instance now ....when you connect a cable from your router to your

PC it tells you that it is connected at 100 Mbps

that's because today with our LAN cards...the maximum they can do is a 100 Mbps!

but then don't forget that speed that they're telling is the speed between

your computer

and the router! Your internet connection maybe is a 1mbps connection!

so if you send 100MB/s data

100 MB per second data it will not go through your

internet because your internet can only do 1 Mbps!

Similarly you go.....

lets say from your bangalore office to New York office... you are sending a file.

So from bangalore office it goes through our gateway.... from gateway we have a 1mbps

slow connection.

It then comes to our bangalore ISP. Bangalore ISP to Mumbai ISP

they have a 100 Mbps line..... very fast

and then from Mumbai to Dubai they have a 10mbps line...

a little slower connection.... from Dubai again to Cairo

they have a 100 bps line and then Cairo to Madrid, let us say

you have a 100 mbps line. So similarly they have

a slower and faster.... different speed connections.

So basically when I say Internet this what happens.... internet...

if you pull off the cloud

it is nothing but a lot of routers... jumping here and there!

Now even if I have a very high speed connection

your data-throughput between your bangalore and New York office will depend on

slower connections in between. So even if I had a

very high speed connection... a 100 Mbps line in Bangalore...

It can only travel at the slowest link in between.

So our slowest link is the 10 Mbps line that we have here.

So from New York office to Bangalore office,

the maximum it can do is the 1 mbps line that we have

in New York. So this is how it works.

This is not the exact data flow from Bangalore to New York.

I have just given you an example... it need not obviously go via Dubai and Cairo...

Maybe it goes through some other location but basically it

actually....the data packet flows through one location to another

location to another location.

So like I said the speed always depends on

different factors..... of the link speed that you have in between.

Another critical factor is of dealey.

Now when I send a data from New York to Banglore

it has to....like we have already discussed... it has to pass through a lot of nodes

in between.

But let's assume that we have another office in Boston

I love Boston, dont I? So lets say we have

Boston office and we send data from New York to Boston office....

it has to pass through less number of nodes and hence

it would reach much more quicker. So

that's another factor. If the distance between the two devices

is long you will

have delay in the communication.

And that's why today, if you see, if you go to Google... even 'Google.com'

for instance... or you go to

'YouTube.com'... they redirect you to a content delivery network

closer to your place. So if you are in Singapore and you say

'google.com' or you go to 'youtube.com'

YouTube would not connect you to the Google Server or YouTube server

in United States. It will connect your to

a content delivery network close to Singapore, may be in Singapore.

So there is not much delay or

there is in-significant delay in the communication and the

the whole process is much much more fast. So that

is the delay part of it. And availability, again for instance

the link between Cairo and Dubai is down.

Communication between New York and Banglore would

not happen or it would happen but then it has to take maybe a longer path.

You might have another path

which goes via russia and then it comes via...

... it goes via China and comes to India and it is a long long

long

process. So thats another thing about availablility. Availability

is if all the links in between are up and running!

Another thing we need to discuss in today video

is network topology. Network topology

...there are three fundamental network topology....The STAR topology, the RING

topology and the BUS topology.

They are very very olden ways of how computers were

connected but even in today's world

they are in use. I will show you how.

Now for instance STAR. How does STAR work? STAR is where all the computers or

devices are connected to a central

switch or a connecting device.

Now if this line goes down it doesn't affect everybody else.... only

this guy goes off the network.

So in RING for instance every

computer is connected to each other. So if this guy goes down

the communication between these 2 devices can still happen through

this way. Right? So that's how

this works. Now in bus

topology .... let's say for instance.... this is again like that....you have a

device here... this is connected to this device... you have another device here that is connected

to that.

So every computer is connected to their own little device.

Right... now if the link goes down here

this part of the network can communicate the each other but not with

another device from the other segment of the network.

That's how a bus network works! Let's see how

it is implemented in today's world. We go back to our old

example that we saw earlier in this video

and if you see this switch

and these systems or PCs are connected

in a star formation - everybody is connected to this central switch!

Here the server also similar thing happens. Everybody is connected to the

switch!

These devices are connected to the access point in STAR formation

or.... so to say!

And if you look at the switch, the switch is connected in

a bus formation. Now if the link goes down here,

this part of the network can communicate with each other but it cannot communicate

with anybody else from this part of the network.

Sometimes you might even have networks where this is connected like

this

and this is connected like this.... so even if this goes down

this switch can still access this network around

this path and they can get access to these

these windows.... I mean... these systems here!

So in real-world the network topology

that we use is called HYBRID - which makes use of the STAR and

RING.... maybe even the BUS.

So it's a combination of all the three or either of them!

And that's how it is...So it is a hybrid network that we use in today's world.

I think that is about all the information that I wanted

to speak about in this first video.

We will further get into a lot of other topics

in our second video. This is the review of what we did

today....Go through all the

topics that is mentioned here and see if you understood.

If you din't you can always go back and try to learn little bit more.

And even after that if you have conclusion if you want more clarity on

any topic...please feel free to write into

'imran.rafai@nwking.org'

and I will look into it and I will answer your queries.

And of-course subscribe to our YouTube channel

and you can keep getting all our videos LIVE

on YouTube. Thank you for watching and

please visit our WEBSITE! BYE.